Boran Pivcic

Photo File – You Spin Me Right Round: A Peek At The CFM56

April 4, 2021Posted in Plane's Anatomy / TechTagged CFM56, CFM56-5B, CFM56-5B4, gas turbine, jet engine, turbofan, turbofan engineLeave a comment

By me
All photos (and videos) me too, copyrighted

Despite there being GA material aplenty in Croatia nowadays, for this next piece I decided once again to go for one of my “periodic airliner exceptions”. The reason this time was the opportunity to photograph an entire CFM International CFM56 engine in the nude, something so rare even for us airliner drivers that I simply could not leave it at “just another set of photos” somewhere on my hard drive.

Admittedly, the mass of bits and bobs that is a jet engine is somewhat underwhelming to look at on a computer screen, especially with no sense of scale; but even then, the sight is more than enough to send the geek-o-meter right off the scale. Working under the assumption that mine wouldn’t be the only one, I rolled up my sleeves and dialed up my carrier’s PR department for an amen to go to town in true Achtung, Skyhawk! style…

It’s far from the most exciting or advanced engine out there… but it still deserves some love for its reliability and longevity! Plus, it’s good for some cool shots – such as here, windmilling with a 30 knot breeze up its tailpipe

The Power Of Flight

Being such an ubiquitous engine, much has already been written about it – so, if no one objects, we’ll cut straight to the chase. The first bit we need to address is the name: C, F, M, 5 and 6. Even a brief search online will quickly reveal that this name is actually a portmanteau of General Electric’s CF6 (Commercial Fan 6) and Snecma’s M56 (Moteur 56). The “problem” here is that this is a bit misleading, since it implies that the CFM56 is a mashup of bits from these two engines. This doesn’t quite work since a) the CF6 is a big brute of an engine that develops 240 kN of thrust (twice that of the most common CFM56)… and b) the M56 never really existed in the real world. Intended to be Snecma’s stab at the 90 kN thrust range, the M56 was still a paper project by the time the CFM International joint venture was announced, with barely the essential tech and concepts worked out.

To make it slightly more complicated, GE’s contribution to the CFM56 is actually based on the F101, a reheated high-performance military engine developed for the original supersonic B-1A Lancer. Use of the CF6 designation came in handy purely out of convenience, since GE and Snecma had already collaborated previously on European production of parts the CF6-50 powering the A300 and A310.

The 50-50 division of work established within CFMI thus sees GE contribute a modified version of the F101’s high pressure section (the high pressure compressor, high pressure turbine and the entire combustion chamber), while Safran (today’s Snecma) supplies the fan, low pressure compressor, low pressure turbine, accessory gearbox and exhaust section, all of which were developed for the stillborn M56.

The specific engine I had the opportunity to photograph is called the CFM56-5B4 SAC, a typical engineering sausage that immediately tells you pretty much all you need to know:

5: developed for use on the Airbus A320 Family*
B: an upgrade of the “first gen” 5A with a modified fan and low pressure compressor
4: developing 120.1 kN for take off and 108.4 continuously
SAC: variant featuring the Single Annular Combustor**

* while it’s easy to assume that “a CFM56 is a CFM56”, quite a lot of engineering has to go into making the engine suitable for use on other airframes. Perhaps the best examples are the -3 and -7 variants developed for the 737-300/400/500 and 600/700/800 respectively, whose gearboxes had to be repositioned and fans made shorted to make them fit under the type’s low wing with reasonable ground clearance (other changes on the -7 include just 24 fan blades versus the 36 on the -5, and a redesigned core to compensate for the fan’s reduced efficiency)

** normally not part of its formal designation, the combustor type does have some bearing on the engine’s performance. In the modern turbofan, the combustion chamber is a doughnut-shaped cavity in the middle of the engine in which fuel is mixed with air and turned into noise. Fitted at the front of this chamber is the combustor, in essence a ring mount for 20 fuel injectors that spray atomized fuel into the chamber. In SAC engines, there is only one set of injectors; in 1995 however, CFMI started offering the Dual Annular Combustor (DAC) option, which featured – obviously – two sets of injectors. The first – called the Pilot Dome – is optimized for lower power settings, while the second one – called the Main Dome – is optimized for high power settings. The Pilot Dome operates in all stages of flight; however, when extra oomph is required (such as during take off or climbout), the Main Dome comes online to increase efficiency and better use the energy in the fuel. While there are some fuel consumption benefits to this setup, the main party piece is better throttle response – and a significant reduction in NOx emissions, reported to be 40-45% over SAC models

*While it may not be as exciting to look at as the fancy GenX or P&W’s Geared Turbofans, the 56 nevertheless has a simple elegance and eye-pleasing symmetry*

Other details? Well, despite being a sizable lump of machinery – 2.6 m long, 1.9 m wide and 2.1 m tall – it tips the scales at just 2,382 kg dry (without oil & hydraulics loaded), and 2,420 kg wet, i.e. fully loaded and ready for installation into the nacelle.

Since I believe that continuing to solely talk numbers would defeat the (hopefully) educational point of this article, it’s high time to get down to the best bits: the photos! 😀 Alas and unfortunately, some of them will not be up to my usual standard; the aircraft that I got to inspect – a pretty stock A319-112 – was undergoing deep maintenance at the time, parked in a hangar with a scorching sunlit day outside. Thus, the situation was one of extreme backlight and unfavorable contrast, which took quite a deal of both physical and electronic work to compensate for (not to mention a ton of sweat). Hopefully though, the sight of all those purposeful do-dads and thingamajigs will make up for it!

The golden engine. To stop it from turning red, its aforementioned 120 kN take-off power is limited to **5 minutes** normally – and up to **10 minutes** in case of an engine failure. Of interest, the three empty slots around the spinner are not missing bolts; they are in fact slots for tools necessary to remove the spinner and access the fan’s inner assembly

Despite being a “middle-of-the-road” engine with a thrust rating of “yawn”, the CFM56 nevertheless looks pretty brutish once you take its clothes off. It’s aggressive wasp-like lines nicely highlight its main bits; from the front, there’s the big fan – the compressor section (with the smallest diameter) – the fat combustion section at the rear – and finally the turbine & exhaust section. Like many other turbofan engines, the CFM56 is a **two spool** design: it has an inner shaft with a High Pressure (HP) turbine driving the HP compressor – and an outer concentric shaft with a Low Pressure (LP) turbine driving the LP compressor and fan. The compressor section itself sports **four LP** and **nine HP** stages; while the turbine section has **a single HP** stage and **four LP** stages. Also, this particular engine is missing its tail cone, which is nearby undergoing some servicing

One of the first things that catches the eye is the size difference between the fan and the core – and consequently, the difference in the mass of air that flows around the core vs the mass that actually goes through it. Called the **bypass ratio**, on the 5B it is **1:5.7** – meaning that the mass of air flowing through the bypass duct (visible to the right) is **5.7 times greater** than the mass of air actually entering the core (and participating in the whole combustion thing). The manuals say that the total mass flow (exhaust + bypass) is **407 kg/s** at take off power; to give a fun but completely useless reference, this means that both engines would need slightly under five and a half hours to suck all the air out of Boeing’s Everett production line (by volume the largest building in the world)

Another detail that does not escape notice is the mass of machinery hanging from the fan case; called the **accessory gearbox**, it turns the rotation of the HP spool into power for a wide variety of essential services, including the **oil pump**, main fuel pump (there’s also an electrical backup), **engine-driven hydraulic pump** (w/ electrical backups as well), **AC generator** and the **FADEC** (the engine’s electronic brain). It also mounts the **pneumatic air starte**r, which uses high pressure air from the APU or an external source to spin the HP spool up for start (electrical starters are not used on engines of this size, since the size of the starter – not to mention the current draw – necessary to bring the HP spool up to the required speed for start would be highly impractical). Of interest, this gearbox was one of the main “trouble areas” when the CFM56 needed to be lodged underneath the lowrider 737…

A nice plan view of the backside of the CFM56 – which required quite a lot of maneuvering, sweating and swearing! One of the most difficult parts of the engine to design, the HP and LP turbines have to operate in some properly difficult conditions; the HP turbine is in a particularly tough spot, being subjected to exhaust gases that measure up to **950°C** on take off (and **915** continuously). To survive this torture for thousands of hours on end, each turbine blade has an elaborate cooling system that ducts air from the pneumatic system THROUGH the blade itself, and then expels it overboard through dozens of tiny pores on the blade surface – thus both cooling the blade from the inside and forming a thin protective film along it on the outside. And just to drive home the point of “hard to design”: there are a total of **650** blades in the HP and LP turbine… despite these tricks though, the blades still suffer from a fascinating phenomenon called **blade creep**, in which the combination of heat and high angular speeds minutely deform and stretch the blade in span, shifting its mass towards the tips; the good news is that this can actually be used to good effect, since by modulating the flow of cooling air, the blade span can be somewhat regulated and thus the gap between the tip of the blade and the compressor casing can be controlled to achieve the best possible efficiency (called the **Turbine Clearance Control (TCC)** system)

Fan art. The largest single moving part in the entire engine, the fan measures **1.73 m** in diameter and sports – as mentioned earlier – **36 blades**. Despite its speed looks though, it (and the entire LP spool) revs at a relatively sedate maximum of **5,200 RPM** (clockwise when viewed from the back), just slightly faster than the redline of a typical automotive Diesel engine. The HP spool is a bit sportier, revving up to as much as **18,513 RPM**; sounds impressive, but it actually perfectly illustrates the physical reality of “the bigger they are, the slower they spin”. For comparison, in the much smaller PW150A out of the Q400, the LP and HP spools spin at 27,000 and 31,150 RPM respectively at max power… while the Q’s “screaming demon” Hamilton Sundstrand APS 1000 APU goes all the way up to 64,154 – fast enough to make itself clearly heard even above the din of the typical airport…

An “upskirt” peek at the fan from the other side reveals yet more fascinating details. In essence, all of the blades on the fan, compressors and turbines are installed at one preset angle – just like the fixed pitch propellers on light aircraft. This means that the blades are only really efficient at a few combinations of forward speed and RPM; change either, and efficiency begins to drop off. Since it is ruinously expensive (and mechanically quite complicated) to make the blades themselves adjustable, jet engines are fitted with **stator vanes** (visible in the foreground) that stabilize and direct the airflow onto the next compressor/turbine stage, thereby preventing eddies that could result in inefficient and unstable engine operation. The vanes come in **static** and **variable** flavors, the latter adjusting their pitch to suit the prevailing conditions (just like the constant speed propeller). Note also the protrusions on the fan blades (visible in the previous shot as well); these are called **shrouds** and are used to give the blade additional rigidity, reduce vibration and alleviate some of the loads on the blade’s inner structure. Predominantly a feature of “old school” engines with titanium blades, they are unnecessary on modern composite fans, since the latter are lighter, far more rigid, and can be shaped more precisely to reduce aerodynamic loads

Another interesting “feature” of shrouds is the noise they make when the engine is windmilling – captured (rather loudly!) in the video below. In essence, the blades of the fan, compressors and turbines are not rigidly fixed to their associated shaft, but are free to move about longitudinally in their mounts. In normal operation and at normal rotation speeds, they set themselves into one position and stay there; but when windmilling (or turning at lower speeds), they jiggle up and down making a racket. Among several benefits, the main point of this freedom of motion is to absorb and dampen the shaft’s vibration, and prevent some of that energy from being transferred to the blades themselves – energy that can cause internal cracks and various fatigue damage, stuff that is very problematic and very hard to detect (and had brought down more than one airliner in the past).

Shrouds add their bit by turning the volume up to 11, since during windmilling they tend to clap loudly against the next blade in line with every rotation. One needs to look no further than a comparison with the -7 series on the 737NG (below): its smaller fan does not need shrouds at all, since its shorter and lighter blades can be dampened just as effectively already at their root (just like compressor and turbine blades). Positive peace & quiet compared to the -5!

An abstract look down the bypass duct. The main features here are two of the four **reverser blocker doors** (visible right side), which open into the **cold stream** (the air flowing through the duct) and deflect a portion of it overboard and forward against the direction of motion to provide braking; note that the **hot stream** (the gases from the core) are not used for this purpose. Like all reverser systems, the one fitted to the CFM56 has a minimum use speed – **70 knots** – below which there is a distinct possibility of the engine drawing in the highly turbulent reversed air, as well as ingesting foreign objects from the runway

And finally, some love for all the other bits of the engine that make it work in the real world: the fuel, electrical, oil, hydraulic and air lines, as well as various mechanical regulators, coolers, mounting points and whatnot. Dominant in view on the right are air ducts for the **bleed air** system, which bleeds air from several points along the HP compressor (the front and middle stages) to pressurize and air condition the cabin. Tucked in to the left-low of the T junction is the **air starter valve**, which ducts high pressure air from the bleed system to the air starter mentioned several photos earlier

Sources:

Airbus – A319/320 Flight Crew Operating Manual (FCOM)
CFM International – 20 years of CFM press release & CFM56 DAC press release
EASA – CFM56-5B Type Certificate Data Sheet (TCDS) (PDF)
General Electric – CFM56 brief history
various CFM56 maintenance manuals + bothering the people who fix them for a living (they know who they are!)

Photo File – Piper PA-34-200 Seneca 9A-LEM

October 22, 2020April 4, 2021Posted in General AviationTagged 9A-LEM, PA-34 Seneca, PA-34-200, Piper, Piper Seneca, Piper Seneca ILeave a comment

By me
All photos me too, copyrighted

In a return to form for a website I claimed would deal with “news from Croatian general aviation” – but which most of the time does nothing of the sort – my second piece for October 2020 could not be more on point: a photo session with the newest addition to the Croatian civil registry, Piper Seneca 9A-LEM. And while Senecas as such hardly qualify for the Endangered Airplane List, this particular example is a nowadays very rare first generation model – and only the second such example I’ve ever come across IRL. Now, if that wasn’t enough to reach for my car keys… 😀

*It may not be the most exciting shape out there… but there are enough nerdy bits on it to keep me occupied for hours!*

Swiss stability

Like with Soviet aircraft – whose designations and serial numbers amount to pretty much the airframe’s entire ID card – you can tell a lot about pre-80s Pipers just by making sense of all the gibberish on their data plates. 9A-LEM’s, for example, reads PA-34-200 with the serial 34–7350327, which translates to:

34 – the type designation for the Seneca family
73 – produced in 1973
50 – model code for the original Seneca series* (the Seneca II would be designated 70, while early Seneca IIIs – the last to use the system – were 33s)
327 – the 327th aircraft produced in 1973 (but not the 327th Seneca overall; with 360 produced in 1972, LEM would be no. 687, excluding the prototype)

The 200 suffix is a nugget as well, since it indicates that this model is powered by normally aspirated, fuel injected, four cylinder Lycoming L/IO-360¹ engines producing 200 HP – making it the only Seneca mark not to use turbocharging. Its occasionally marginal performance at altitude (particularly in the climb) meant it would soon give way to the PA-34-200T Seneca II, powered by six cylinder Continental L/TSIO-360 engines developing the same 200 HP – but now equipped with turbochargers that could maintain that output all the way to 12,000 ft. Though this did wonders for overall performance, the subsequent PA-34-220T Seneca III would up the take off power to 220 HP in order to cope with the type’s constant mass increases (max continuous remained at 200), a solution that would also be re-used for the Seneca IV – before finally being upgraded to 220 HP both for take off an continuously on today’s Seneca V (achieved by fitting a different engine variant and improved turbocharger w/ intercooler).

