Category: Plane’s Anatomy / Tech

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

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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 starter, 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 speeddy 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:

Tech – A Flying Fashion Victim: The PC-6 Engine Saga

Posted in General Aviation, Plane's Anatomy / TechTagged , , 1 Comment

By me

In a dazzling display of consistency, my research for a magazine article about S5-CAM – the Pilatus PC-6 that had visited Lučko some months ago – took only moments to veer completely off track, invariably as soon as I began to delve deeper into the type’s rich history :). The culprit for my deviation was the fantastic database at www.pc-6.com, documenting in amazing detail the life and times of this amazing aircraft.

Such huge collection of sometimes obscure information was right up my runway, so with my initial research goal completely forgotten, I began to read through the type’s version list. Pretty soon I began to notice that the PC-6 had a tendency to change engines as often as I change clothes, prompting me to dig even deeper and attempt to make a list of all the powerplants (and their evolutions) that had ever been fitted to the Porter… 🙂

From A to D

While the PC-6 is today universally – and pretty much exclusively – associated with the venerable PT6A turboprop, the design actually had much more humble beginnings, starting out in life as “just another piston”. First flying back in 1959, the original PC-6 had been equipped with a Lycoming GSO-480 engine, whose six supercharged (S prefix) cylinders, linked to a reduction gearbox (G prefix), produced around 340 HP (the reason why this series is also known as the PC-6/340). Despite the comparatively low power – and the piston engine’s well known anemia at altitude – the Porter prototype had nevertheless managed to capture the period record for the highest (successful 🙂 ) landing, touching down at an impressive 18,856 feet somewhere in the Himalayas.

However, the GSO-480 was quite a complicated and temperamental thing to run and maintain, leading pretty soon to the development of a simpler model called the PC-6/275, powered by a normally aspirated – but still geared – 250 HP GO-480. But the loss of 90 HP – a whopping 26% – over the equally heavy standard model had meant the performance suffered dramatically, spurring the introduction of the follow-on PC-6/350, equipped with a fuel injected (I prefix) IGO-480 developing a much more reasonable 350 HP.

The apex of the piston PC-6 however did not come until 1970 – rather late by large piston standards – with the brutal PC-6/D, powered by the monstrous eight cylinder Lycoming TIO-720 producing a sizable 400 HP. One of the more ludicrous ideas to come out of the Lycoming works, the 11.8 liter TIO-720 was created by joining together two IO-360s and then – for that little extra something – screwing on a massive turbocharger (T prefix). Despite the power and potency of the engine – which had also been used to great effect on the Piper PA-24-400 Comanche and the PA-36-375 Pawnee Brave – it was very heavy and its rear cylinders were notoriously prone to overheating. The superiority of turboprops – which had been introduced to the PC-6 line nine years earlier – had slammed the final nail into the coffin of the D model, the program being quietly dropped after just one prototype had been completed.

The French Connection

This “first contact” with the turbine came in 1961 with the 523 HP Turbomeca Astazou IIE, creating the PC-6/A, the first of the Turbo Porters. A very light, compact and durable engine, the Astazou would go on to become one of the world’s great small turboprops – but would sadly have a short and largely unremarkable career on the PC-6. The only major revamp in the period was the one-of PC-6/Ax, powered by the new Astazou X which had – through the addition of another compressor stage – been boosted to 573 HP. This model was followed by the very similar PC-6/A1 and PC-6/A2, which had only differed in engine versions (Astazou XII and XIVE respectively) with no change in power. All in all, only 43 Astazou-powered examples were ever built, all of which were eventually re-engined with the PT6A – thus confining the A models to the pages of history…

What would eventually become the PC-6 we know today had started emerging in the mid-60s, when the Astazou of one example was swapped for a 550 HP PT6A-6A, creating the enduring legend – the PC-6/B. This first foray into PT6 World was however short lived, with only 12 examples produced before the introduction of the definitive early B model, the PC-6/B1-H2, sporting the PT6A-20 of equal power output, but higher torque.

Like fine wine (or cheese 😀 ), the PT6 PC-6 would then take some time to mature – 17 years in fact until the arrival of the penultimate Turbo Porter, the PC-6/B2-H2 of 1984. Representing 80% of the way to today’s standard, the B2-H2 was fitted with a 680 HP PT6A-27, flat rated down to the “original” 550 HP. While this may seem like a questionable move, it does have a raft of benefits for a “hauler” designed for operations at high weights and in all weather conditions. The first advantage is the engine’s larger core, which gives a measurable increase in torque throughout its operating range without a (significant) increase in fuel consumption. Additionally, running slower and cooler than it was designed for means engine wear is noticeably reduced, boosting overall reliability and noticeably prolonging the engine’s service life.

However, the biggest advantage is a stable power output regardless of outside air temperature. In a conventional non-flat-rated system, the maximum power the engine can produce with the throttle wide open – the so called thermodynamic power – varies greatly with air density, itself a function of air temperature. The higher the temp, the lower the density and vice-versa. When the density is low, the mass flow through the engine is reduced, the combustion efficiency is reduced and the engine’s thermal limits are more constricting – all of which results in a reduced power output. Conversely, when the density is high – such as on a cold day – the mass flow is high, combustion efficiency is high and the engine runs cooler, allowing more fuel to be injected and thus produce more power. The upshot is that an engine producing, say, 1000 HP in standard conditions (15 degrees Centigrade, used for all performance specs) may produce upward of 1100 HP at 0 Centigrade and as low as 900 HP at 30 Centigrade – which complicates performance calculations and adversely affects the aircraft’s overall performance. Obviously enough, the more critical condition is at lower densities – since very few pilots will object to having additional pep at takeoff :D.

Flat rating systems get around this issue (up to a point of course) specifically by limiting the engine’s maximum power so they always have a reserve to compensate for any drop in output due to reduced density. In the case of the PC-6, the capacity to produce that additional 130 HP is used to compensate for the reduced efficiency at higher temperatures, allowing the engine to produce its stated 550 HP regardless of outside conditions. Additionally, since the same principle applies to the reduction in density with altitude, flat-rated engines have a lower power decay while climbing, and can produce their stated power to a higher altitude, helping out greatly in hot-and-high operations.

Having finally sorted the engine out (after decades of trying 😀 ), Pilatus then turned to the other remaining propulsion item – the propeller – replacing the usual three-blade unit with a new four-blade model, creating today’s production standard PC-6/B2-H4.

However, while Pilatus themselves had stopped fiddling with the powerplant, the Porter’s users had other ideas and decided to carry on the tradition themselves. An immensely popular skydive platform, the PC-6 had at time been found wanting for power in the climb, leading to the logical idea of refitting it with a more powerful engine. This was eventually achieved in 2001, when an old B2-H2 was upgraded with the 750 HP PT6A-34 (flat rated to 620 HP), becoming the progenitor of a series of 30 such conversions (both H2s and H4s), all done under a new Supplementary Type Certificate.

The Alpine Yank

But the “fulfillment” of the PT6A installation is not the whole of the PC-6 engine saga – not by a long shot :). The success of the first turboprop models had created a lot of interest on the other side of the Atlantic, where operators were keen on a home-grown version using locally-available components. Not oblivious to the huge potential of the aircraft on the American – and especially SOUTH American – market, Pilatus quickly complied with demand, and in 1964 struck a deal with Fairchild-Hiller to produce the aircraft under license in the States. Initially, the aircraft rolling off the line were stock B models – but it took the locals only a year to come up with their own version, the PC-6/C, powered now by the 575 HP Garrett (AiResearch) TPE-331-25D.

Generally “confined” to the US market, the C models would eventually rise to worldwide fame, thanks most of all to the PC-6/C2, known in military service as the AU-23A Peacemaker. A type still happily flying with the Royal Thai Air Force, the AU-23A is/was powered by the 665 HP TPE-331-1-101F, and had flown into the spotlight during its exploits in the skies of Vietnam, Laos and Cambodia. Another C2 had also landed in the record books, having performed an amazing 424 take offs and landings in a single day, a feat achieved over 21 consecutive hours without breaks (except for oil and fuel top ups)…

Chronologically out of tune, the last of the C models was the the PC-6/C1 of 1969, powered by a 576 HP TPE-331-1-100. Apparently a TPE conversion intended for the European market, the C1 eventually ended up being just a one-of model, with the PC-6 already having a suitable engine in the form of the PT6A :).

