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?

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/

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?

"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?

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.

"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

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"

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.

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

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