Why are there no small turboprops?

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.

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.

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

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

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.