Overview – piston:

  • PC-6 (PC-6/340) – Lycoming GSO-480-B1A6 (340 HP) (1959)
  • PC-6/275 – Lycoming GO-480-D1A (250 HP) (1960)
  • PC-6/350 – Lycoming IGO-480-A1A (350 HP) (1961)
  • PC-6/D – Lycoming TIO-720-C1A2 (400 HP) (1970)

Overview – turboprop:

  • PC-6/A – Turbomeca Astazou IIE (523 HP) (1961)
  • PC-6/Ax – Turbomeca Astazou X (573 HP) (1964)
  • PC-6/A1 – Turbomeca Astazou XII (573 HP) (1967)
  • PC-6/A2 – Turbomeca Astazou XIVE (573 HP) (1967)
  • PC-6/B – Pratt & Whitney Canada PT6A-6A (550 HP) (1964)
  • PC-6/B1-H2 – Pratt & Whitney Canada PT6A-20 (550 HP) (1967)
  • PC-6/B2-H2 – Pratt & Whitney Canada PT6A-27 (680 / 550 HP flat rated) (1984)
  • PC-6/B2-H4 – Pratt & Whitney Canada PT6A-27 (680 / 550 HP flat rated) (1996)
  • PC-6/B2 (mod) – Pratt & Whitney Canada PT6A-34 (750 / 620 HP flat rated) (2001)
  • PC-6/C – Garrett (AiResearch) TPE-331-25D (575 HP) (1965)
  • PC-6/C2 – Garrett (AiResearch) TPE-331-1-101F (665 HP) (1967)
  • PC-6/C1 – Garrett (AiResearch) TPE-331-1-100 (576 HP) (1969)

Sources:

Photo & Video Report – 9A-BKS Roaring Again

Posted in General Aviation, Plane's Anatomy / Tech, VideoTagged 2 Comments

By me
Photo & video me too (copyrighted)

A couple of years ago when I first started this blog, I made mention of a skydive-configured Cessna 185 Carryall that had been involved in a landing accident awhile back, and had remained confined to the corner of the hangar ever since. The topic of one of my early Plane’s Anatomy posts, this specific, slightly understated ( 😀 ) aircraft had recently been thrust into the local spotlight again, this time when it finally coughed back to life after its long rest.

Overall not a particularly interesting or exciting aircraft by any objective measure – just a regular 185 – 9A-BKS is nevertheless one of the most endeared and endearing aircraft at Lučko; a charismatic fuel-to-noise converter that had at one point or the other served as a jump platform for virtually every skydiver in the area. Quite a loud aircraft, sporting a two-blade transsonic prop, BKS had cut a distinctive high pitched noise that could be heard all the way to the suburbs of Zagreb – some 10 km away – and pretty much represented the main symbol of the airfield.

The noise stopped however at the beginning of 2008, when BKS’ pilot braked a bit too hard on landing, sending the prop tips into the ground. While the aircraft itself had suffered no damage, the propeller was ruined and the engine overstressed by the sudden stop, both necessitating a thorough – and thoroughly expensive – overhaul. These costs, coupled with the operator’s poor financial state (which continues to this day) had dragged repairs through more than four years, until BKS finally fired up on 10 June this year 🙂 .

Naturally, I was ready to immortalize the event with my camera – even though it had meant a whole day of waiting at the airfield on an empty stomach 😀 – and even decided  to shoot a spot of video to capture the moment.

But, “first start” was much overshadowed by the death of one of our most beloved skydivers, who tragically died on a jump at a county fair while we were preparing to light BKS. In view of that, both the following photo and video are dedicated to our dear Jasna 😦 .

Trying to avoid a “Carryall haircut” as I attempt to bring out the raw power and poise of the 185. Ran for the first time since overhaul, the engine had lost most of it characteristic deep roar, sounding for awhile like an 8.5 liter sewing machine. With just a few minutes of operation on the clock when this was taken, the engine still hadn’t fully drawn in oil and lubricated all of its parts – most notably the valves and valve seats – leaving it clanking like it’s falling apart

Short Photo Report – Piper PA-30-160 Twin Comanche, N55AG

Posted in Plane's Anatomy / Tech, Rare AircraftTagged , , , 1 Comment

By me
All photos me too, copyrighted

Apart from arriving in questionable style – a 30 year old Skyhawk is not the most elegant of aircraft it must be said 😀 – an added benefit of flying to the coast during the tourist season is that you can always find some interesting aircraft when you get there. Being quite close to the central European mainland, Croatia’s five coastal international airports and three port-of-entry airfields offer a convenient way of reaching the Adriatic without much undue hassle, providing the locals with a steady and varied flow of interesting light (and occasionally heavy) aircraft :).

And while by the end of May the season had still not reached full steam – with the aftershocks of the recession still being felt across Europe – I was confident that, for my last Instrument Rating training flight, I’d be rewarded with something really nice :D. My destination for the day, Zadar’s Zemunik Airbase/Airport, has a history of interesting GA aircraft, its strategic location at the midpoint of the country’s coast providing easy access to a number of well known and frequently visited destinations – all the places that a man with a plane might visit :).

With that in mind, I had crossed my fingers and hoped for the best. Thankfully, my luck held out, and this is what I’d found… 🙂

My first ever Twin Comanche! 🙂 Developed from the PA-24 Comanche single - in it's -400 series for a long time one of the fastest piston singles ever produced - the PA-30 is powered by two Lycoming IO-320s, each developing 160 HP from four cylinders. In essence the same engines that power - among other things - the Skyhawk and Piper Warrior, coupled with constant speed props they give the PA-30 a cruise fuel consumption of just 16 GPH, making it one of the most economical aircraft in its class

Unlike similar single-to-twin conversions (such as the Beech TravelAir developed from the Bonanza), the Twin Comanche was developed out-of-house by Ed Swearingen, a man well known for his high-speed piston twin modifications. Designed to replace Piper's own Apache twin - whose big brother, the Aztec, can be barely seen in the background - the normally aspirated Twin Comanche can zip along at 172 knots and 20,000 ft, and with a full 120 gallons aboard continue on for more than a 1000 NM. A pretty solid set of numbers for a "weedy" 320 HP!

Alongside the normally aspirated models (which I believe this one is, couldn't find its data plaque), the PA-30 was also offered in turbocharged and turbonormalised versions (see bottom of post). Some models were also offered with 200 HP engines, while the later PA-39 Twin Comanche C/R (the 39 is no typo 🙂 ) received engines spinning in opposite directions (C/R = counter-rotating) to remove the "critical engine" effect during a single engine failure

Looking quite good in its simple, retro scheme. Though registered in the USA, it is possible that N55AG is permanently based in Europe (most probably the UK), but for various reasons kept on the US register

Time again for a little (engine) digression to make sense of all the turbo- terminology :D. Essentially, all piston engines have two key parameters that define their power output: the RPM and the manifold pressure, the pressure of air in the intake manifold (part of the intake system) – and consequently the cylinders. On a normally aspirated (atmospheric) engine at sea level, the maximum manifold pressure, achieved at full throttle, will never exceed about 28-30 inches mercury – or, more plainly, atmospheric pressure. As the aircraft climbs however, the air pressure drops and the manifold pressure drops with it. This results in a progressive decrease in power until the altitude at which the power produced is just sufficient to hold the aircraft in the air without sinking. This altitude is – in a nutshell – the fabled ceiling, above which the aircraft cannot climb no matter how much the pilot wants it to :). Depending on the displacement and HP of the engine – and the power requirements of its associated aircraft – for normally aspirated engines this altitude is between 10 and 20,000 ft.

If you had wanted to increase this altitude, the most practical way would simply be to either delay the manifold pressure drop so that it doesn’t start immediately after sea level but somewhere higher up, or widen the manifold pressure range so that you have more “pressure reserve” before you reach the point above which you cannot climb.

On modern engines, both of these are achieved by use of the turbocharger. A familiar component from automobile engines – especially Diesels – this is a high-speed compressor ramming air into the cylinders at high pressure, and is driven by a turbine (a glorified windmill 😀 ) spun by the engine’s exhaust gasses (hence the much-misused “turbo” prefix). In aviation applications, the turbocharger is always variable-speed, controlled by a component known as the waste gate, which controls the amount of exhaust gas ducted over the turbine, hence varying its speed. As the aircraft starts climbing from sea level, the waste gate progressively increases the speed of the compressor – thus increasing the amount of air rammed into the cylinders – to keep maximum manifold pressure attained at sea level regardless of the drop of atmospheric pressure and density.

If the climb continues when the compressor reaches its maximum speed, it can no longer compensate for the decreasing pressure, and the manifold pressure starts to drop (the compressor remains spinning at top speed). The altitude at which this occurs is called the critical altitude, and for most modern turbocharged pistons it is between 8,000 and 10,000 ft (though on pressurized aircraft, with their big high-volume compressors, this can be as high as 15-17,000 ft).

