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

[[email protected]]

In rec.aviation.owning R. David Steele /omega> wrote:
> What has happened to the development of the diesel aircraft
> engines? As far as I have seen, only Diamond has a production
> aircraft with diesel engines (they flew one across the Atlantic,
> with 5.76 gph).

See http://www.avweb.com/ the column entitled Motor Head #2: Excerpts
from the Oshkosh Notebook.

> And it looks like the small jets are pushing the turbo props and
> the twin piston engines. Is it a matter of time before it will
> be cheaper to just buy a small jet?

I'm not holding my breath on that one.

What puzzles me is why there doesn't appear to be anyone working on
turbines in the range of 160 to 250 HP for aircraft.

The upside to diesels is Jet-A is cheaper and more available just about
everywhere outside the US.

The downside is they tend to be heavier than the gas engines they would
replace, reducing the usefull load.

Turbines run on Jet-A and tend to be a lot lighter.

Put a 180 HP turbine in a 172 and you would have a real 4 place A/C,
though one with a long, funny looking nose to make the W/B work out.


--
Jim Pennino

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[Dude]

I don't see the fuel burn on the small turbines competing with the diesels,
but there are some attempts at getting close to the Lycosaur level.

Here is one - http://www.innodyn.com/

Don't know anything about them though.

As for light jets pushing down demand for twin piston and turbo props, you
are correct. You mentioned Diamond, and they are going straight after the
light twin and turbine single engine market with their single engine jet.
If you will accept a single engine, the economics seem to make sense to go
that route rather than with an equally expensive Piper or Beech plane.

It will be interesting to see what will happen. Some missions will likely
push folks to stick with the prop planes though.

[Thomas Borchert]

R.,

> What has happened to the development of the diesel aircraft
> engines? As far as I have seen, only Diamond has a production
> aircraft with diesel engines (they flew one across the Atlantic,
> with 5.76 gph).
>

In the European market, Diamond offers both the single-engine DA40 and
the DA42 twin with Thielert Centurion engines. More than 100 of these
engines are flying. in the US, only the DA42 is offered. Also, Thielert
in Europe offers retrofit kits for Cessna 172s and Piper Warriors. Of
those, 30 or so are flying.

All other diesels I know of are not yet available in a certified kit,
although by now the sma retrofit to the 182 might be available.

--
Thomas Borchert (EDDH)

[Dylan Smith]

In article >, wrote:
> Put a 180 HP turbine in a 172 and you would have a real 4 place A/C,
> though one with a long, funny looking nose to make the W/B work out.

The trouble is the missions a C172 flies (typically short distances, low
altitudes) makes a turbine incredibly fuel inefficient - all that useful
load would be taken up by the fully-filled additional tanks you'd need
to fly the same distance as the 180hp piston version. Just take a look
at the turbine Piper Meridian for some of the problems that has - if you
want to take 4 people in a Meridian, you have barely an hour of fuel
with basic IFR reserves. Top the tanks for decent range and it's a 2
person plane.

For normal light GA altitudes, a recip diesel is much better suited -
the extra weight is offset by not needing anywhere near as much fuel,
and it's efficient at the low altitudes we tend to fly at.

--
Dylan Smith, Castletown, Isle of Man
Flying: http://www.dylansmith.net
Frontier Elite Universe: http://www.alioth.net
"Maintain thine airspeed, lest the ground come up and smite thee"

[C Kingsbury]

wrote in message >...
>
> > And it looks like the small jets are pushing the turbo props and
> > the twin piston engines. Is it a matter of time before it will
> > be cheaper to just buy a small jet?
>
> I'm not holding my breath on that one.

Well, they may not compete with 30-year-old twin cessnas selling for
200k, but a new Baron goes for around 1.2 million, so the comparison
is more relevant than you might think.