* while it does appear in a number of sources on the Internet, the first Seneca series was never formally called the Seneca I; only the four later generations had a Roman numeral to their name

The first of the original Seneca’s several dead giveaways are the boxy engine nacelles – all lumps, bumps and intakes – and the **1.93 meter** two-blade, constant speed, fully feathering prop. The type’s familiar three-blade unit of the same span would appear only in 1979 on the Seneca III – and even then initially as just an optional extra

For a light aircraft that’s pushing half a decade in service – and which you would expect has seen its fair share of commercial operators and flight schools – LEM had led an unusually quiet life, having only ever had two previous identities: N56394 for delivery, and HB-LEM from September 1973 to February 2020. Interestingly, its time in Switzerland – among some pretty high terrain – was spent accident-free and in the hands of just one private owner, having never seen a single student or contract pilot in the nearly 5,800 flight hours it had logged over there. In fact, the only blot on its record that I could find is an airprox incident in 2018 that ended without damage.

Proving that you can’t run away from school forever, this would change on 28 February when HB-LEM landed at Pisarovina-Bratina Airfield (LDZR), a private airstrip near Zagreb owned by local flight training provider Pan Avia. Through a combination of maintenance, paperwork and just plain old corona crisis, it would take nearly seven months for it to join the active fleet, by which time it would become known as 9A-LEM. Unsurprisingly, it will be used by future airliner drivers for their Multi Engine Piston (MEP) training, a task for which many operators said it was well suited, despite its asthmatic climb performance on one engine (somewhere around the 400 FPM mark in a typical training configuration, less – but only just – than the purpose-built PA-44 Seminole trainer).

American recycling

Having established that LEM’s history is squeaky clean and disappointingly straightforward, it’s time to get down to best part: the nerdy details! Even though the Seneca had looked thoroughly modern and quite cool when it went on sale in 1972 (particularly in comparison with Piper’s other twins, the 50s PA-23 Aztec and 60s PA-30/39 Twin Comanche), the truth of the matter is that it was still very much a “real Piper”: essentially designed on the back of common off-the-shelf components and structural bits & bobs of the company’s other aircraft. Indeed, the main parts donor – contributing the fuselage, wing, tail, interior and cockpit – was the six seat PA-32 Cherokee Six, traces of which would remain easily identifiable (as will become obvious later!) well until the early 80s Seneca III.

The first of the many telltale signs of the Seneca’s Cherokee Six DNA are the square windows, copied over bolt-for-bolt. With the coming of the Seneca II, they would receive rounded edges – and then be fully recontoured and resized on the Seneca IV (the III would introduce a third set in the cargo bay)

And while you’d be hard pressed to find a manufacturer that did not dip into its own parts bin for every new design, Piper is widely acknowledged for elevating this “Lego approach” to wholly new levels. By keeping things simple and not trying to reinvent the wheel – except in rare moments of madness such as the PA-31P Pressurized Navajo or the PA-35 Pocono regional airliner – they were able to produce good, reliable, middle-of-the-road aircraft quickly and on comparatively small budgets. Low development costs then translated into reasonable showroom prices, which were frequently worth the design’s long-term dynamic, economic and operational inefficiencies.

The Seneca had managed to pull this trick off as well, with the original series being such a hit that 933 would be sold before production shifted to the improved Seneca II in 1975. Piper’s continual pig-headed tinkering with the design and near-constant performance upgrades made the hard-to-kill twin relevant even into the 21st century, with Senecas still rolling off the production lines after nearly 5,050 have been built.

The doors (both in location and size) are another throwback to the Cherokee Six. Some authors even said that if you took the Seneca’s wings off, you pretty much wouldn’t be able to tell the two apart…

Piper archaeology

Having been based on the structure of a single-engine airplane – which was not originally envisaged or scaled to carry the extra mass of a second engine and the additional fuel to feed it – the first generation Seneca naturally had its fair share of limitations. Depending on the fit and equipment options selected, the empty weight for most examples hovered around the 1,200 kg | 2,650 lbs mark – noticeably more than the 820 kg | 1,810 lbs of the PA-32. With full fuel – 371 l | 98 USG (260 kg | 590 lbs) across two wing tanks – you were left with only 355 kg | 760 lbs to play with before hitting the 1,815 kg | 4,000 lbs Maximum Take Off Mass (MTOM). Even considering that people in the 70s were, on the whole, slimmer than they are today, this made for a useful load of only four 75 kg | 165 lbs adult males with 5 kg | 11 lbs of baggage each.

If you wanted to max out the cabin and use all the six seats you paid for, you could be looking at barely 190 l | 50 USG worth of fuel. And while that would be classified as “a lot” on the Cherokee Six, the Seneca’s fuel consumption of 18 USG/h at 65% power meant it would suck its tanks dry in around two hours and 45 minutes. Knock 45 minutes off for Final Reserve Fuel, 30 minutes for a reasonable Alternate w/ a bit of holding, and 15 minutes for Contingency (to compensate for imprecise performance charts, calculation errors and weather avoidance), and you’d end up with an effective endurance of just one hour and 15 minutes – barely 370 km | 200 NM at the 295 km/h | 160 kts cruise speed you’d get at 9,000 ft. Throw in high temperatures, headwinds and “weekend fliers” who may not know all the tricks of economy flight – precise leaning, finding the best fuel/speed/wind ratio, least-fuel climb and descent profiles, etc – and that could very well drop below the 60 minutes mark.

This of course did not fly under Piper’s radar, and pretty soon it came up with an option to boost MTOM to 1,905 kg | 4,200 lbs. Essentially a “paper exercise” in stretching the rules while remaining firmly within them, this mod did not involve any structural changes to the aircraft – but merely the provision that this increase is possible as long as the aircraft’s Maximum Zero Fuel Mass (MZFM) does not exceed the original MTOM (1,185 kg | 4,000 lbs)**.

** in simple terms, the MZFM represents the maximum mass the aircraft may have with no fuel in its wing tanks (i.e. basic structure + payload + fuel in any other tanks other than wing). When loaded with fuel, wing tanks weigh the entire wing down and alleviate some of the upward bending moment caused by lift; and since lift counters mass, the heavier the aircraft, the more lift is needed and the larger the bending moment will be. If the moment is too large, it can cause significant structural damage to the wing – thus the mass of the airplane has to be limited so that in the case of fuel exhaustion, the moment would remain within safe limits. In an extreme example, this meant you could not load you Seneca with stuff up to a mass of 1,860 kg | 4,100 lbs and then just add 45 kg | 100 lbs worth of fuel – since if (or rather when) you ran out, the wings could buckle

In practice, this did go some way to addressing the type’s fuel issues, but there were a few traps along the way – chief among which was the Maximum Landing Mass (MLM). In the “six 75 kg male” scenario above, the mass of the loaded aircraft without fuel on board (Actual Zero Fuel Mass, AZFM) would be 1,680 kg | 3,700 lbs, which meant you could now conceivably take 225 kg | 485 lbs (320 l | 81 USG) of fuel, giving you a much more agreeable endurance of 4.5 hours. Factoring in the same Reserve, Alternate and Contingency Fuel, you got a solid three hours, or approx. 900 km | 485 NM of range (to keep things simple, the math assumes the same cruise speed and fuel consumption as before, despite the higher weight).

The trick***, however, was that the MLM remained unchanged, and was equal to the MZFM and old MTOM. So on landing, the mass of the airplane, everything/body on board and the fuel remaining had to be 1,815 kg | 4,000 lbs or less. So if you packed all six seats, fueled your bird to the brim and then flew for just one hour, you were going to be overweight on landing. The same issue also limited the load; if you planned everything right, you’d have landed at your destination with Reserve and Alternate fuel remaining – roughly 85 l | 22 USG (60 kg | 135 lbs) using the numbers above. With an empty weight of 1,200 kg, your load then could not exceed 555 kg | 1,225 lbs – which is right on the limit for today’s average passenger weights (six 80 kg | 175 lbs males with 10 kg | 22 lbs of baggage each).

*** another issue to be mindful of was a significant drop in performance at the new MTOM, particularly on one engine. The manuals show that the absolute single-engine ceiling went down from 6,600 to 5,000 ft – while the max sea level rate of climb on one engine dropped from a meager 230 FPM to just 190…

While this explanation is, admittedly, a bit long-winded and heavy on the numbers (being a byproduct of my own airline flight planning traumas), it does serve a couple of vital functions: one, LEM has the 4,200 option on it – and two, it goes to show just how “offbeat cool” and charmingly flawed the original Seneca really is. And more is to follow!

Since it was intended right from the outset to be a comfortable and serious touring aircraft with an eye on commercial ops, its systems, avionics and general equipment fit are considerably more extensive than on any previous Piper light twin. On the outside, the most notable is the optional de-icing system, available in several different configurations – but in the event taken up in full by the vast majority of aircraft, LEM included. Certified for flight into known icing conditions, it uses traditional pneumatic boots for the wing and tail surfaces (inflated by the same vacuum pump that drives the primary instruments, albeit a more powerful model to cope with the higher demand), while the props, fuel tank vents and windshield – where equipped – are heated electrically (in addition to the usual Pitot tube heat).

The limitations of electrical systems on light aircraft mean that “windshield heating” can be a bit misleading. While it is indeed physically possible to install full-pane heaters as seen on airliners, their current draw would simply be too much for the types of generators fitted to piston engines – especially in case of an engine failure at night and in icing conditions, when demand for electricity from the remaining unit is at its highest. To get around this issue, many twins and high performance singles use so-called “plate heaters” or “hot plates”, bolt-on heated glass frames whose size is small enough to avoid overtaxing the airplane’s electrical network – but still big enough to provide at least some form of forward visibility. Information on the net suggests this model has a **15 A** current draw – for comparison some five amps less than the propeller heaters

Inside, the “front office” could be equipped with enough kit to rival some high-end twins, with a full IFR suite being standard – and buyers offered enough avionics options to fill several pages (quite literally). Since LEM was intended to operate in the occasionally complex weather conditions common to the Swiss Alps, it sports pretty much everything it was possible to fit, and had over the years been retouched with more modern avionics in place of the old 70s Kings, Narcos and Bendixes. The setup as of October 2020 includes:

Sandel SN3308 Electronic Horizontal Situation Indicator (EHSI)
Garmin GNS530 NAV1/COM1 w/ FLARM input from an external module
Bendix King KX 165 TSO NAV2/COM2
Bendix KN 62A TSO DME
Garmin GTX 330 transponder
S-Tec Fifty Five X two-axis autopilot w/ ST-645 remote announciator
S-Tec ST-360 altitude alerter
King KWX 50 TSO weather radar
King KRA 10 radio altimeter
and a PS Engineering PMA 6000M audio panel

The type’s “quirky coolness” continues on the inside as well with more bits of the Cherokee Six. A familiar sight to Warrior drivers, Piper’s traditional panel layout does have its drawbacks on the Seneca – clutter and a lack of space being the biggest ones. Despite that, it would be carried forward all the way to the Seneca III, at which point it would be made taller, more efficient and fully metal, allowing for a far more ergonomic layout. A neat detail is the hand pump next to the sill, which inflates the seal around the door in order to reduce wind noise and prevent entry of cold air in flight

The lack of space on the main panel is so acute that pretty much all electrical and light switches had to be relocated to a custom panel on the pilot’s left. In the Seneca III and above, these would be moved to where they (sort of) belong, on the main panel under the yoke and near the plot’s left knee; while far from ideal, this did free up some elbow room and reduced the likelihood of inadvertent switch activation (the narrower, tighter Seminole also sports a roughly similar panel)

Few things beat the night-time on the flight deck – no matter how small. This sight brings me back to my own MEP training on the Seminole and Turbo Seminole 10 years ago (which had a broadly similar panel, though with less stuff). Unfortunately, while setting up this shot – and doing it quickly as not to drain the battery – I apparently nudged the tripod to the side, so the photo is at a bit of a (frustrating) angle…

Back in the cabin, there are few surprises – the biggest being the seating arrangement, with two rows of two seats all facing forward. Yet another hand down from the Cherokee Six, it would be retained even on early examples of the Seneca II, at which time the familiar “club layout” – two rows facing each other – would be introduced as an optional extra (and finally made standard on the Seneca III).

Even on cursory inspection, it is obvious that LEM was very well cared for – and the simple, clean & classy cabin further proves it. The seats had been reupholstered in leather not too long ago and are quite comfortable despite being a bit on the small side. In the later club configuration, the rear row would be pushed slightly back into the cargo bay to give both sets of passengers usable legroom

One of the reasons late model Senecas were (and still are) popular with air taxi operators is that passengers did not have to climb up onto the wing to get in – unlike on the original. To get at the second row of seats with any dignity, you have to squeeze through the copilot’s door, past the front seat, and then plonk yourself down without hitting your head on the roof-mounted air gaspers. A detail that also catches the eye is the space between the second row seats; it was wide enough to actually allow installation of an optional “jump seat”, bringing the total capacity to **seven** (this would also be offered on Seneca IIs that did not have club seating; in the latter arrangement, this space would be occupied by a hollow armrest used for storing drinks and small items)

*While the sitting position in the second row is OK as such – even for me at 1.9 m in the vertical – legroom can be an issue if the crew is taller and needs to move their seats further back*

Given LEM’s overall state – nearly mint, with just a few flakes of (original) paint missing – I was not the least bit surprised to learn that its previous owner did quite a bit more over the years than just reupholster the seats. To get a bit more go out of its limited power, LEM sports several aftermarket aerodynamic tweaks, the most obvious being LoPresti Zip Tips. One of the many upgrades² from the workshop of famed “speed merchant” Roy LoPresti, Zip Tips are carefully profiled wingtip extensions that alter the dynamics of wingtip vortices, rotating air currents that form when high pressure air below the wing tries to flow over its tip to the low pressure area above. Since the aircraft is continually moving forwards as this is happening, this swirling flow ends up being left behind the tip – in clear air – quickly developing into a full-blown vortex that slowly sinks and eventually dissipates when it uses its energy up (usually within a minute on Seneca-sized aircraft). As well as being the root cause of wake turbulence, these vortices also disturb the flow of air coming off the upper surface of the wing (the “downwash”), altering its direction so that the wing now operates at a lower Angle of Attack (AoA), reducing its lift. To compensate, the aircraft now has to either fly faster or at a higher pitch in order to maintain level flight, which increases both drag and fuel burn.

