Why are there no small turboprops? [Archive]

Peter Duniho

May 24th 04, 07:35 AM

"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

Dylan Smith

May 24th 04, 12:12 PM

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"

tony

May 24th 04, 01:29 PM

>
>> 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.

Peter Hovorka

May 24th 04, 01:50 PM

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

Peter Hovorka

May 24th 04, 01:59 PM

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

G.R. Patterson III

May 24th 04, 02:48 PM

Greg Copeland wrote:
>
> Is simple economics the answer? $30k piston versus something like $80k
> turbine, or something like that?

It's certainly one answer. The price on that Maule is $450,000. With an IO-540, it's
$173,420.

I've read that there are technical problems building small turbines; ie. the smaller
the diameter of the turbine, the faster the blades must spin to produce power.

George Patterson
I childproofed my house, but they *still* get in.

G.R. Patterson III

May 24th 04, 02:53 PM

tony wrote:
>
> 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.

Kerosene is much cheaper than 140 octane avgas, and turbines are easier to maintain
than large Pratt & Whitney radials. Neither of these facts is pertinent to light
aircraft.

George Patterson
I childproofed my house, but they *still* get in.

John Gaquin

May 24th 04, 02:58 PM

"tony" > wrote in message
> >
> 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.
>

'Tis true that kerosene was substantially cheaper than very high octane
gasoline (typically 140+, iirc) then, but the main reasons were 1) maint
cost -- those high powered turbo-supercharged radials on the Connies and
DC-7s were tweaked to within an inch of their lives, and would fail
regularly. (My brother-in-law's father worked for AA in BOS in that era,
and the standing joke was that they put four engines on those things so they
could arrive with at least two or three); and 2) cruise speed/payload -- the
transition to jet transports allowed schedulers to carry many more
passengers at about 50% more speed. The implications of this change on
system capacity and operation, particularly trans-continental and
trans-oceanic flights, were astounding and very far reaching.

Barney Rubble

May 24th 04, 02:59 PM

Slightly off-topic, why has no-on mentioned diesel engines (that run on
Jet-A1)? This has got to be the way to go, better economy, better operation
at altitude, simpler mechanicals (less to break) and FADEC/ECU controlled?
For the majority of GA this has got to be the long-term answer, even in the
US. Europe is leading the way on this topic, oh did I mention gas prices?

- BR
"G.R. Patterson III" > wrote in message
...
>
>
> tony wrote:
> >
> > 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.
>
> Kerosene is much cheaper than 140 octane avgas, and turbines are easier to
maintain
> than large Pratt & Whitney radials. Neither of these facts is pertinent to
light
> aircraft.
>
> George Patterson
> I childproofed my house, but they *still* get in.

Rick Durden

May 24th 04, 03:03 PM

Thomas,

There are some smaller turboprops but the economics just aren't there
to put them into mass production. The market is quite small and the
specific fuel consumption of a turbine versus a piston means that if
you put it on your Cessna 210, for example, you can't carry enough
fuel to get anywhere and still put people in the cabin. Plus, the
simple cost of the technology and the metals to handle the heat in a
turbine engine makes it almost impossible to compete with other types
of engines in that horsepower range.

There was an article on the subject of specific fuel consumption and
load carrying ability of turbines in little airplanes in Aviation
Consumer a couple of years back.

For the 100-300 hp range it looks as if going back to diesels, as was
explored in the 1930s, may be appropriate.

All the best,
Rick

"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?

Robert M. Gary

May 24th 04, 05:36 PM

"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?

Cessna 210's and Bonanza's can be found with turbo prop retrofits.
These engines run a long time but when its time for a hot overhaul,
its going to cost you an arm and a leg.

Mike Rapoport

May 24th 04, 06:26 PM

Cost and effficiency. Small turbines are very expensive fuel guzzlers.
Large turbines (airliner size) are efficient but small ones aren't. The
1000hp engines on my MU-2 have a bsfc of .52 and smaller engines would be
even worse. Piston engines are in the .40 area. Diesels are more
promising.

Mike
MU-2

"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?
>
>

Bob Gardner

May 24th 04, 08:23 PM

Author Stuart Woods has a Malibu with a turbo engine, and I have seen a
turbo-powered 206.