> What puzzles me is why there doesn't appear to be anyone working on
> turbines in the range of 160 to 250 HP for aircraft.
>...
> Put a 180 HP turbine in a 172 and you would have a real 4 place A/C,
> though one with a long, funny looking nose to make the W/B work out.

The flight profile of a 172- low altitude and low speed- are the
opposite of what a turbine likes to operate in. What you'd have is a
horrendous gas-guzzler, unless you feel like climbing up into the
flight levels.

-cwk.

[Stefan]

C Kingsbury wrote:

> Well, they may not compete with 30-year-old twin cessnas selling for
> 200k, but a new Baron goes for around 1.2 million, so the comparison
> is more relevant than you might think.

Diamond's goal is to sell its D-Jet for under 1 million. However,
operating costs will be a different story I guess.

Stefan

[C J Campbell]

"R. David Steele" /OMEGA> wrote in message
...
> What has happened to the development of the diesel aircraft
> engines? As far as I have seen, only Diamond has a production
> aircraft with diesel engines (they flew one across the Atlantic,
> with 5.76 gph).
>

The DA42 currently has a diesel engine, but Diamond is experimenting with a
Lycoming. Although they say that this would be for the European market only
and no decision has been made on a certification program, the fact is that
American pilots would probably be much more interested in this version. It
offers more power for about the same fuel burn and gas here is not much more
expensive than diesel.

I am very interested in one of these planes, especially the DA42 Observer
camera platform.

> And it looks like the small jets are pushing the turbo props and
> the twin piston engines. Is it a matter of time before it will
> be cheaper to just buy a small jet?

Acquisition cost is one thing; operating cost is another. Turbines use much
more fuel and are far more difficult to insure. There will always be a place
for turboprops like the Caravan or Pilatus and for small piston twins.

[Thomas Borchert]

C,

> Although they say that this would be for the European market only

AFAIK, they say just the opposite (to me, at least): The Lyc version would be
for the US market. It's also a matter of using the DA42 in a training
environment, where pilots still need to be trained for three levers, not the
single one the Thielert has.

> It
> offers more power for about the same fuel burn and gas here is not much more
> expensive than diesel.
>

Huh? Same fuel burn? Hardly.

--
Thomas Borchert (EDDH)

[Kees Mies]

Thomas Borchert > wrote in message >...
> All other diesels I know of are not yet available in a certified kit,
> although by now the sma retrofit to the 182 might be available.
There is at least one, I believe it is either a C172 or C182.
I can not tell the difference, all planes with the wings on top are
just cessnas to me.
Anyway, it is used as a jump plane operating from Seppe(EHSE) with a
SMA engine.
Call sign PH-PAC.

-Kees

[[email protected]]

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.

[Roy Smith]

In article >,
) wrote:

> 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.

It is certainly possible to build much larger piston engines than that.
How about http://www.bath.ac.uk/~ccsshb/12cyl/

[[email protected]]

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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[Stefan]

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

[[email protected]]

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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[Mike Rapoport]

> wrote in message
...
> 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


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?

Mike
MU-2

[Mike Rapoport]

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
>
> Remove -spam-sux to reply.

[[email protected]]

In rec.aviation.owning Mike Rapoport > wrote:

> > wrote in message
> ...
> >
> > 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

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[[email protected]]

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.

[Mike Rapoport]

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

[Mike Rapoport]

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://www.pwc.ca/en/3_0/3_0_2/3_0_2_1_2.asp_2/3_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.

[[email protected]]

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

[[email protected]]

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.

[[email protected]]

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://www.pwc.ca/en/3_0/3_0_2/3_0_2_1_2.asp_2/3_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.

[[email protected]]

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.

[Mike Rapoport]

> 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

[Mike Rapoport]

> 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://www.pwc.ca/en/3_0/3_0_2/3_0_2_1_2.asp_2/3_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

[[email protected]]

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://www.pwc.ca/en/3_0/3_0_2/3_0_2_1_2.asp_2/3_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.

[[email protected]]

In rec.aviation.owning Mike Rapoport > wrote:

> > wrote in message
> ...

