Why no gas turbine engines in light a/c?

[fireflybob]

Many years ago (decades in fact) a small gas turbine engine (turboprop) was fitted to a Chipmunk and I recall seeing this a/c at Farnborough.

So my question is why, with the increasing cost of avgas, nobody has appeared to come up with a gas turbine engine which could be fitted to light a/c? The Piper Malibu has a large gas turbine - why not one to fit a PA28 or PA38 etc.

Lower running costs (using Jet A1), better reliability, longer engine life and more simplicity - so please guys, why not?

[what next]

...so please guys, why not?

1. The price of the turbine engine exceeds the value of most light aircraft. Mass production will not reduce engine prices significantly because of the high precision required and expensive temperature-resistant materials.

2. Poor efficiency of gas turbines at low level and low speed.

3. Noise.

4. More fireproofing / themal blanketing required. Heavy and expensive.

There have been many attempts to fit gas turbine engines to small aircraft and even road vehicles during the last five decades. None of them resulted in series production.

[Whopity]

A new Type rating and a new role for TRTOs. Win Win all round!

[Fuji Abound]

Cost, r and d budgets, or lack of, market size.

The pt6 is too large but rolls have developed a smaller and cheaper engine with rumours that it may be done soon, probably stalled by the current economic climate.

It is a good idea.

[FlyingStone]

Ever seen eye-watering price of a new turboprop engine? I think PT6's price (the engine put into most single turboprops) is rougly around half a million €. The next problem with turboprop engines is that they are very inefficient at low altitudes, which is exactly the reason (except helicopters) why they are put into aircraft which tend to be flown above FL150.

About the running costs, as with all things on this world - there are two sides. Turbine engine do have greater reliability and cheaper fuel, but I don't think specific fuel consumption would differ so much at FL100 (for flight without using supplemental oxygen for example) between atmosferic (or turbocharged) piston engine in LOP operation and turboprop. As for the longer life, it's probably true, TBOs are longer, but the price of an overhaul is similary increased, so it's not really an advantage. Of course, if you do 4000 hours a year and would like to have an overhaul every two years instead of twice a year, than turbine is probably the way to go.

Turbine engines are generally more reliable than piston engines, but they are usually operated by much more experienced pilots, which usually keep the engine parameters within limits. Lycontinentals (at least low-powered one found in PA28/38, C172 ...) can be operated almost (well, I wouldn't go from full power Vx climb into Vne dive with idle throttle) in any way and still make it to a TBO with perhaps changing a cylinder or two. Most of piston engines (except some high-powered turbo/super-charged and Rotax under-sized engines) also have equal takeoff (maximum) power and maximum continuous power, which basically means you can fly the aircraft from brakes off to top of descent with all three forward and it is highly likely you won't do much (if any) damage. Besides, most turbine engines require very laminar airflow through the engine to prevent compressor stall (and thus damage), which actually eliminates option to do serious (continuous) flight training with them, such as stalls, unusual attitudes, spins, ...

I think the future for low-powered spam cans are diesel engines, which have relatively good efficiency, they can run on Jet A-1 (this is the real advantage), the ones currently on market have FADEC, which makes them attractive to pilots who don't/won't/can't understand piston engine management. Leave the turbine engines for pressurized aircraft, which can really use them to their full potential.

[treadigraph]

That was a Rover gas turbine in the Chipmunk, also fitted to an Auster and a Currie Wot! There was a gas tubine Rover car in the museum at Syon Park when I went there about twenty or thirty years ago.

There are some turbine Lancairs in the US and there have been turbine conversions to Bonanzas, C210s and C206s - Beech also built a turbine Bonanza (the Lightning?) themselves but I don't believe it got beyond the prototype. But I guess the folk flying these would generally be going higher than yer average PA-28.

(There's also a twin jet Cri Cri about - or is it Jetex powered? :})

[Unusual Attitude]

Just the ticket....

Sonex Aircraft Hornets' Nest Research and Development (http://www.sonexaircraft.com/research/subsonex.html)

Not a turboprop but still looks fun!