Bob Gardner

"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?
>
>

David CL Francis

May 24th 04, 10:33 PM

On Mon, 24 May 2004 at 13:48:53 in message
>, G.R. Patterson III
> wrote:
>It's certainly one answer. The price on that Maule is $450,000. With an IO-540, it's
>$173,420.
>
>I've read that there are technical problems building small turbines; ie. the smaller
>the diameter of the turbine, the faster the blades must spin to produce power.

Did you know you can buy true turbo jets for model aircraft? They cost
about $3000 and give about 20 lb thrust, They are around 4" in diameter.
--
David CL Francis

David CL Francis

May 24th 04, 10:39 PM

On Sun, 23 May 2004 at 23:35:35 in message
>, Peter Duniho
> wrote:
>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.

Can you explain why the efficiency of turbines is much higher at
altitude? What sort of efficiency are you talking about?
--
David CL Francis

Robert M. Gary

May 24th 04, 11:23 PM

"Mike Rapoport" > wrote in message et>...

> Diesels are more
> promising.

And can run on the same gas.

Morgans

May 24th 04, 11:53 PM

"Robert M. Gary" > wrote in message
om...
> "Mike Rapoport" > wrote in message
et>...
>
> > Diesels are more
> > promising.
>
> And can run on the same gas.

Only some can run on jet fuel. Jet fuel has almost no lubrication
qualities, while diesel does. Jet fuel will eat up some things, like fuel
pumps.
--
Jim in NC

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Peter Duniho

May 25th 04, 01:31 AM

"David CL Francis" > wrote in message
...
> [...]
> Can you explain why the efficiency of turbines is much higher at
> altitude? What sort of efficiency are you talking about?

Mainly the same reason turbocharged reciprocating engines operate more
efficiently at altitude. You're carrying around a compressor that just
isn't all that useful down low. Once you get higher, where there's less
drag, you get more "bang for the buck" out of the engine. Of course, as
Mike Rapaport pointed out, there's also the issue of efficiency with respect
to the size of the engine (independent of operating altitude).

The bottom line with respect to that point is that, for the purposes a
typical 100-300hp engine would be used, reciprocating engines are more
practical.

Pete

G.R. Patterson III

May 25th 04, 01:40 AM

Barney Rubble wrote:
>
> Slightly off-topic, why has no-on mentioned diesel engines (that run on
> Jet-A1)? This has got to be the way to go, better economy, better operation
> at altitude, simpler mechanicals (less to break) and FADEC/ECU controlled?

Actually, because of the higher compression ratios, the mechanicals are not simpler.

> For the majority of GA this has got to be the long-term answer, even in the
> US.

I agree. They are more expensive than gas-burners, but it will be nice when it
becomes possible to replace my O-320 with a diesel in the 180hp range (IMO).

George Patterson
I childproofed my house, but they *still* get in.

G.R. Patterson III

May 25th 04, 01:42 AM

Morgans wrote:
>
> Only some can run on jet fuel. Jet fuel has almost no lubrication
> qualities, while diesel does. Jet fuel will eat up some things, like fuel
> pumps.

Any diesel designed for aircraft will be designed to run on jet fuel. Doesn't make
any sense to do it any other way.

George Patterson
I childproofed my house, but they *still* get in.

Morgans

May 25th 04, 03:50 AM

"David CL Francis"
>
> Did you know you can buy true turbo jets for model aircraft? They cost
> about $3000 and give about 20 lb thrust, They are around 4" in diameter.
> --
> David CL Francis

And wear out in a few hundred hours, at best, and consume vast quantities of
fuel.
--
Jim in NC

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Gerald Sylvester

May 25th 04, 03:53 AM

> Did you know you can buy true turbo jets for model aircraft? They cost
> about $3000 and give about 20 lb thrust, They are around 4" in diameter.

I was out for a bike ride and passed by a model radio controlled
airport. A guy was taxiing out and I was thiking, "Oh that is
a ducted fan (or whatever the heck they call it)." I then said to
a guy, "Man that sounds like a turbine." He told me it was.
I went home looked it up online. This is what I came up with.

http://jetcatusa.sitewavesonline.net/p200.html
http://www.jethangar.com/

This guy had an F-14 and some other fighter plane. They had
operable brakes too. Cool but at that price, I could have
paid for my PPL and my IA too....well almost.

