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

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In rec.aviation.owning Mike Rapoport wrote:

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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


You are missing the point. Everyone agrees that small turbines can be
built, the issue is fuel consumption. What is the specific fuel
consumption
per lb of thrust?

Not quite "everyone" has signed on to that notion and you are one of few
that has wanted to talk about numbers as opposed to making sweeping
statements.

For the 16.5 lb thrust engine it is 1.8 lb/hr-lb thrust, but I doubt fuel
efficiency is a design criteria in a model airplane engine.

The question remains, at what HP level, based on the physics of the
engines,
does the crossover from piston to turbine occur?

As additional criteria, assume specific fuel consumption is the most
important parameter and that the A/C spends the majority of its time in
flight not doing touch and goes.


--
Jim Pennino



I think that you can look at the market to see where the crossover occurs.
THere are currently no production piston aircraft engines over 450hp and
there are no aircraft turbines under 400hp.

Mike
MU-2

In rec.aviation.owning Mike Rapoport wrote:

wrote in message
...

snip

The question remains, at what HP level, based on the physics of the
engines,
does the crossover from piston to turbine occur?

As additional criteria, assume specific fuel consumption is the most
important parameter and that the A/C spends the majority of its time in
flight not doing touch and goes.


I think that you can look at the market to see where the crossover occurs.
THere are currently no production piston aircraft engines over 450hp and
there are no aircraft turbines under 400hp.

There's lots of ground turbines under 400hp so we know there's a market
there; i.e. they must be practical and competive with pistons or they
wouldn't sell.

I thought the Chinese were still making a big radial, but I could be
wrong on that one and it is a bit of a nit.

If gasoline hadn't risen to twice the price of Jet-A (at least in parts
of Europe), no one would be seriously discussing diesel engines for
aircraft or actively developing them as several manufacturers are now.

So put it this way, if it were the turbine makers instead of the diesel
makers that jumped on this bandwagon, what would be their smallest
engine?


--
Jim Pennino

Remove -spam-sux to reply.

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If gasoline hadn't risen to twice the price of Jet-A (at least in parts
of Europe)

3 times. At least for avgas.

Paul

I think that you can look at the market to see where the crossover
occurs.
THere are currently no production piston aircraft engines over 450hp
and
there are no aircraft turbines under 400hp.

There's lots of ground turbines under 400hp so we know there's a market
there; [...]

A ground turbine runs at almost constant speed, near its design point,
so even at small dimension can still be fuel efficient. Part load fuel
consumption of a gas turbine is a bit too high, particularly for GA
aircraft (considering their flight pprofile).

--
Fritz

"Fritz" wrote in message
...
A ground turbine runs at almost constant speed, near its design point,
so even at small dimension can still be fuel efficient. Part load fuel
consumption of a gas turbine is a bit too high, particularly for GA
aircraft (considering their flight pprofile).

Hmmm...define "fuel efficient"?

Your comment brings to mind the Toyota Prius hybrid engine. It essentially
has a "continuously variable transmission" that doesn't involve a
complicated, maintenance-hungry belt or chain and pully system.

I wonder if the answer to bringing turbine engines to small airplanes might
not be using a hybrid system. The weight of the batteries (which is
substantial) is offset by the relatively low weight of the rest of the power
train. The engine would only run during climbs, and when the batteries need
to be recharged. Biggest problem I see right off the bat is the problem of
starting and stopping the turbine frequently...my understanding is that
there are "issues" there, but I don't know what they are, or whether they
can be addressed by design.

Using such a system, a turbine could be run "at almost constant speed, near
its design point", while accomodating a variety of power settings.

All that said, someone else mentioned turbine-engined locomotives; that's a
much bigger power demand and yet somehow diesel-electric engines wound up
the standard. I suppose looking at the history of train locomotives might
offer some insight into how feasible hybrid technology might be for
airplanes. It might be that there are some unsolveable problems, or it
might be that we're at a stage in engine development now where things that
used to be problems aren't anymore.

Pete