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

Remove -spam-sux to reply.

[Peter Duniho]

> 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.

Me either. But if you believe the manufacturer's claims, it is just a
matter of time. Several of the "mini jet" designs under development are
cheaper than the existing turboprop models, single or twin, and cost about
the same as new piston twins.

Of course, you can't actually buy any of them right now, and it remains to
be seen what they will actually cost if and when they make it to market.

> 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.

GA Flyer just included an "engines in development" article as part of their
Oshkosh coverage, and had a picture of exactly that, as well as a mention in
the article of the company producing the small turbines (I think they said
all for turboprop installations).

They are out there...you just need to look. Don't get distracted by the
lack of certificated engines, or lack of interest in certification. Not all
of the engine research and development going on is aimed at the certificated
market.

Pete

[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

[Mike Rapoport]

"Peter Duniho" > wrote in message
...
> > 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.
>
> Me either. But if you believe the manufacturer's claims, it is just a
> matter of time. Several of the "mini jet" designs under development are
> cheaper than the existing turboprop models, single or twin, and cost about
> the same as new piston twins.
>
> Of course, you can't actually buy any of them right now, and it remains to
> be seen what they will actually cost if and when they make it to market.
>
>> 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.

Small turbines are inherently inefficient so you are unlikely to see them in
this power range. The fuel consumption might be double that of a diesel.

Mike
MU-2


>
> GA Flyer just included an "engines in development" article as part of
> their
> Oshkosh coverage, and had a picture of exactly that, as well as a mention
> in
> the article of the company producing the small turbines (I think they said
> all for turboprop installations).
>
> They are out there...you just need to look. Don't get distracted by the
> lack of certificated engines, or lack of interest in certification. Not
> all
> of the engine research and development going on is aimed at the
> certificated
> market.
>
> Pete
>
>

[Peter Duniho]

"Mike Rapoport" > wrote in message
nk.net...
> Small turbines are inherently inefficient so you are unlikely to see them
in > this power range.

You're not listening. I already HAVE seen them in that power range. The
likelihood of having done so is irrelevant, since it's already happened.

> The fuel consumption might be double that of a diesel.

It might be be, I don't know. Nevertheless, they do exist...

Pete

[Mike Rapoport]

I meant that you are unlikely to see them on production aircraft. Sorry I
wasn't clearer.

Mike
MU-2


"Peter Duniho" > wrote in message
...
> "Mike Rapoport" > wrote in message
> nk.net...
>> Small turbines are inherently inefficient so you are unlikely to see them
> in > this power range.
>
> You're not listening. I already HAVE seen them in that power range. The
> likelihood of having done so is irrelevant, since it's already happened.
>
>> The fuel consumption might be double that of a diesel.
>
> It might be be, I don't know. Nevertheless, they do exist...
>
> Pete
>
>

[Peter Duniho]

"Mike Rapoport" > wrote in message
nk.net...
> I meant that you are unlikely to see them on production aircraft.

I'll buy that.

Though, I wouldn't go so far as to say it could never happen. Who knows?
Maybe there's an application where reduced weight or increased reliability
is more important, or perhaps the "fundamental" inefficiencies of small
turbines will turn out to not be so fundamental after all.

But you are right, for now the existing low-power turbines show no sign of
being targeted for certified, production aircraft.

Pete

[Mike Rapoport]

"Peter Duniho" > wrote in message
...
> "Mike Rapoport" > wrote in message
> nk.net...
>> I meant that you are unlikely to see them on production aircraft.
>
> I'll buy that.
>
> Though, I wouldn't go so far as to say it could never happen. Who knows?
> Maybe there's an application where reduced weight or increased reliability
> is more important, or perhaps the "fundamental" inefficiencies of small
> turbines will turn out to not be so fundamental after all.
>
> But you are right, for now the existing low-power turbines show no sign of
> being targeted for certified, production aircraft.
>
> Pete
>

My understanding is that the reason that small turbines are less efficient
than large ones is because of efficiency losses at the tips of both the
compressor and turbine and the internal drag of the engine surfaces. Both
of these issues get more pronounced as things get smaller. Similiar to a
pipe with a cross sectional area of 1"sq flowing less than half as much
fluid as one with a cross section of 2" sq.

That is not to say that the engines will not get more efficient, it just
means that small turbines will be less efficient than large ones.