Because the turbocharger also widens the manifold pressure range, the pressure now has a longer way to fall before it reaches the point where the power produced is equal to the power needed (though, depending on type, turbocharged engines may have a higher minimum manifold pressure in order to produce enough exhaust gasses to keep the compressor spinning at max. speed). For example, the TSIO-360 engines on the Piper Seneca III have a maximum manifold pressure of 40 in Hg, roughly 10 more than atmospheric pressure. A more extreme example were the big radials of WW2 which could sustain up to 70 in Hg for short periods! A side effect of this is that the increased amount of air in the cylinders means that the amount of fuel has to be increased as well to keep the fuel-air mixture stable, which can significantly increase available power.

When both of these effects combine, the ceiling can increase to over 30,000 ft – though more often than not aircraft are limited to a lower altitude due to other design factors. For example, the Beech Duke has an absolute ceiling of a tad over 30,000 ft; but it is limited to 25,000 ft operationally because of limits of its pressurization system.

For all the turbocharger’s plus points there’s naturally a raft of minuses – the biggest being the aforementioned increase in the amount of fuel injected, meaning an increase in fuel consumption. This is exacerbated by the fact that while a normally aspirated engine gradually uses less fuel as it climbs (due to the dropping manifold pressure), the turbocharged engine does not and burns the same amount as at sea level. Only after passing the critical altitude – when the manifold pressure starts to drop – does the consumption start reducing with altitude “as it should” :).

Another problem is engine wear and tear. Most of today’s turbocharged piston engines – especially the lower displacement ones – are derived from normally aspirated models that operate at significantly lower pressures and temperatures. And while virtually all of these “mainstream” piston engines are designed and built with the possibility of turbocharging in mind, this is somewhat of a “jack of all trades, master of none” solution – if you make the engine turbo-proof, it’ll most probably be heavy and uncompetitive in the normally aspirated market; if you make it to sweep away the normally aspirated competition, it may be too light and brittle to withstand a lifetime of turbocharging. Another issue is cooling – the rarefied air at altitude is not so good at carrying away heat as the dense air near the surface. On a normally aspirated engine, the engine temps reduce with altitude, so the rarer air can still do its cooling job effectively. On a turbocharged engine, you have the same reduced cooling but – up until the critical altitude – just as much heat produced as at sea level.

Most engines have struck a good balance between the two, though the price to pay is a reduced Time Between Overhaul (TBO) and a slight reduction in service life due to the stress the whole engine block has to absorb (this is the reason why automotive Diesel engines – which work at much higher pressures than petrol engines – are made out of steel instead of aluminium). Some engines even have to have special operating procedures to enable them to meet their TBOs: for example, the Mooney Bravo – powered by the Turbocharged Lycoming Sabre (TLS) sporting a whopping great compressor – has to descend at a high throttle setting and airbrakes extended to avoid shock-cooling the engine!

And that’s all fine and dandy – but what if all you wanted was better altitude performance and to avoid all the hassles and problems stated above? What if you live in Switzerland and your airfield’s pattern altitude is 15,000 ft? 😀 Or, on a more serious note, in Croatia where you want to jump as high as practicable above the Velebit mountain range on a 35 C day, but generally don’t need the extra power?

One practical, working solution is the turbonormalised engine. Identical in design, operation and construction to the standard turbocharged engine, it nevertheless differs in one significant detail: while turbocharged engines increase the manifold pressure above normal atmospheric, turbonormalised ones do not, operating continually in the 28-30 in Hg range until the critical altitude. While this may sound less significant than it is made to be – and even appear to be a step back, given that there is no power increase – it does neutralize some of the standard engine’s operational problems, most notably increased wear and tear. With the engine now continually operating within normally aspirated pressure limits, the TBO penalty can be significantly reduced – but not completely removed, since cooling (as described above) is still an issue, but on a lower scale.

Because the engine is now operating in a lower pressure range, the direct fuel consumption is also reduced and at its greatest pretty much equals what the normally aspirated engine would burn at maximum throttle at sea level. But, as before, this fuel burn is kept to a higher altitude, so it’s not as rosy as it sounds, especially if – as in the situations described above – you just need the extra altitude performance to clear obstacles, but normally spend your time below the engine’s critical altitude at sea level consumption.

Despite this, the turbonormalised engine has met with some success, mostly on small displacement engines of light singles and twins – but, being somewhat of a niche product designed for a specific application, hasn’t become as widespread as the normal turbo (yet). To many people, just the ceiling increase and slightly better performance do not offset the added maintenance costs of the compressor and turbine, leading many manufacturers to simply select the “full package” classic turbo – or go turboprop – giving their customers more for their money…

Okay, this little and short digression has gotten a bit out of hand :D. Consider it as a bonus feature to the original photo report… 😀

NOTE: for more detailed information on turbonormalised engines – my text being somewhat abbreviated for simplicity’s sake – you can go to here

Engine Photo Report – A Pair Of Famous Soviet Turbines…

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By me
All photos me too, copyrighted

Among the many interesting things that can be found in the hangar of my university’s aviation department, the “engine gallery” as I call it always catches my attention. While not extensive or comprehensive in any way, it does have two very interesting exhibits – neither of which have any application whatsoever to the department’s small fleet of Skyhawks and a single Seminole 😀 (though I sometimes hope they could have). Dusty and pretty much ignored, they are two of the probably most famous Soviet turbines ever produced – the Klimov TV2 turboshaft and the Tumansky R-11/13/25 afterburning turbojet…

First up is the Klimov TV2-117A, powering the most popular medium-lift helicopter ever made - the Mil Mi-8 :). A surprisingly small package, the TV2-117 produces 1500 SHP for takeoff, and weighs - who would have thought - about 330 kg. More than 16,000 have been produced, clocking over 100.000.000 flight hours since 1964... the donor of this particular engine was probably one of the Croatian Air Force's Mi-8MTV-1s (and sorry for the poor lighting, it was a bright day outside. And don't ask about the Skyhawk in the back, long story 😀 )

Essentially a large turboprop turning a very large propeller, the turboshaft engine needs a relatively low mass flow of air and can make do with a small intake. The pipes and casings on top of the intake are the engine accessories - the generator, starter, oil reservoir, pumps etc - which normally sit inside the fuselage; however, for practical reasons, this engine was mounted on the frame upside down

Out back is the part that gives this engine type its name, the main power shaft. This connects to the gearbox, which then transmits the power to both the main and the tail rotors

The TV2 in its natural environment - on an Mi-8 :). Note how little space the engines themselves take up... the caps on the intakes up front, a distinctive feature on many helicopters, are air filters - on the Mi-8 specific to later military and some civil models - which permit operations in dusty environments

The second gem is the quite small, but also quite loud, Tumansky R-13 turbojet that powers the two-seat Mikoyan-Gurevich MiG-21UM. Rated at 63,7 kN with reheat, the R-13 (right) is just one part of the MiG-21's powerplant, which also includes the intake and the exhaust (left)...

This though requires a bit of a winded explanation that would not really fit into the photo description box :D. Far from being a simple pipe, the exhaust has a vital role to play as part of the reheat system. Normally, for a fire to burn – and reheat is, in a fashion, just that – oxygen is required. On a turbofan, where there is a substantial amount of air being ducted around the engine core, it is a straightforward matter to divert some of it into the exhaust to aid the combustion of the additional fuel being injected. On a turbojet however, you have to get creative :). The solution adopted for the R-11/13/25 family – and I believe for other turbojets as well – was to duct a small amount of air around the core, just enough to sustain the reheat. The more astute will have noticed that in the above photo, the exhaust has another pipe inside, perforated in the front by a series of small holes. When this assembly is mounted on the back of the engine, air – forced between the two pipes by the low pressure compressor – is blown through the holes, supplying the reheat with oxygen.

A handy size comparison, with a note: unlike the two-seat MiG-21UM, the single-seat 21bis pictured here uses a more powerful 69,6 kN R-25, itself a development of the R-13 - however, externally they look the same and are the same size, so it'll do :). Note also that the nose cone - part of the intake system - is in the fully extended position for supersonic flight. As such, it keeps the shockwave from entering - and damaging - the engine, as well as slowing the air down to subsonic speeds before it reaches the compressors

A rear view of the R-13 showing the flame stabilizers, an integral part of the reheat system

A rear view down the tailpipe of an operational 21bis, showing the R-25's different (circular) flame stabilizers. Note how far the engine itself is deep within the airframe...

