Tag: Šentvid

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

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By me
All photos me too, copyrighted

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

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

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

Born to Haul

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

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

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

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

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

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

On the DOT

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

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

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

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

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

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

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

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

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By me
All photos me too, copyrighted

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

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

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

Blackhawk Up

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

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

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

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

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

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

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

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

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

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

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

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

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