Mike
MU-2

[[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

Remove -spam-sux to reply.

[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

Remove -spam-sux to reply.

[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

Remove -spam-sux to reply.

[[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.

[Peter Duniho]

"Mike Rapoport" > wrote in message
nk.net...
> 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.

As you yourself pointed out, that 940hp engine is derated to 675hp. You
don't need a 940hp piston engine to provide the equivalent power, and a
675hp piston engine is not out of the question (for example, the Orenda V8
turbine replacement engines are in that ballpark, if I recall correctly).

Of course, the Orenda design is a good example of the general philosophy
that piston engines are more efficient, and cheaper to own and operate.
After all, why would anyone replace a turbine with a piston engine, if the
piston engine weren't cheaper? So I'm not saying this somehow disproves
your point...I'm just saying that you need to make sure you compare apples
to apples (and claiming that you need a 1000hp piston engine to do the same
thing a 1000hp turbine does is not comparing apples to apples).

> [...] The engineers designing airplanes
> are not totally stupid, if it made sense to install 400hp turbines they
> would do so.

I agree the engineers are not totally stupid. I disagree that just because
it hasn't made sense so far, that it will not make sense in the future. It
really just depends on what factors influenced the original decision.

Am I saying that I think it will make sense in the future? No...I don't
know enough about the technology to be able to answer that question myself.
But so far, the people who do know about the technology haven't provided any
information that would suggest to me that the future will be completely void
of lower-power turbines.

>[...]
> 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. [...]

Would a HSI cost the same on a smaller turbine? Does a HSI cost the same
for the PT-6 as it costs for whatever gargantuan engines the 777 uses?

Inspections and overhauls for piston engines generally scale up with engine
size, so it seems to me you need to compare apples to apples by comparing
the cost of a HSI and/or overhaul with the cost of an inspection on a
similarly powered piston engine.

> 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.

The same thing could theoretically be said about piston engine technology.
I suppose, in fact, that's one of the most compelling arguments in favor of
your claim: all of the engine technologies are relatively mature, so it's
reasonably safe to compare cost/benefit ratios at this time and assume that
they will remain similar in the future.

But can we be *sure* of that? You might think you can, but I'm not going to
claim that I can.

Pete

[Roy Smith]

It occurs to me that compared to a piston engine, the turbine is 1) more
expensive, and 2) more reliable. But, why are those things true?
Looking at it another way, is there some inherent reason why piston
engines are cheaper to produce? Is there also some inherent reason why
they're less reliable?

If I were to give you the $/HP budget a turbine designer has to work
with, would you be able to design a piston engine that was as reliable
as a turbine?

[G.R. Patterson III]

Roy Smith wrote:
>
> Looking at it another way, is there some inherent reason why piston
> engines are cheaper to produce?

The materials are cheaper and the tolerances (especially balancing) much looser.

> Is there also some inherent reason why
> they're less reliable?

The internal pressures are higher and the moving parts are constantly and rapidly
reversing direction.

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

[Peter Duniho]

"Roy Smith" > wrote in message
...
> It occurs to me that compared to a piston engine, the turbine is 1) more
> expensive, and 2) more reliable. But, why are those things true?
> Looking at it another way, is there some inherent reason why piston
> engines are cheaper to produce? Is there also some inherent reason why
> they're less reliable?

I believe that there are at least two factors:

A turbine needs to be constructed out of more expensive materials, because
of higher temperatures involved in the operation of the engine, and it needs
to be constructed to higher tolerances, because it's very sensitive to
imbalances. These contribute to cost.

On the other hand, a turbine has no parts that reverse direction, while a
piston engine has many such parts. So the turbine suffers less stress, when
constructed correctly, than a piston engine does. It's also "simpler", in
the sense that the engine doesn't need as many moving parts to accomplish
the same thing. These contribute to reliability.

The above ignores higher maintenance costs, which are probably related to
several factors, including cost of parts, cost of training for a mechanic,
and stricter maintenance guidelines (meaning maintenance happens more often
and is more thorough).

> If I were to give you the $/HP budget a turbine designer has to work
> with, would you be able to design a piston engine that was as reliable
> as a turbine?

Well, one problem is that the assertion that turbines are more reliable is,
in my opinion, unproved. A well-maintained piston engine can be VERY
reliable, while a poorly maintained turbine might not last very long at all.
It's hard to know for sure, because most turbines are operated in an
environment where there are strict maintenance standards. Those standards
applied to piston engines might well result equally reliable piston engines.