And to finish it all off, an artsy view of the first low pressure compresor stages of the R-13... took me a good half hour to get this right 🙂

Post Update 2 – Technical Museum Aircraft (Again)

Posted in History, Museums, Plane's Anatomy / Tech, Rare AircraftTagged , 2 Comments

By me
All photos me too, copyrighted

With a growing fascination for the Technical Museum and the few – but fine – aviation exhibits within, today I was back there yet again, camera ready to cover anything I had missed in my previous report :). A definite case of I-need-a-life-ism, but my research for the first post on the topic had revealed that the Museum had definitely traded quantity for quality (or rather rarity), so I was naturally keen to see what else was I missing out on…

This odd-looking little thing is an ex-Yu UTVA BC-3, popularly known as the "Trojka" ("Three"). Developed shortly after WW2 by Boris Cijan - hence BC - for Ikarus as the model 251, and later produced by UTVA, only 80-ish of these this fabric-covered trainer/tourers were ever made

While not the most beautiful aircraft ever designed, the BC-3 did apparently provide excellent visibility from the cockpit. Weighing only 600 kg, a 65 HP Walter Mikron engine provided sufficient power

Oddly suitable against all the wood, YU-30-15 (also referred to as YU-3015) is an ex-Yu UTVA Jastreb ("Hawk") glider. Couldn't find out much about it except that it had been operated by AK Ljubljana in Slovenia

For those who don't find open cockpits exciting enough, we have the UTVA Čavka ("Jackdraw") :). Designed by Ivan Šoštarić back in 1939, gliders of this type were in use all the way to till the 70s, proving easy to fly (contrary to the way they look) and easy to maintain (precisely the way they look)

Pretty much the only aircraft in contemporary Croatian colors in the Museum, this Albatros AE-209 ultralight is also the newest - and feels decidedly out of place among the biplanes and early gliders 🙂

Something a little bit different now :). The tail section of what my friends in the know say is a Hurricane. The donor was probably one of the Hurricane Mk.IVs operated by the YuAF in the years following WW2 (being passed down from either the Partisan Air Force or the RAF's Balkan Air Force)

The previously featured YU-HAL from a more flattering perspective :). I'm not sure it will be visible, but this helicopter has the entire control panel moved to the side of the cockpit, rather than in front of the pilot. Don't know if this is a standard feature on the whole type though... note also the exposed tail rotor pitch control mechanism running on top of the tail boom

An artsy difference in size :). The DAR-9's 160 HP 7-cyl radial against the Thunderbolt's monstrous 2500 HP twin row 18 cylinder volcano

A small, noisy engine, an open cockpit and a view full of wing and bracing wires... I must admit I envy the people who get to fly my two favorite German biplanes 🙂

Biplanes galore! Too bad they're just museum pieces...

Suck, Squeeze, Bang, Blow:

Having said in the original post that I had only photographed the engines I thought interesting – and given my post-visit realization that EVERYTHING in the Museum is interesting 😀 – I decided to go back there and properly finish the job. And I’m glad I did, because quite a few gems had managed to sneak by me that first time…

First up is the Italian Alfa Romeo 115-I. Produced in 1937 (when the design - based on the de Havilland Gypsy Six - was just a year old), this specific engine produced 195 HP out of six inverted inline cylinders. It's rather diminutive size and power meant it was suitable for training, liaison and reconnassance aircraft

Also from Italy is the Alfa Romeo 126-RC-34 of 1935. Based on the British Bristol Pegasus, this 9 cyl 750 HP engine saw use on a number of famous Italian aircraft - such as the Savoia-Marchetti SM.81 Pipistrelo transport and the curvy SM.79 Sparviero three-engine medium bomber - as well as some Junkers Ju-52 transports

Out back. With 11,000 built, the 125/126/128 family powered virtually all Italian three-engined aircraft (the different sub-types being based on different versions of either the mentioned Bristol Pegasus or the company's Jupiter engine)

A legend I cannot believe I had missed - the Wright GR-1820 Cyclone 9, here in its 760 HP F-56 variant. One of the great radial engines of WW2, in all variants it had powered dozens of aircraft, including the B-17 Flying Fortress, the original DC-2 and -3, the legendary Douglas Dauntless divebomber, the FM-2 Wildcat (a Grumman F4F produced under licence by General Motors), the Grumman HU-16 Albatross amphibian and the Lockheed Hudson, one of the first American contemporary aircraft to see combat in WW2

Something from Austria for a change :). One of the oldest engines on display, this 214 HP six-cyl was produced in Vienna in 1912! A search on the net gives indication that this could be a Hiero 6 or a Hiero E, designed by Otto Hieronimus, used on a number of WW1 reconnassance aircraft

Labeled simply as a "Jupiter" and produced in Belgrade in 1935 (in the then Kingdom of Yugoslavia), I believe this 500 HP engine is a licence-built version of the British Bristol Jupiter. Produced widely under licence in more than a dozen countries worldwide, the original Jupiter - one of the most reliable radials of all time - had naturally evolved into a number of different designs; some of the more interesting ones are the Bramo 323 Fafnir - powering (ironically) Germany's Focke-Wulf Fw.200 martime patrol aircraft and the superlative Dornier Do-17 light bomber (as well as the experimental Focke-Angelis Fa.223 helicopter!) - the Alfa Romeo 126-RC-35 (a close relation of the -34 featured several photos up), as well as the Soviet Union's Shvetsov M-22, powering the famous Polikarpov I-16 fighter

And now, an oddity... a inline 6-cyl labelled as the French Lorraine-Dietrich 12Eb. However, all sources on the net state that the 12Eb was a W12 - of similar configuration to the Benz Bz.DV featured in the previous post - so I've no idea what to make of this. The plaque says the engine was built in 1928 and produced 450 KS, which sounds a bit much for a 6-cyl...

More Lorraine-Dietrich confusion (it's becoming obvious they're French, no? :D) with the LD13. A V12 from 1924 (according to the plaque), this engine produces 400 HP - but I couldn't find any trace of it on the net, so it too is left open to interpretation 🙂

Another - less controversial - legend: the Bristol Mercury :). During its rather long lifetime, it had powered a number of notable designs including the Blenheim light bomber and the Gloster Gladiator - one of the world's last biplane fighters - as well as the relatively successful Polish PZL.11 fighter and Sweden's SAAB 17 fighter-bomber. This specific engine was produced in 1935 and developed 850 HP

An interesting little structural tidbit - the Mercury's reduction gearbox :). This permitted the engine to run at a high number of RPM, while keeping the prop at a lower number to keep its tips below the speed of sound

Another small, unobtrusive, but very interesting gem :). The plaque identifies this as a "Salmson", produced by GAZ in Russia in 1918. Salmson, a French engineering company, is noted - not widely unfortunately - for being one of the first companies to make purpose-built aircraft engines. This engine, stated as producing 120 HP, is I believe a Salmson 9, though my internet search noted that that model used to produce significantly more power...

And to finish this report off, a very rarely seen part of the aircraft engine - the crankshaft :). This particular one is from an Alfa Romeo engine, but it didn't say which one - a 6 cyl (probably inline) by the looks of it...

Plane’s Anatomy – Servicing a Cessna 185

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By me
All photos me too, copyrighted

Down for the count pretty much since the time I’ve started this blog, 9A-BKS is the one remaining (and interesting) Lučko resident I’ve never profiled here. A very nice Cessna A185F Skywagon/Carryall, it had suffered a propstrike almost a year ago (if my count is correct), and was in never a presentable enough state to be featured here. However, with the onset of winter and a reduction in flying activities, it was decided to finally fix it up, giving it a complete service and refit along the way. Naturally, I was ready and waiting with my camera when it all started… 🙂

BKS back in happier days. Sporting a very distinctive high-vis paint scheme - and an equally distinctive transsonic prop - it was always an attention-grabber. Manufactured in 1985 and owned by AK Zagreb, it is used exclusively for skydive flights

Our small taildragger air force on a typical Lučko day - skydivers, aerobatic flights, training ops, glider flights...

A bit less glamorous here in the present... though the aircraft itself had suffered no damage during the propstrike, the prop and engine were knackered and needed to be completely refurbished and rebuilt - so BKS had spent a considerable time looking less than dignified

Apparently the locals don't really like BKS flying above their heads :D. Showing just how many access panels there are on the 185's wing... the ones near the leading edge allow for relatively easy inspection of the electrical cabling for the wingtip lights and the wing strut joint, while the those nearer the fuselage give (some) access to the Pitot system, part of the gravity fuel system and the electric flap motors and their cables. The outboard and trailing edge ones give access to the aileron control cable, which was being inspected as part of the service (the aileron being removed first)

Up front, the firewall had to be cleaned and sanded down before the engine could be mounted back on. Among the cables seen are the prop, mixture and throttle controls, as well as control & data cables for various engine instruments (RPM, manifold pressure, oil temp and pressure, EGT, CHT...)