[AdamFrisch]

The reason is basically greed and aviations best old friend: conservatism. Nothing happens in aviation without either legislative enforcement or promise of even more greed. The truth is they have been on a gravy train with turbines and could charge whatever they want. If you're on the type certificate as the only engine certified for an aircraft, well, then the incitement to make them cheap is all gone. They have you over a barrel.

I repost from another thread:

Engineering-wise, there is nothing today that suggests they are hard to make. The tolerances are far lower than in many other industries where none such price hiking appears. Let's not forget they were certified and approved when they were still hand made on lathes and manual mills. Today we have robotic CNC vertical mill stations that have more productivity and much higher tolerances. Neither are the materials used very exciting or expensive.

We could have had a myriad of small turboprops in every LSA and Cessna since the 60's, but they chose to ignore that because the times were good and the military could be relied on to overpay for their stuff - ever wondered why every aerospace manufacturer ever devised has gone after military contracts? One doesn't have to be a genius to figure that one out.

Make a certified 100-300shp turboprop and sell it for the same as a piston engine and you'd see massive sales. If the RC guys at Jetcat, Wren and AMT can make working turbines in their sheds and sell them for $3000, then most certainly RR and the good old boys can make money selling theirs slightly bigger ones for $100K a pop. Yes, I know there are differences between the examples, but they're more similar than they are different.

[gasax]

You could certainly makes a turbine somewhat cheaper than the present prices would suggest.

But that would not address the major problem that all turbines ahve - their fundemental lack of efficiency. As soon as JetA1 becomes taxed - as inevitably it will do, the 'advantages' of a turbine vanish and you are left with a high power to weight ration and terrible fuel consumption, noise and pollution. So not an obvious powerplant for the future as fuel costs increase.

[glider12000]

Try gliding and you can buy one of these..

‪HPH 304 Shark Jet glider‬‏ - YouTube

Home - HpH Sailplanes Sole UK Agency (http://www.hphuk.co.uk/)

[gasax]

The advert for it gives the game away "Optimal fuel consumption of 17L per 100Km" which is pretty terrible - let alone the noise......

Lovely idea and a terrific novelty - until the local gliding club gets the noise complaints

[BackPacker]

In gliding, range/fuel consumption is not nearly an issue as is installed weight/size. And I think even a sailplane like that can be winch-launched to prevent noise issues.

That just leaves the situation where you run out of thermals and want to prevent an off-airport landing. For that you would need, what, half an hour to an hour of fuel?

[Rocket2]

gasax
The noise from a jet powered glider is far far less than the persistent sound of a demeted bee that the Solo/Rotax powered turbo-gliders make

[AdamFrisch]

The RR250-C20 that delivers around 400 shp and is standard in most lighter helicopters burns around 26gph. It is not impossible to assume that a smaller turboprop in the 100-150shp range could get to around 10-13gph at low altitudes. Up high, that figure will drop with a bout 50% to around 7-10gph, I'm guessing. Granted, this is more than a piston engine, but still pretty competitive considering the price difference of Jet A1 and Avgas in Europe. Not to mention the availability.

Price difference in the US is almost non-existent, so therefore the incitement might be less. Availability of Avgas is also much better, but that's going to change.

[gasax]

The terrible fuel consumption is only acceptable now because of the differentials introduced by taxation.

Looking at yachting - where the use of 'red diesel' is now subject to a 60/40 regime of taxation - and the EU are about to instigate action against the UK as it does not think this is acceptable (they want 100% taxation as in much of the rest of the EU). One political decision and the whole thing is over.

So we have turbine engines - which could probably be a bit cheaper to build, but which guzzle fuel - which is ok so long as it is not really taxed.

And for what is it worth the only small turbine I've experience of was on a microlight at Sun 'n Fun and it made as much noise as a full size jet aircraft!

I had always lusted after a turbine Maule - until the day I met a man who had one. With full tanks it is a single seater, with 4 people (FAA types) it has about 100 odd minutes endurance......