I think one interesting way to address your question is to look at what
causes engine failures. In piston engines, it's usually some secondary
component, such as fuel delivery or oil circulation. When it's a primary
component, often it's something that's either suffered from poor operation
techniques (valves and pistons, for example) or a manufacturing defect
(crankshafts).

Turbines do suffer from manufacturing defects (if I recall, there was an
uncontained failure in the 90's on some rear-engine jet -- 727, DC-9 or
something like that -- where the blade failure was due to some metallurgical
problem). But they have stricter maintenance regimes (which more often will
catch problems with secondary components), and perhaps more importantly,
they have stricter operating standards and instrumentation to monitor
operation (for example, overtemp operation is strictly monitored and limits
specified, and if those limits are exceeded, the engine is automatically up
for inspection and/or repair).

Which is a long way of saying that I think it's entirely possible that if
you spent as much on a piston engine as you might spend on a turbine, and
followed similar practices with respect to operation and maintenance, you
could achieve similar reliability rates.

Pete

[G.R. Patterson III]

Peter Duniho wrote:
>
> Well, one problem is that the assertion that turbines are more reliable is,
> in my opinion, unproved. A well-maintained piston engine can be VERY
> reliable, while a poorly maintained turbine might not last very long at all.
> It's hard to know for sure, because most turbines are operated in an
> environment where there are strict maintenance standards. Those standards
> applied to piston engines might well result equally reliable piston engines.

Perhaps a study of the durability of engines used for things like APUs, rather than
aircraft powerplants would be informative. Such engines, both piston and turbine, are
likely to be only moderately well maintained.

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

[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.

[Dude]

If you really wanted to know...

You could likely compare figures derived from different models of armored
fighting vehicles. Also, military aircraft used to have a mix a long time
ago.


"Peter Duniho" > wrote in message
...
> "Roy Smith" > wrote in message
> ...
> > It occurs to me that compared to a piston engine, the turbine is 1) more
> > expensive, and 2) more reliable. But, why are those things true?
> > Looking at it another way, is there some inherent reason why piston
> > engines are cheaper to produce? Is there also some inherent reason why
> > they're less reliable?
>
> I believe that there are at least two factors:
>
> A turbine needs to be constructed out of more expensive materials, because
> of higher temperatures involved in the operation of the engine, and it
needs
> to be constructed to higher tolerances, because it's very sensitive to
> imbalances. These contribute to cost.
>
> On the other hand, a turbine has no parts that reverse direction, while a
> piston engine has many such parts. So the turbine suffers less stress,
when
> constructed correctly, than a piston engine does. It's also "simpler", in
> the sense that the engine doesn't need as many moving parts to accomplish
> the same thing. These contribute to reliability.
>
> The above ignores higher maintenance costs, which are probably related to
> several factors, including cost of parts, cost of training for a mechanic,
> and stricter maintenance guidelines (meaning maintenance happens more
often
> and is more thorough).
>
> > If I were to give you the $/HP budget a turbine designer has to work
> > with, would you be able to design a piston engine that was as reliable
> > as a turbine?
>
> Well, one problem is that the assertion that turbines are more reliable
is,
> in my opinion, unproved. A well-maintained piston engine can be VERY
> reliable, while a poorly maintained turbine might not last very long at
all.
> It's hard to know for sure, because most turbines are operated in an
> environment where there are strict maintenance standards. Those standards
> applied to piston engines might well result equally reliable piston
engines.
>
> I think one interesting way to address your question is to look at what
> causes engine failures. In piston engines, it's usually some secondary
> component, such as fuel delivery or oil circulation. When it's a primary
> component, often it's something that's either suffered from poor operation
> techniques (valves and pistons, for example) or a manufacturing defect
> (crankshafts).
>
> Turbines do suffer from manufacturing defects (if I recall, there was an
> uncontained failure in the 90's on some rear-engine jet -- 727, DC-9 or
> something like that -- where the blade failure was due to some
metallurgical
> problem). But they have stricter maintenance regimes (which more often
will
> catch problems with secondary components), and perhaps more importantly,
> they have stricter operating standards and instrumentation to monitor
> operation (for example, overtemp operation is strictly monitored and
limits
> specified, and if those limits are exceeded, the engine is automatically
up
> for inspection and/or repair).
>
> Which is a long way of saying that I think it's entirely possible that if
> you spent as much on a piston engine as you might spend on a turbine, and
> followed similar practices with respect to operation and maintenance, you
> could achieve similar reliability rates.
>
> Pete
>
>

