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

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

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.

wrote

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

Care to calculate the pounds of thrust per pound of fuel for that turbojet,
then do the same for a piston engine?
--
Jim in NC


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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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Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.762 / Virus Database: 510 - Release Date: 9/13/2004

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.

In rec.aviation.owning wrote:
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.

That's probably true, but Cessna's page just says SHP 675.

I shouldn't expect real technical information from a marketing page.

--
Jim Pennino

Remove -spam-sux to reply.

wrote in message
...
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.


A lot of them are used to power natural gas compressors way out in the
middle of nowhere and reliability is much more important than fuel
efficiency and you have a large suitable fuel supply availible.

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?

Given the high initial cost of turbines and the hgiher fuel comsumption, I
doubt that turbines would be competitive with gasoline engines given current
price differentials between the two fuels. The beauty of a diesel aircraft
engine is that it should cost the same as a gas engine, has fewer parts,
uses less fuel and lasts longer. The turbine engine is more reliable but
costs more and uses more fuel. The lower the hp the less competitive the
turbine gets against the diesel.

Mike
MU-2

wrote

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).
--
Jim Pennino

You are not taking into account the weight problem. If an aircraft designed
to carry 70 gallons, instead has to carry 140 gallons, there will be no
weight capacity left to carry the pilot, let alone anything else.
--
Jim in NC


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Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.762 / Virus Database: 510 - Release Date: 9/13/2004

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