Why are there no small turboprops?

"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.

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

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

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.

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.

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.

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.

"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.