[Mike Rapoport]

"Peter Duniho" > wrote in message
...
> "Mike Rapoport" > wrote in message
> nk.net...
>> 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.
>
> As you yourself pointed out, that 940hp engine is derated to 675hp. You
> don't need a 940hp piston engine to provide the equivalent power, and a
> 675hp piston engine is not out of the question (for example, the Orenda V8
> turbine replacement engines are in that ballpark, if I recall correctly).

Large snip.

I agree that it is difficult to compare different types of engines apples to
apples since the power and specific fuel consumption curves are so
different.. I have two airplanes, one turbine and one piston. Both engines
are well suited for their applications. In the Helio, power is often set to
15"MP to keep the speed down in turbulent, low altitude mountain flying. A
turbine would be horribly inefficient operated like this. In the MU-2,
power is set close to the torque or temp limits from takeoff until reaching
about 16,000' on the descent. A piston engine operated flat out like this
wouldn't last long, particularly at high altitude. Both powerplanes have
their place although I think that diesels will eventually replace gasoline
piston engines because of their efficiency, long life and simplicity.

Mike
MU-2

[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

[Paul Sengupta]

"Peter Duniho" > wrote in message
...
> Turbines do suffer from manufacturing defects (if I recall, there was an
> uncontained failure in the 90's on some rear-engine jet -- 727, DC-9 or
> something like that -- where the blade failure was due to some
metallurgical
> problem).

Sioux City DC10.

Paul

[Paul Sengupta]

"Peter Duniho" > wrote in message
...
> Turbines do suffer from manufacturing defects

http://www.tc.faa.gov/its/cmd/visitors/data/AAR-430/turbine.pdf

[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

[Peter Duniho]

"Paul Sengupta" > wrote in message
...
>> Turbines do suffer from manufacturing defects (if I recall, there was an
>> uncontained failure in the 90's on some rear-engine jet -- 727, DC-9 or
>> something like that -- where the blade failure was due to some
> metallurgical
>> problem).
>
> Sioux City DC10.

Not actually the accident I'm thinking of. But yes, that's another example
of blade failure (did they eventually determine it was a manufacturing
defect, or a maintenance problem?).

The accident to which I was referring only involved one or two fatalities,
of a passenger or of passengers sitting right next to the engine.

Pete

[Mike H]

I believe you are referring to a Delta MD-80/88 that
was taking off from Pensacola. I think there were
two killed and a couple of injuries.

Mike Pvt/IFT N44979 PA28-181 at RYY

Peter Duniho wrote:
> "Paul Sengupta" > wrote in message
> ...
>
>>>Turbines do suffer from manufacturing defects (if I recall, there was an
>>>uncontained failure in the 90's on some rear-engine jet -- 727, DC-9 or
>>>something like that -- where the blade failure was due to some
>>
>>metallurgical
>>
>>>problem).
>>
>>Sioux City DC10.
>
>
> Not actually the accident I'm thinking of. But yes, that's another example
> of blade failure (did they eventually determine it was a manufacturing
> defect, or a maintenance problem?).
>
> The accident to which I was referring only involved one or two fatalities,
> of a passenger or of passengers sitting right next to the engine.
>
> Pete
>
>

[David Lesher]

"Peter Duniho" > writes:


>Not actually the accident I'm thinking of. But yes, that's another example
>of blade failure (did they eventually determine it was a manufacturing
>defect, or a maintenance problem?).

>The accident to which I was referring only involved one or two fatalities,
>of a passenger or of passengers sitting right next to the engine.


I recall it as well. DC-9, I believe...

--
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

[David Lesher]

Mike H > writes:

>I believe you are referring to a Delta MD-80/88 that
>was taking off from Pensacola. I think there were
>two killed and a couple of injuries.


http://www.ntsb.gov/ntsb/brief.asp?ev_id=20001208X06203&key=1

--
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

[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.
>
>
>

[Paul Sengupta]

"Peter Duniho" > wrote in message
...
> "Paul Sengupta" > wrote in message
> ...
> >> Turbines do suffer from manufacturing defects (if I recall, there was
an
> >> uncontained failure in the 90's on some rear-engine jet -- 727, DC-9 or
> >> something like that -- where the blade failure was due to some
> > metallurgical
> >> problem).
> >
> > Sioux City DC10.
>
> Not actually the accident I'm thinking of. But yes, that's another
example
> of blade failure (did they eventually determine it was a manufacturing
> defect, or a maintenance problem?).