<snip>

> > 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.

True.

> > 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.

Your first sentence overlooks the fact that turbines are currently
competitive at the Caravan level, but I pretty much agree with the
rest.

OK, let's say I buy into about 400hp as the "up to now" crossover point.

Given the current fuel cost differential, where would you expect that point
to move to assuming the engines were available?

--
Jim Pennino

Remove -spam-sux to reply.

[G.R. Patterson III]

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.

[Mike Rapoport]

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://www.pwc.ca/en/3_0/3_0_2/3_0_2_1_2.asp_2/3_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 in message
...
> In rec.aviation.owning Mike Rapoport > wrote:
>
>> > wrote in message
>> ...
>
> <snip>
>
>> > 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.
>
> True.
>
>> > 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.
>
> Your first sentence overlooks the fact that turbines are currently
> competitive at the Caravan level, but I pretty much agree with the
> rest.
>

I don's see that I've overlooked something relative to the Caravan. The
Caravan has a 940hp engine. There is currently no suitable piston engine to
power such a large, single engine airplane. It couldn't be anything other
than a turbine.


> OK, let's say I buy into about 400hp as the "up to now" crossover point.

Even 400hp is not an economic crossover. It just represents the limit of
what is practical in small aircraft turbine engines. The 400hp Allison
turbine is really a helicopter engine anyway. The smallest practical
application seems to be the around the Meridian/Caravan/TBM 700 size range
and these engines are all around 1000hp. The engineers designing airplanes
are not totally stupid, if it made sense to install 400hp turbines they
would do so.

> Given the current fuel cost differential, where would you expect that
> point
> to move to assuming the engines were available?
>
It depends on how powerful diesels get for aircraft. Under several thousand
horsepower the diesel will always be cheaper and more fuel efficient than
anything else. There probably isn't an economic crossover point for
gasoline engines either unless the fuel price spread is artificially raised
even higher than it is now. You have to remember that the HSI and overhaul
costs on turbines is much greater than the cost of overhaul on a piston
engine. Given that the small turbine is going to consume a lot more fuel
and cost more to build and maintain it will never be cheaper.

Turbines will be used in applications where cost is a secondary
consideration to high power and high reliability. The gas turbine is a
mature 60yr old technology, huge improvements in cost or efficiency are
somewhat unlikely.

For a really efficient turbine see http://www.turbokart.com/about_ge90.htm


> Jim Pennino
>
> Remove -spam-sux to reply.

[Roy Smith]

"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 are:

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.

[[email protected]]

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 are:

> 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:
> 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.

Well, the Rabbit I had was built with exactly the same block, pistons,
crank, etc, as the gas version. The basicly just slapped a shallower
head on the thing to increase the compression ratio.

We drove the car into the ground at about 160k miles. We replaced
pretty much all of the accessories (starter, water pump, alternator,
radiator, etc) at least once, and the clutch wore out at about 110k, and
the body was more rust than steel, and the electrical system was a mess,
but the core engine was just fine.

The only thing that ever happened to the engine core was a blown head
gasket, but that was really my fault. We had chronic overheating
problems due to a leak in the cooling system that we didn't fix for a
while. Eventually, the gasket said, "OK, if you want to keep abusing me
like that, I'm outta here".

[[email protected]]

In rec.aviation.owning Roy Smith > wrote:
> wrote:
> > 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.

> Well, the Rabbit I had was built with exactly the same block, pistons,
> crank, etc, as the gas version. The basicly just slapped a shallower
> head on the thing to increase the compression ratio.

> We drove the car into the ground at about 160k miles. We replaced
> pretty much all of the accessories (starter, water pump, alternator,
> radiator, etc) at least once, and the clutch wore out at about 110k, and
> the body was more rust than steel, and the electrical system was a mess,
> but the core engine was just fine.