Based on the 1940s research by German aerodynamicist Sighard Hoerner (who did most of the legwork on the superlative Fi-156 Storch) and the 1920s ideas of aviation pioneer Ludwig Prandtl, Zip Tips work by extending the upper end of the wingtip beyond the actual end of the wing, forcing the vortex to form further out – and then use its kinetic energy and inertia to push it away from the tip so it remains clear of the downwash. Since Zip Tips are actually wingtip extensions, they also increase wing area slightly and up the **aspect ratio (AR)**, the ratio between wing span and the chord that has a major influence on vortex strength (the higher the AR, the weaker the vortex). Another trick is relocating the navigation and strobe lights into a common cluster with the landing light; this reduces drag, further smooths the airflow around the tip, and makes the Hoerner Effect more effective – but at the price of reduced visibility of the lights. LoPresti don’t publicly say what the net results are – but I’ve read reports that people have been getting approximately **5 knots** more in the cruise on the same power. Improvements in the rate of climb – particularly on one engine – remain a mystery; informed speculation suggests that **up to 50 FPM** would be a realistic figure. As fitted to LEM, the tips also include the Boom Beam, a High Intensity Discharge (HID) landing light that boasts a 20-fold increase in luminosity over factory lights, 20,000 lux vs 1,000

Other LoPresti mods fitted to LEM include:

Speed Seals – fair over the gap between the wing and flaps to prevent the high pressure air underneath the wing from escaping upwards, which gives 2 knots more in the cruise + a bit of extra maneuverability in the roll
gear fairings – improve the airflow around the main gear wheel well (which is not covered by the gear doors when the landing gear is retracted), reducing drag and noise and reportedly adding a further 3 knots

All in all, the LoPresti kit on LEM should be good for a solid 10 knots extra in the cruise at the same power setting – though the actual gains will depend on atmospheric conditions and flight regime, and may not be that impressive in the type of low-weight, low-altitude, low-speed situations that are typical of MEP training.

Money had been spent under the hood as well, with the engines sporting a full set of GAMInjectors, aftermarket fuel injectors developed by General Aviation Modifications that are built and calibrated to much much tighter tolerances than Lycoming’s own factory units – and provide a more uniform fuel/air mixture across all four cylinders, giving better power delivery and a quicker throttle response with reduced engine wear and lower fuel consumption.

The lopsided airplane. Surprise surprise, the wing is another Cherokee Six item, sporting the same planform, the same **NACA 65-415** airfoil and the same 7° dihedral (the upward angle of the wing) – but now with two meters of span more, 12 vs 10. Unlike the Cherokee Six though, early Senecas were prone to Dutch Roll in turbulent conditions, an uncomfortable combination of rolling and yawing motion that did not always sit well with passengers. A byproduct of a design’s optimization for efficient cruising flight, the Dutch Roll occurs when the aircraft’s roll stability (along the longitudinal axis) is more powerful and acts more quickly than its directional stability (in yaw along the vertical axis, provided by the vertical stabilizer). When the aircraft is disturbed from straight & level flight, the coupling of these two stabilities sets the airplane up for an oscillating slipping motion that – left alone – can persist for quite some time. Dihedral wings increase roll stability and thus tend to exacerbate this effect – as do the Seneca’s draggy engine nacelles, increased wingspan and longer nose with a larger side area, all of which create additional & unhelpful yawing and rolling moments that combine together to cause problems the Cherokee Six did not have. This tendency would be corrected to a degree on the Seneca II with a modification of the rudder (in order to increase the vertical stabilizer’s responsiveness), which would eventually be offered as a retrofit for the originals as well

Intended to be user friendly even for less experience pilots, the first gen Seneca had interconnected ailerons and rudder (by means of light springs), so that when the control wheel was turned to initiate a roll, the rudder would automatically deflect to counter the adverse yaw (also useful with an engine out). However, this made the controls feel quite heavy, so the springs were removed on the Seneca II. As is common on most pre-80s Pipers, the flaps are actuated mechanically by a lever on the floor between the front seats, and can extend to **10°**, **25°** and **45°** (electrical flaps would debut only in 1985 on the Seneca III, being a necessity since that version’s larger flaps required too much muscle power to actuate)

Third time’s the charm

Naturally, this being Achtung, Skyhawk!, it was only a matter of time before I’d try and fit LEM into some sort of wider historical context. As I was combing through its history while preparing this piece, I began to recall seeing mention of other early Senecas that had carried the 9A prefix. And sure enough, having checked my historic registry, I discovered that there were indeed two examples preceding LEM, both – sadly – well before I had my first camera:

9A-BIL | 1973 | s/n 34-7350314: just 12 airframes ahead of LEM, not much is nowadays known about BIL, except that it had previously been operated by Lošinjska plovidba out of Lošinj Airport (LSZ/LDLO). The only recent mention I have of it is from 2017 under the identity N351MC, when its registration was cancelled by the FAA (even though Flight Radar 24 showed this reg active in July 2020)

9A-BPW | 1972 | s/n 34-7250191: originally registered N4978T for delivery, BPW would spend the first 20 years of its life in Germany as D-GEAR, before being be delivered to the AK Zadar flying club of Zadar Airport (ZAD/LDZA) sometime in mid-1992; it would later pass to North Adria Aviation of Vrsar Airfield (LDPV) – and then join Airmed of Spain as EC-HCA, where it is still happily flying as of October 2020

Being lucky #3, LEM is poised to outlive them all, with tentative plans already being made for further avionics upgrades and a fresh new paint job. And all the students that have flown so far it have been reported to like it very much – so it may even get off easy in life… 😀 (speaking as a former MEP student!)

*What photo shoot would be complete without having a bit of fun? It is also interesting how the shadows and contrast seem to make the Seneca look far meaner in the dark…*

¹ in common with many other Piper light twins, all Seneca models have counterrotating engines, where the left propeller spins in the normal clockwise direction (when viewed from the back) – but the right propeller spins counterclockwise (hence L for “left turning”). The idea behind this approach is to improve handling in an engine-out situation by removing what’s called the critical engine. In a nutshell, each propeller blade generates more lift going downwards than going up; hence, one part of the prop disc will always produce a higher lift than the other. In engines with the normal clockwise spin, the lift will thus be greatest on the right side of the disc.

On conventional twins – both engines spinning clockwise – this becomes an issue during an engine failure. Should one engine go belly-up, the other one has to keep the airplane in the air – and that means it has to run at maximum continuous power for the prop to produce the highest possible lift. In this situation, failure of the #2 engine is the “lesser evil”, since the right side of the #1 prop disc is fairly close to the fuselage/Center of Gravity (CG) – so the highest lift will be acting on a short arm and thus produce a comparatively small yawing moment. However, should the #1 engine fail, the right side of the #2 prop disc is considerably further out – so both the arm and the yawing moment will be correspondingly higher.

The only way to counter this moment in any of the above cases is with the rudder; but, since its effectiveness depends on speed, there is a point below which it will not be able to generate enough lift to oppose the yaw. This point is called the minimum control speed in the air (V_MCA), and effectively represents the aircraft’s minimum permissible speed on one engine. Unsurprisingly, it is higher if the #1 fails since the yawing moment is higher – and is taken in practice as the value to be printed in manuals and indicated on instruments in order to avoid confusion in the heat of the moment (and provide an additional safety margin). For this reason, the #1 engine is called critical.

In a counterrotating setup however, the #2 engine rotates counterclockwise, so the part of the disc that produces the greatest lift is now inboard of the engine, next to the fuselage – and on an equal arm to that of engine #1. Now there is NO critical engine, since failure of either will result in a yawing moment of the same magnitude. Despite this – and for the reasons stated above – the Seneca POH will nevertheless reference V_MCA to engine #1, a nice round 70 knots on the first gen models, a full 10 knots above the stalling speed. But, while handy, this solution is practical solely on light piston twins, since the #2 engine has to be built slightly differently (“ass forward”) to both spin in the opposite direction AND fit in a cowling of the same size – which is far from cheap even on the types of “little bangers” used on Seneca-sized aircraft.

² at this point, you may be wondering why it took a funny old man in a small factory to fix something Piper itself – with all its vast resources – failed to do. The answer, as ever, lies in cost/benefit analyses: in bygone times of cheap airplanes and even cheaper fuel, “small issues” such as wasteful wingtip vortices were not considered problematic enough at Seneca speeds and utilization rates to warrant fixing – especially since the fix itself was bound to increase cost, complexity and/or adversely affect payload (the latter always a premium on the early Seneca).

However, times, priorities and fuel prices do change, leading many third-party providers – LoPresti, Knots 4U, Laminar Flow Systems, etc – to tackle with problems like these on a wide variety of light aircraft, using materials and manufacturing techniques that simply did not exist (or were prohibitively expensive) when those aircraft were first designed. But, that’s not to say they are immune from the cost/benefit demon – far from it in fact. The Zip Tips for the 1st gen Seneca, for example, cost USD 4.000 without installation – which may not make much financial sense for an owner who doesn’t fly nearly enough to recoup the cost within a reasonable time frame, despite them offering a clear benefit in both fuel consumption and overall efficiency.

As ever, I’d like to extend my sincerest thanks to Mr. Domagoj Čingel – owner of Pan Avia (and, by extension, 9A-LEM) – as well as my Q400 colleague F/O Nikola Renčelj for his detailed knowledge of aerodynamics and help in making a coherent picture of all the mechanisms and gains of LEM’s LoPresti mods!

Sources:

AOPA – Turbo Arrow review
Aviation Consumer – Speed Mods article
AvWeb – Seneca series overview and Seneca used aircraft guide
FAA – PA-34 Type Certificate Data Sheet (TCDS) (PDF)
PA-34-200 and PA-34-200T Pilot Operating Handbooks
Piper Owners Society – What To Do If Your Airplane Is Slow article
Piper Parts Manual
Plane & Pilot – Seneca series overview
Plane Check – Seneca flight test
Whelen Aerospace Technologies – LoPresti Zip Tips and Speed Seal product page

Incident – LDZL Storm Damage 04 OCT 2020

October 4, 2020April 5, 2021Posted in Incident / AccidentTagged LDZL, Lučko, Lučko storm, Lučko storm damageLeave a comment

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All photos me too, copyrighted

On the night of 03 October at around 21:00-22:00 local time, Lučko Airfield (LDZL) suffered a hit by a powerful squall line that caused considerable material damage – but, fortunately, no human (or animal) casualties. According to information available at the time of writing (subject to update), the airfield was struck by sudden gale-force winds and hail, with wind speeds in excess of 65 knots (as recorded by the anemometer just before it failed).

As of 16:00 local on 04 October, the damage to aircraft includes:

Reims FR172F Rocket | 9A-DMJ: flipped over, heavy damage
Cessna 150M | 9A-DEY: flipped over, heavy damage
Piper PA-18-150 Super Cub | 9A-DBS: struck by hangar door, heavy damage
Scheibe SF-25B Falke | 9A-DGZ: struck by hangar door, heavy damage
Pilatus B4-PC11AF | 9A-GPA: struck by debris, superficial damage
Storm Century 04 | YL-ARV: struck by hail, light damage
Mil Mi-8MTV-1/Mi-171Sh (4-5 machines): struck by hail, rotor damage

In the same period, the damage to infrastructure is:

main hangar: doors blown in, partial roof collapse
police hangar annex: light roof damage
Delta Air canvas hangar: severe damage
fuel pump: protective housing damaged

Unsurprisingly, the airfield has been closed for a week, as per the following NOTAM:

AERODROME CLOSED TO ALL TFC EXCEPT POLICE AND MIL HEL. 04 OCT 00:04 2020 UNTIL 11 OCT 22:00 2020. CREATED: 04 OCT 00:06 2020

UPDATE: as of the evening of 05 October, the above NOTAM is no longer in force; the airfield is now open once again

More information and photos as the situation develops!

Photo updates:

*The perfect metaphor for the day: clear skies abd beautiful flying weather viewed through the mangled tail of a Cessna 150…*

*Temporary repairs to the main hangar doors, until the original two sections (on the floor) can be reinstalled*

*In jail. All airworthy aircraft had quickly been relocated to other parts of the airfield, with only DGZ, DBS and grounded Starduster Too 9A-DID remaining inside*

Changelog:

04 OCT 12:00 local – initial info
04 OCT 16:00 local – aircraft and infrastructure damage revised
04 OCT 16:30 local – new photos added
05 OCT 21:00 local – airfield status updated

Photo File – Flying In The Time Of Corona: Foreign GA Snapshots

September 24, 2020April 5, 2021Posted in General AviationTagged Cessna, Cessna 210, Cessna P210R, D-EKYS, D-ENBR, DG300, Duruble Edelweiss, Duruble RD.03, F-CFVL, F-HBSF, F-PGDR, Glaser-Dirks, Glaser-Dirks DG-300, LDDU, LDSP, LDVC, LDZD, LDZL, Mooney, Mooney M-20J, OK-TKN, Partenavia, Partenavia P68, Pilatus, Pilatus PC-6, Ruschmeyer, Ruschmeyer R90, Storm Century, YL-ARV, Z3-DAMLeave a comment

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While going through my photo database in search of material for my previous Flying In The Time Of Corona photo file, I discovered that there’s plenty of stuff in there for a follow-up post as well – but this time focusing solely on foreign visitors to Croatia’s many coastal airports (+ Lučko of course). Like our own birds, these too could not be scared off that easily, arriving into the country in quantity and quality rarely seen even in years past. And since it would be rude of me to keep them all for myself, another summer time Photo File is obviously in order! (to build on the two bonus Cessna 172RGs already featured in their own post)

Before they can learn how to fly, young gliders must first learn how to taxi. To make that big step easier, their owners often fit them with training wheels and take them for short strolls around the apron. With time, they will progress to longer walks all the way to the runway – and eventually, when they feel more comfortable at the airport, they will finally be able to spread their wings and start flying all on their own…

A 210 on a hill… in the middle of an airport… next to a fire trainer… by a fuel farm… in the shade of an olive grove… well, that’s this week taken care of! What may eventually become the new static exhibit at Split Airport (SPU/LDSP), OK-TKN had arrived into town unexpectedly following an in-flight engine failure, and is now caught up in the financial and logistical nightmare of getting it going again…

Another skydive PC-6 – and another drive to see it right after the night shift. What makes this 2006 example a little bit more special is that it sports the 680 HP PT6A-34 engine instead of the stock 550 HP 27 series – and is seen carrying the type’s somewhat uncommon external fuel tanks. Carrying another 200 liters each, they give the PC-6 an impressive seven hour endurance – itself quite a neat trick on workdays when F-HBSF is used as an aerial imaging platform (for skydive ops they’re empty, but to simplify handling they’re usually left on the wing, since their performance penalty is quite small all things considered)

One of only 30 or so ever made (and the second one to end up in front of my camera), this beautiful Ruschmeyer R90 is one of those fantastic “what could have been” machines that make GA so special. Designed by Horst Ruschmeyer of Hannover in Germany, the R90 was an attempt to bring together all the cutting edge tech of the late 80s and combine it into a high-performance four-seat touring aircraft made squarely to European – rather than American – measure. Built entirely out of fiberglass (which was tested to destruction) and sporting a speedy laminar flow wing, it could touch 300 km/h in the cruise on just 230 HP – making it faster than pretty much every other aircraft of its power class. Its real party piece, however, was its noise signature: at full chat, it could do just 66 dB – roughly equivalent to the noise level of a typical office, and some 8 dB below the strictest level required by law. To do this, it was fitted with specially-designed exhaust stacks and a bespoke short-span four-blade composite prop – while the engine itself, a Lycoming IO-540, was actually derated down to 230 HP from its default 260 to cut down on all the yelling. Beautifully finished and with handling characteristics that were described as “a real treat”, the 230RG was supposed to launch an entire family of aircraft, including everything from a 190 HP fixed-gear “budget” model to a 470 HP Rolls-Royce 250 powered speed machine. Unfortunately, the design took until 1990 to sufficiently mature, by which time the market had slumped so hard that even Cessna had to throw in the towel. The results were depressingly predictable: after just five years of production and a single variant, the Ruschmeyer works filed for bankruptcy – and, despite attempts by other companies to revive the design, that was that for the sleek little R90…