[Mike Cross]

Here you go - Turbine clipped-wing Luscombe
http://www.ideamillproducts.com/images/luscombe.gif

and of course there was the BD5J
http://30.media.tumblr.com/tumblr_le9v9xuNVp1qdta56o1_400.jpg

the jet-powered hang glider
&#x202a]‪Jet powered Hang Glider‬‏ - YouTube

and of course who can forget the jet powered shopping trolley
http://www.2dayblog.com/images/2008/february/rocketcart_1.jpg

[Basil]

most turbine engines require very laminar airflow through the engine to prevent compressor stall (and thus damage), which actually eliminates option to do serious (continuous) flight training with them, such as stalls, unusual attitudes, spins, ...

Wasn't a problem in the JP. What could be a little embarrassing was the lag from idle to producing usable power - IIRC, being a single spool pure jet, about 8 seconds - which could lead to an elevated pulse rate if a practice glide approach went wrong :ooh:

p.s. I don't think diesels are really sorted out yet and that would seem the way to go esp. multi-fuel.

[AdamFrisch]

The wonderful Extra 500 which basically employs the RR250-C20 has a gas burn of about 80L/hr at 200kts, and can be reduced down to 60L/hr at 170kts according to figures. That's about 15gph if you really want economy. For a 6 seater, that really is pretty good gas mileage.

http://www.adamfrisch.com/images/extra1.jpg

[B2N2]

OK, the weight argument is BS, turbine engines are much lighter then their piston counterparts.
Innodyn Turbine Update ... Keep Waiting (http://www.avweb.com/avwebflash/briefs/190287-1.html)

The problem has been the fuel burn. It seems to be very hard to get them below 8-10 gallons/100 HP.
In the US more and more EXPerimentals are using a turbine engine.
Unfortunately these smaller ones are not certified.
You could take a Pa28, make it experimental and bolt on a Innodyne Turbine.

Here is a nice RV-8;RV-8 Turbine N333JB (http://web.mac.com/lechnerl/RV-8_Turbine_Homepage/RV-8_Turbine.html)

I would go turbine in a heart beat..5000 hrs TBO is hard to beat.

[Mike Cross]

and of course there's the Kestrel, which started life as the Farnborough F1

http://www.kestrel.aero/images/pic-4.jpg

[gasax]

oh do pay attention people - The Extra - price $1.7M, I'll have a brace please - imagine how much cheaper with a piston engine?

The Kestrel - guide price £2.8M - oh I'll just have one then!

[AdamFrisch]

Half of that price is to greedy engine manufacturers!

[gasax]

Try chiselling a single crystal hot section turbine blade and then work out how much it actually costs. And then produce a couple of hundred.

You are much more likely to be abducted by aliens than be able to knock out a 'cheap' turbine.... Remember "the truth is out there". In many cases a very long way out there!!!!

[Charles E Taylor]

Why no gas turbine engines in light a/c?

None?

‪Glasair Turbine G-icbm‬‏ - YouTube





Charlie

[fireflybob]

thanks for all the posts and information - Charlie I love that Glasair one!

[Zulu Alpha]

http://www.caa.co.uk/docs/GImages/G-ICBM001.jpg

I talked to the builder and he reckoned that over the engine life there was no cost difference between a 6 cylinder Avgas and a turbine. This took into account the initial cost, TBO, fuel and the higher speed of the turbine.

[gasax]

Given the performance of a turbine Glasair I suspect that tips the 'balance a bit.

From what I recall a RR250 is around $250k, the hot end inspection at 1750hrs is about $80k. An IO540 $65k - fuel at 60 lt/ht - say $150 in the Uk. So $260k in fuel for 1750 hrs, plus the initial 55 makes $325k. The turbine still works out rather more expensive - but the performance is very impressive. I've seen this aricraft fly and if I could I would!

Given the ability to climb near vertically the costs do seem to be worth it!

Better hope the tax on JetA1 does not increase - it would deprive us of some spectacular machines

[172driver]

Have to say I LOVE the reg on this one ! Probably a fitting description.:ok:

[Zulu Alpha]

gasax,

You are working it out per hour. Try working it out per mile as if flies quite a bit faster.