Gerald

Morgans

May 25th 04, 03:53 AM

"G.R. Patterson III" > wrote

> Any diesel designed for aircraft will be designed to run on jet fuel.
Doesn't make
> any sense to do it any other way.
>
> George Patterson

Right. I was commenting on the fact that not all diesels will run on jet
fuel, not airplane diesels. Did I mis-read? Won't be the last time.
--
Jim in NC

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Capt.Doug

May 25th 04, 05:00 AM

>"Thomas J. Paladino Jr." wrote in message The Maule is almost more
> on par with a Cessna Caravan, not a 182 or 172.

The Maule M-7 series is about the size of a C-172. It is a 4 seater. The
Caravan can have up to 14 + 2 seats.

> 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?

In general, turboprop engines don't match fuel consumption with piston
engines until over the 300 horsepower range. The metals required for a
durable, efficient turbine engine are expensive. If a manufacturer produced
a turbine such as you describe, airframe manufacturers would be clamoring
over each other to install them on their airframes. You don't see it
happening because such an engine doesn't exist (yet).

D.

Jeff

May 25th 04, 06:13 AM

there is a company making small turbo props, I cant remember the name of them,
but they have a 200 HP one

"Thomas J. Paladino Jr." wrote:

> 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?

Jeff

May 25th 04, 06:21 AM

here you go, they do exist
http://www.atpcoinc.com/Pages/Products.html

"Thomas J. Paladino Jr." wrote:

> 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?

Jeff

May 25th 04, 06:24 AM

the lanceair has a turbo prop version, I saw one take off few months back, fast
little airplane

Bob Gardner wrote:

> Author Stuart Woods has a Malibu with a turbo engine, and I have seen a
> turbo-powered 206.
>
> Bob Gardner
>
> "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?
> >
> >

Tom Sixkiller

May 25th 04, 08:10 AM

"Robert M. Gary" > wrote in message
om...
> "Mike Rapoport" > wrote in message
et>...
>
> > Diesels are more
> > promising.
>
> And can run on the same gas.

And there's other sources for diesel...and maybe you can smoke it, too.

http://www.artistictreasure.com/learnmorecleanair.html

Bob Martin

May 25th 04, 12:30 PM

"Peter Duniho" > wrote in message >...

> 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

I know there's been an RV-4T - they grafted a turboprop onto the front
of an RV-4. I think the biggest problem they had (besides fuel
consumption) was that they didn't mount the exhaust stacks right, and
it "backed up" a bit in the engine.

GeorgeB

May 25th 04, 01:45 PM

On Tue, 25 May 2004 00:40:15 GMT, "G.R. Patterson III"
> wrote:

>Barney Rubble wrote:
>>
>> Slightly off-topic, why has no-on mentioned diesel engines (that run on
>> Jet-A1)? This has got to be the way to go, better economy, better operation
>> at altitude, simpler mechanicals (less to break) and FADEC/ECU controlled?
>
>Actually, because of the higher compression ratios, the mechanicals are not simpler.

I know that the forces generated during compression are higher at a
higher compresion ratio, but I cannot imagine that they are higher
than the power forces. Now whether the power forces (peak) are higher
in a compression ignition engine ... maybe (and probably), but I've
never seen data from conn rod strain gages.

Ash Wyllie

May 25th 04, 02:04 PM

G.R. Patterson III opined

>Greg Copeland wrote:
>>
>> Is simple economics the answer? $30k piston versus something like $80k
>> turbine, or something like that?

>It's certainly one answer. The price on that Maule is $450,000. With an
>IO-540, it's
>$173,420.

>I've read that there are technical problems building small turbines; ie. the
>smaller the diameter of the turbine, the faster the blades must spin to
>produce power.
>
The biggie is edge effects. There is a minimum clearance between the turbine
and the case, and that clearance is independent of the diameter of the
turbine. So small turbines have much higher tip losses.

-ash
Cthulhu for President!
Why vote for a lesser evil?

[email protected]

May 25th 04, 02:13 PM

On Tue, 25 May 2004 00:40:15 GMT, "G.R. Patterson III"
> wrote:

>Actually, because of the higher compression ratios, the mechanicals are not simpler.

Well sort of. Some two stroke cycle diesels don't have overhead
valves. No diesel has a spark ignition system. This type of engine
could be considered mechanically more simple than a four stroke cycle
engine.