So similar, yet so different: two “budget speedsters” that show just what can be done with some clever engineering and a bit of compromise. An aircraft that had set new standards for efficiency in its class, the Mooney M-20J (on top) was rebranded as the “201” when it became the first four-seat touring aircraft to reach 201 miles per hour (175 kts; 320 km/h) on just 200 HP. Though it had paid the price in payload and interior space – and required an extensive aerodynamic cleanup by the legendary Roy LoPresti – the J had set the stage for today’s M-20V, which needs only 280 HP and a turbocharger to cruise at 242 kts (450 km/h)… two thirds of the Q400’s maximum speed // But the more interesting machine is the Duruble RD.03 Edelweiss, an aircraft that needs only 180 HP and a fixed-pitch prop to do 147 kts (270 km/h) while sipping just 8.7 gallons an hour – roughly what a Cessna 172 would drink, using exactly the same engine and prop, to do 110 kts (204 km/h). What’s even more fascinating is that the RD.03 is actually a homebuilt, and was designed in the 70s by Roland Duruble, a marine engineer by trade. Other interesting bits include hydraulically operated landing gear and flaps, the latter extending automatically to the desired setting in response to airspeed – stuff unheard of even on turboprop twins. Another neat trick is that the horizontal stabilizer has a slight dihedral – it is mounted at an upward angle – so that it remains clear of the turbulence coming off the flaps (an effect that is quite pronounced on the Q400 at Flaps 35, and results in noticeable airframe vibration). This particular machine had been completed in 2003, and aside from the uprated 180 HP engine (the type standard is 160), it also sports a Lancair-style air intake that gives an additional performance and efficiency boost. In fact, the build is so sweet that it had featured in several GA magazines – often with the tagline “France’s homebuilt Mooney”

I may be small – but at least I’m weird. An aircraft whose elegance immediately belies its Italian origins, the Partenavia P.68 boasts quite an unusual cocktail of characteristics for a “serious six-seat touring aircraft”: a high cantilever wing, a pair of “small” IO-360 engines and – most interesting of all – fixed landing gear. But, while this may raise eyebrows, there’s quite a lot of method to its madness: from the outset, the P.68 was designed to be an efficient, affordable and user-friendly alternative to conventional twins of the 1970s, using sleek lines and clever aerodynamics to cruise at 300 km/h on just 2x 200 HP – and calculating that the drag penalty of the gear is a lesser evil than the weight, cost and complexity of retractable units (an approach later also taken by Cirrus). And it worked: in continuous production since 1971, more than 430 have been sold so far – including 20 of its glass-nosed patrol & observation models, the P.68 Observer & Observer 2 – making it one of Italy’s most successful GA designs. And if it reminds you somewhat of Tecnam’s new P.2012 Traveler, rest assured that the resemblance is NOT coincidental: the P.68 was in fact penned by the brothers Luigi and Giovanni Pascale, who would in 1986 go on to found the same “Costruzioni Aeronautiche Tecnam”…

Another speedy Italian Job – but with an unusual address (in Latvia no less). One of the many LSA designs to come out of Italy during the late 80s homebuilt boom, the Century 04 is a fixed-gear derivative of the earlier Century RG, featuring a 100 HP Rotax 912 w/ a constant speed prop – both of which are good for a solid 200 km/h in the cruise while sipping just 10-15 liters per hour. With space for a proper 2+2 config – but sporting only two seats to give more baggage space – YL-ARV will likely become a Lučko native soon…

Photo File – Flying In The Time Of Corona: Croatian GA Snapshots

September 6, 2020April 5, 2021Posted in General AviationTagged 9A-DJZ, 9A-DLJ, 9A-DMJ, 9A-DVB, 9A-DZG, 9A-PAD, Beech 76, Beech Duchess, D-KRMP, DBV, Dimona, Dubrovnik, FR172, Hoffman H36, LDDU, LDPM, LDSP, LDZL, Lučko, Medulin, PA-44, Piper Cherokee, Piper PA-18, Piper PA-28, Piper Seneca, Piper Super Cub, Reims Rocket, Scheibe, Scheibe Falke, SF-25, Vlaho PA-181 Comment

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Due to reasons beyond my control (to put it mildly), I had quite a bit of free time on my hands this summer, which I decided to spend – like in the good ol’ days – by enjoying the scenery at various airports and airfields throughout the land. While one would have assumed that the lockdown (pretty mild in Croatia, but still keenly felt) would have had a negative impact on GA ops, the truth of the matter was that the number of aircraft buzzing about had actually increased – which meant that there were always plentiful photo opportunities wherever you went. A perfect setting then to get the camera out and see what I’d been missing over the winter… 😀

If you’re sad for the demise of Cold War underground air bases and bomb-proof aircraft hangars, don’t despair – Dubrovnik Airport (DBV/LDDU) has something for you! Not so much a Hardened Aircraft Shelter as a “Hardened Vehicle Garage”, the brand new semi-subterranean storage depot along the airport’s northwestern perimeter may seem like an unlikely place for aircraft photography… but as you can see, it pulls it off nicely!

Concentration at 120% as a young colleague readies his ship for a late afternoon training flight. Somewhat fortunately, this student-weary veteran of the Croatian Aviation Training Center – to whose weariness I myself had actively contributed a decade ago – will soon give way to…

… this. It’s startup may not have been as smoky as I would have liked (thankfully for the engine!), but it was nevertheless worth frying like sushi on the superheated apron to catch my first ever Duchess. Conceived on the same train of thought as the Seminole, the 76 was always a typical Beech design: built up to a standard rather than down to a price. Unfortunately, that made it quite expensive to buy and maintain, meaning that only 437 would ever be produced… barely half the Seminole’s ~930 (and counting). Ironically, being a replacement for 9A-DZG means that Walter Beech may still have a tiny last chuckle!

Number 2 for departure after three incoming arrivals, holding short on a parallel runway being used as a taxiway since it is too close for proper simultaneous operations… this is not Lučko – it’s Gatwick on grass!

*Of course he’s happy – he’s going flying… and on an aircraft he built himself from the wheels up, and from parts of half a dozen factory Super Cubs!*

The 70s are back – as an airplane. While this “50 Shades Of Brown” interior may not be all that hot by today’s style standards, it is nevertheless so throwback cool that it warrants a “10/10 would sit” rating! (it also helps that the entire cockpit is crisp, clean, neat – and fully original, with the same trim it had back in 1986 when it rolled off the production line) (and yes, despite the D- reg, this machine is a fully-fledged local)

Even on its own territory, the Reims Rocket is a shy and reclusive species, easily frightened by noise and sudden movement. Because its colorful plumage makes it easy prey for photographers, it has evolved the ability to escape and hide quickly and without warning; always approach it silently and patiently, using local terrain and foliage for cover whenever possible…

And finally, one little Cherokee I’m VERY happy to see again! Covered previously in two some of my earliest posts here (part #1 and #2), DJZ is the sole “pre-Warrior” PA-28 in the country, and had years & years ago been based at Dubrovnik (DBV/LDDU). Unfortunately, a while back it had fallen on some hard times and was left to rot in the corner of the apron. Thankfully, about a year ago it had been brought to Medulin Airfield (LDPM) in Istria, where it is now undergoing a complete restoration – and will be happily flying already in early 2021!

Photo File – Gulfs Galore: G-III N32MJ + G-II-B N4NR @ LDZA

August 29, 2020April 5, 2021Posted in Rare AircraftTagged G-1159, G-1159A, G-1159B, Gulfstream, Gulfstream II, Gulfstream II-B, Gulfstream III, LDZA, N32MJ, N4NR, ZAG, Zagreb AirportLeave a comment

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Having always been on Team Gulfstream when it came to range-topping business jets – and living in a touristy country where the rich and famous (used to) come to let off some steam – I naturally had plenty of opportunity to enjoy the many fine forms of the Big Gulf. Down at the coast the G-IV, G-V and latterly the mighty G650 were as common as trees, and there was virtually no seaside airport without at least half a dozen of them at any one time.

However, the “older gentlemen” of the family – the original G-II and G-III – had continually eluded me, and several years came by and went until I finally managed to snap one. Making the same mistake as before, I kept thinking “well, that’s it, I’ve seen one now and never again”… right up until they started appearing in measurable numbers all over the place, including – very conveniently – at my base airport, Zagreb Intl (ZAG/LDZA)…

Gulfstream Aerospace G-1159A Gulfstream III • N32MJ

The first one off the bat is a mint 1982 G-III with the serial 460, owned by the basketball world’s own Magic Johnson. Since I do not watch sports, I cannot comment on Mr. Johnson’s professional career; but he is very obviously a man of culture, since – despite everything – he chooses to own an “oldtimer” that’s so loud it has to be silenced by law!

*It may be plain while and surrounded by newer, fancier & flashier birds – but N32MJ nevertheless manages to dominate the GA apron with ease!*

While these large cabin jets tend to lead comparatively simple and quiet lives, N32MJ has a history that can rival any MD-80: by my count, it had carried 10 separate registrations and passed through the hands of 12 different owners! (the full list can be found at Plane Logger) What is interesting for us here and now is that in 2005 it would pass from jet legend Clay Lacy to court legend Magic Johnson, with the intervening 15 years representing by far its longest stint with a single operator…

So, while this particular airplane probably has quite a few stories to tell, the G-III as a whole has a good one too. While it sometimes takes a keen eye to tell it apart from other members of its extended family, the III is probably the definitive landmark Gulfstream, since it was the one to set the stage – in terms of performance, comfort and style – for all the models that came subsequently. To make it even better, its glorious shape – delicate, elegant, powerful and brutish all at once – actually has its roots in a – turboprop 😀 .

And while the very mention of the P Word may raise a few eyebrows, the machine in question is probably one of the most beautiful t-props of them all: the dashing and elegant G-159 Gulfstream. Grumman’s attempt to offer the business market something better than a converted WW2 light/medium bomber, the G-159 was on its debut in 1958 one of the world’s first purpose-built large executive aircraft, sporting a comfortable and pressurized cabin for 8-24 passengers* (w/ the type’s famous oval windows), an advanced flight deck, transcontinental range and a pair of very loud – but also very tough and reliable – Rolls-Royce Darts rated at 2,190 HP each.

* according to many of the sources I found, the voluminous cabin allowed for numerous configurations with large differences in total capacity. The most luxurious setup seated only eight; the Sardine Can Special could squeeze 24; while the most common variant had space for 10-12. There was even a version called the G-159C (five of which were built), aimed at the regional airline market; a 3.25 meter fuselage stretch brought the total capacity to 37, roughly equal to the much later DHC-8-100

By the mid 60s though, the rise of the business jet could not be ignored anymore; names such as Lockheed JetStar, Rockwell Sabreliner, Dassault Falcon and Hawker-Siddeley HS.125 had grown into a credible threat, which meant that the G-159 could not hope to compete for much longer solely on its superior capacity, fuel economy and airfield performance. To stay in the game, Grumman decided to build on the 159’s success and turn it once more into the ultimate business transport. To that end, in 1966 they took its entire cabin and forward section (including the nose gear), stuck on a bespoke swept wing w/ increased fuel capacity, a rakish T-tail, and a pair of howling Rolls-Royce Spey low-bypass turbofans in the back (still a quieter fit than the Darts!), thus creating the daddy: the G-1159 Gulfstream II**, the first jet Gulf.

** on its introduction, the G-159 – which would remain in production for two more years – would be renamed into Gulfstream I

While a quantum leap in performance over the G-I – being the first bizjet to cross the Atlantic non-stop – by the mid 70s the G-II was itself becoming a bit dated, and would soon start to face some worrying competition from (among others) the upstart Canadair Challenger – the first modern large cabin jet designed from the ground up for the business role. In reply, Grumman would in 1979 take the G-II and:

stretch the fuselage by 0.6 meters
re-contour the entire radome and windscreen
redesign the wing to incorporate 1.8 meters more span and a more efficient leading edge
add striking 1.5 meter winglets (inspired by those on the Learjet 28 Longhorn, the first bizjet to carry them)
up the luxury to 11
revamp the cockpit to include more glass and automation

and christen the result the G-1159A Gulfstream III. Despite having sold only a modest 202 examples, the G-III was such a conceptual hit that it immediately set the standards for what a proper Gulfstream should be (despite its inefficient and gas-guzzling engines).

Indeed, the hugely successful 1985 G-IV – more than 900 sold over multiple versions – is actually a lengthened G-III with a tweaked wing, a full glass cockpit and power provided by modern Rolls-Royce Tay high-bypass turbofans. Even the G-V of 1995 shares the same DNA, being a longer, fully re-winged G-IV powered the brand new Rolls-Royce/BMW BR710. Only with the coming of the clean sheet G650 did the old G-II/III finally decide to lay down and die…

*Despite the “Eurowhite” paint job (which is actually new), N32MJ does carry a few tokens of Mr. Johnson’s sporting life: his old basketball team on one side…*

*… and the baseball team he owns on the other*

There’s just something about a quarter side view of a classic Gulf… interestingly, N32MJ was parked at Zagreb immobile for approximately two weeks while Mr. Johnson was down on the Adriatic coast, despite an abundance of airports that could (and had the space) to accommodate a G-III…

You know your airplane is good when it needs a muzzle. For those unfamiliar with them, “hush kits” – seen here at the back of the engine – are aftermarket air mixers fitted to older generation low-bypass turbofans to reduce their noise signature. They work by providing additional mixing of outside air and exhaust gases, which reduces the shearing forces between them that are the main cause of “jet engine noise”. In many Western countries, they are nowadays an essential piece of kit to even get in. The units fitted to N32MJ are QTA Stage 3 models, by far the most popular choice for Spey-powered Gulfs (of note, the gap between the engine and mixer accommodates the reverser buckets when open)

*Rarely are there aircraft whose looks combine characteristics that are so different: elegant, but brutish… delicate, but powerful… discreet, but imposing…*

Gulfstream Aerospace G-1159B Gulfstream II-B • N4NR

Just as the G-III’s advancement carried forward onto the G-IV, they also filtered backwards onto the old G-II. In 1981 – a year after its production ended – Gulfstream offered the G-1159B Gulfstream II-B upgrade, which would see the III’s wing and cockpit setup mated to existing G-IIs (the only other factory variant of the II was the G-II-TT, fitted with tip tanks; only 18 are known to have been so equipped). Offered until 1987, 44 machines had been converted to this standard – including our example, the non-hush-kitted N4NR.

