Why are there no small turboprops?

On Tue, 25 May 2004, Tom Sixkiller wrote:


"Robert M. Gary" wrote in message
om...
"Mike Rapoport" wrote in message
link.net...

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.

"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.

"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

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

"Gerald Sylvester" wrote in message
ink.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

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

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.

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

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.

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

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.