Inside, everything is nice and fluffy :). The sound and thermal insulation - some form of synthetic foam I think - normally hidden away beneath the upholstery (which will incidentally also be changed)

Where the aileron should be. The actual control cable can be seen right by the single access panel

Closeup of the right-hand flap, lowered to give easier access to its guide rails. Like most light Cessnas, the 185 uses Fowler flaps which, in addition to lowering, slide backwards to increase the effective wing area as well as the Angle of Attack

Inside the bare cabin. Configured for skydive flights, BKS usually only has a rear bench, maximizing the number of skydivers that could be carried while reducing weight for better performance

Already featured in my previous piston engine post is BKS's (rebuilt) 8.5 liter six cyl IO-520-D, putting out approx. 300 HP

Photo Report – Power To The Masses! A photo run-through of some aircraft piston engines

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By me
All photos me too

Undoubtedly one of the most important parts of any aircraft – gliders exempted 🙂 – the engine, a noisy and brutish mass of metal, is often overlooked and neglected by those not of a technical background. And who can blame them – the intangible mass of pipes, wires and often ugly casings and blocks looks best when not seen at all, hiding under often elaborately-shaped cowls. But despite their complete lack of visual elegance, engines  – pistons especially – remain quite interesting things. A gyrating, rotating and vibrating mass of steel that looks and sounds like it’s going to tear itself to pieces any minute, the piston engine – despite all its operating faults – retains a charm of sorts, a soul. Temperamental and often complicated, they still have that whiff of the golden age of aviation about them, when pilots didn’t simply flip a switch to START and then ON.

With that in mind, I’ve assembled a small collection of engine shots, taken during my prowling round Lučko. Unfortunately, I’ve never had the opportunity to photograph those of our two radial beauties, the I-3 and An-2 9A-DIZ, so this article will pretty much be an American Affair :).

1. How to ruin a perfectly good piston engine:

Apart from all the physical ways you could do this, American manufacturers have taken it one step further – admittedly reducing confusion in the process. Powerful-sounding names such as Merlin, Griffon, Sabre, Hercules, Wasp and the like were replaced by dull numerical codes such as R-2800, V-1510, TSIO-360, AEIO-540 and so on. However, there is some logic in it all and before we dive into the photos, it may be best to demystify this naming numerology.

This sequence of letters and numbers pretty much amounts to the engine’s ID card, listing virtually all the information necessary for the end operator/pilot. It is divided into three sections, which can be broken down as follows:

The engine type – the alphabet soup section, which gives some of the engine’s construction and equipment details. This includes the cylinder arrangement, ancilliaries such as turbochargers and inverted flight systems, as well as any other significant device. Some common ones are:

O – opposed (“boxer”) cylinder layout
R – radial
V – “V” arrangement

T – turbocharged
TS – turbosupercharged (an old term for “turbocharged”)
AE – aerobatic
I – fuel injected
G – geared
L – left-hand rotation, for twin-engined aircraft where one engine would rotate in the opposite direction to cancel out a number of adverse effects during a single engine failure

and so on. These can be combined together to list everything the engine is equipped with.

Cylinder displacement – the numbers. These show the displacement of all cylinders expressed in cubic inches. These are mostly standardized, with the common ones being 200, 360, 540 and 550. For us in the metric system, multiply this number by 16.387 to get the displacement in cubic centimeters.

The details – the last section which can be alphanumerical and lists random details such as for example crankshaft type, sub-version, a specific oil system and so on. There is no exact decode system for this, as it pretty much depends on the manufacturer’s internal coding preferences – and in any case is not relevant for the pilot.

In the end you end up with something like O-200-A, which would be a boxer engine displacing 200 cubic inches, in the A version. Similarly, the Beech Duke profiled here some time ago has two TSIO-540s, which are turbocharged and fuel injected boxers with a displacement of 540 cu in.  Another twin, the Piper Seneca, has one LTSIO-360, which is a left-hand rotation turbocharged injected boxer with a displacement of 360 cubic inches (the other is a “standard” TSIO-360). Aerobatic aircraft – the Zivko Edge 540 for example – may have an AEIO-540, an injected boxer with an inverted flight fuel and oil system, 540 cu in.

The other type codes, such as R and V are very rare nowadays, having gone out of widespread use with the demise of radial and V-block engine production in the years after WW2. Note that these codes apply to American engines, while other manufacturers use other designations. Rotax for example has the 800 and 900 series, Vedneyev has the legendary M-14 radial and Thielert has/had the Centurion. But since 90% of the engines to be shown here are American – or models built under license in Europe – I decided to concentrate predominantly on them.

2. Start dammit, start!

The engines chosen come in two basic varieties, the “four pop” for the smaller birds and the “six pack” for the heavy haulers – and we even have one two-stroke two-cyl! 🙂 These represent everything from a flexwing microlight to the Seneca twin, so we have plenty to choose from…

The tinyiest of the tiny, the two-stroke Rotax 582 developing 64 HP and powering the previously reviewed Apollo Racer GT microlight
The tinyiest of the tiny, the two-stroke Rotax 582 developing 64 HP and powering the previously reviewed Apollo Racer GT microlight

I must admit that my Rotax Spotting Skills are often short of the mark, but this looks like a 914, possibly 80 HP. Being mounted on a gyrocopter, this seems about right...
I must admit that my Rotax Spotting Skills are often short of the mark, but this looks like a 914, possibly 80 HP. Being mounted on a gyrocopter, that seems about right...

The Cessna 150's immortal 100 HP Continental O-200-A :). Powering generations of pilots on their first flights, the O-200 has also been licence-built by Rolls-Royce (though these tend to be rare-ish nowadays - I've only ever seen two)
The Cessna 150's immortal 100 HP Continental O-200-A :). Powering generations of pilots on their first flights, the O-200 has also been license-built by Rolls-Royce (though these tend to be rare-ish nowadays - I've only ever seen two)

Progressing upwards is the Super Cub's most common engine, the 150 HP Lycoming O-320. Some versions - most notably those used in mountaneous areas such as the Alps - have been uprated to 180 HP, a pretty chunky amount of power for the light and "lifty" Super Cub
Progressing upwards is the Super Cub's most common engine, the 150 HP Lycoming O-320. Some versions - most notably those used in mountainous areas such as the Alps - have been uprated to 180 HP, a pretty chunky amount of power for the light and "lifty" Super Cub

On par with the O-200 is the Cessna Skyhawk's 160 HP Lycoming O-360. Just one in a long line of engines that have powered the 172, the O-360 had replaced the earlier six-cyl 145 HP O-300 and the 160 HP "four pop" O-320, to be in turn replaced by the direct injection IO-360s of today's 172R (160 HP) and 172SP (180 HP)
On par with the O-200 is the Cessna Skyhawk's 160 HP Lycoming O-360. Just one in a long line of engines that have powered the 172, the O-360 had replaced the earlier six-cyl 145 HP O-300 and the 160 HP "four pop" O-320, to be in turn replaced by the fuel injected IO-360s of today's 172R (160 HP) and 172SP (180 HP)

The most powerful four-cyl to be featured here is the Cardinal RG's 200 HP Lycoming O-360. A development of the 172's O-360, it had first developed 180 HP for the fixed-gear Cardinals and finally uprated to cater for the RG model's increased weight
The most powerful four-cyl to be featured here is the Cardinal RG's 200 HP Lycoming O-360. A development of the 172's O-360, it had first developed 180 HP for the fixed-gear Cardinals and finally uprated to cater for the RG model's increased weight

The first six-cyl here belongs to the Reims FR172 Rocket, the most powerful Skyhawk development so far (the earlier F model is pictured here). A Continental direct injection IO-360, it has the same capacity of the four-cyl model - and, as far as I've been able to find out, uses the same cylinders with a shorter piston travel. Interestingly, the air intake and its filter are right on top of the engine, an unique solution that prevents intake ice at the cost of some performance
The first six-cyl here belongs to the Reims FR172 Rocket, the most powerful Skyhawk development so far (the earlier F model is pictured here). A Continental IO-360, it has the same capacity of the four-cyl model - and, as far as I've been able to find out, uses the same cylinders with a shorter piston travel. Interestingly, the air intake and its filter are right on top of the engine, an unique solution that prevents intake ice at the cost of some performance

A very similar - but turbocharged - TSIO-360 powering the Piper Seneca with its 220 HP continuous. Has a big air filter this thing...
A very similar - but turbocharged - TSIO-360 powering the Piper Seneca with its 220 HP continuous. Has a big air filter this thing...