They say it was a manufacturing defect about the size of a grain of
sand.

http://www.ntsb.gov/speeches/former/hall/jh970912.htm

"Metallurgical examination of the titanium fan hub revealed that a fatigue
crack originated from an inclusion near the surface of the hub's bore. The
inclusion had been formed during the titanium vacuum-melting process at the
time of manufacture about 2 decades earlier, which developed an internal
cavity during final machining and/or shot peening. At the time of
manufacture, the fan hub had been ultrasonic and macroetch inspected."

> The accident to which I was referring only involved one or two fatalities,
> of a passenger or of passengers sitting right next to the engine.

Yes, I know the one you're talking about.

It's mentioned on the page referenced above:
"We will soon conclude our investigation on that Delta Air Lines MD-88
engine failure I mentioned earlier. Metallurgical examination of the
fracture surface of that fan hub revealed that a fatigue crack had
originated from a machining defect in a tie rod hole. Further, the fan hub
had been fluorescent particle inspected only seven months before the
failure, when the crack was estimated to be approximately ½-inch long."

Also http://www.ntsb.gov/pressrel/1998/980113d.htm

Paul

[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

[Peter Duniho]

"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

[Ted Azito]

> Small turbines are inherently inefficient so you are unlikely to see them in
> this power range. The fuel consumption might be double that of a diesel.

It's not true, first off. Although bigger engines have advantages of
Reynolds numbers and such, small and large are relative terms. The
relationship of BSFC of heavy diesels and industrial gas turbines in
steady state peak operation is pretty constant across engines from the
size of an 855 cid Cummins to the really big guys with four foot
bores. The turbocharged diesels are somewhat more efficient but
nowhere near 2:1.

The "secret" of linearizing gas turbine performance across a wide
range of output power is thermal feedback, or regeneration. Look
carefully at the real progenitor of the Cruise Missile turbojet...

[Don Hammer]

On 29 Sep 2004 12:35:58 -0700, (Ted Azito)
wrote:

>> Small turbines are inherently inefficient so you are unlikely to see them in
>> this power range. The fuel consumption might be double that of a diesel.
>
> It's not true, first off. Although bigger engines have advantages of
>Reynolds numbers and such, small and large are relative terms. The
>relationship of BSFC of heavy diesels and industrial gas turbines in
>steady state peak operation is pretty constant across engines from the
>size of an 855 cid Cummins to the really big guys with four foot
>bores. The turbocharged diesels are somewhat more efficient but
>nowhere near 2:1.
>
> The "secret" of linearizing gas turbine performance across a wide
>range of output power is thermal feedback, or regeneration. Look
>carefully at the real progenitor of the Cruise Missile turbojet...

Spent my life around turbine aircraft, so I don't know a thing about
large piston engines. I don't understand what you mean by "Reynolds
numbers and such" I thought that Reynolds numbers are used in airfoil
calculations, but I may be wrong.

From my experience, a turbine is most efficient when operated near its
max temperature. That's why we cruise them at over 95% RPM. The other
way we can operate them efficiently is to go high - drag goes way down
and the thrust required goes down with it. One of the major
improvements to efficiency has been because of the metallurgy and
running them at a higher temperature. Years ago we used 150 degree
thermostats in our cars. They're probably at least 200 degrees today.
The only reason - better thermal efficiency (gas mileage).

A turbine engine doesn't have any touching parts in the working
sections. What that means is there are huge air gaps between blades,
rotors etc. In other words, no piston rings. Static, you can blow
right through them. The tips of the rotating parts don't touch
either, so there are gaps. I'm no engineer, but I would think that
as a turbine gets smaller the ratio of air leak to "working stuff"
would be greater and there would reach a point that fuel specifics
wouldn't be in your favor. That's probably why most of the small
engines down to micro-turbines use centrifugal compresses instead of
axial flow. In other words, the centrifugal, by design, leaks less.