> The only thing that ever happened to the engine core was a blown head
> gasket, but that was really my fault. We had chronic overheating
> problems due to a leak in the cooling system that we didn't fix for a
> while. Eventually, the gasket said, "OK, if you want to keep abusing me
> like that, I'm outta here".

The debacle I'm talking about was Chevey's (?) attempt to power pickups
with a gas engine converted to diesel by basically the same method.

You can get away with this if the basic engine is strong to start with
and you're not trying to pull too many horses out of it.

--
Jim Pennino

Remove -spam-sux to reply.

[C Kingsbury]

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

> > 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.

Large mobile electric generators are another common ground-based
application. Don't forget that weight and size are also relatively
unimportant in these applications, which makes a lot of engineering
problems much easier.

> > 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.
>
> Your first sentence overlooks the fact that turbines are currently
> competitive at the Caravan level, but I pretty much agree with the
> rest.

Airplanes are designed around engines. Want to know what a
piston-powered Caravan looks like? It's called a Cessna 402.

The 'van is a pretty idiosyncratic plane- basically a flying box
truck. Great for hauling a heavy load a short distance into a small
strip. Sure, there's a bunch of rich boys out there flying them
around, too, but I suspect economics do not factor into their decision
in any way. The guys putting these things on amphibious floats with
executive interiors could probably afford to operate them even if they
only ran on vintage Champagne. A mainstream pilot can get a hell of a
lot more utility out of a SR-22 or 206 for probably 1/3rd or less of
the costs.

> OK, let's say I buy into about 400hp as the "up to now" crossover point.
>
> Given the current fuel cost differential, where would you expect that point
> to move to assuming the engines were available?

Considering that all the aviation diesels are being built to run on
jet-A, I'd say it's going to stay right where it is.

The only compromise we have to make with the diesels is to give up a
little useful load, otherwise they are equal or better on all counts.
Why isn't that enough for everybody to be excited about?

Best,
-cwk.

[David Lesher]

>> Well, the Rabbit I had was built with exactly the same block, pistons,
>> crank, etc, as the gas version. The basicly just slapped a shallower
>> head on the thing to increase the compression ratio.

I could have sworn the Rabbit Diesel had a way different engine,
but I could be wrong.


>The debacle I'm talking about was Chevey's (?) attempt to power pickups
>with a gas engine converted to diesel by basically the same method.

Not pickups AFAIK; station wagons and maybe sedans. This was Roger
Smith at his finest.

A friend bought one with a dead@55000 mile engine. It was an stock
gas block; no where NEAR beefy enough. The blowby was so bad, the
engine soiled itself at every seal; he'd get 250 miles to the quart;
all leakage. At least it didn't rust!

It had a one-of-kind starter and flywheel. The distributor was
replaced with a vacuum pump to drive the HVAC door flaps. It had
dual batteries, designed wrong. The brakes were run off the PS pump,
so when the engine stalled, stop NOW.

He put in a gas 350 and drove it for 10 years more.

--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

[[email protected]]

In rec.aviation.owning David Lesher > wrote:

> >> Well, the Rabbit I had was built with exactly the same block, pistons,
> >> crank, etc, as the gas version. The basicly just slapped a shallower
> >> head on the thing to increase the compression ratio.

> I could have sworn the Rabbit Diesel had a way different engine,
> but I could be wrong.


> >The debacle I'm talking about was Chevey's (?) attempt to power pickups
> >with a gas engine converted to diesel by basically the same method.

> Not pickups AFAIK; station wagons and maybe sedans. This was Roger
> Smith at his finest.

> A friend bought one with a dead@55000 mile engine. It was an stock
> gas block; no where NEAR beefy enough. The blowby was so bad, the
> engine soiled itself at every seal; he'd get 250 miles to the quart;
> all leakage. At least it didn't rust!

> It had a one-of-kind starter and flywheel. The distributor was
> replaced with a vacuum pump to drive the HVAC door flaps. It had
> dual batteries, designed wrong. The brakes were run off the PS pump,
> so when the engine stalled, stop NOW.