But the fuel pump is a lot more complex and higher pressure, and most
diesels have either a turbo supercharger or a mechanically driven
supercharger, or both.

See <http://www.deltahawkengines.com/index.htm> for an example of a
very cool V four two stroke diesel engine intended for the homebuilt
market initially, and perhaps eventual certification.

Corky Scott

Paul Sengupta

May 25th 04, 03:27 PM

"Gerald Sylvester" > wrote in message
nk.net...
> > Did you know you can buy true turbo jets for model aircraft? They cost
> > about $3000 and give about 20 lb thrust, They are around 4" in diameter.
>
> I then said to
> a guy, "Man that sounds like a turbine." He told me it was.

This is what we were talking about earlier with the jet
engines on the Cri-cri.

http://www.amtjets.com/gallery_real_plain.html

Some more "normal" and some unusual applications:
http://www.amtjets.com/gallery.html

Paul

Friedrich Ostertag

May 25th 04, 11:40 PM

Hi George,

>>> Slightly off-topic, why has no-on mentioned diesel engines (that
>>> run on Jet-A1)? This has got to be the way to go, better economy,
>>> better operation at altitude, simpler mechanicals (less to break)
>>> and FADEC/ECU controlled?
>>
>> Actually, because of the higher compression ratios, the mechanicals
>> are not simpler.
>
> I know that the forces generated during compression are higher at a
> higher compresion ratio, but I cannot imagine that they are higher
> than the power forces.
> Now whether the power forces (peak) are higher
> in a compression ignition engine ... maybe (and probably), but I've
> never seen data from conn rod strain gages.

Peak pressure during combustion is about twice as high on a diesel
engine compared to a spark ignition engine (about 160 bar / 2400 psi
vs. 80 bar / 1200 psi). Hence the heavier build of diesels. On the plus
side, diesels run about 200 degC cooler than SI-engines even though
most diesels are turbocharged vs. naturally aspirated gasolines.

However diesels are MUCH more simple in mixture control - there is
none. You just inject the amount of fuel you need to burn to achieve
the desired torque. On gasoline (spark ignition) engines you control
the engine torque by restricting the air flow with a throttle. You then
have to match the fuel flow to the varying air flow pretty precisely.

Also, the entire ignition system, spark plugs, magnets, is omitted on a
diesel. 50% of engine problems on aviation piston engines is related to
ignition problems.

regards,
Friedrich

--
for personal email please remove "entfernen" from my adress

David CL Francis

May 26th 04, 01:27 AM

On Mon, 24 May 2004 at 17:31:12 in message
>, Peter Duniho
> wrote:
>"David CL Francis" > wrote in message
...
>> [...]
>> Can you explain why the efficiency of turbines is much higher at
>> altitude? What sort of efficiency are you talking about?
>
>Mainly the same reason turbocharged reciprocating engines operate more
>efficiently at altitude. You're carrying around a compressor that just
>isn't all that useful down low. Once you get higher, where there's less
>drag, you get more "bang for the buck" out of the engine. Of course, as
>Mike Rapaport pointed out, there's also the issue of efficiency with respect
>to the size of the engine (independent of operating altitude).
>
But is that efficiency? I would have thought that efficiency was
measurement by a parameter like pounds of fuel used per effective shaft
horsepower per hour. That certainly changes with altitude but not so
much.

--
David CL Francis

Brian Burger

May 26th 04, 03:50 AM

On Tue, 25 May 2004, Tom Sixkiller wrote:

>
> "Robert M. Gary" > wrote in message
> om...
> > "Mike Rapoport" > wrote in message
> et>...
> >
> > > Diesels are more
> > > promising.
> >
> > And can run on the same gas.
>
> And there's other sources for diesel...and maybe you can smoke it, too.
>
> http://www.artistictreasure.com/learnmorecleanair.html

Smoke my fuel! <grin> Actually, industrial hemp - the stuff they make/will
make biodiesel, t-shirts, etc out of - has practically NO THC content. THC
is the stuff in pot that actually makes you high.

Industrial hemp is THC-free to the point where you'd have to smoke pounds
and pounds of the stuff to get enough THC into your blood - and the smoke
would kill you dead first!

Brian.