*Lost in the mist and overcast. To see a G-II in the 21st century is something… to see one WITHOUT hush kits is a different matter entirely!*

Completed in 1978 under the serial 255, this odd bird had started out in life as N442A of the Aramco Steel Corporation. In 1984, it would pass into the hands of Rockwell International, where it would soon become N4NR – and, presumably, be converted to the II-B standard. It would stay with Rockwell’s various incarnations all the way until 2001, after which it would pass through the hands of several venture capital corporations (list also at Plane Logger), finally ending up with the somewhat cryptic Global Mission LLC in 2008.

That all was not going well in its world became obvious in November 2018, when its first (and last) arrival into Zagreb was met with a pre-planned sting operation ran by the Croatian Police, acting on information provided by the US Drug Enforcement Agency (DEA). Though some of the details are still not entirely clear, official press releases stated that the crew of two were flying in from Mali with a kilo of very pure cocaine, a sample of the payment to local arms dealers for a shipment of Soviet-era man-portable anti-aircraft systems, assault rifles, ammunition and other military gear – all stuff that was scheduled to be passed onto a Malian Islamist terror group.

Immediately impounded as evidence, it sat sealed for a few years in the corner of the GA apron, awaiting the end of the investigation and some future auction where it would be sold off to whoever cares. Informed opinion at the time (eventually to be proved pretty accurate) suggested that it would never fly again, since it is in pretty poor condition*** – and the costs of returning it to airworthy state and bringing it up to code are not encouraging…

*** indeed, it has been mentioned informally that is had started out for Zagreb three previous times before returning back to Mali with technical issues

While you’d be hard pressed to tell it apart from the G-III from most angles, the dead giveaway is the old G-I-style nose. While it is very cool in its own right, it almost looks like the G-IIIs rural cousin…

*Jumpin’ Jehoshaphat? More like Forgotten Jehoshaphat! In 2020, N4NR would be moved to the far end of the apron (to a spot just under its horizontal stabilizer) and left to the elements…*

Sources:

Corporate Jet Investor – Gulfstream bizjet history
Plane Logger – N32MJ & N4NR histories
Wikipedia – G-II, G-III, G-IV & G-V entries

Photo File – The Swing-Leg Skyhawk: Cessna 172RG Cutlass RG

August 23, 2020April 5, 2021Posted in General AviationTagged C172, C172RG, Cessna, Cessna 172, Cessna 172RG, Cessna Cutlass4 Comments

By me
All photos me too, copyrighted

To properly kick off my return here after an unintentional pause of nine months (!), I’ve decided to revisit an aircraft type I had mentioned in passing some time ago – seeing that, by a stroke of sheer dumb luck, I managed to snap TWO in the space of just one week (which is twice as many as I’d managed over the past 18 years). The machine in question – as the post title infers – is the Retractable Gear (RG) version of the common Cessna 172, an aircraft whose rarity and cool factor is matched only by its apparent uselessness and absurdity…

*A mint 172RG, in a modern paint scheme, under clear skies on a beautiful summer morning… I could do worse for a pre-dawn spotting session I must admit!*

Swinging 80s

To immediately get an idea of why the 172RG stands out like a sore thumb within the traditionally conservative Skyhawk family, it seems best to start off with its main party pieces, as compared to the stock 172P of the same period (1980):

fully retractable gear
a longer snout to house the nose gear when retracted
cowl flaps
a 180 HP Lycoming O-360-F1A6 w/ constant speed prop (vs the standard 160 HP O-320 and fixed pitch unit)
a 66 USG fuel capacity (up from the standard 42)
and a 1,202 kg MTOM (vs the 1,088 of the P)

Performance-wise, the extra grunt (particularly the increased efficiency of the constant speed prop) and cleaner lines meant the RG could pull up to a 20 knot lead over the stock P, with High Speed Cruise pegged at 140 knots. The new prop also made for slightly better after take-off climb performance (800 fpm vs 700), while the increased fuel tankage gave a pretty chunky range boost, from 440 up to as much as 770 NM.

*Cutlass #2 undergoing a wheels-up restoration after a (heh) wheels-up landing in Germany. You can definitely tell it apart in a normal Skyhawk crowd!*

However, the ~80 kg added by the gear retraction mechanism also upped the empty weight, now standing at 740 kg vs the P’s 660. Normally, this was not much of a payload issue if you took on only your required fuel – but if you went all out and brimmed the tanks, you’d be left with barely 260 kg of headroom… roughly two 2020 adult males, some luggage and all the stuff normally carried around when away from home (additional oil, tow bar, cockpit/wing covers, emergency equipment, survival kits, …).

The higher MTOM also made for longer take-off and landing runs, both up by roughly 70 meters even on concrete; and while some owners have been known to fly them out of rough fields (and even back country strips), it generally goes without saying that the new legs did not take too kindly to prolonged use on the types of runways normal 172s take for granted.

While the main gear legs are no thinner than those on the standard 172 (where they’re set inside streamlined fairings), Cessna’s electro-hydraulic RG systems are quite complicated things and can go bananas even when mollycoddled. As on the 177RG, 182RG and 210, the main legs of first swing downwards and the fold back into recesses in the fuselage (barely visible here). Early 210s – which were the first to use the system – also had main wheel well doors, but they proved problematic and were deleted well before the 172RG appeared

The Cessna Retractable Dance. Go to 0:30 for retraction and 1:30 for extension. You’ll note that the pilot leaves the gear down for quite some time after take-off; the standard wisdom on RG Cessnas is to leave it hanging until clearing obstacles, since the retraction sequence causes so much drag it can noticeably impair climb performance at a critical stage (this is also SOP on airliners during windshear escape maneuvers). Indeed, the main legs drop by a whopping 60 centimetres during retraction!

Maintenance-wise, private owners, commercial operators and various incident reports all tend to agree that the upsides of its commonality with the stock 172 are frequently balanced out by the many gremlins of the RG system – though user experiences vary considerably, particularly when comparing leisure and training ops.

Persistent weak spots and items that require frequent inspection are the main electric-driven hydraulic pump, down-stop pads that (if damaged) may prevent the main gear legs from locking down, and the main gear pivots that are worn out by the legs’ aerobatics during retraction and extension. There’s also the need to periodically cycle the gear on the ground during checks – which requires jacks and additional man-hours – as well as the costs of servicing the propeller governor (though that’s a pretty standard job).

And while none of these are deal-breakers in themselves – the 182RG and 210 say Hiii! – the cost-benefit math of doing all that on a lowly 172 did not make the RG everyone’s cup of tea…

Mission-ready

So, when all was said and done, the 172RG was a cheap & simple aircraft made expensive & complicated for just a few marginal gains – so much that even the fixed gear 210 HP Reims FR172 Rocket could keep up with it in a pinch (and for noticeably less money). What’s more, if you really wanted the “Full RG Experience”, five numbers up was the (slightly) more powerful, (much) more efficient, (oodles) more comfortable and (far) more elegant 177RG Cardinal – an aircraft conceived outright for the touring role, offering 182 series frills without many of its financial chills.

The 172RG thus appears to be – in technical terms – a complete crock. However, outright performance and mass market appeal are not what this airplane is about; its forte was to corner a very specific niche of the training market by offering a suitable and affordable “quick fix” for a problem few manufacturers seemed interested in tackling.

The niche in question was for what’s termed a complex aircraft, a surprising demanding specification that calls for a simple, easy-to-fly, robust and cost-effective airplane that can also boast toys such as flaps, retractable gear and constant speed props – all the complicated and fiddly stuff that future airline drivers are supposed to deal with (did mine on an old, student-weary PA-44, so the full set of traumas is there!)*.

And with the Skyhawk’s 25 years of active service to its name, the type’s well-known middle-of-the-road handling, off-the-shelf components (even the landing gear, nicked off the Cardinal), a reliable and frugal powerplant and a developed global support network, the 172RG had hit all the nails it needed to hit. Even though it would be born on the eve of Cessna’s decade-long single engine production pause, 1,191 would be made between 1980 and 1984… not bad for a niche design!**

* the original specification for complex aircraft had not set a specific minimum power limit; in 1997 however, the FAA set the bar at a minimum 200 HP, thus disqualifying the 172RG. However, the type still remains in widespread use as an introductory platform for more complex touring machinery – as well as a charismatic “left field” personal airplane

** though there are frequent parallels with the Beech 24 Sierra and the Piper Arrow, the 172RG is actually not a direct competitor to either. Both designs boast thirstier 200 HP fuel-injected engines (the Arrow with the option of turbocharging), better performance, more amenities – and are generally set up more for the posh end of the touring market; their closest Cessna analogue would be the aforementioned 177 Cardinal. The only aircraft on equal footing with the 172RG was the very first version of the Arrow – the 180 HP PA-28R-180 – which debuted in 1967 and remained in production for only a couple of years before being superseded by the first of the 200 HP models

What’s in a name?

While all of the above ticks quite a few Achtung, Skyhawk! boxes, one more thing remains that is very worthy of mention: it’s name.

While it does say “Cessna 172” on the tin, the 172RG is techno-legally not a purebred Skyhawk – but rather an offshoot of the nearly forgotten 175 Skylark. Billed as the next step towards the larger 182 (a role that would later be filled by the 177), the 175 was in essence an up-market high-trim version of the 1956 172A, fitted with a geared 175 HP Continental GO-300 instead of the standard direct-drive 145 HP O-300. Unfortunately, reduction gearboxes were at the time an unheard of feature on such a small civilian engine, meaning that very few pilots had ever encountered one before. The specific way in which such an engine had to be handled – flown at around the 3000 RPM mark – was so alien and absurd to private pilots that many drove them at the more usual 2000-2200 RPM, leading to a ton of breakdowns, failures and bad PR. By 1962, things had gotten so bad that Cessna was forced to pull the plug on the entire design, and retire both the 175 designation and the Skylark name…

A stunning late model 1962 Skylark with the original GO-300. Note the hump on top of the cowling; the propeller axis had to be raised up in order to accommodate the reduction gearbox without relocating the engine mounts

To salvage at least some of the effort invested in the design, the company decided to keep the 175’s Type Certificate (and some mechanical bits) and use them as the legal basis for all future high-performance variants of the 172:

the 195 HP R172 Hawk XP
the 210 HP Reims FR172 Rocket
the military T-41 Mescalero
and the 172RG

Traces of the Skylark’s original DNA can still be seen in the R172, FR172 and T-41, since they all sport the tall narrow-track landing gear of the 172A, which would be replaced by the squatter wider-track variant we all know and love on the subsequent 172B.

However, this would not be the end of Cessna’s marketing shenanigans; in 1983, the company would launch the 172Q Cutlass (sans RG), an attempt to “schlepp” on the RG image by fitting the 172P with a 180 HP Lycoming O-360-A4N driving a fixed pitch prop. Quite a rare model today – which did not offer much meaningful superiority over the P – only a handful would ever be built before the Skyhawk family as a whole went into its prolonged 80s coma…

Fixer Upper

While at this point in any normal Achtung, Skyhawk! post I’d go off with a ton of (more or less) descriptive external photos, in this instance I decided to “stay inside”, since the opportunity to snoop around a full-blown rebuild (currently at ~60%) was an opportunity too good to miss! The photos are not my best work – it’s hard to maneuver my 1.91 m frame w/ camera and tripod inside a 172 – but hopefully they’ll be interesting enough for the common avgeek!

I don’t know… it feels something is missing… free from all its kit, the Skyhawk panel looks far more commodious than it actually is! Note the (now very visible) sections for the flight and navigation instruments and the radio stack. Before its wheels-up landing and rebuild, D-EGGF also sported an autopilot (fitted above the glove compartment), and will – when completed – also carry a full set of digital engine instruments. Note also the rudder trim wheel next to the elevator trim; a very useful convenience/borderline necessity with a constant speed prop

A peek “behind the scenes” shows just how many wires, cables, ducts – and even chain drives – there are in a light aircraft. The complexity, weight and maintenance headaches of the average analogue panel have been one of the key drivers behind modern glass cockpit systems built around digital buses and remote sensing systems

Lots of wires… and lots of levers too. With carburetor heat, throttle, prop, mixture and cowl flaps controls, the 172RG could be handful for inexperienced pilots used to the trouble-free operation of the classic Skyhawk (but ideal for the well-meaning masochism of flight training!). Indeed, this was Cessna’s most complicated throttle quadrant short of the 182 (even the 177RG had one level less, being fuel injected)

The most out-of-place level in a Skyhawk: the landing gear handle. One of the more unconventional operational features of Cessna’s RG system is that the “gear up and locked” lamp is – red… which on everything up to and including airliners means either “NOT locked” or “in transit”. Somewhat annoyingly, the light remains continually illuminated as long as the gear is retracted… which is mildly disconcerting from a Q400 driver’s perspective!

Like all RG airplanes, the 172 has a backup gear extension system, whose lever is located under a cover between the front seats. The trick here is that it is just a hand pump, to be used in case the electric one fails (~35 strokes are necessary, according to the POH); it still requires the hydraulic system to be fully operational, and there is no gravity drop or a standalone reserve hydro system. This “unusual feature” is the 172RG’s main Achilles’ heel: the gear is actually held up by hydraulic pressure, and to keep it from dropping, the hydraulic pump occasionally operates in flight to keep the pressure within limits (between 1000 and 1500 PSI). However, if there’s a leak in the system – which seems to happen with some frequency – the pump’s operation will simply dump the hydraulic fluid overboard, eventually emptying the entire system and rendering the gear completely inoperable

The more normal end of the Cessna RG system. The nose wheel doors are mechanically connected to the nose leg so they open and close with gear motion; their biggest operational problem is that they’re quite large and hang low, so it’s easy to damage them if you’re a bit too enthusiastic with the tow bar

Who would have thought that all of this cabling lies hidden behind the teeny panel of the Skyhawk? Another detail unique to the 172RG is the raised floor (best visible below the CDI), necessary to accommodate the main gear legs when retracted. The main wheels however stow behind the normal luggage compartment, so the loss of space there is minimal

Boxes boxes everywhere, not a place to sit… thankfully, the lack of space for maneuvering about with a tripod is taken up by some pretty cool kit: Garmin G5 x2, GMA350, GNC225… should be quite a looker when finished, very much looking forward to trying it out!

As ever, I would like to extend my sincere thanks to Dorian Delić of Medulin Airfield (LDPM) in Istria, for allowing me to snoop through his family’s hangar and drool a bit over D-EGGF!

Aircraft pictured:

D-EGGF: c/n 172RG-0301 • mfd 1980 • ex. N107JB
D-EPAW: c/n 172RG-0757 • mfd 1980 • ex. N6532V, I-ALEU

Sources:

AOPA – C172RG article
AvWeb – C172RG article
Cessna Flyer Association – C172RG article
RisingUp Aviation – C172P, C172Q & C172RG specs
Sporty’s Academy – C172RG POH (PDF)
Sporty’s Network – C172RG differences (PDF)

Photo File – Contrafun: Flying On The Kamov Ka-26

November 2, 2019April 5, 2021Posted in General Aviation, Rare AircraftTagged Budaors, HA-MIG, HA-MPB, Hiller, Hiller UH-12, Ka-26, Kamov, Kamov Ka-26, LHBS, UH-122 Comments

By me
All photos me too, copyrighted

Even though I’ve been a fixed wing driver from Day One (private and training helicopters being so rare in Croatia), I’ve nevertheless always maintained a fancy for all things rotary. Indeed, my first ever flight – back when I was just a toddler – had been on a Yugoslav Air Force Mi-8, followed up later in adulthood with hops on the Bell 429 demonstrator, and with Red Bull’s own Rainer Wilke on the fully aerobatic Bo-105 (an experience I’m not likely to forget!). From then on however, my contact with the helicopter world had been reduced to being on the working end of the camera viewfinder – a situation that would dramatically change for the better in the summer of 2019 🙂 .