A numerical oddity is the Aero-3's Lycoming O-435-A, developing 195 HP from six cylinders. Another interesting solution can be seen here - the exhaust pipes all lead into a "muffling chaber", where outside air - fed by the pipe extending from the front of the cowl - is apprently mixed with the exhaust to reduce noise levels
A numerical oddity is the Aero-3's Lycoming O-435-A, developing 195 HP from six cylinders. Another interesting solution can be seen here - the exhaust pipes all lead to a "muffling chamber", where outside air - fed by the pipe extending from the front of the cowl - is apparently mixed with the exhaust to reduce noise levels

All alone with no plane to power - yet - is our Skywagon's IO-520-D, putting out 270-300 HP (not exactly sure with this specific engine). Seen dismounted after a prologned service after a propstrike
All alone with no plane to power - yet - is our Skywagon's IO-520-D, putting out 270-300 HP (not exactly sure with this specific engine). Seen dismounted after a prolonged service following a propstrike

And finally the "big guns" - the whopping large (as far as these thing go nowadays) Continental IO-550, developing 300 HP in the Beech A36 Bonanza. To put it into perspective, 500 cu in is about 9 liters, which is truck engine range :)
And finally the "big guns" - the whopping large (as far as these things go nowadays) Continental IO-550, developing 300 HP in the Beech A36 Bonanza. To put it into perspective, 550 cu in is about 9 liters, which is truck engine range 🙂

And here’s hoping this will soon be updated with some radial action, as well as – keeping my fingers crossed – the monstrous 385 HP TIO-540 powering our local Cessna Pressurized Centurion :).

Post Update – Plane’s Anatomy, AT-402 Episode

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Everything by me, as usual

Just wanted to add a small update to my previous AT-402 anatomy post. Driving to the field today, I came across 9A-DKJ being packed into a freight container for a trip to somewhere. Not waisting the opportunity, I snapped a quick photo…

How to pack an airplane... as noted before, the engines and prop had already been removed for overhaul, so all that was left was to take down the wings and landing gear (which are to the left outside the photo)
How to pack an airplane... as noted before, the engines and prop had already been removed for overhaul, so all that was left was to take down the wings and landing gear (which are to the left outside the photo)

Tech – Where Little Planes Come From: A Visit to the Diamond Aircraft Factory, February 2008

Posted in Plane's Anatomy / Tech4 Comments

By Boran Pivčić
All photos author

There always comes the time when young pilots ask their senior instructors: “Where do little planes come from?” :). In an attempt to answer that question, I was sent – as part of Aeronautika, a local aviation mag I write for – to the Diamond Aircraft works in Wiener Neustadt, Austria, a nice 4 hour hop by bus (a very nice one at that) away from Zagreb.

1. The factory

Diamond’s main works – as well as the main admin center – is located at the small airfield of Wiener Neustadt-Ost (ICAO location indicator: LOAN) just outside the small town of the same name, some 50 km south of Vienna. Though not as famous as the company’s London works in Ontario, Canada, this is the site where Diamond aircraft first came into being – and were first produced for a number of years.

Wiener Neustadt-Ost and the complex that has grown around it. The factory itself consists of just a couple of buildings running parallel to the runway - everything else has been built around the (economic success) of the factory, and even includes a shopping mall and swimming pool :)
Wiener Neustadt-Ost and the complex that has grown around it. The factory itself consists of just a couple of buildings running parallel to the runway - everything else has been built around the (economic success) of the factory, and even includes a shopping mall and swimming pool 🙂

The site itself was also well known for one the bigger Messerschmitt factories outside of Germany proper during WW2. The actual buildings though were leveled late in the war by USAAF’s 15th Air Force aircraft based in Italy, but one of the aircraft produced here has managed to survive the war and is now part of Diamond’s aircraft museum, located on the present factory grounds.

A beautifully preserved Bf.109G-6 at the Diamond museum
A beautifully preserved Bf.109G-6 at the Diamond museum

The modern complex is designed to provide everything needed for aircraft production, from basic materials and components all the way through to final assembly and painting. Outsourcing is a no-no here :). Christian Dries, the man behind Diamond Aircraft, half-jokingly told us that the only thing in this factory they hadn’t made themselves are the aircon units – even the tables were designed and built in house. Sounds like an expensive approach, but ask Boeing about their current experiences with letting other people make your planes… :). This in-house system not only reduces production errors, but considerably speeds up construction as well, which can now be done at the same standard of quality throughout.

Oh my God, it's full of Stars! A view down the LOAN ramp is enough to make even the hardest man drool...
Oh my God, it's full of Stars! A view down the LOAN ramp is enough to make even the hardest man drool...

As of late 2008., the factory complex also includes Diamond’s own engine manufacturing facility, where the new AustoEngines piston Diesels – naturally, Diamond-designed – will be built. Though it may appear that the whole AustroEngines venture is a direct response to Thielert’s recent financial woes, Mr. Dries told us (back in February) that they’re just finishing the paperwork for an engine production line – so it may have been on the cards for awhile now.

2. The aircraft

The majority of the aircraft built at this site are DA-40 Stars and DA-42 Twin Stars, as well as their Airborne Sensors modifications (there’ll be a follow-up on that division here soon 🙂 ). At the time of our visit, most of the aircraft on the assembly line were Twin Stars, so I’ll concentrate on them.

Basically a Star with an additional engine, hidden behind some modifications, the Twin Star was the first twin-engined aircraft designed from the outset to use Diesel principle engines. Ironically, it’s the only Diesel aircraft that received a avgas piston conversion (with two 180 HP IO-360s as seen on the Piper Seminole), but those are few in number despite the waxing and waning fortunes of Thielert, the German company that supplied the first mass produced Diesel engines, the Centurion 1.7 and 2.0.

Sharing pretty much the same basic fuselage as the Star, the DA-42 is a four seater – and along with the aforementioned Seminole, the only twin in this configuration in production today. While the front of the cabin is roomy and airy thanks to that extensively glazed canopy, the rear is a bit claustrophobic and cramped I must say – but at my 1.92 meters, many aircraft are :). But, with twin engine safety and a total fuel burn of a Cessna 172, we can forgive it that :). The Garmin G1000 glass cockpit suite is a standard and playing with it on the demo aircraft I must say it has some amazing features – but this, coupled with FADEC-controlled engines, in my opinion makes the Twin Star a bit too easy to fly. It’s like playing a flight simulator, which may lead to a bout of unfounded self confidence and an erosion in basic piloting (and common sense) skills. The Twin Star almost thinks by itself…

OE-FEF, a specced-up Platinum demo model that I got a ride on later
OE-FEF, a specced-up Platinum demo model that I got a ride on later

For the Twin Star’s specs, you can visit Diamond’s website at: http://www.diamond-air.at/da42_twin_star+M52087573ab0.html

3. The production process

The tour, led by Mr. Dries, took us – as mentioned – through the whole production process. We were allowed to photograph everything we wanted – except the starting procedure for molding and preparing the composites. Though this is a significant process – because all the major components, wings, tail, fuselage, are built here – there’ll still be plenty to see as all of those are put together.

It all begins here. Composite materials like fiberglass (green) and carbon fibre (black) are moulded, shaped and impregnated separately before being put together into their final shape, as seen here. After this is complete, the aircraft will be disassembled again for painting and systems installation
It all begins here. Composite materials like fiberglass (green) and carbon fibre (black) are molded, shaped and impregnated separately before being put together into their final shape, as seen here. After this is complete, the aircraft will be disassembled again for painting and systems installation

As the aircraft is being built, it progresses through the several interconnected hangars, coming out finally at the other side of the airfield. This ensures a steady and clean flow through the factory and prevents… traffic jams :).

Inner (I think) wing elements, with flaps being fitted and calibrated.
Outer wing elements, with flaps being fitted and calibrated.

A jigsaw puzzle. Wingroots, engine bays and control surfaces are shown here, painted and ready for reassembly onto the aircraft.
The jigsaw puzzle. Wingroots, engine bays and control surfaces are shown here, painted and ready for reassembly onto the aircraft.