Tom Sixkiller

May 26th 04, 04:04 AM

"Brian Burger" > wrote in message
ia.tc.ca...
> On Tue, 25 May 2004, Tom Sixkiller wrote:
> >
> > And there's other sources for diesel...and maybe you can smoke it, too.
> >
> > http://www.artistictreasure.com/learnmorecleanair.html
>
> Smoke my fuel! <grin> Actually, industrial hemp - the stuff they make/will
> make biodiesel, t-shirts, etc out of - has practically NO THC content. THC
> is the stuff in pot that actually makes you high.

:~)

> Industrial hemp is THC-free to the point where you'd have to smoke pounds
> and pounds of the stuff to get enough THC into your blood - and the smoke
> would kill you dead first!

I remember reading something a few years ago from the Libertarians about the
history of hemp (paper, for instance...the paper on which the Constitution,
Declaration of Independence, other... were written) and the many uses for it
today (medicine, the industrial applications that you mention, etc.) but the
anti-druggies have made it far too restrictive.

Peter Duniho

May 26th 04, 10:55 PM

"David CL Francis" > wrote in message
...
> [...]
> But is that efficiency? I would have thought that efficiency was
> measurement by a parameter like pounds of fuel used per effective shaft
> horsepower per hour. That certainly changes with altitude but not so
> much.

Sorry, I didn't realize this was a scientific forum, where there's only one
definition of "efficiency".

Are you trying to say that turbine engines are just as efficient to use at
the lower altitudes as they are at higher altitudes? I would disagree with
that. If you're not saying that, I'm at a loss as to what your point is.

Even if you want to measure efficiency only by something like specific fuel
consumption, small turbines still don't win out, regardless of altitude.
They are inherently inefficient, due to reasons already mentioned in this
thread.

Or looked at another way, a low horsepower engine intended for use only at
lower altitudes is too small to be efficient, while one intended for use at
higher altitudes will be severely derated when operated at low altitudes if
the engine is to provide sufficient power at the higher altitudes, which is
again, a waste (and waste implies low efficiency).

In aviation (or any other application, for that matter), you cannot look
simply at one single aspect of efficiency. For an engine to be viable, it
needs to provide an overall efficiency greater than competing engines. Low
horsepower turbines simply don't meet that requirement, and for an
installation intended to be flown at higher altitudes, the overall
efficiency suffers at lower altitudes.

We are talking about the real world here, not a laboratory.

Pete

Roger Halstead

May 27th 04, 03:22 AM

On Tue, 25 May 2004 15:27:33 +0100, "Paul Sengupta"
> wrote:

>"Gerald Sylvester" > wrote in message
nk.net...
>> > Did you know you can buy true turbo jets for model aircraft? They cost
>> > about $3000 and give about 20 lb thrust, They are around 4" in diameter.

I think you'll find they cost a *lot* more than that.

OTOH it takes a big airplane to cary enough fuel to go any where
behind a turbine (jet or prop)

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com
>>
>> I then said to
>> a guy, "Man that sounds like a turbine." He told me it was.
>
>This is what we were talking about earlier with the jet
>engines on the Cri-cri.
>
>http://www.amtjets.com/gallery_real_plain.html
>
>Some more "normal" and some unusual applications:
>http://www.amtjets.com/gallery.html
>
>Paul
>

Roger Halstead

May 27th 04, 03:26 AM

On Mon, 24 May 2004 00:28:44 -0500, Greg Copeland >
wrote:

>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?

Turbines drink fuel like crazy at low altitude. They are more
reliable, run smooth, and have more reserve power than piston
engines, but what a thirst.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

Roger Halstead

May 27th 04, 03:29 AM

On Mon, 24 May 2004 13:48:53 GMT, "G.R. Patterson III"
> wrote:

>
>
>Greg Copeland wrote:
>>
>> Is simple economics the answer? $30k piston versus something like $80k
>> turbine, or something like that?
>
>It's certainly one answer. The price on that Maule is $450,000. With an IO-540, it's
>$173,420.
>
>I've read that there are technical problems building small turbines; ie. the smaller
>the diameter of the turbine, the faster the blades must spin to produce power.

Look at the specs on those turbines used in model airplanes. The RPM
is almost unbelieveable.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com
>
>George Patterson
> I childproofed my house, but they *still* get in.

