Diesel aircraft engines and are the light jets pushing out the twins?

In rec.aviation.owning wrote:
A gas turbine scales up easily and but is nearly impossible to scale
down. The auto manuacturers found that out in the 1940s - remember
the "car of the future" on the covers of Popular Science et al?
Turbines for cars are further away now than they were 55 years ago.
The turbine suffers from excessive fuel consumption at part throttle
(the piston engine is incredibly flexible that way)and in smaller HP
installations.

So much of the useful load of an aircraft is fuel, that fuel
efficiency is very important for overall mission performance.

The problem of an engine is to find the most efficient way to expand a
certain flow rate of compressed hot gas to atmospheric pressures. A
turbine can do this with large mass flow rates, but as the flow rates
become smaller, the turbine speeds (rpm) must increase enormously and
the centrifugal accelerations get out of hand. On the other hand, a
piston can process an expansion efficiently with small flow rates.

Think of it this way - a model airplane engine can be made to run with
1/20 of a cubic inch (.049 cu inch to even .010 cu inch), but piston
engine aircraft became impractical above a few thousand HP. That is
the range of practicality for a piston concept.

An engineering prof once said - if the gas turbine had been invented
first, the piston engine would have been looked on an ingeneous
solution to the turbine's material and speed and power range problems.

Diesels may eventually make it. They have a weight problem that may
be offset by a lower specific fuel consumption, but for a given
operating condition, spark ignition engines can nearly approach the
consumption of diesels by using turbo compounding and operation only
at full throttle.

While not quite a .049, here's a 3.7" in diameter, 2.6 lb turbine
that produces 16.5 lb of thrust.

http://jetcatusa.sitewavesonline.net/p70.html

Their biggest turbine is 5.12", 5 lb, and produces 45 lb of thrust.

Here's another outfit that sells a 3.5" diameter, 7.25" long, 1.9 lb
turbine with 11.4 lb of thrust.

http://www.swbturbines.com/model_turbines.htm

Now granted these are turbojets, not turboprops, but it appears to me
that making small turbines is possible...


--
Jim Pennino

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wrote:

Now granted these are turbojets, not turboprops, but it appears to me
that making small turbines is possible...

Nobody ever said that it's not possible. It's just not economical and
will never be.

Stefan

In rec.aviation.owning Stefan wrote:
wrote:

Now granted these are turbojets, not turboprops, but it appears to me
that making small turbines is possible...

Nobody ever said that it's not possible. It's just not economical and
will never be.

Stefan

Several people have said that but I've yet to see any analysis (with
numbers) to back up that contention.

Since (current) turbines are terribly inefficient at low throttle, I can
see the problem with an aircraft that spends most of the time doing
touch and goes.

But where is the crossover point as dictated by the physics of turbines?

C-182? C-209? Caravan? Whoops, that last one is already a turbine.

--
Jim Pennino

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About the size of the Caravan 900hp+

Mike
MU-2

wrote in message
...
In rec.aviation.owning Stefan wrote:
wrote:

Now granted these are turbojets, not turboprops, but it appears to me
that making small turbines is possible...

Nobody ever said that it's not possible. It's just not economical and
will never be.

Stefan

Several people have said that but I've yet to see any analysis (with
numbers) to back up that contention.

Since (current) turbines are terribly inefficient at low throttle, I can
see the problem with an aircraft that spends most of the time doing
touch and goes.

But where is the crossover point as dictated by the physics of turbines?

C-182? C-209? Caravan? Whoops, that last one is already a turbine.

--
Jim Pennino

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In rec.aviation.owning Mike Rapoport wrote:
About the size of the Caravan 900hp+

Mike
MU-2

According to the Cessna website, the current Caravan is 675hp.

--
Jim Pennino

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The Caravan has a 940hp engine flat rated to 675hp. Turbines are typically
flat rated so that the engine can make rated power to reasonable altitudes
and temperatures without having to design the gearbox for the full
thermodynamic horsepower. To keep the comparison with piston engines apples
to apples you need to use thermodynamic ratings.

http://www.pwc.ca/en/3_0/3_0http://w.../3_0_2_1_2.asp

To put some numbers on things, the engines in my MU-2 have a specific fuel
consumption of .55lb/hp/hr and a piston engine is about .45 and diesels can
be under .40. Huge (ship) diesels can be under .30. Compare your model
aircraft engines with the TFE731-60 used on the Falcon 900EX which uses
..405lb/lb thrust/hr

Mike
MU-2


wrote in message
...
In rec.aviation.owning Mike Rapoport wrote:
About the size of the Caravan 900hp+

Mike
MU-2

According to the Cessna website, the current Caravan is 675hp.

--
Jim Pennino

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Mike,

TCM IO-520/550's running LOP are about .39-.40 BPSC according to the GAMI
folks, the SEMA engine is about .33-.35 from their specs. At 70K for their
engine conversion and the cost of JetA being within 10% of the cost of 100LL
at most GA airports I ageree with you and don't think we'll see a lot
diesel's in the near future.

The Diamond Twin really impresses me, can' t wait for an independent
(non-Flying or other slick mag) pilot report to see how it really does.

Ernie
BE36 E-160
KDVO


"Mike Rapoport" wrote in message
k.net...
The Caravan has a 940hp engine flat rated to 675hp. Turbines are typically
flat rated so that the engine can make rated power to reasonable altitudes
and temperatures without having to design the gearbox for the full
thermodynamic horsepower. To keep the comparison with piston engines
apples to apples you need to use thermodynamic ratings.

http://www.pwc.ca/en/3_0/3_0http://w.../3_0_2_1_2.asp

To put some numbers on things, the engines in my MU-2 have a specific fuel
consumption of .55lb/hp/hr and a piston engine is about .45 and diesels
can be under .40. Huge (ship) diesels can be under .30. Compare your
model aircraft engines with the TFE731-60 used on the Falcon 900EX which
uses .405lb/lb thrust/hr

Mike
MU-2


wrote in message
...
In rec.aviation.owning Mike Rapoport
wrote:
About the size of the Caravan 900hp+

Mike
MU-2

According to the Cessna website, the current Caravan is 675hp.

--
Jim Pennino

Remove -spam-sux to reply.

On Fri, 17 Sep 2004 22:31:17 +0000 (UTC),
wrote:

In rec.aviation.owning Mike Rapoport wrote:
About the size of the Caravan 900hp+

Mike
MU-2

According to the Cessna website, the current Caravan is 675hp.

According to PWCa's website:

PT6A-114A

Take-off rating
Thermo ESHP 940
Mechanical SHP 675
Shaft RPM 1900

Perhaps Mr. Rapoport has spent some time driving behind a turbo-prop
(or two) and is a little more familiar with what these numbers mean
than you are.

TC

wrote in message
...
In rec.aviation.owning Mike Rapoport wrote:
About the size of the Caravan 900hp+

Mike
MU-2

According to the Cessna website, the current Caravan is 675hp.

--
Jim Pennino

What is the useful load left over of a Caravan, after you fuel it for a 900
NM plus reserves trip?

Oh, also, how about stopping the cross posting. Pick one.
--
Jim in NC


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wrote:

But where is the crossover point as dictated by the physics of turbines?

Allison makes a 420 hp unit. That's about as small as they go.

C-182? C-209? Caravan? Whoops, that last one is already a turbine.

Maule M-7.

George Patterson
If a man gets into a fight 3,000 miles away from home, he *had* to have
been looking for it.