A bit of the same here. These fuselage joint elements bear most of the dynamic loads on the aircraft in flight, as they transfer the lift generated by the wing onto the fuselage
A bit of the same here. These fuselage joint elements bear most of the dynamic loads on the aircraft in flight, as they transfer the lift generated by the wing onto the fuselage

Starting to grow into a recogniseable aircraft again. The elements from the previous photos are here being joined to the rest of the fuselage
Starting to grow into a recognizable aircraft again. The elements from the previous photos are here being joined to the rest of the fuselage, while on the inside the G1000 system and some avionics would soon be fitted

Next, mounting the engines on the frame. Once properly loaded, the aircraft can lowered onto their landing gear and stand on their feet freely like the example in the background
Next, mounting the engines on the frame. Once properly loaded, the aircraft can be lowered onto their landing gear and stand on their feet freely like the example in the background

The Twin Star's piece de resistance - the Thielert Centurion 2.0 engine. Both the 1.7 and 2.0 develop the same 135 HP, the difference being in capacity - 1.7 vs 2.0 liters, far less than an equivalent avgas engine - and some changes to the turbocharger system. A condensed mass of wires and pipes, this is not a purpose-built aircraft engine, but a converted and heavily-modified Mercedes roadcar Diesel tweaked to accept more volatile Jet A fuel
The Twin Star's (former) piece de resistance - the Thielert Centurion 2.0 engine. Both the 1.7 and 2.0 develop the same 135 HP, the difference being in capacity - 1.7 vs 2.0 liters, far less than in an equivalent avgas engine - and some changes to the turbocharger system. A condensed mass of wires and pipes, this is not a purpose-built aircraft engine, but a converted and heavily-modified Mercedes roadcar Diesel tweaked to accept more volatile Jet A fuel. Despite that, the fuel consumption is less than half of that of similar avgas engines, with the additional benefit that - at least in Europe - Jet A is considerably cheaper than avgas

With the wings on, the aircraft are towed to the next hangar for systems assembly. Most of the basic framework for the electrics, as well as the G1000 suite, had already been fitted during structural assembly
With the wings on, the aircraft are towed to the next hangar for systems assembly. Most of the basic framework for the electrics had already been fitted during structural assembly

Nearing completion. This DA-42MPP - Multi-Purpose Platform - will eventually join the Diamond Airborne Sensing fleet also stationed at Wiener Neustadt
Nearing completion. This DA-42MPP - Multi-Purpose Platform - will eventually join the Diamond Airborne Sensing fleet also stationed at Wiener Neustadt

Engine controls and instruments being connected to the engine
Engine controls and instruments being connected to the engine. Unlike the Star and Twin Star, the DA-20 Katana sports a Rotax 4 cyl avgas engine, which comes in 80 and 100 HP normally aspirated versions, and a "top-of-the-line" 115 HP turbocharged model (though I must admit I've never seen that one on a Katana)

Almost done. Systems test, checking whether everything works as advertised
Almost done. Systems test, checking whether everything inside works as advertised

With the diagnostics done, the aircraft is essentially complete - and just in time for a wash to clean up residue, oil and fingerprints. Once fully done in the factory, it will be flight tested by a test pilot to see whether everything actually works in flight, which will also give the engines a chance to deconserve
With the diagnostics done, the aircraft is essentially complete - and just in time for a wash to clean up residue, oil, grease and fingerprints. Once fully done in the factory, it will be flight tested by a test pilot to see whether everything actually works in flight, which will also give the engines a chance to deconserve

Final checks on another example. The grey stripes on the wing and stabilizers are the de-icing system elements
Final checks on another example. The grey stripes on the wing and stabilizers are the de-icing system elements, permitting the little Twin Star to boldly go where even bigger aircraft can't

Set and done. Depending on the customer's wishes, the aircraft can now be painted in a number of stock or custom paintschemes
Set and done. Depending on the customer's wishes, the aircraft can now be painted in a number of stock or custom paintschemes

One such example already painted - and costing €700.000 :)
One such example already painted - and costing €700.000 🙂

The end product shining in the afternoon light
The end product shining in the afternoon light

4. Aboard the Twin Star

As well as being shown around the place, all of us – assorted journalists and wannabes like me 🙂 – got a demo flight on the previously pictured OE-FEF Platinum Twin Star. The flight, though short at about 15 minutes, was designed to showcase the G1000 suite, as well as the aircraft’s handling and engine-out characteristics. Being just a photographer – and not a cameraman – I was relegated to the back seat with a friend, denying me the opportunity I had dearly wanted: to fly the TStar myself. But be it as it may, the rear seat wasn’t all that bad – apart from being a bit cramped for a person my size as I already menioned.

Lifting off Wiener Neustadt's 1,067 m runway 10 to the sight of six brand new, factory fresh Twin Stars waiting outside after assembly. The big grille you see on the nacelle is the coolant system radiatior - being originally a car engine, the Centurion is water cooled.
Lifting off Wiener Neustadt's 1,067 m runway 10 to the sight of six brand new, factory fresh Twin Stars waiting outside after assembly. The big grille you see on the nacelle is the coolant radiator - being originally a car engine, the Centurion is water cooled

The takeoff performance was very good even fully loaded – and don’t let the puny 135 HP engines fool you. When you have to turn a prop up front, torque is what you need. The more torque you have, the bigger the prop you can turn, making better use of the available power. And a turbocharged Diesel has enough torque to go around, so the takeoff and climb performance shouldn’t be surprising.

Another subjective observation I made is that the Twin Star appears to be fairly loud in the cabin. I’ve flown on our aeroclub Piper Seneca III – an old, 70-tech aircraft with big, mean six cylinder engines and soundproofing from the Ford Model T – and it was noticeably quieter than the TStar. The excellent David Clark headphones in OE-FEF, wired into a comprehensive intercom system, greatly helped matters though, but one would have expected the aircraft to be somewhat quieter.

A view of the picturesque Austrian countryside, with the foothills of the Alps in the distance
A view of the picturesque Austrian countryside, with the foothills of the Alps in the distance

While we were climbing, our pilot showed off some of the G1000’s capabilities. Describing those would take a couple of dozen pages – and is common knowledge on the net – so I’ll skip that. But suffice to say that everything you really need, you’ll find it in there somewhere. But I stay by my earlier comment that a glass cockpit of this sophistication can be a double-edged sword, despite its cool factor and greatly increased reliability over the old steam gauge cockpits. It’s easy to forget basic navigation and flying skills when you have a computer running the show.

Typical composite reflections add to a general feel of "clean" and "precise" of the TStar
Typical composite reflections add to a general feel of "clean" and "precise" about the TStar

After we’ve reached what I judged to be about 3,000 feet (didn’t bother to look at the altitude readout on the G1000), the real demonstration started – what good is a twin if you can’t kill off an engine inflight? 🙂 Not being a display of showing off, but a very worthwhile safety demo – international aviation regulations state that all twin engined aircraft have to be able to maintain altitude on the power of one engine. Naturally, that altitude is lower than with both engines, but it’s better than losing it you’ll agree.

What would have been a worrying sight in normal cirumstances is here an excellent display of the TStar's fine engine-out handling.
What would have been a worrying sight in normal cirumstances is here an excellent display of the TStar's fine engine-out handling.

After that was done with, the pilot flew a some random gentle maneuvers in the aerodrome zone above LOAN and offered the controls to the almost pale cameraman sitting upfront – who promptly declined. I was about to explode at that point, cause I had wanted to do that, but was ousted by someone with better credentials and a third of the guts (though – to compensate – the guy had trice my girth 🙂 ).

Some flying fun after the serious stuff had been taken care of
Some fun flying after the serious stuff had been taken care of

Soon enough, our 15 minutes were up, so the we turned back to the field. Either to demonstrate the TStar’s descent capabilities with everything hanging out – gear and full flaps – or simply to shave off some time, the pilot flew a tight, high speed descending turn toward RWY 10, lining up less than 500 meters from the threshold.

Tight right base for RWY 10, with both the runway and the Diamond works easily and clearly visible
Tight right base for RWY 10, with both the runway and the Diamond works easily and clearly visible

Going down the fast way. You can see the proximity of the runway to the rest of the town... there must be some awesome spotting positions here :)
Going down the fast way. You can see the nearness of the runway to the rest of the town... there must be some awesome spotting positions here 🙂

Given the TStar’s low weight and some glider-ish characteristics inherited from the Star – which inherited those from the Katana, which itself dates back to the HK-36 Dimona motorglider – landing was predictably soft with little flaring needed. Despite the diminutive size of the wheels, I remember the brakes being quite powerful, with the aircraft stopping in about 300-350 meters (though it could do better I presume if you really hit the pedals).

There being still a few people in line for the flight, we got out of the aircraft pretty quickly, but not before I managed to snap a shot of the panel (unfortunately with the G1000 off).