Roger Halstead

May 27th 04, 03:36 AM

On Mon, 24 May 2004 22:50:55 -0400, "Morgans"
> wrote:

>
>"David CL Francis"
>>
>> Did you know you can buy true turbo jets for model aircraft? They cost
>> about $3000 and give about 20 lb thrust, They are around 4" in diameter.
>> --
>> David CL Francis
>
>And wear out in a few hundred hours, at best, and consume vast quantities of
>fuel.
I just did the figures on the one above. If I didn't make any
mistakes, that tiny engine burns almost as much as a 300 HP IO550.

The pair of them on the Cri-Cri would be burning in the neighborhood
of 30 GPH at full power.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

G.R. Patterson III

May 27th 04, 04:25 AM

Morgans wrote:
>
> And wear out in a few hundred hours, at best, and consume vast quantities of
> fuel.

If they wear out that fast, how well does that Cri-Cri fly on one engine? Seems to me
that would be a real problem fairly regularly.

George Patterson
None of us is as dumb as all of us.

Big John

May 27th 04, 04:28 AM

Peter

As I have posted before. On the early Jets (F-80A/B) it took 21
seconds to accelerate from idle rpm to full rpm. You made your go
around decision on base leg.

In actul practive, we only reduced rpm to around 65% (idle was 35%) in
the pattern until "we had the runway made", to reduce the spool up
time.

Since those days, they have decreased the spool up time to a pittance
..

On turbo props however, they run the engine at a constant rpm during
flight and all you do with the throttle is change the prop pitch. With
this you can go from no thrust to full thrust instantly.

Fly safe.

Big John

On Mon, 24 May 2004 14:50:46 +0200, Peter Hovorka >
wrote:

>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
>

Big John

May 27th 04, 05:26 AM

Barney

See my post (new thread) on SMA Diesels that are FAA certified and
delivery is starting for a 230 HP, 4 cyl version. No price quoted, but
best guess is $80K-$90K

Big John
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

On Mon, 24 May 2004 08:59:51 -0500, "Barney Rubble"
> wrote:

>Slightly off-topic, why has no-on mentioned diesel engines (that run on
>Jet-A1)? This has got to be the way to go, better economy, better operation
>at altitude, simpler mechanicals (less to break) and FADEC/ECU controlled?
>For the majority of GA this has got to be the long-term answer, even in the
>US. Europe is leading the way on this topic, oh did I mention gas prices?
>
>- BR
>"G.R. Patterson III" > wrote in message
...
>>
>>
>> tony wrote:
>> >
>> > 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.
>>
>> Kerosene is much cheaper than 140 octane avgas, and turbines are easier to
>maintain
>> than large Pratt & Whitney radials. Neither of these facts is pertinent to
>light
>> aircraft.
>>
>> George Patterson
>> I childproofed my house, but they *still* get in.
>

Paul Sengupta

May 27th 04, 12:03 PM

"Roger Halstead" > wrote in message
...
> On Tue, 25 May 2004 15:27:33 +0100, "Paul Sengupta"
> > wrote:
>
> >"Gerald Sylvester" > wrote in message
> nk.net...
> >> > Did you know you can buy true turbo jets for model aircraft? They
cost
> >> > about $3000 and give about 20 lb thrust, They are around 4" in
diameter.
>
> I think you'll find they cost a *lot* more than that.

AMT's prices (excluding tax) start from 2972.00 Euros.
http://www.amt.nl/form_pricelist.php

Or build your own... :-)
http://www.artesjet.com/components.htm

As for fuel consumption, the above site gives a thrust of 92.3N. It gives
fuel
consumption of 0.154kg/N/H. So that's 14kg per hour. About 20 litres? What
is the specific gravity of propane? One of the pages for the Cobra engine on
the
Cri-cri says 0.8kg/N/H.

Paul

Mike Rapoport

May 27th 04, 07:20 PM

Sort of. The efficiency of a turbine engine is related to EGT (actually ITT
but we measure EGT and then compute ITT). The efficiency peaks at peak
temperature. In practice you are right because you generally can't reach
peak EGT at low altitudes since most turbine engines are flat rated. Also
because of the relationship between EGT and efficiency, turbines are really
inefficient at low power settings (with corrasponding low EGTs). As an
example, TPE331-10 engines (1020hp flat rated to 776eshp) use about
220lbs/hr at sea level just to keep the engine running (0 effective hp),
240lb/hr to produce 10% power and they use about 475lb/hr to produce 100%
power, so it takes half the fuel to produce 10% of the power. This makes
sense when you think about it. All the things that consume power
(compressor, gearbox, accesories) are consuming just as much power at 10% as
at 100% so the all the additional fuel is going into power production.