> He put in a gas 350 and drove it for 10 years more.

> --
> A host is a host from coast to
> & no one will talk to a host that's close........[v].(301) 56-LINUX
> Unless the host (that isn't close).........................pob 1433
> is busy, hung or dead....................................20915-1433

There were pickups.

A friend bought one new and had the engine blow at about 40k miles.

Thanks to California smog laws, he found his choices were replace it
with another new diesel (big bucks) or get an old gas engine and convert
it to propane and try to recover some of the investment. This was way
before 50k warranties.

--
Jim Pennino

Remove -spam-sux to reply.

[Newps]

wrote:


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

It is a problem. It is solved by heating the fuel.

[David Lesher]

writes:



>There were pickups.

>A friend bought one new and had the engine blow at about 40k miles.

>Thanks to California smog laws, he found his choices were replace it
>with another new diesel (big bucks) or get an old gas engine and convert
>it to propane and try to recover some of the investment. This was way
>before 50k warranties.


Err, my friend bought the car from an office neighbor, after it had
been stolen and partially stripped. [Wheels, radio... He actually
drove it home on 4 borrowed space-saver spares...]

About a month before, the injector pump croaked. Amazingly, when it
arrived at the dealership on a towtruck, the speedometer said 49,986
miles. I disclaim any knowledge as to how that could have been.

They bitched, but put in a new pump under warranty. [By that time,
I suspected they rather all the OlsmoDiesels went to Burning Man or
similar.] I can't recall what was [not] covered, but that pump
was.

The Diesels that last, the Mercedes 240D, for example, are group-up
designs. And they do weigh more than gas blocks.

Any talk about Jet-A jelling sounds....bogus.. There's an ongoing
issue with DC-9's and 'cold-soak' of the fuel; causing icing
on short turn arounds. You'd think they'd suffer from any jelling
but...
--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

[Jim Knoyle]

"Newps" > wrote in message
...
>
>
> wrote:
>
>
> >
> > If gelling of Jet-A were a problem, airliners would be falling out of
> > the sky on a regular basis.
>
> It is a problem. It is solved by heating the fuel.
>
.... and since hydraulic fluid needs cooling they locate the hyd.cooling
coils inside the fuel tank(s). That helps solve two problems.

[Bob Moore]

Excerpted from other posts.......

>Any talk about Jet-A jelling sounds....bogus..

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

>It is a problem. It is solved by heating the fuel.


It is a problem on long flights at high altitudes and high
latitudes. The fuel filters on the Boeings that I flew
were heated to prevent the screens from "waxing" over.
The fuel itself was not heated. The filters were heated
with hot engine bleed air and heated for one minute every
thirty minutes when the fuel temperature dropped below zero
degrees celsius.

At PanAm, we had three procedures for dealing with extremely
low temperatures across the North Atlantic.

1. Re-route to a more southernly (warmer) route.
2. Reduce altitude to a warmer OAT.
3. Increase speed for a greater friction effect on the tanks.
At around M.80, the Ram Air Temperature is about thirty
degrees higher than the True Air Temperature.

All of these required extra fuel of course and we depended
on the Dispatcher providing a good Temp Aloft forecast.

Bob Moore
ATP B-707 B-727
PanAm (retired)

[Dude]

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://www.pwc.ca/en/3_0/3_0_2/3_0_2_1_2.asp_2/3_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]

