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#1
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Why are there no small turboprops?
I have always wondered why there are no small GA turboprops. It seems like
most of the major problems & maintenance issues associated with GA aircraft are related to the piston motor, and as far as I can tell, turboprops are much more reliable, fuel efficient, smoother running and easier to maintain. So it begs the question, why are there no small turboprops in the 100-300hp range for use on GA aircraft? I would think that turbine engines of this size would be relatively easy to produce, and would be ideal for GA applications. The smoother operation and lower vibration levels would also ease wear and tear on the entire airframe and avionics components. So what's the deal? Does turbine technology not translate downwards very well? Would it be cost prohibitive? Am I entirely missing something? |
#2
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Thomas J. Paladino Jr. wrote:
I have always wondered why there are no small GA turboprops. GOOGLE is your friend. http://www.mauleairinc.com/Our_Planes/Maule_M-7-420AC/ |
#3
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On Mon, 24 May 2004 05:16:31 +0000, Shiver Me Timbers wrote:
Thomas J. Paladino Jr. wrote: I have always wondered why there are no small GA turboprops. GOOGLE is your friend. http://www.mauleairinc.com/Our_Planes/Maule_M-7-420AC/ I've always wondered the same. To take his question and run with it, why are small turbo props not the defacto engine used throughout small GA planes? Seems to me that a variety of small jets and turbo props could be made, which are just as safe and have slightly better performance envelopes than currently exist while having less failures and vibration to boot. Is simple economics the answer? $30k piston versus something like $80k turbine, or something like that? |
#4
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"Shiver Me Timbers" wrote in message ... Thomas J. Paladino Jr. wrote: I have always wondered why there are no small GA turboprops. GOOGLE is your friend. http://www.mauleairinc.com/Our_Planes/Maule_M-7-420AC/ Yeah, but that Maule is a pretty big and specialized aircraft, and the turbine is 420hp; I specified from 100-300hp. Enough to power the average Cessnas and Pipers, or any other average GA plane. The Maule is almost more on par with a Cessna Caravan, not a 182 or 172. Either way, I'll rephrase the question a bit; why are there not more small turboprops available for GA, and why are they not standard accross more models? |
#5
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Thomas J. Paladino Jr. wrote:
why are there not more small turboprops available for GA, and why are they not standard accross more models? Well as the newsgroup knows.... I'm just a little armchair lurker, but if I had to stick my tongue out and make a guess, I would say that right across the board from purchase, operational costs which includes that dirty word fuel, to that pesky but necessary item called insurance that the biggest reason that you can't find those turbine jobbies is because of that dreaded word.... money. |
#6
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"Thomas J. Paladino Jr." wrote in message
... I have always wondered why there are no small GA turboprops. It seems like most of the major problems & maintenance issues associated with GA aircraft are related to the piston motor, and as far as I can tell, turboprops are much more reliable, fuel efficient, smoother running and easier to maintain. So it begs the question, why are there no small turboprops in the 100-300hp range for use on GA aircraft? I would think that turbine engines of this size would be relatively easy to produce, and would be ideal for GA applications. The smoother operation and lower vibration levels would also ease wear and tear on the entire airframe and avionics components. So what's the deal? Does turbine technology not translate downwards very well? Would it be cost prohibitive? Am I entirely missing something? I just read Peter Garrison (of Flying Magazine) claiming that, no they don't scale down well. On the other hand, we just saw in this newsgroup links to the Cri Cri twin turbojet airplane, so obviously it can be done. Some issues however... Turbines operate much more efficiently at altitude, and planes with less than 300 hp (especially those with significantly less than 300 hp) just aren't flown that high normally. Also, while they are more reliable, they are also more complex in certain ways (in spite of the fundamental concept being simpler), and they are more finicky about proper operation. With respect to your understanding of turbine engines: * "Much more reliable" -- probably true, but turbine engines in service are almost exclusively operated under a different maintenance standard than most piston engines. It's hard to do an apples to apples comparison. * "Fuel efficient" -- not down low where most light airplanes are flying. If the engine isn't significantly compressing the intake air, the turbine is doing a lot of unnecessary work, wasting fuel in the process. * "Smoother running" -- without a doubt. But this is probably lowest on the engine priority list, and piston engines can be made that run pretty smoothly as well. * "Easier to maintain" -- for whom? My mechanic might have a theoretical understanding of turbine engines, with some small amount of practical experience (for all I know), but I am sure that he doesn't work on them on a regular basis. I don't even know where I'd go to get a turbine engine worked on, but I'll bet wherever it is, it costs a LOT more than my mechanic charges. Of course, the biggest reason is probably simply the one related to certifying small turbines for light plane use. The turbines that *have* made it to small aircraft are ones that are already certified for other installations, and are higher power than what you're talking about. As far as I know, no one's certified a 100-300hp turbine engine for any airplane, so the first one is going to be really expensive, and will require a lot of sales just to break even. As for the theoretical advantages you mention, I'm not convinced those would be as significant as you're implying, nor that they would offset the added expense of going with a turbine. As far as I am aware, engine vibration has a negligible effect on airframe health, and on avionics lifetime. Heat due to poor ventilation kills avionics much more than engine vibration does, and most modern avionics are pretty hard to kill in the first place. Airframes