[Green Knight]

Well there is the other way around this, certainly for machines like the Glasair and Lancair (although they do seem to have more imaginative pricing), it needs a bit more work for me to want to put it in an aircraft, but it powers our research vehicles (mainly tracked through electric drive) just fine.

Efficiency is in the middle between the Walter and an Austro.

Walter 601 = 0.68lb/hp/hr (£0.374/hp/hr)
ADM RR1 = 0.52lb/hp/hr (£0.286/hp/hr)
Lycoming TIO540 = 0.47lb/hp/hr (0.59/hp/hr)
Austro = 0.4lb/hp/hr (£0.22/hp/hr)

JET A1 = £1/litre (~£0.55/lb)
100LL = £2/litre (~£1.26/lb)

But the inverse is true for the weight, power is also quite limited at the moment, I spoke to Textron and they hope to have something workable in a 4 cylinder form this time next year, but it wont be cheap!

In the mean time I guess we will keep plugging away at the RR1 and 192kg isnt to shabby for 300KW (400HP), although this is on a 75% full power duty cycle, so will require more work and derating. The main aero application is currently seen as APU (for those that dont want to spend $600k on the equivalent item from honeywell). There is probibly a bit more weight saving to come out the rotors and the end casings, so may find ~-18kg.


Im not sure how quick ICBM is but 400hp should give you 300+kts

[magpienja]

Goes quite well in a Landrover.

http://www.youtube.com/watch?v=W0-i2ZTjgeo&feature=related

Nick.

[IO540]

JET A1 = £1/litre (~£0.55/lb)
100LL = £2/litre (~£1.26/lb)

I don't think so, with the tax on avtur for private use.

Not sure how they are working the collection though.....

[flyingfemme]

Cost is the main reason why light turboprops are not more common. You can buy a turbine conversion for your 206, 210 or Bonanza - starting around half a million dollars. An uncertified engine is available for quite a bit less if you are flying experimental but this is not an option for Europe-based aircraft.
You also need a higher level of technical expertise to maintain one on a homebuilt.
Jet fuel is taxed, for private use, in Euroland so the running cost benefit no longer exists.
Pilot training is also an issue - type ratings etc for turbine power on the eastern side of the Atlantic. Probably quite awkward to define in an uncertified model.
Change, in aviation, is very expensive (because the authorities say so) so don't expect any in the near future.

[IO540]

There is little incentive to make turbines work because they burn much more fuel per HP than pistons, and the only way to recoup some of the loss is by getting a high TAS gain which means flying high, say FL200+, which is possible but difficult unless pressurised (oxygen flow is high at those levels, as I know having flown at FL200 a number of times in the TB20, and one has to breathe so deliberately that this is not a game for "kids" etc) and there are very few pressurised airframes around.

The PA46 is the one good case for a conversion - the Jetprop. That works very well, and is much cheaper to run than say a TBM. OTOH it has the build quality and strength of a Piper, not a TBM :)

[VMC-on-top]

Jet fuel is taxed, for private use

I thought this was only a proposal by the uk govt at the moment and hadn't reached legislation yet?

[flyingfemme]

In the UK jet fuel is taxed by consent - when you buy a tankful there is a statement on the uplift form to be signed so you certify if it is for "personal pleasure" use. If it is, you are expected to make a declaration to HMRC and send it in to them with a cheque. I think the duty rate is about 52ppl.
You will, of course, have paid VAT on it, if not for export - probably at 5%.
Across the rest of Europe there is generally no choice; VAT and duty are added to the bill automatically, unless you can provide an AOC with your tail number clearly stated. This is actually contrary to EU law, which allows any non-private pleasure user to uplift duty free fuel.
The Isle of Man does not allow AOC use on their register but many M reg aircraft are corporate and, therefore, business use. They helpfully provide an official certificate of "business" use to show to fuellers but it is mostly dismissed and the taxes charged.
Rebates of duty, as with the UK "drawback", are pretty much unavailable anywhere else.

[Piltdown Man]

Why not? Certification costs - Conversion costs - Fuel Burn (slightly more per hour for most GA folk) - New price - More training (even thought they are simpler!) - Heavy Duty Battery requirements (and maybe even GPUs).

PM