The airplane efficiency is related to altitude. It takes a lot less thrust
to move an airplane at any given TAS at 30K' where the are is only 30% as
dense than at sea level.

Mike
MU-2

"Peter Duniho" > wrote in message
...
> "David CL Francis" > wrote in message
> ...
> > [...]
> > But is that efficiency? I would have thought that efficiency was
> > measurement by a parameter like pounds of fuel used per effective shaft
> > horsepower per hour. That certainly changes with altitude but not so
> > much.
>
> Sorry, I didn't realize this was a scientific forum, where there's only
one
> definition of "efficiency".
>
> Are you trying to say that turbine engines are just as efficient to use at
> the lower altitudes as they are at higher altitudes? I would disagree
with
> that. If you're not saying that, I'm at a loss as to what your point is.
>
> Even if you want to measure efficiency only by something like specific
fuel
> consumption, small turbines still don't win out, regardless of altitude.
> They are inherently inefficient, due to reasons already mentioned in this
> thread.
>
> Or looked at another way, a low horsepower engine intended for use only at
> lower altitudes is too small to be efficient, while one intended for use
at
> higher altitudes will be severely derated when operated at low altitudes
if
> the engine is to provide sufficient power at the higher altitudes, which
is
> again, a waste (and waste implies low efficiency).
>
> In aviation (or any other application, for that matter), you cannot look
> simply at one single aspect of efficiency. For an engine to be viable, it
> needs to provide an overall efficiency greater than competing engines.
Low
> horsepower turbines simply don't meet that requirement, and for an
> installation intended to be flown at higher altitudes, the overall
> efficiency suffers at lower altitudes.
>
> We are talking about the real world here, not a laboratory.
>
> Pete
>
>

David CL Francis

May 27th 04, 10:42 PM

On Thu, 27 May 2004 at 02:26:52 in message
>, Roger Halstead
> wrote:
>Turbines drink fuel like crazy at low altitude. They are more
>reliable, run smooth, and have more reserve power than piston
>engines, but what a thirst.

Can you direct us to any quantitative information on this please?
--
David CL Francis

David CL Francis

May 27th 04, 11:26 PM

On Thu, 27 May 2004 at 18:20:14 in message
. net>, Mike Rapoport
> wrote:

>The airplane efficiency is related to altitude. It takes a lot less thrust
>to move an airplane at any given TAS at 30K' where the are is only 30% as
>dense than at sea level.

Help me here. I am struggling to find out more information but I have a
bit of a problem with that statement. I probably misunderstand what you
are saying and I may have it wrong I admit. In essence it is correct but
you normally fly at much higher TAS at altitude than at sea level.

It seems to me that if you want range you fly the aircraft at the AoA
that provides the best overall lift/drag ratio.

Let us suppose that is a ratio of 10. Then at the appropriate speed for
that height the drag (and therefore the thrust requirement) will be one
tenth of the weight, since in level flight lift must equal weight.
--
David CL Francis

Peter Duniho

May 29th 04, 12:25 AM

"David CL Francis" > wrote in message
...
> [...]
> Let us suppose that is a ratio of 10. Then at the appropriate speed for
> that height the drag (and therefore the thrust requirement) will be one
> tenth of the weight, since in level flight lift must equal weight.

How is that different from what Mike said?

He basically said, keep speed constant, and required thrust is reduced.
You're saying, keep required thrust constant, and speed is higher. Those
seem to me to be two ways of saying the same thing.

Aren't they?

Pete

David Goudie

May 29th 04, 08:38 AM

It's not economical to use a small turbo contrasted to the payload.
"G.R. Patterson III" > wrote in message
...
>
>
> Morgans wrote:
> >
> > And wear out in a few hundred hours, at best, and consume vast
quantities of
> > fuel.
>
> If they wear out that fast, how well does that Cri-Cri fly on one engine?
Seems to me
> that would be a real problem fairly regularly.
>
> George Patterson
> None of us is as dumb as all of us.