Having been aware of my long-standing desire to photograph a piston engine Kamov up close, a friend from neighboring Hungary – himself an avid helicopter spotter – had managed to do me one better, arranging not only a “free hand” photo session… but also a short semi-aerobatic flight. The only string attached was that I get my arse to Budapest on my own accord – a condition I was more than happy to accept! 😀

*It may be the textbook definition of the world “fugly” – but on that day it was the most beautiful helo in the world!*

The HA Ka

The rather colorful bird that would be my ride for the day goes under the name HA-MPB, and sports the serial 77 061 09 – a typical Soviet sausage that tells you (almost) everything you need to know:

77 … manufactured in 1977
061 … as part the 61st batch made (out of 65 in total)
09 … and the ninth example in the batch

This puts it among the youngest examples of the 848 made in total between 1969 and 1978 – and one of at least 149 that would eventually serve in Hungary (either straight from the factory, or through resales). Unlike the vast majority of its brethren however, MPB is still very much active, and spends most of its uptime dusting crops up and down the country. Indeed, on this day it had popped into Budaörs Airfield (LHBS, not a stranger to me) solely to participate in the upcoming Budaörs Airshow, following which it would quickly depart back into the southern fields and resume normal operations 🙂 .

While my roster at work had prevented me from staying the show’s full three days, I had nevertheless had ample time to pour over MPB in much detail. Though many of the design’s finer nuances will inevitably be lost on me – Fixed Wing Guy, remember* – there is nevertheless still enough eye candy here to arouse the interest of even the most basic aviation enthusiast!

* any corrections from whirlybird drivers would be most welcome!

*Getting ready for the day’s practice run with a lick of paint and a thorough wash. Despite the performance penalties of the extra weight, MPB would fly its routine in full crop spraying kit…*

In addition to their distinctive main spray bars, many Ka-26s feature a secondary unit slung from the horizontal stabilizer. Specs I found online indicate that with all three in operation, the average 26 could dispense up to 12 liters of fluid per minute (though dispersion system upgrades in 1978 and 1979 would improve on that by a couple of liters/minute)

In the crop dusting configuration, the hopper can accommodate up to 900 kg of fluid. A neat trick is that it’s actually part of a removable payload module that can be easily taken out in the field, and replaced with the minimum of specialized tools by a selection of other factory-made modules (passenger, ambulance, freight platform, sling hook, …)

Not your usual view! Despite its unwieldy look and apparent bulk, from the top it is obvious that the Ka-26 is actually quite compact, sporting the minimum amount of structure necessary to bring together the engines, cabin, rotor system and payload module. There blades themselves are actually composite and very light, and feature substantial leading edge protection at their tips – all of which gives them a solid 5000 hour service life, even in the rough-and-tough going at low altitude

The party piece of (almost) every Kamov design: the counter-rotating coaxial main rotor. Though mechanically more complex than the conventional arrangement, this setup allows for greatly increased efficiency, since the blade area – which produces the lift – is now doubled, and there are no mechanical and friction losses inherent to the tail rotor and its transmission system (which also does wonders during autorotation). Another benefit – epitomized by the Ka-50/52 gunships – is a very high degree of maneuverability in all axes, as well as a much more neutral mass distribution that does wonders for hover characteristics, general handling and overall agility

Arretir! Drawing heavily upon Kamov’s naval experience, the Ka-26 could be equipped with a full IFR panel and some pretty sophisticated kit for its class – stuff that didn’t always sit well with operators, since it tended to add complexity and increased maintenance costs. Many examples (especially those used at very low altitude) would be stripped down in actual operations; MPB however had retained most of its factory setup, minus the blind flying gear

*Having spent the majority of its life in Hungary, MPB sports a typically curious mix of Russian and Hungarian dials, which do add a lot of charm to the cockpit…*

Being one of the very few (maybe even only) production light helicopter with TWO piston engines, the Ka-26 does sport a lot of powerplant-related switches and knobs – so much so that it seems you need three arms to successfully start it first time out…

More traces of the Ka-26’s Soviet design heritage: the single primer pump in the middle (which is turned into the direction of the desired engine before being actuated), and the air system valve w/ pressure gauge, which provides the juice for the main wheel brakes (a common solution on Soviet aircraft to avoid the weight penalties and poor cold weather performance of conventional hydraulics)

Another icon of Soviet general aviation: the venerable and dependable M-14 nine cylinder radial, here in its V-26 version developing 325 HP. To tackle the unique aspects of helicopter flight – high RPM, high throttle and low (or no) forward airspeed, the fit on the Ka-26 features powerful cooling fans (visible behind the fully opened cowl flaps), which force air over the cylinders to keep them sufficiently cool regardless of flight regime. They also make a LOT of noise!

*Two big Soviet radials, two huge coaxial rotors, a traditional cockpit fan – and a semi-aerobatic duet with a 1950s Hiller UH-12… yep, didn’t mind the four hour drive one way!*

One a pristine vintage “oldtimer”, the other a no-nonsense everyday working machine… one conventional on Lycoming power, the other coaxial with twin radials… one user-friendly Western, the other utilitarian Eastern… fun is guaranteed! Another interesting feature of the Ka-26 – negated here by the open door – is that the cabin is actually pressurized to slightly above ambient, to prevent spray and chemicals getting in during crop dusting ops

And finally, a bit of video from the inside… admittedly, not the best quality (the lighting was marginal all throughout the day), but hopefully the action will make up for it! Also not the piercing turbine-like noise in both clips; those are the aforementioned cooling fans spinning their heads off 😀 .

Bonus content: Hiller UH-12D • HA-MIG

Drooling all over the Ka-26 is fine and well – but when you get to fly in a duet with a vintage Hiller, you should at least try to make an effort to snap it as well! 😀 Returning back to the apron after our run, I was lucky enough to stumble upon said helicopter and its owner, who kindly allowed me to snoop around and bit and soak up the beauty of one of the world’s earliest mass produced light helicopters…

Halfway through a thorough wash following its practice display. Manufactured in 1959 with the serial 1145, MIG would serve first with the US Army as 58-5496, before going civilian as N67664 and N16MQ. Sold to Hungary in 1997 (as one of a number of UH-12s coming into the country during the 90s), it would eventually end up in the hands of Fly-Coop, one of the largest aircraft operators of the Budapest area. Note the exposed tail rotor transmission atop the tail boom

Though the type normally sports the six cylinder Lycoming VO-435 developing 265 HP, this particular machine had at one point been retrofitted with the more powerful Lycoming VO-540, developing a chunky 305 HP (it showed during the display!). Of note is the engine V prefix, which stands for “vertical” – denoting the modifications for the only possible way of installing it into a light helicopter

A panel that can easily provoke traumas in anyone who had flown a 1960s Cessna – no rhyme or reason in the layout, and made by someone who studied economics, not ergonomics. That notwithstanding, surely a cool place to sit!

Traditionally, I would like to extend my sincerest thanks to all the people – ground and air crews alike – that had made this photo shoot possible, particularly Gergely C.!

Sources:

Air History – Ka-26 production list (PDF) + serial decode (also PDF)
Aviainfo.hu – MA-MIG data and history
Aviastar.org – Ka-26 history

Photo File – Pratt My Ride: The PT6 Cessna 206, S5-DOT

April 22, 2019April 5, 2021Posted in General AviationTagged Cessna 206, Cessna 206 PT6A, Cessna 206 skydive, Cessna 206 turboprop, S5-DOT, Turbine 206, turbine Cessna 206, Turbine Conversions, Šentvid2 Comments

By me
All photos me too, copyrighted

Some choices in life are actually pretty easy to make. Take, for example, my options the other day following a 4 AM wake-up to work a dawn flight: A) get some sleep; B) get some exercise; or C) drive an hour and half (one way) to a neighboring country to try and catch a pretty rare turbine Cessna 206… I mean, the choice is self-selecting! 😀

The machine that had managed to score higher than my own bed (!) is a Turbine Conversions Turbine 206, a fresh crack at mating a mid-life Cessna 206 airframe to a (moderately) powerful low-altitude turboprop engine. But, whereas the most successful attempt so far – the Soloy 206 – is based around the same Rolls-Royce/Allison 250 series engine used on the Bell JetRanger, Turbine Conversions’ mod relies instead on the far more famous Pratt & Whintey PT6A – and is the first time this engine had ever been fitted and certified on a member of the Stationair family. With only three examples flying in Europe so far, delaying sleep was definitely a better call, so I plonked myself into the car and went off to see what’s what 🙂 .

*A real Quasimodo: ugly as hell on the outside, but with a heart of pure gold underneath*

Born to Haul

The recipe for this sort of thing has always been pretty straightforward: take an older generation utility 206, give it a large improvement in hauling performance as cheaply and simply as possible – and then make it work on paper so that it can legally carry paying passengers. And while sticking in an engine that may be worth three times the rest of the aircraft may not sound like the best way to do it, the idea does have a fair amount of economic sense behind it. Stationairs have always been tough birds with long lives, so even a model several decades old can be reasonably expected to have quite a few years of service left; being several decades old means that they were likely paid off in full ages ago, and have none of the fiscal baggage that newer models are often burdened with; and they can be cheap to buy, spares are plentiful, support is available worldwide – and there’s enough accumulated user experience out there that even a fresh operator can learn the ropes quickly and without undue trouble.

Get all of these right (admittedly, not an easy task!) and the turbine conversion can end up being a pretty cheap, sufficiently efficient and very reliable ticket into the utility turboprop world, especially for smaller operators who cannot afford a bespoke type such as the Pilatus PC-6, PAC 750 or Quest Kodiak – or are in regions where Avgas is fast becoming a thing of the past. Get it right and even the conversion’s many downsides – such as fuselage-limited capacity and higher long-term operating costs – may not be critical enough to offset the advantages of having a turboprop – ANY turboprop – at your disposal.

To try and achieve the above, Turbine Conversions – a longtime PW&C user – decided to bank once again on the company’s most famous engine, which – while heavier and more expensive all round than the RR 250 – has an enviable reputation and true global reach on its side. Initially, the mod started out with the 550 HP PT6A-20, but this was changed before production began to the equally powerful PT6A-21 – the difference being that the -21 is in essence a de-rated version of the 680 HP PT6A-27, which retains the latter’s more potent core for a bit added torque and improved hot-and-high performance.

Being a cheap-and-cheerful “firewall forward” solution intended for the rough-and-tough utility market, the Turbine 206 is not really loaded with features; apart from the new engine and its associated accessories, propeller, mountings and structural changes, the only things that stand out are custom exhaust stacks that eek out a bit more thrust – as well as the company’s own air inlet design with is said to improve the flow of air into the engine. The upgrade is rounded out by an Electronics International MVP-50 digital display panel – which replaces all traditional steam gauges – as well as modified engine control levers to cater for its different operation.

Unlike turbine conversions of touring aircraft – where the interior often has to match the performance – both Soloy and Turbine Conversion mods retain the utilitarian equipment levels of the aircraft they were based on. Really the only dead giveaway that there are 550 horses living up front is the MVP-50 display, located above the right-hand panel guard

Another change – albeit not as easily noticed – are the engine control levers, which now behave differently to those on the piston 206. The throttle lever now has to incorporate a reverse function, the prop has to have feather – while the condition lever is actually simpler, with just two discrete positions (HIGH IDLE & CUT OFF)

On the DOT

While all of this is pretty interesting in itself, the machine I had actually gone out to see is just that bit more special 🙂 . Nowadays called S5-DOT, in its past life as N7351Q it had actually served as the prototype and validation vehicle for the entire Turbine 206 mod, and was the one put to the test in order to receive the Supplemental Type Certificate (STC) needed for sale and commercial use.

Originally a stock U206F manufactured in January 1973 with the serial U206-02179, DOT is a fresh addition to the fleet of Letalski klub Šentvid, based at the picturesque airfield of Šentvid pri Stični – the same place I had gone last year to have a one-on-one with another Cessna turbine mod. Replacing the smorgasbord of outside aircraft that previously had to be leased at significant cost, DOT has arrived right on the dot for the beginning of the commercial skydive season – so with any luck, it should be a frequent dot on the Slovenian sky!

Rolling full laden toward RWY 14 for another afternoon run. Though turbine power could not change the type’s hauling capacity all that much, it did wonders for both take-off and climb performance at high weights – not an insignificant feature given the close-in hills in all directions and high daytime temperatures…

Like all piston-to-PT6 conversions, the Turbine 206 looks quite brutish from the front. Note also the offset propeller (and engine) installation, designed to reduce the adverse gyroscopic and aerodynamic effects of the new powerplant

*Waiting for the next load. Like any self-respecting skydive machine, DOT has a full set of handles, steps and door covers, and can comfortably accommodate up to six skydivers at once*

The Dependable Engine (unless you’re talking about the GTF!). An interesting operational feature is that engine starts are performed with the assistance of an outside battery kart, since the huge current draw from repeated spool ups would drastically shorten the service life of the on board battery

As always, I would like to thank the people who made this photo shoot possible – in particular Mr. Tone Dolenšek, who spent quite some time keeping me company and answering my Achtung, Skyhawk!-y questions!

Sources:

IAS Canada – PT6A version list

Photo File – Moraning Around: Flying The Rallye 150

April 19, 2019April 5, 2021Posted in General AviationTagged LDZL, Lučko, Morane, Morane Rallye, Morane-Saulnier, MS.890, MS.892, Rallye 150, SOCATA, SOCATA Rallye, SP-IKY3 Comments

By me
All photos me too, copyrighted

It had always been said that the gut feeling is a powerful tool and that it would be wise to (at least occasionally) listen to what it has to say. Returning home from town one day, I decided to do just that, and on a whim stopped off at my base airfield of Lučko (LDZL) to see what’s up – since, hey, it was on my way anyway. Rolling onto the parking lot, I noticed a Morane-Saulnier Rallye standing in front of the hangar, the same machine I had seen at Zagreb (ZAG/LDZA) a few days earlier. Sporting a Polish reg, it had immediately caught my attention – so, naturally, I headed over to see what’s what.

It would transpire that its owner had moved to Zagreb for work, and would be basing his airplane here at Lučko. Immediately intrigued (even more than before), I struck up a conversation, which would culminate some two hours later with an invitation to eventually go flying 😀 . Having always had a thing for the Rallye family, I needed little persuasion – so a day later we met up again for a one-hour introductory flight around the vicinity 🙂 .