"C Kingsbury" > wrote in message
om...
> wrote in message
> >...
>> In rec.aviation.owning Mike Rapoport >
>> wrote:
>>
>> > > wrote in message
>> > ...
>
>> > 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.
>
> Large mobile electric generators are another common ground-based
> application. Don't forget that weight and size are also relatively
> unimportant in these applications, which makes a lot of engineering
> problems much easier.
>
>> > 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.
>>
>> Your first sentence overlooks the fact that turbines are currently
>> competitive at the Caravan level, but I pretty much agree with the
>> rest.
>
> Airplanes are designed around engines. Want to know what a
> piston-powered Caravan looks like? It's called a Cessna 402.
>
> The 'van is a pretty idiosyncratic plane- basically a flying box
> truck. Great for hauling a heavy load a short distance into a small
> strip. Sure, there's a bunch of rich boys out there flying them
> around, too, but I suspect economics do not factor into their decision
> in any way. The guys putting these things on amphibious floats with
> executive interiors could probably afford to operate them even if they
> only ran on vintage Champagne. A mainstream pilot can get a hell of a
> lot more utility out of a SR-22 or 206 for probably 1/3rd or less of
> the costs.
>
>> OK, let's say I buy into about 400hp as the "up to now" crossover point.
>>
>> Given the current fuel cost differential, where would you expect that
>> point
>> to move to assuming the engines were available?
>
> Considering that all the aviation diesels are being built to run on
> jet-A, I'd say it's going to stay right where it is.
>
> The only compromise we have to make with the diesels is to give up a
> little useful load, otherwise they are equal or better on all counts.
> Why isn't that enough for everybody to be excited about?
>
> Best,
> -cwk.

Why do we have to give up useful load? On most flights of any duration, the
savings in fuel required will more than make up for the increase in engine
weight (if any)

Mike
MU-2

[Paul Sengupta]

> wrote in message
...
> 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

[Michael Houghton]

Howdy!

In article >,
Roy Smith > wrote:
>In article >,
> ) wrote:
>
>> 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.
>
>It is certainly possible to build much larger piston engines than that.
>How about http://www.bath.ac.uk/~ccsshb/12cyl/

But it is a *little bit* impractical as an *aircraft* engine...

yours,
Michael


--
Michael and MJ Houghton | Herveus d'Ormonde and Megan O'Donnelly
| White Wolf and the Phoenix
Bowie, MD, USA | Tablet and Inkle bands, and other stuff
| http://www.radix.net/~herveus/

[Stefan]

Roy Smith wrote:

> It is certainly possible to build much larger piston engines than that.
> How about http://www.bath.ac.uk/~ccsshb/12cyl/

Ah! I've always wondered how that Antonov 225 Mrija was powered...

Stefan

[Ernie Ganas]

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://www.pwc.ca/en/3_0/3_0_2/3_0_2_1_2.asp_2/3_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.
>
>
>

[Pete Zaitcev]

On Fri, 17 Sep 2004 12:13:49 -0700, 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.
>[...]

This is not my recollection. What killed auto turbines was their
spool-up and spool-down time, and gearboxes for 20,000 RPMs.

BTW, remember the rail engines. The turbines there tried to compete
well into 1960s. They were killed by their short overhaul time,
not fuel consumption.

-- Pete

[[email protected]]

In rec.aviation.owning Pete Zaitcev > wrote:
> On Fri, 17 Sep 2004 12:13:49 -0700, 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.
> >[...]

> This is not my recollection. What killed auto turbines was their
> spool-up and spool-down time, and gearboxes for 20,000 RPMs.

> BTW, remember the rail engines. The turbines there tried to compete
> well into 1960s. They were killed by their short overhaul time,
> not fuel consumption.

> -- Pete

According to a guy I worked with who worked on the Chrysler turbine car,
the problem that was the straw that broke the camel's back was the under
the hood temperature being too high for all the other stuff under the
hood, i.e. wiper motors, relays, etc.

--
Jim Pennino

Remove -spam-sux to reply.

[Fritz]

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

[Fritz]

>> 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

[Ted Azito]

>
> AFAIK, they say just the opposite (to me, at least): The Lyc version would be
> for the US market. It's also a matter of using the DA42 in a training
> environment, where pilots still need to be trained for three levers, not the
> single one the Thielert has.

In a sane world the rule would be "single pilot IFR=single lever power control".