David CL Francis

May 30th 04, 09:44 PM

On Fri, 28 May 2004 at 16:25:22 in message
>, Peter Duniho
> wrote:

>He basically said, keep speed constant, and required thrust is reduced.
>You're saying, keep required thrust constant, and speed is higher. Those
>seem to me to be two ways of saying the same thing.

What I was trying to point out (cautiously) is that talking about huge
reductions of drag at altitude may be misleading. If you fly at best A0A
all the time then the drag is almost independent of altitude. If that is
correct then the work done per mile is also constant and range is also
almost independent of altitude. But that sounds horribly revolutionary.
:-(

Doing that you would always get there faster at altitude.
--
David CL Francis

Dan Thomas

May 31st 04, 03:09 AM

A few years ago at Arlington I saw a turboprop made from an APU. 150
hp, $20,000 or so, 18 GPH. Would have gone nicely on my Jodel, but
with a 15 gallon tank I sure wouldn't have gone far. Not too many were
sold, I think, but others were converted for small homebuilt
helicopters, where the power-to weight ratio was more welcome.
A small propeller has poor efficiency, especially in takeoff and
climb, so serious propeller-driven aircraft use large, slow-turning
props to get the most out of the available horses. It's more efficient
to accelerate a large volume of air to a low speed than a small volume
to a high speed, since prop drag increases with the square of the
increase in speed.
A small turbine has the same drawbacks. That small diameter has a
tiny area, so the gases must be accelerated to a really high speed to
get any useable thrust. That same small diameter also applies more
drag to the flow, the same way a small pipe impedes flow more than a
large one for a given rate of flow. The power turbine that converts
exhaust gas flow to shaft torque is similarly handicapped, so
efficiencies fall off dramatically as diameter goes down. The most
efficient turbines are the really big ones that are driving large,
slow-turning props or large fans (which are often also geared).
So for the money a piston engine is still a better bet, and
probably will be until some totally different principle is invented. I
wish we weren't still burning stuff (1600's steam engine technology)
to get motion, whether turbines or pistons or rockets, but I don't
suppose anyone will have a workable nuclear fusion engine, built by
Lycoming, in my lifetime.
It would probably still have magnetos.

Dan

Jeff > wrote in message >...
> there is a company making small turbo props, I cant remember the name of them,
> but they have a 200 HP one
>
> "Thomas J. Paladino Jr." wrote:
>
> > 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?

Jerry Kurata

June 5th 04, 02:43 PM

AOA and L/D curves are not based on TAS but CAS.

"David CL Francis" > wrote in message
...
> On Thu, 27 May 2004 at 18:20:14 in message
> . net>, Mike Rapoport
> > wrote:
>
> >The airplane efficiency is related to altitude. It takes a lot less
thrust
> >to move an airplane at any given TAS at 30K' where the are is only 30% as
> >dense than at sea level.
>
> Help me here. I am struggling to find out more information but I have a
> bit of a problem with that statement. I probably misunderstand what you
> are saying and I may have it wrong I admit. In essence it is correct but
> you normally fly at much higher TAS at altitude than at sea level.
>
> It seems to me that if you want range you fly the aircraft at the AoA
> that provides the best overall lift/drag ratio.
>
> Let us suppose that is a ratio of 10. Then at the appropriate speed for
> that height the drag (and therefore the thrust requirement) will be one
> tenth of the weight, since in level flight lift must equal weight.
> --
> David CL Francis

J. Hansen

June 8th 04, 02:57 PM

(Rick Durden) wrote in message >...
> Thomas,
>
> There are some smaller turboprops but the economics just aren't there
> to put them into mass production. The market is quite small and the
> specific fuel consumption of a turbine versus a piston means that if
> you put it on your Cessna 210, for example, you can't carry enough
> fuel to get anywhere and still put people in the cabin. Plus, the
> simple cost of the technology and the metals to handle the heat in a
> turbine engine makes it almost impossible to compete with other types
> of engines in that horsepower range.

Actually there is a turboprop conversion for the P210 called the Silver Eagle.
(see http://www.onaircraft.com). The stats look pretty good to me. Cruising
speed of 215 kts and a range of 1030 nm with a full fuel payload of 735 pounds,
or a range of about 780 nm with a payload of 930 pounds (if you don't use the
aux tank added in the conversion). You can even use reverse thrust to back up.
Of course it doesn't come cheap though.