There is a reason that airliners are almost all two-engine. A large
engine of 100,000 lbs thrust is much more efficient than two 50,000 lb
engines. That's why they are parking 747's and buying 777's. It's
not the cost of the engines. Over their service life, the engine
costs are nothing compared to the fuel they burn.

[Dean Wilkinson]

The increased fuel efficiency of the 777 engines is not strictly due
to their size. They are a newer generation design with very high
bypass and advanced FADEC controllers. The 747 engines are an older
design. Also, the 777 is a more aerodynamically efficient airplane
than the 747.

The other big advantage of two engines vs. 4 is cost of ownership in
terms of maintenance and spares. Its less expensive to maintain two
engines per plane than 4. Also, statistically speaking, the
probability of an engine failure per flight hour is lower for the 777
than it is for the 747 since it has fewer engines to fail. Believe it
or not... this was demonstrated to me when I worked at Boeing on the
777 development.

Dean

Don Hammer > wrote in message >...
> On 29 Sep 2004 12:35:58 -0700, (Ted Azito)
> wrote:
>
> >> Small turbines are inherently inefficient so you are unlikely to see them in
> >> this power range. The fuel consumption might be double that of a diesel.
> >
> > It's not true, first off. Although bigger engines have advantages of
> >Reynolds numbers and such, small and large are relative terms. The
> >relationship of BSFC of heavy diesels and industrial gas turbines in
> >steady state peak operation is pretty constant across engines from the
> >size of an 855 cid Cummins to the really big guys with four foot
> >bores. The turbocharged diesels are somewhat more efficient but
> >nowhere near 2:1.
> >
> > The "secret" of linearizing gas turbine performance across a wide
> >range of output power is thermal feedback, or regeneration. Look
> >carefully at the real progenitor of the Cruise Missile turbojet...
>
> Spent my life around turbine aircraft, so I don't know a thing about
> large piston engines. I don't understand what you mean by "Reynolds
> numbers and such" I thought that Reynolds numbers are used in airfoil
> calculations, but I may be wrong.
>
> From my experience, a turbine is most efficient when operated near its
> max temperature. That's why we cruise them at over 95% RPM. The other
> way we can operate them efficiently is to go high - drag goes way down
> and the thrust required goes down with it. One of the major
> improvements to efficiency has been because of the metallurgy and
> running them at a higher temperature. Years ago we used 150 degree
> thermostats in our cars. They're probably at least 200 degrees today.
> The only reason - better thermal efficiency (gas mileage).
>
> A turbine engine doesn't have any touching parts in the working
> sections. What that means is there are huge air gaps between blades,
> rotors etc. In other words, no piston rings. Static, you can blow
> right through them. The tips of the rotating parts don't touch
> either, so there are gaps. I'm no engineer, but I would think that
> as a turbine gets smaller the ratio of air leak to "working stuff"
> would be greater and there would reach a point that fuel specifics
> wouldn't be in your favor. That's probably why most of the small
> engines down to micro-turbines use centrifugal compresses instead of
> axial flow. In other words, the centrifugal, by design, leaks less.
>
> There is a reason that airliners are almost all two-engine. A large
> engine of 100,000 lbs thrust is much more efficient than two 50,000 lb
> engines. That's why they are parking 747's and buying 777's. It's
> not the cost of the engines. Over their service life, the engine
> costs are nothing compared to the fuel they burn.

[Don Hammer]

I don't disagree with you Dean on the spares issue etc., but as I see
it is you add up the cost of the engine and spares and then the fuel
used over 40K hours or so and see where the real $ are.

I also don't disagree about two different vintage engines; newer are
more efficient, but look at the SFC on a CF6 of about 40K thrust and a
CF34 of 9K thrust (same vintage) and I bet the larger engine has the
upper hand; maybe not.

Good discussion subject and it would be interesting to hear from
others who know what they are talking about. Obviously anything I say
comes from being around these things, not because I profess to be any
kind of authority. Any aircraft turbine engineers out there? Neat
thing about aviation is there is always something to be learned.

[Ted Azito]

Firstly, all gas turbine rotors-compressor and turbine-are airfoils,
and that's why engine (and airframe) designs don't scale perfectly for
aerodynamic performance: air, in effect, has a finite size.

All engines are more efficient as the delta between the hot parts and
the cold parts increases, per Carnot. That said the primary reason car
engines run hotter than before is not because of direct thermal
efficiency but for emissions and also because smaller radiators can be
used.

