Why no gas turbine engines in light a/c?
Thread Starter
Why no gas turbine engines in light a/c?
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?
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?
Join Date: Aug 2000
Location: Near Stuttgart, Germany
Posts: 1,096
Likes: 0
Received 1 Like
on
1 Post
...so please guys, why not?
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.
Join Date: May 2001
Location: UK
Posts: 4,631
Likes: 0
Received 0 Likes
on
0 Posts
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.
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.
Join Date: Apr 2010
Location: IRS NAV ONLY
Posts: 1,230
Likes: 0
Received 0 Likes
on
0 Posts
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.
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.
Gnome de PPRuNe
Join Date: Jan 2002
Location: Too close to Croydon for comfort
Age: 60
Posts: 12,656
Received 315 Likes
on
175 Posts
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?
)
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?
)
Join Date: Apr 1999
Location: The frozen north....
Age: 49
Posts: 547
Likes: 0
Received 1 Like
on
1 Post
Just the ticket....
Sonex Aircraft Hornets' Nest Research and Development
Not a turboprop but still looks fun!
Sonex Aircraft Hornets' Nest Research and Development
Not a turboprop but still looks fun!
Join Date: Sep 2006
Location: Los Angeles, USA
Age: 52
Posts: 1,631
Likes: 0
Received 0 Likes
on
0 Posts
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.
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.
Join Date: Jan 2002
Location: Aberdeen
Posts: 1,234
Likes: 0
Received 0 Likes
on
0 Posts
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.
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.
Join Date: Dec 2003
Location: United Kingdom
Age: 40
Posts: 261
Likes: 0
Received 0 Likes
on
0 Posts
Join Date: Jan 2002
Location: Aberdeen
Posts: 1,234
Likes: 0
Received 0 Likes
on
0 Posts
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
Lovely idea and a terrific novelty - until the local gliding club gets the noise complaints
Join Date: Feb 2007
Location: Amsterdam
Posts: 4,598
Likes: 0
Received 0 Likes
on
0 Posts
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?
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?
Join Date: Sep 2006
Location: Los Angeles, USA
Age: 52
Posts: 1,631
Likes: 0
Received 0 Likes
on
0 Posts
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.
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.
Join Date: Jan 2002
Location: Aberdeen
Posts: 1,234
Likes: 0
Received 0 Likes
on
0 Posts
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......
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......
Join Date: Sep 2002
Location: Savannah GA & Portsmouth UK
Posts: 1,784
Likes: 0
Received 0 Likes
on
0 Posts
Here you go - Turbine clipped-wing Luscombe
and of course there was the BD5J
the jet-powered hang glider
and of course who can forget the jet powered shopping trolley
and of course there was the BD5J
the jet-powered hang glider
and of course who can forget the jet powered shopping trolley
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, ...
p.s. I don't think diesels are really sorted out yet and that would seem the way to go esp. multi-fuel.
Join Date: Sep 2006
Location: Los Angeles, USA
Age: 52
Posts: 1,631
Likes: 0
Received 0 Likes
on
0 Posts
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.
OK, the weight argument is BS, turbine engines are much lighter then their piston counterparts.
Innodyn Turbine Update ... Keep Waiting
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
I would go turbine in a heart beat..5000 hrs TBO is hard to beat.
Innodyn Turbine Update ... Keep Waiting
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
I would go turbine in a heart beat..5000 hrs TBO is hard to beat.
