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

In rec.aviation.owning Mike Rapoport wrote:
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

OK, that explains that.

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

Aha, numbers!

So if one assumes the motivation to switch from a piston to a turbine is
the price of gas is roughly twice Jet-A, the crossover point would be a
turbine that did about .8 (to allow for the weight difference in the fuels).

Any idea how small (in appropriate terms of hp) current technology can make
a turbine with that consumption?


--
Jim Pennino

Remove -spam-sux to reply.

wrote in message
...
In rec.aviation.owning Mike Rapoport wrote:
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

OK, that explains that.

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

Aha, numbers!

So if one assumes the motivation to switch from a piston to a turbine is
the price of gas is roughly twice Jet-A, the crossover point would be a
turbine that did about .8 (to allow for the weight difference in the
fuels).

Any idea how small (in appropriate terms of hp) current technology can
make
a turbine with that consumption?


--
Jim Pennino

That would be the economic crossover point if the engines cost the same. Of
course a plane that needed twice the fuel (in lbs) to achieve the same
performance wouldn't have much useful load or range.

Mike
MU-2

In rec.aviation.owning Mike Rapoport wrote:

wrote in message
...
In rec.aviation.owning Mike Rapoport wrote:
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

OK, that explains that.

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

Aha, numbers!

So if one assumes the motivation to switch from a piston to a turbine is
the price of gas is roughly twice Jet-A, the crossover point would be a
turbine that did about .8 (to allow for the weight difference in the
fuels).

Any idea how small (in appropriate terms of hp) current technology can
make
a turbine with that consumption?


--
Jim Pennino

That would be the economic crossover point if the engines cost the same. Of
course a plane that needed twice the fuel (in lbs) to achieve the same
performance wouldn't have much useful load or range.

Dropping a diesel in an airplane costs a bunch. The justification is the
cost is recovered in lowered fuel costs.

Your second point is certainly valid though and a minor problem with the
diesels according to the AVweb article on them.


--
Jim Pennino

Remove -spam-sux to reply.

A diesel doesn't cost any more that a piston engine. A STC'd conversion
costs more but, in a new airplane the cost should be the same.

Mike
MU-2


wrote in message
...
In rec.aviation.owning Mike Rapoport wrote:

wrote in message
...
In rec.aviation.owning Mike Rapoport
wrote:
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

OK, that explains that.

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

Aha, numbers!

So if one assumes the motivation to switch from a piston to a turbine
is
the price of gas is roughly twice Jet-A, the crossover point would be a
turbine that did about .8 (to allow for the weight difference in the
fuels).

Any idea how small (in appropriate terms of hp) current technology can
make
a turbine with that consumption?


--
Jim Pennino

That would be the economic crossover point if the engines cost the same.
Of
course a plane that needed twice the fuel (in lbs) to achieve the same
performance wouldn't have much useful load or range.

Dropping a diesel in an airplane costs a bunch. The justification is the
cost is recovered in lowered fuel costs.

Your second point is certainly valid though and a minor problem with the
diesels according to the AVweb article on them.


--
Jim Pennino

Remove -spam-sux to reply.

"Mike Rapoport" wrote:
A diesel doesn't cost any more that a piston engine. A STC'd conversion
costs more but, in a new airplane the cost should be the same.

Right. Some people seem to think that diesels are somehow magic. The
basic construction of a diesel and a gasoline engine are almost
identical. The only differences I can think of a

1) Higher compression ratio. This could be done with a longer-throw
crankshaft, a taller piston, a lower head, or some combination of all
three.

2) A fancier (higher-pressure) injector pump.

3) No spark plugs. Which means no ignition system (be it electronic or
magnetos).

4) Possibly the addition of some kind of starting assist such as glow
plugs.

The biggest problem I can see with a diesel is cold-weather operation.
I used to have a diesel car (1980's era VW Rabbit). It was a bitch to
start in really cold weather. If the glow plugs were in good shape, you
were fine down to about 20 F. Once you got down below about 10 F, you
probably weren't going to get it started without a preheat.

Somewhere down around 15 F, normal diesel fuel starts to gel. These are
temperatures commonly experienced aloft even at the altitudes spam cans
fly at in the winter in temperate climates. It would be real bad news
to get the engine going, only to have the fuel gel up in the tanks when
you reached cruising altitude. But, I suppose the Jet-A folks have
figured out the right additives to solve that problem.

In rec.aviation.owning Roy Smith wrote:
"Mike Rapoport" wrote:
A diesel doesn't cost any more that a piston engine. A STC'd conversion
costs more but, in a new airplane the cost should be the same.

Right. Some people seem to think that diesels are somehow magic. The
basic construction of a diesel and a gasoline engine are almost
identical. The only differences I can think of a

1) Higher compression ratio. This could be done with a longer-throw
crankshaft, a taller piston, a lower head, or some combination of all
three.

2) A fancier (higher-pressure) injector pump.

3) No spark plugs. Which means no ignition system (be it electronic or
magnetos).

4) Possibly the addition of some kind of starting assist such as glow
plugs.

The biggest problem I can see with a diesel is cold-weather operation.
I used to have a diesel car (1980's era VW Rabbit). It was a bitch to
start in really cold weather. If the glow plugs were in good shape, you
were fine down to about 20 F. Once you got down below about 10 F, you
probably weren't going to get it started without a preheat.

Somewhere down around 15 F, normal diesel fuel starts to gel. These are
temperatures commonly experienced aloft even at the altitudes spam cans
fly at in the winter in temperate climates. It would be real bad news
to get the engine going, only to have the fuel gel up in the tanks when
you reached cruising altitude. But, I suppose the Jet-A folks have
figured out the right additives to solve that problem.

Because of the higher compression ratio, a diesel has to be built
"beefier" than a gas engine to last as the automakers found out when
they tried a direct conversion on their gas engines in the 80's.

All the aircraft diesels have a constant speed prop and FADEC.

If gelling of Jet-A were a problem, airliners would be falling out of
the sky on a regular basis.

--
Jim Pennino

Remove -spam-sux to reply.

Roy Smith wrote:

But, I suppose the Jet-A folks have
figured out the right additives to solve that problem.

Oil-fuel heat exchange?

--
Fritz

Aha,

But much of the cost is due to changing components other than the engine.

If you had a glass cockpit, and fuel system that were compatible to start
with, then all you would need to change was the engine, mount, prop, sending
units, and software.

That would seem to be less than what the europeans are giong through to put
the Theilert in a skyhawk.




wrote in message
...
In rec.aviation.owning Mike Rapoport wrote:

wrote in message
...
In rec.aviation.owning Mike Rapoport
wrote:
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

OK, that explains that.

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

Aha, numbers!

So if one assumes the motivation to switch from a piston to a turbine
is
the price of gas is roughly twice Jet-A, the crossover point would be
a
turbine that did about .8 (to allow for the weight difference in the
fuels).

Any idea how small (in appropriate terms of hp) current technology can
make
a turbine with that consumption?


--
Jim Pennino

That would be the economic crossover point if the engines cost the same.
Of
course a plane that needed twice the fuel (in lbs) to achieve the same
performance wouldn't have much useful load or range.

Dropping a diesel in an airplane costs a bunch. The justification is the
cost is recovered in lowered fuel costs.

Your second point is certainly valid though and a minor problem with the
diesels according to the AVweb article on them.


--
Jim Pennino

Remove -spam-sux to reply.