Large turbines are actually designed to wear themselves in at times
as creepage brings the blades out and they ever so slightly lathe
themselves down, opening up the stator surface as they do. Active
clearance control using bleed air is another nifty feature of big
engines. Working against the economics of big fan engines is the fan
case being bigger than normal shipping means can handle. Also, a
serious FOD, midair, or controller failure resulting in an engine
writeoff is a much bigger capital hit:someone has to write a big
check.

The less the number of engines the greater probability that one
engine will fail. However the consequence of one engine failing
becomes directly higher. One engine out on a B-52 is a marginal
consideration: one engine out on a single turns your mission to worst
case recovery (find an airport, off airport landing, ditch, or
bailout/eject depending on the aircraft and terrain underneath.)

An exception to this rule is the light twin, most of which are really
1 1/2 engine airplanes to start with, and which tend to be flown by
hobbyists and part-timers. Statistics show that engine failures in
light twins kill more people than engine failures in singles, for a
lot of reasons. Cessna, Piper, and Beech knew this since roughly 1960
and their response for 25 years was, buy more liability insurance.
When high interest rates in 1986 made the reinsurance market for this
untenable, "they could no longer make reciprocating-engine aircraft".

ETOPS-Engines Turn Or People Swim!

[Matt Whiting]

Dean Wilkinson wrote:
> The increased fuel efficiency of the 777 engines is not strictly due
> to their size. They are a newer generation design with very high
> bypass and advanced FADEC controllers. The 747 engines are an older
> design. Also, the 777 is a more aerodynamically efficient airplane
> than the 747.
>
> The other big advantage of two engines vs. 4 is cost of ownership in
> terms of maintenance and spares. Its less expensive to maintain two
> engines per plane than 4. Also, statistically speaking, the
> probability of an engine failure per flight hour is lower for the 777
> than it is for the 747 since it has fewer engines to fail. Believe it
> or not... this was demonstrated to me when I worked at Boeing on the
> 777 development.

True, but the probability of losing all of the engines at the same time
is greater with only two engines as opposed to four.

Matt

[Dustin Rinebold]

>>Statistics show that engine failures in
>>light twins kill more people than engine failures in singles,

My understanding is that this statistic only applies to engine
failures that result in accidents. Left out are all the twins that had
engine failures and landed safely.

[Dean Wilkinson]

>
> True, but the probability of losing all of the engines at the same time
> is greater with only two engines as opposed to four.
>
> Matt

Not necessarily...

There has never been a historical case of a twin engine jetliner
losing both engines at once due to unrelated failures. All twin
engine failures have been due to a common cause; fuel starvation being
the prime reason.

Here are some examples of related engine failures:

A four engine 747 had all four engines flame out at the same time when
it flew into the ash cloud of Mt. Redoubt in Alaska, and only managed
to restart three of them after losing over 10,000 feet of altitude.

A four engine Airbus A340 made a dead-stick landing at Lajes in the
Azores after running of fuel due to a combination fuel leak and fuel
system management problem.

A 767 (twin) made an emergency landing in Canada on a drag strip after
losing both engines due to a miscalculation during fueling.

The probability of an ETOPS plane losing both engines in a single
flight due to unrelated failures is extremely remote. That doesn't
mean it can never happen, but it is less likely than winning the
lottery.

[[email protected]]

In rec.aviation.owning Dean Wilkinson > wrote:
> >
> > True, but the probability of losing all of the engines at the same time
> > is greater with only two engines as opposed to four.
> >
> > Matt

> Not necessarily...

> There has never been a historical case of a twin engine jetliner
> losing both engines at once due to unrelated failures. All twin
> engine failures have been due to a common cause; fuel starvation being
> the prime reason.

> Here are some examples of related engine failures:

> A four engine 747 had all four engines flame out at the same time when
> it flew into the ash cloud of Mt. Redoubt in Alaska, and only managed
> to restart three of them after losing over 10,000 feet of altitude.

> A four engine Airbus A340 made a dead-stick landing at Lajes in the
> Azores after running of fuel due to a combination fuel leak and fuel
> system management problem.

> A 767 (twin) made an emergency landing in Canada on a drag strip after
> losing both engines due to a miscalculation during fueling.

> The probability of an ETOPS plane losing both engines in a single
> flight due to unrelated failures is extremely remote. That doesn't
> mean it can never happen, but it is less likely than winning the
> lottery.