break after they are overstressed, or they corrode, or they are flown in heavy turbulence for tens of thousands of hours. I've never heard anyone suggest that engine vibration breaks airframes. I would guess that weight would be the biggest real advantage for using a turbine, but that may be offset by having to carry more fuel (it certainly is in the existing single-engine turbine variants), and certainly would be offset by the added complication of changes to the aircraft design to accomodate the change in weight distribution and other things required to work with a turbine engine. Bottom line: to reiterate what I wrote above, I suspect the single biggest reason turbines aren't used is expense. For a Normal certificate airplane, the certification process for the first small turbine would cost a fortune. For experimentals, it sounds like (from one of George's earlier posts) that people ARE looking to incorporate small turbines into light airplanes, but I doubt it's cost effective. As near as I can tell, for a given horsepower, turbines are simply more expensive and for sure it's harder to find someone qualified to work on them. Maybe one day they'll be ubiquitous in a wide variety of applications, and they'll start showing up in light airplanes too. But it seems to me that until there's a huge market for certificated low-horsepower turbine engines, no one's going to bother working on them. Pete |
#7
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In article , Thomas J. Paladino Jr. wrote:
So it begs the question, why are there no small turboprops in the 100-300hp range for use on GA aircraft? Cost. I believe even the relatively small turbines are two orders of magnitude more expensive than the piston engine of the same power. Turbines tend to have parts made from exotic metals that aren't straightforward to manufacture. Also, small turbines are markedly less fuel efficient than a piston engine of the same horsepower (especially at the altitudes we fly at). If it wasn't for the exhorbitant cost of a new turbine, I'd far prefer them - easier to operate, cooling issues aren't as problematic, and with modern electronic control I'm sure that operating one can be made damn-foolproof, not just foolproof. -- Dylan Smith, Castletown, Isle of Man Flying: http://www.dylansmith.net Frontier Elite Universe: http://www.alioth.net "Maintain thine airspeed, lest the ground come up and smite thee" |
#8
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So it begs the question, why are there no small turboprops in the 100-300hp range for use on GA aircraft? Cost. I believe even the relatively small turbines are two orders of magnitude more expensive than the piston engine of the same power. Turbines tend to have parts made from exotic metals that aren't straightforward to manufacture. Also, small turbines are markedly less fuel efficient than a piston engine of the same horsepower (especially at the altitudes we fly at). If it wasn't for the exhorbitant cost of a new turbine, I'd far prefer them - easier to operate, cooling issues aren't as problematic, and with modern electronic control I'm sure that operating one can be made damn-foolproof, not just foolproof. I'm ignorate of the technology, but seem to remember the airlines went to jets because fuel costs were lower and they were lest costly to keep running. If they scaled down well, I expect we'd see them in hybred cars long before they'd be in general aviation aircraft. You don't need rapid response times in a hybred, but the 'spool-up' time in a small plane could take a lot of getting used to by pilots who need lots of throttle jockeying to land their airplanes. I take that back -- it wouldn't take a lot of time, there'd be aluminum junk that used to be airplanes near the approach end of lots of airports. |
#9
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Hi tony,
I'm ignorate of the technology, but seem to remember the airlines went to jets because fuel costs were lower and they were lest costly to keep running. .... and because passengers appreciated not to arrive in a three-engine Connie after departing in a four engine a few hours ago. Enginge failures were a main issue on that. If they scaled down well, I expect we'd see them in hybred cars long before they'd be in general aviation aircraft. You don't need rapid response times in a hybred, but the 'spool-up' time in a small plane could take a lot of getting used to by pilots who need lots of throttle jockeying to land their airplanes. I take that back -- it wouldn't take a lot of time, there'd be aluminum junk that used to be airplanes near the approach end of lots of airports. I don't think so. Spool up time on modern turbines is marginal compared with early turboprop/jet engines. Compared with the workload a high power piston is causing, every turbine would be much safer. I bet on that. Regards, Peter |
#10
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Hi Greg,
I've always wondered the same. To take his question and run with it, why are small turbo props not the defacto engine used throughout small GA planes? As said before by Peter Duniho, they simply don't suit well. There scaling down is making them inefficient, there fuel consumption - especially at lower altitutes - is higher, so is the amount of fuel to be loaded for the same distance. If you take a look at the turboprop conversions 'done' to the P210, the Bonanza and so on, you'll find that there range is reduced. Some conversions cope with this by improving the load (more hp, proved to fly with a few extra pounds). But all in all that makes these planes not more efficient - especially the ones normally operated at lower altitudes - the ones without pressurization. Seems to me that a variety of small jets and turbo props could be made, which are just as safe and have slightly better performance envelopes than currently exist while having less failures and vibration to boot. There _will_ be a lot of new small jets - but none of them in a 'normal' price range of a spam can. The engines are much to costly for that. Lowest priced jet - if completed - will be the D-Jet by Diamond Aircraft. Single engine jet with a maximum FL of 250 (and I just can't see how they will cope with making this engine efficient at that altitude...) Is simple economics the answer? $30k piston versus something like $80k turbine, or something like that? Much more. Especially maintenance is cruel. Turbines do have less moving parts, but the parts are of a much higher quality and the personnel is trained as hell... regards, Peter |
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