The simple and uncluttered cockpit of the TStar. You don't really have much to push or play with in there, a single throttle level for each engine - the prop and mix being FADEC-controlled - a starting switch or two and lights and heating. Excuse the prints, but in the process of showing of various bits of info on the displays, touching them is inevitable
The simple and uncluttered cockpit of the TStar. You don't really have much to push or play with in here, a single throttle level for each engine - the prop and mix being FADEC-controlled - a starting switch or two and lights and heating. Excuse the prints, but in the process of showing of various bits of info on the displays, touching them is inevitable

Getting ready to go back out there after a two-minute turnaround
Getting ready to go back out there after a quick two-minute turnaround

All in all, the TStar is a sweet little machine and an excellent showcase of what is possible with present technology, brining single-engine economy into the reliable twin engine world. Coupled with the G1000 and docile and forgiving handling, the Twin Star is well on the way to becoming  a very popular tourer, possibly reactivating a the four-seat twin niche that many manufacturers have abandoned some years ago. But – and I’m sorry about restating this again and again – it’s too… protective of its pilot, both in handling and pilotage, to be the ultimate tourer in my book.

Plane’s Anatomy – Air Tractor AT-402

Posted in Plane's Anatomy / TechLeave a comment

By Boran Pivčić
All photos (and some screwdriver work) author

About a month or so back, I got the almost-unique opportunity to peek into the internal workings of two Air Tractor AT-402 cropdusters (9A-DKG and -DKJ) sitting around at Lučko. Having been parked there for a good part of eight years, they finally went up for sale and some prospective buyers wanted to have a looksee under the hood. Through a long chain of events, I ended up being there – and of course didn’t miss the opportunity to have a photo field day :). Going to the airfield without my camera… bah!

A bit about the planes themselves first – as their name suggests, these are rough-and-tough utility machines, designed for continuous 24/7 back-water, dirt-strip torture. As such, they’re built to last, utilising proven, classic technology. Designed to be dismantled with little more than a screwdriver (and liberal amounts of WD40 in our case), ATs of all marks – 300s, 400s, 500s and 800s – hold few surprises under the skin. But they’re simple and uncluttered and a good showcase of aircraft structural solutions.

The 402 version came about when someone decided to ditch the earlier versions’ 600 HP Pratt&Whitney R-985 9 cyl piston radial and replace it with a more reliable – and far simpler – turboprop. Since the 400 series, all ATs have been produced in this configuration, with engines of varying outputs to cater for increasing weights. The current standard is the AT-802 wheeled model and the AT-802AF Fire Boss amphibian. Despite being designed primarily for cropdusting, most 802s today are used for firebombing. Indeed, the Croatian Air Force operates both variants down at the coast (one wheeled, three Fire Bosses) with notable success.

And now, a step-by-step condensed lesson in aircraft structures :).

The naked plane. A general overview of the 402 (9A-DKG) with all side panels removed. Despite its imposing size, the AT is basically full of hot air :). Of note is the thick and juicy wing profile, providing a lot of lift at low speeds. The consequence of this increased lift - drag - is not so important here, as speed and cruising efficiency were not high on the design priorities list
The naked plane. A general overview of the 402 (9A-DKG) with all side panels removed. Despite its imposing size, the AT is basically full of hot air :). Of note is the thick and juicy wing profile, providing a lot of lift at low speeds. The consequence of this increased lift - drag - is not so important here, as speed and cruising efficiency were not high on the design priorities list

Rear quarterview showing some of the internal structure. Like most light aircraft, the AT series uses a frame construction, much like the one you see on construction cranes. The frame - which absorbs all inflight loads and holds the structure together - is covered by panels to make the whole thing aerodynamic. These "panels" can be made from a wide range of materials, wood and fabric in the olden days and aluminium today - though composites and glass and carbon fibre are becoming increasingly common
Rear quarterview showing some of the internal structure. Like most light aircraft, the AT series uses a frame construction, much like the one you see on construction cranes. The frame - which absorbs all inflight loads and holds the structure together - is covered by panels to make the whole thing aerodynamic. These "panels" can be made from a wide range of materials, wood and fabric in the olden days and aluminium today - though composites and glass and carbon fibre are becoming increasingly common

Removing the other side panel adds some clarity to the shot. Easily visible now is the control linkage, linking the control stick and pedals in the cockpit with the rear control surfaces. The rod you can see going through the structure controls the elevator, while the thin gray cables running along the outside of the structure are linked to the rudder
Removing the other side panel adds some clarity to the shot. Easily visible now is the control linkage, linking the control stick and pedals in the cockpit with the rear control surfaces. The rod you can see going through the structure controls the elevator, while the thin gray cables running along the outside of the structure are linked to the rudder

Turbo power! Up close with the Pratt&Whitney PT6A-15AG 715 HP turboprop. Like all turboprops, the PT6 is a small package for the power it delivers, with most of the space in the back taken up by auxilliary and ancilliary devices such as the starter, generator, oil pumps, control links, air intake and the odd cooler or two
Turbo power! Up close with the Pratt&Whitney PT6A-15AG 715 HP turboprop. Like all turboprops, the PT6 is a small package for the power it delivers, with most of the space in the back taken up by auxilliary and ancilliary devices such as the starter, generator, oil pumps, control links, air intake and the odd cooler or two

View from a different angle. Again like most turboprops, the PT6 is a free-turbine reverse-flow engine, meaning it's installed ass backwards :). To avoid going into detail, this makes the engine lighter and hence more efficient - and explains why the exhaust pipes are located up front: the back of the engine is thre. Because its front is now deeper in the engine bay, it has to be fed by the air intake visible under the nose
View from a different angle. Again like most turboprops, the PT6 is a free-turbine reverse-flow engine, meaning it's installed ass backwards :). To avoid going into detail, this makes the engine lighter and hence more efficient - and explains why the exhaust pipes are located up front: the back of the engine is there. Because its front is now deeper in the engine bay, it has to be fed by the air intake visible under the nose

A wider view of the nose. Despite looking thin and whimpy, the landing gear is QUITE strong. During factory testing, the designers mounted a four-ton cement block on top of the landing gear assembly (just the gear, not the whole plane) and let it drop from a height of two-three meters (4 tons corresponding to the maximum takeoff weight of the plane). After spreading out and absorbing the weight, the gear sprung - sprung, with a four-ton block on it's back! - back into its original shape... on another note, the brownish thing between the engine bay and cabin is the hopper, with a capacity of 1,500 liters. During cropdusting, this would have contained the cropspray solution, while during firefighting either water or, more commonly, fire retardant
A wider view of the nose. Despite looking thin and whimpy, the landing gear is QUITE strong. During factory testing, the designers mounted a four-ton cement block on top of the landing gear assembly (just the gear, not the whole plane) and let it drop from a height of two-three meters (4 tons corresponding to the maximum takeoff weight of the plane). After spreading out and absorbing the weight, the gear sprung - sprung, with a four-ton block on it's back! - back into its original shape... on another note, the brownish thing between the engine bay and cabin is the hopper, with a capacity of 1,500 liters. During cropdusting, this would have contained the cropspray solution, while during firefighting either water or, more commonly, fire retardant

A more recent photo of DKG with its engine and prop removed for overhaul. Only when you disconnect all the pipes, cables and wires do you realise how big a mess the engine bay can be
A more recent photo of DKG with its engine and prop removed for overhaul. Only when you disconnect all the pipes, cables and wires do you realise how big a mess the engine bay can be

Closeup of the engine mount. This is basically all that holds the engine connected to the rest of the plane :). But, like the landing gear shown previously, this is built to last. Also visible is the back of the bay is the firewall, "the part of the plane specifically designed to let in fire and smoke" as the joke goes :). In serious-world, it prevents any fire in the bay from reaching the rest of the plane, be it the chemical hopper, cabin or any part of the structure
Closeup of the engine mount. This is basically all that holds the engine connected to the rest of the plane :). But, like the landing gear shown previously, this is built to last. Also visible is the back of the bay is the firewall, "the part of the plane specifically designed to let in fire and smoke" as the joke goes :). In serious-world, it prevents any fire in the bay from reaching the rest of the plane, be it the chemical hopper, cabin or any part of the structure

And last but not least, a view down the lower engine bay. The air filter that feed the engine with nice, clean air is the most imposing feature. Despite the turboprop's somewhat higher resistance to dust than piston engines, bad filtering can lead to a rapid decrease in engine performance and more often than not serious damage to the compressor
And last but not least, a view down the lower engine bay. The air filter that feed the engine with nice, clean air is the most imposing feature. Despite the turboprop's somewhat higher resistance to dust than piston engines, bad filtering can lead to a rapid decrease in engine performance and more often than not serious damage to the compressor