In keeping with character, I had my camera ready and my brain open to impressions, keen on getting some proper Achtung, Skyhawk! material – possibly even enough to repeat my previous UTVA U-75 piece. However, in the end I decided to take the opportunity to simply cruise around at leisure and enjoy the view, so apart from a couple of basic maneuvers to get a feel for the aircraft – and several touch-and-goes to judge its landing characteristics and low-speed behavior – we spent most of our time zipping around straight & level, with just an occasional spot of moderate maneuvering. Nevertheless, I felt it fitting to try and hazard a few parallels with both the U-75 and the C172 I normally fly, if anything to attempt to illustrate some of the charm and charisma of one of France’s most successful and timeless designs…

Author’s note: despite these parallels, this is NOT a proper, professional review – as was also the case with the U-75 – since I have neither the skills, experience nor qualifications to make any sort of objective conclusion or comparison. Rather, this is just a condensed (if structured) personal experience of a life-long GA fan, a bit of light reading that I hope enthusiasts could find interesting!

*The proper way to enjoy your first flight on a new type: sunny skies above, excellent light all around and fine terrain below!*

Rallye around

The little bird in question is a 1973 SOCATA* MS.892E Rallye 150, sporting the reg SP-IKY and serial 12238. As its name implies, it has 150 HP on tap, provided by a garden variety Lycoming O-320-E2A – the same basic unit found in the most common Cessna 172 variants (the M and N) and the Piper Warrior – which spins an equally common 1.93 m McCauley 1C series two-blade fixed pitch propeller (though a 1.88 m Sensenich M.74 can also be fitted). With 980 kg of Maximum Take Off Mass to move, this combination gives roughly the same performance ballpark as the other two, while a fuel capacity of between 180 (standard tanks, fitted to SP-IKY) and 220 liters (optional long-range fit) gives broadly similar endurance and range.

* though the basic design – the MS.880 – was designed by Morane-Saulnier, by the time the MS.890 rolled by, the company had been incorporated into the Societe de Construction d’Avions de Tourisme et d’Affaires, the Company for the Manufacture of Touring and Business Aircraft – or SOCATA for short

As was the case with the U-75, the type’s specifics (and indeed its charm) become apparent only after you stop looking at the numbers and start fiddling with the aircraft itself. The interior, for example, looks deceptively small from the outside; my fears of fitting in – being 1.9 meters tall and all – turned out to be completely unfounded, since the front seats provide space enough fore, aft and to the sides to rival the Cessna 182 (a near-identical experience to that of the U-75). The only letdown at this point was the height of the convex canopy, which was a bit restrictive with headphones on (the Utva says hi again); however, in my case sliding the seat fully backwards did the trick – and even though I could have done with a few more centimeters of extra headroom even then, I was never really uncomfortable at any one point.

Top of the world, ma! Flying, both on and off work, a high wing aircraft, this is somewhat of an unusual perspective for me. As on most low-wing aircraft, climbing aboard is as easy as step-grab-pull; being lower off the ground than the U-75 (though slightly higher than the PA-28), the process is also not awkward nor physically strenuous. One slight complaint is that the size of the canopy precludes the fitting of handles, meaning you have to grab hold of the canopy frame if you need help to haul yourself aboard

The large sliding canopy means that getting in is a complete non-issue. However, since the wing spar passes underneath the front seats – and an additional cross-brace is needed to keep the fuselage stiff since it lacks a load-bearing roof – leg space in the back is a bit of an issue… you definitely cannot stretch out like you can do in the 172. Interestingly, the same issue plagued the U-75’s four-seat variant – U-75A – but was not a worry since only three were ever made…

Once inside and with the seat fully back, I found the sitting position to be one of the best I’ve ever experienced in a light aircraft, with good elbow room, all controls within easy reach – and a near-ideal position and distance of both the control wheel and rudder pedals. Unlike some Cessna 172s I’ve flown, I could turn the wheel fully** to either side without interference from my legs, and never needed any gymnastics to fully actuate both at once (not even when crossing them as if to initiate a side slip).

** conversely, a colleague of roughly the same height and build flew the more powerful Rallye 180 that comes equipped with a stick as standard; he reported that in some conditions, he could not always move it to the sideways stops without first moving his knees to the side

Being a low wing aircraft designed for (among other things) flight instruction and utility roles, the view outside is, unsurprisingly, very good. Since the canopy frame is not load bearing (unlike on the U-75), it can be pretty thin and light, making it unobtrusive (conversely, the large frame of the UTVA gives the impression of peering through a postbox, though it is very easy to get used to). A notable criticism from my end is the aforementioned convex canopy shape; its low front lip means you either have to fly with it slid back to half-open, or fully closed, otherwise there’s no space left for your head

Though SP-IKY’s owner – who also had an original MS.880 – says that pretty much no two Rallye cockpit setups are alike, this one is pretty conventional, with the usual Basic T and all levers and switches where you’d expect to find them in any Cessna. Unlike 80s 172s however, the Rallye has two sets of warning lights below the glareshield, as well as more engine instruments as standard (such as CHT, EGT, carburetor temperature and the like). A sign that the MS.890 series was from the outset intended for utility roles is the red pull handle at the top of the panel, which operates the tail hook (also a standard fit, as on the U-75). Another feature of the MS.890 series are the electric flaps; the original 880 had a Piper-like mechanical system operated by a lever between the seats. Naturally, being designed in Europe, at least one instrument has to be Metric – in this case the Airspeed Indicator (ASI)

With a slat and a bump

Once ready to start, things move in pretty much the same manner as on any O-320-equipped aircraft. The major difference here is that the Rallye does not have a standalone primer pump; priming is achieved by operating the electrical backup pump and then advancing the throttle lever several times to its forward stop (five worked wonders for us that day). The electrical pump is also used when switching between tanks to ensure a positive fuel feed until the engine-driven pump builds up enough pressure in the pipes (like the PA-28 – and unlike the C172 and U-75 – the little Morane does not have the option of drawing fuel from both tanks at the same time).

Taxiing out is pretty straightforward despite the lack of nose wheel steering and a reliance entirely on differential braking. Mercifully, the Rallye has conventional Cessna-style pedals, heel for rudder, toe for brakes – and not separate controls for each as seen on the U-75. Since the aircraft had – as mentioned – been designed for utility roles from the outset, the brakes are quite powerful, which makes ground maneuvering pretty easy after a bit of stumbling about (SP-IKY’s excellent pedal feedback certainly helped… changing direction, not the stumbling 😀 ). With some practice, very tight turns are possible – but my lack of experience on the type and Lučko’s wide apron and taxiways made that redundant (at least at this stage). However, as soon as I rolled off the smooth apron and onto the grass taxiway, I ran straight into another issue: keeping a constant speed across the uneven ground requires some practice, since even a slight jab at the brakes to maintain direction results in a noticeable drop in speed. After some time (the taxi to the RWY 10R end takes awhile!), I got the hang of adding a brief burst of power with each brake application – standard stuff, but it definitely feels odd after stepping out of an aircraft with nose wheel steering.

Having successfully – albeit far from elegantly – reached the holding point, it was time to experience the Rallye’s party piece: its wonderfully quirky full-length retractable slats. A feature seen on many short take off designs, slats do their magic by channeling additional air through the gap between themselves and the wing. The benefits are most prominent in the most difficult regime of them all – flight at high Angle of Attack (AoA) and low speed – where they help the airflow to stick to the wing down more of its chord, delaying its separation and the resulting stall. Apart from obvious benefits to general handling and a reduction in the stall speed, this also serves another vital function: it keeps the air flowing over the ailerons, ensuring adequate roll control even at very low speeds – and reducing the risk of the downgoing aileron increasing the AoA to the point of stalling the entire wingtip (the reason why some STOL planes have slats only on the outer sections of the wing).

A sure sign that an airplane means business! Of interest, sporting full length retractable slats is quite unusual for an aircraft of this size; in most cases, they’re either fixed (then called “slots”) or fitted, as mentioned, only to the outer portions of the wing

As on many light aircraft that feature them (up to the 5.5 ton An-2), the Rallye’s slats are fully automatic, and are “operated” by changes in air pressure along the leading edge of the wing; at high AoA, the reduction in pressure simply pulls them out of their retracted position – while the increase in pressure as AoA begins to reduce pushes them back in. All good, solid aerodynamics – the quirk being that on take-off and landing they deploy so suddenly and loudly that you’d be excused for thinking something fell off the airplane (a point SP-IKY’s owner was keen to stress before departure… and one on which he was not exaggerating by any means).

The Big Bang occurred – as foretold – at around 60 km/h (32 kn), roughly halfway to our briefed 100 km/h (54 kn) rotation speed. With the two of us on board, very nearly full tanks, flaps at their first notch (15°) and a 5 knot headwind component, we left the ground in just under 300 meters – not a bad show for a draggy and bumpy runway, and considering that we opted for the standard vs short take off technique (which would have called for maximum flaps and a rotation speed of just 85 km/h (46 kn) ). The performance specs for a full aircraft call for 365 m over a 50 ft obstacle in standard conditions, so that puts us almost right on the money.

The slats came into their own again immediately after departure, staying fully deployed throughout the initial climb and allowing for sprightly “vertical performance”. Whereas the 172 becomes asthmatic immediately after leaving the ground effect with the flaps still down, the Rallye never missed a beat, and we were quickly at our 130 km/h (70 kn) climb speed while still in configuration, doing a not-at-all-bad 700 FPM. With flaps retracted, our vertical speed increased to 800-900 FPM, slightly better than what a similarly loaded N model Skyhawk could do in these conditions (bearing in mind our 10 horsepower deficit).

Interestingly, throughout the entire climb to pattern altitude – and particularly during turns around the circuit – the slats kept extending and partially retracting in response to airflow changes (it was a slightly turbulent day too), being designed to fully stow only above 150 km/h (81 kn) in straight & level flight conditions. An observation that particularly intrigued me is that despite their constant motion, I had very little sense of it in the control wheel, and needed to make almost no corrective input to compensate for their effect – which inspired a good deal of confidence in the Rallye’s handling as a whole.

As noted previously, my plan for the day was to spend most of the time just cruising around, soaking up the low wing views – and giving the owner a tour of the Lučko CTR and some of its more pertinent features and points. Because of this, I had not gone through the same set of PPL skill test maneuvers as I did with the U-75; but nevertheless, I did get to spend enough time at low speed and high AoA to at least get a basic & very rough idea of what the little Rallye is capable of.

Straight off the bat, I was impressed with how docile it behaved in all of the flight regimes I went through – equally as impressed as I was when I first flew the U-75, which shares that very same trait. The smaller and “hotter” wing (9.6 m span / 79.8 kg/m² loading vs 9.73 m / 65.3 kg/m² for the U-75 and 10.97 m / 64.4 kg/m² for the Skyhawk) made for sprightly maneuvering, while the slats kept things from getting out of hand even at low speeds. Indeed, even at 100 km/h, the Rallye exhibited none of the hesitation in pitch and roll common to slow-going C172s – and no sense in the control wheel of impeding drama should you reduce speed and/or increase AoA further. Put simply, even in the limited experience I had that day – and considering my acknowledged lack of flight test credentials, knowledge or skills – through the controls it felt like it could cheerfully handle reasonably everything you threw at it without much fuss or undue effort.

Other characteristics that I very much liked were the effective vertical stabilizer and powerful rudder, which made for very little footwork in any turn and at any speed – yet another parallel with the U-75. Interestingly though, SP-IKY needed very little right foot even during the take off roll and climb, a stark contrast to S5-DCI, the Utva I had the privilege to fly; though this may be simply down to the specific rigging of their rudder tabs.

Keeping up with the Skyhawks

The manuals, however, suggest that the aerodynamics that make this possible do come at a price in the cruise. The Pilot Operating Handbook (POH) for the MS.892 quotes a True Air Speed (TAS) of 160 km/h (86 kn) at 55% power (2,300 RPM) in standard conditions at 500 m (1,650 ft); the C172N POH states 53% power (2,200 RPM) will give you 185 km/h (100 kn) TAS in standard conditions at 2,000 ft.

In a particularly fortunate turn of events, 2,200 RPM just happens to be the setting I use most often on the 172 – while 2,300 RPM was the number SP-IKY’s owner suggested I stick to since we weren’t really in a hurry to get anywhere. Likewise, I do most of my local flying at 2,000 ft – like I did in the Rallye – usually traveling with just one other person on board – like I did in the Rallye – so I conveniently ended up with a somewhat solid baseline from which to try and work out how they actually behave in real life (bearing in mind that one example a poor statistic makes!). In these sort of mid-spring conditions with temperatures between 10 and 20° Centigrade, 2,200 RPM on the N model Skyhawk usually gives me about 175 km/h (95 kn) indicated; on that specific day, with an OAT of 18° C on the ground, 2,300 on the Rallye showed me 180 km/h (97 kn) on the ASI.

The difference may be down to the engine or prop or even the number of dead bugs on the wing; whatever the cause, it does seem to indicate that in the sort of everyday flying practiced around here – mostly low altitude across short to moderate distances – performance-wise both the mid-model 172 and the Rallye have very little between them (the discovery of the century considering the vast 10 HP difference 😀 )***.

*** one other route performance metric – fuel consumption – is a bit difficult to compare precisely, since SP-IKY does not have a fuel flow meter. However, the owner had told me he uses 9 GPH as a low altitude benchmark – which is within tolerances of the measured ~8.5 GPH I see in the same conditions on our 172N’s engine monitoring system

Same altitude, same speed, same region – but a different view… flashing back to my first cross-country flights and related cross-country flight traumas (many caused by our famous hilltop church-to-hilltop church navigation method)!

AS_SPIKY_190510_002 — *First time on an aircraft with a sliding canopy – and loving the photo possibilities!*

Other stuff? Well, apart from improved visibility (and the option of opening the canopy in flight for a bit of natural aircon), the experience of cruising in the Rallye vs cruising in the 172 boils down mostly to subjective criteria and the differences in trim and furnishings of individual aircraft – something the U-75 in particular does not suffer from, since its production run was just 4% of the Rallye’s (and 0.3% of the Skyhawk’s), with only one “military spec” trim level provided. Personally, the only niggle I had that’s worth writing home about is the overly sensitive pitch trim wheel, with very little rotation producing a very noticeable result; a situation I had also encountered on the U-75, with the added trouble of S5-DCI’s wheel having been far coarser and generally significantly less user-friendly than SP-IKY’s.

The Rallye, however, comes back into its own once on approach. The wing’s low-speed finesse becomes obvious already on base leg, since the airplane’s 1/13 glide ratio in clean configuration (achieved at 140 km/h (76 kn) ) means it does take a bit more persuasion to go down than the 172N (which sports a 1/9.2 glide ratio; mind you, the U-75 “outclasses” them both at just… 1/8.4). Selecting flaps to the second and final notch (30°) makes things easier, resulting in a standard approach speed of 120 km/h (65 kn) – a figure that can be brought down to 105 km/h (57 kn) in an emergency.

Flying the final approach is generally pretty humdrum, with the only real difference being the better visibility over the nose, which does wonders for depth perception and glide path control. Life starts to become interesting again once in the flare, not only due to the cushioning effect of the low wing – but also to the quirkiness of the slats, which will suddenly**** slam fully open at around 90 km/h (49 kn), setting you up for an embarrassing ballooning float if you’re not fully ready for it (as I was not). Having “seen the elephant”, my subsequent approaches were… hmm… less worse, and with more experience I am certain I would be able to plant it gently right onto the aiming point, using all the benefits of the slats to their fullest. One of these was actually obvious right from the outset, since the Rallye has an uncharacteristically flat (but still two-point) touchdown attitude, which affords an excellent view ahead – a consequence of the improved airflow along the entire wing that allows the same lift to be generated at a lower AoA… and thus at a lower pitch.

**** the reason why the slats are so “quirky” – i.e. why they extended so suddenly and so late in the landing – has everything to do with the oft-misinterpreted aerodynamic principle behind them. Despite constantly using SPEED to describe their operation – indeed, the 150 km/h retraction and 90 km/h extension are straight from the POH – the slats in fact respond solely to ANGLE OF ATTACK. In the climb, the AoA is high, and the air pressure on the upper wing surface low enough to keep the slats fully or partially extended; on the approach however, the combination of the shallow downward path of the aircraft and the extended flaps means that the AoA is still moderate (despite the low speed), and the air pressure is still such that the slats can be kept pressed in. The flare itself – when the AoA suddenly increases to near stalling values – is the first time during a normal approach and landing that adequate pressure conditions for slat extension actually exist.

Their dependence on AoA also means that you can essentially activate them at any speed – provided you increase the AoA sufficiently enough. If you take the Rallye to its maneuvering speed of 210 km/h (113 kn) – the maximum speed at which a full control deflection will not cause structural damage to the airframe – and yank it over into a combat break, the slats will pop open instantly, despite being 64 kn above their “landing extension speed”.

Unfortunately, the day’s conditions meant I had no opportunity to see how it behaves in a crosswind, something I was particularly interested in due to the possibility of significant sideways drift in the float – and scraping the wingtip along the ground with too enthusiastic a correction. The manual itself quotes a crosswind component limit of 20 kn – noticeably higher than that of both the 172 (15 kn) and U-75 (8 kn).

*The wide cabin, extensive glazing and narrow cowl all make for surprisingly good views downward, which makes life far easier in the circuit*

Lučko’s rough runway also made for a good test of the type’s trailing link suspension, which sports a similar setup to that of the U-75. Though the Utva is far superior in its handling of uneven terrain – having been designed from Day 1 for eventual wartime operation out of auxiliary dispersal fields – the Rallye handled things with ease, ironing out the bumps without any undue sloshing from side to side. On the last, full stop landing, we needed roughly 300 meters to decelerate from touchdown to taxi speed, using only as much braking as was necessary to maintain direction; the manual quotes a 265 meter landing distance over a 50 ft obstacle for a fully loaded airplane (980 kg Maximum Landing Mass), which seems easily attainable by avoiding greasers and applying maximum braking immediately after touchdown (as well as flaring late and letting the slat extension slow your rate of descent).

*Spiky ticking itself cool after our sortie… definitely one of the better flying experiences of the year so far!*

Vive la France!

Though I must once again stress that one hour aloft with no professional flight test background does not make for reliable (or even usable) conclusions, on a purely subjective note I was as smitten with the Rallye as I was with the U-75. Despite being multipurpose machines that can, like the C172, do many things well, both could boast a fun factor that was completely alien to the Skyhawk, comparable even to (dare I say it?) the Super Cub and Citabria. While that may simply be down to my perception of their specifics – such as the Rallye’s slatted low-speed wing or the Utva’s military heritage – both are a hoot beyond even subjective doubt, and can boast a mix of genuine joie de vivre and everyday usability that’s tough to beat.

Or could that be a just low wing thing? 😀

ADDENDUM – 7 JUN: it may have taken me awhile – for the Q400 bids often during the summer! – but eventually I managed to plonk myself back into the left seat of SP-IKY and finally head into one of Lučko’s training zones for a bit of air work. Due to my pretty obvious fascination with its slats, I’d decided to put it through a couple of textbook stalls and see what’s what on that edge of the envelope…

In short, the Rallye’s behavior was just as one would expect – but with a slight twist. Throughout the entire maneuver, SP-IKY held rock-steady despite the day’s turbulence, and showed no inclination to drop either wing even as the indicated airspeed reduced to below 90 km/h (49 kn); indeed, even my attempts to provoke it with a bit of aileron came to naught, and it kept at it well into the 70 km/h (38 kn) range. When the stall finally did come, it was as dramatic as watching paint dry: just a slight forward tug on the wheel and all was well… not even U-75 “went” so cleanly. If anything, the slats meant that the wing regained a healthy airflow as soon as the AoA reduced even slightly, returning to “normality” at a pitch that would be quite unnatural on a non-slatted wing. The downside of this ease of recovery is that it can be quite deceptive, and a conscious effort is needed to continue to push the nose down and build up a healthy AoA margin, despite all feeling well in the wheel.

And the twist? As on landing, the sudden deployment of the slats and the resulting rapid increase in lift along the entire wing can come as quite a surprise, leading to a pronounced and very visible ballooning motion that looks and feels VERY odd… as the following vid shows! Even more so, in a more aggressive stall, the change in airflow distribution will actually rock the ailerons slightly; aerodynamically this is not much of an issue – since at that point the wing still has quite a bit of life in it left – but an instinctive/panicked counter movement of the wheel could in some conditions cause more problems than it solves…

As always, I would like to extend my sincere thanks to Lukasz for the opportunity to fly his baby and cross another aircraft from my To Fly List!

Changelog:

7 June 2019: stall characteristics + video added
10 May 2019: added slat operation videos + additional photos

Sources:

EASA – MS.890 series Type Certificate Data Sheet (PDF)
MS.892 & C172N Pilot Operating Handbooks

Photo File – Looking Out Of 2018

March 7, 2019April 5, 2021Posted in Aerial ViewsTagged Aerial views, cockpit view, in-flight photoLeave a comment

By me
All photos me too, copyrighted

Once again, regular as clockwork, the winter calm has come down on the Croatian GA scene. Even though the weather has been eerily cooperative of late – hardly any snow even – light aircraft ops have been few and far in between, most machines either having their long sleep in the hangar or flying up and down to the coast for the season. So, while I wait for things to start up again, here are a couple of highlights from my autumn/winter/pre-spring “getting paid to stare out the window” collection 🙂 .

*A bit of anticyclonic weather here, some freezing temperatures there, mix it all in with a dawn arrival and voilà – one very happy first officer!*

Getting up at 4 AM to go to work: not really a fan. Greeting the dawn like this as a consequence: like it very much! Layer cloud, rain, icing, fog and clear skies – and all of them happening at the same time. Damn I love this job!

*For some reason, getting stuck in a dawn holding pattern went down pretty well with me this morning…*

Bursting out of a deep cloud bank into a windy and turbulent seaside morning. With surface winds hovering around the 30 knot mark – and winds aloft in treble figures even at turboprop altitudes – the views were guaranteed to be impressive…

*Enjoying a spot of late afternoon cloudsurfing near the Eternal City as a wall of nasty thunderstorms starts to build over Naples out in the distance…*

Soaking up the majesty of Italy’s Gran Sasso mountain range as we zip past on our way west. Dominated by the Corno Grande – the country’s highest non-Alpine peak – Gran Sasso is perhaps most famous as the setting of Operation Eiche, an audacious 1943 airborne assault by German special forces to rescue Benito Mussolini, then being held under arrest in a hotel on the Campo Imperatore highlands (the depression in the center). Having reached the site in assault gliders, the attacking troops had quickly overwhelmed the defenders and shuffled Mussolini to a waiting Fieseler Storch, which – though dangerously overloaded – managed to eventually lift off and head for the Pratica di Mare airbase, located very near Rome’s present Fiumicino Airport. In a particular twist, our flight path that day had taken us along almost exactly the same route, a trip that took us 15 minutes in a warm cockpit with tea in hand – as opposed to the harrowing hour it took the Storch barely clinging to the air in bitterly cold winter (not to mention having Mussolini as a passenger and Hitler waiting anxiously in Berlin for news)… nowadays the entire range is a designated national park, known for its pristine nature and ski slopes – as well as the world’s largest underground particle research laboratory (the Laboratori Nazionali del Gran Sasso), and an out-station of the Rome Observatory tracking and cataloging orbital bodies passing near the Earth (Near Earth Objects, NEOs)

They say “Blue Monday” is the most depressing day of the year… “Blue Tuesday” however seems to be a far better deal! No room for gloom when you get to greet the dawn above the sleepy, anticyclonic Alps…

*There are fine views of the Alps at sundown… and then there’s this one. Zipping past the several Tauern subranges as we sneak under a nasty jetstream blanketing most of Austria…*

Bonus content: while all of these airliner views are fine and dandy, I could not in good conscience post them without shoehorning a bit of GA in 😀 . So, to balance things out, here’s one shot (+ video) from the good old C172 and the paying to stare out the window collection!

A piston single, a backwoods grass runway, a deep anticyclone and all the time in the world – feels good to be back in the old saddle! One of the first private airstrips in Croatia, Zvekovac (LDZE) has always been a GA favorite; located just 20 minutes away from Lučko (LDZL), it’s a perfect place for a short afternoon getaway (especially when there’s a barbecue in the mix somewhere)

Photo File – My Kingdom For Some Horsepower: The Caravan Blackhawk XP42

October 1, 2018April 5, 2021Posted in General AviationTagged Blackhawk XP42, Caravan Blackhawk, Cessna, Cessna 208, Cessna 208 Blackhawk, Cessna 208 skydive, Cessna Caravan, D-FOXY, Šentvid1 Comment

By me
All photos me too, copyrighted

It is perhaps a sign of the state of general aviation on the Balkans that the arrival of a single Cessna Caravan can stir up so much interest that even people from neighboring countries head over to see it. While a perfectly common “garden variety” airplane everywhere else, the 208 is still a pretty exotic beast in these parts, with myself having come across only four examples in the 16 years I’ve spent hanging around light aircraft. Therefore I could be excused for packing up my photo gear and driving 120 km one way to Šentvid Airfield in Slovenia in order to catch it 😀 .

The machine in my sights, however, had a bit more going for it than just being a big Cessna with a turbine. On the one hand, it is a comparatively rare short-body Caravan I – and on the other it sports the impressive Blackhawk XP42 engine conversion that is not that common even in the more affluent bits of Europe. So as it spent its three days there hauling skydivers to altitude, I could take my sweet time and get to know it Achtung, Skyhawk! style 🙂 .

A handful of horses in the back – and 850 charging straight at me. Looking imposing in the soft afternoon light, D-FOXY returns from yet another series of skydive runs. Manufactured in 1999 with the serial 208-00303, Foxy spent its early years in the US, flying as a seaplane under the name N984J. In 2006 it would move to Italy as I-SEAA, before heading north into Germany in 2013, where it would eventually lose its floats, get buff and become a no-nonsense jump platform

Blackhawk Up

Though much can be said about the qualities and exploits of the rugged Caravan, what interested me most in this case was in fact Foxy’s nose job. One of the many products to come out of the Blackhawk Engineering works – the people who put third-party turboprop upgrades on the map – the XP42 mod involves replacing the 208’s standard engine (in this instance a “small series” 675 HP PT6A-114A*) with a much more potent “medium series” 850 HP PT6A-42A. In addition to the improved power, the 42’s larger core also noticeably adds to the torque, with take-off figures now up from 2,535 to 3,045 Nm. To soak all this up, the original three-blade 2.69 m McCauley prop gives way to a variety of four- and five-blade aluminum and composite units, with Foxy in particular sporting a conventional 2.54 m Hartzell for a bit of extra ground clearance.

* up until serial number 208-00276, most short-body Caravans were powered by the 600 HP PT6A-114 unit. From aircraft 277 onward, they switched to the same 114A as used by the bigger Grand Caravan. Also of note is PW&C’s engine class system: “small series” engines develop between 500 and 900 HP, “medium series” cover the 850-1,050 range – while “large series” go from 750 all the way to 1,900.

But, the XP42 upgrade is as much about added grunt as it is about the nature of its delivery. Unlike a simple engine swap, this conversion is what’s called a “firewall forward solution”, which includes – where necessary – extensive modification to the engine compartment itself in order to get the most out of the new powerplant. Since the majority of XP42s will be used for rough-and-tough hauling in arduous conditions, the folks at Blackhawk had gone to some length to make the upgrade more than just a course of steroids. To this end, the most obvious alteration is to the cowl, now widened at the front to accommodate a 40% larger oil cooler in order to keep things in the green even during operations in hot-and-high conditions or repeated back-to-back flight cycles. The new twin exhaust stacks (a consequence of the 42’s slightly different architecture) can be profiled to either eek more thrust out of the exhaust gasses (5 knots worth in fact) – or increase mass flow at the expense of cruising efficiency to lower turbine temperatures during the type of prolonged high-power climb common to skydive ops.

*For comparison, a stock Caravan I, here in its military U-27 guise. Note the single large exhaust duct and narrow cowl*

Other stuff? Well, the engine is now mounted at four points instead of three, there’s an improved air intake system with a modified inertial separator to further reduce the likelihood of foreign object ingestion at rough strips, the battery is now a Li-ion affair instead of lead/acid to save roughly 13 kg in weight – and there’s an optional 325 A starter generator instead of the stock 200 A unit to reduce wear and tear on the engine by shortening spool up and light up times. The package is also rounded up by custom Hawkeye engine gauges, generally similar to the Caravan’s originals – but now with an additional digital readout for most parameters.

Dear passengers, your flight is now ready for boarding. Though all of you will leave half way, we would like to thank you for flying with us! Though the prop is now noticeably shorter in span, it still spins at very similar speeds as the original, meaning the XP42 is still a pretty quiet machine, even at full chat

A peek under Foxy’s skirt. Though the 42A sports a larger core than the 114A, it is only 27 kg heavier dry, 190 vs 163 kg. Interestingly, it is also 34,7 cm longer than the 114A (1.68 vs 1.34 m) – but at the same time 13.2 cm narrower, sporting a 46.4 cm diameter vs the “smaller engine’s” 59.6. Also note the fuel/oil heat exchanger at the extreme right, which helps cool the oil by transferring some of its heat to the fuel on its way to the combustion chamber

*And the conversion’s other party piece, the new oil cooler. A pretty good illustration why the XP42’s nose now looks like it had been rammed into a wall!*

In addition to Blackhawk’s efforts to keep oil temperatures manageable even during repeated short cycles (as well as the day’s very agreeable 17 degrees Centigrade on the ground), Foxy came equipped with a custom cooling adapter, essentially three fans running off a 12 volt external battery that circulate air through the oil cooler to prevent the formation of local hot spots when the engine is not operating

With a load of between 10 and 15 skydivers every 15-20 minutes, Foxy’s modification sure had their work cut out for them (even more so since start-ups are more critical to turbine engine wear than running hours)!

*What a truly wonderful way of spending an afternoon: sitting on the ground behind a revving 850 HP short-body Caravan to the background of rolling hills and lush forest…*

As always, I would like to thank the very friendly staff at Šentvid Airfield – as well as Foxy’s pilot for allowing me to snoop around the aircraft inside & out!

Sources:

Avbuyer – Blackhawk Modifications profile
Blackhawk Modifications – Cessna Caravan Vx Upgrade and XP42 article
EASA – Cessna 208, PT6A-100 series and PT6A-41 series Type Certificate Data Sheets (PDF)
Pratt & Whitney Canada – PT6A family overview
Seaplane Magazine – Caravan MT Propeller article

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