Not quite; the probability of all engines failing decreases with the
number of engines if all engines have the same probability of failing.

Whether or not this will actually happen is highly dependent on the
probability of the individual engine failing.

Since airline engines tend to be well maintained, and hence the probablity
of failure low, one could reasonably say the chances of multiple engine
failures (no common cause) is quite remote.

However, a friend of mine that spent lots of time in B-52s relates the
tale of the time they lost 3 engines (no common cause) during flight
and a fourth engine on final getting "that big piece of crap" back on
the ground.

--
Jim Pennino

Remove -spam-sux to reply.

[Dean Wilkinson]

Jim,

Please don't reply in such a way as to make it appear that I said something
that I did not. It was Matt Whiting that made the comment about losing all
engines on a twin being more likely than losing all four. I didn't say
that, and I know that is not true.

Dean
> wrote in message
...
> In rec.aviation.owning Dean Wilkinson > wrote:
> > >
> > > True, but the probability of losing all of the engines at the same
time
> > > is greater with only two engines as opposed to four.
> > >
> > > Matt
>
> > Not necessarily...
>
> > There has never been a historical case of a twin engine jetliner
> > losing both engines at once due to unrelated failures. All twin
> > engine failures have been due to a common cause; fuel starvation being
> > the prime reason.
>
> > Here are some examples of related engine failures:
>
> > A four engine 747 had all four engines flame out at the same time when
> > it flew into the ash cloud of Mt. Redoubt in Alaska, and only managed
> > to restart three of them after losing over 10,000 feet of altitude.
>
> > A four engine Airbus A340 made a dead-stick landing at Lajes in the
> > Azores after running of fuel due to a combination fuel leak and fuel
> > system management problem.
>
> > A 767 (twin) made an emergency landing in Canada on a drag strip after
> > losing both engines due to a miscalculation during fueling.
>
> > The probability of an ETOPS plane losing both engines in a single
> > flight due to unrelated failures is extremely remote. That doesn't
> > mean it can never happen, but it is less likely than winning the
> > lottery.
>
> Not quite; the probability of all engines failing decreases with the
> number of engines if all engines have the same probability of failing.
>
> Whether or not this will actually happen is highly dependent on the
> probability of the individual engine failing.
>
> Since airline engines tend to be well maintained, and hence the probablity
> of failure low, one could reasonably say the chances of multiple engine
> failures (no common cause) is quite remote.
>
> However, a friend of mine that spent lots of time in B-52s relates the
> tale of the time they lost 3 engines (no common cause) during flight
> and a fourth engine on final getting "that big piece of crap" back on
> the ground.
>
> --
> Jim Pennino
>
> Remove -spam-sux to reply.

[[email protected]]

In rec.aviation.owning Dean Wilkinson > wrote:
> Jim,

> Please don't reply in such a way as to make it appear that I said something
> that I did not. It was Matt Whiting that made the comment about losing all
> engines on a twin being more likely than losing all four. I didn't say
> that, and I know that is not true.

Ummm, I posted a followup to the entire post as received without editing
any previous content.

The depth of the '>' characters at the beginning of the lines should show
who said what and my response was to the latest post, i.e. that of Matt
Whiting.

--
Jim Pennino

Remove -spam-sux to reply.

[Robert Briggs]

wrote:
> Dean Wilkinson wrote:

> > The probability of an ETOPS plane losing both engines in a single
> > flight due to unrelated failures is extremely remote. That doesn't
> > mean it can never happen, but it is less likely than winning the
> > lottery.
>
> Not quite; the probability of all engines failing decreases with the
> number of engines if all engines have the same probability of failing.

That looks fair enough at first sight, but, as you go on to say, it
is "highly dependent on the probability of the individual engine
failing".

The whole point of ETOPS is that the *requirements* for the engines
are rather stricter than those for airliners with three or more
engines, since once you've got a single failure the other fan had
jolly well better keep turning.

With three or more engines, a second failure during diversion is
much less likely to be catastrophic.

Of course, if you take two pairs of ETOPS engines, fit them to a
four-motor aeroplane, and maintain them to ETOPS standards then
the probability of losing all of them from unrelated failures is
exceedingly small - *way* down in the noise of multiple failures
with a *common* cause.

[[email protected]]

In rec.aviation.owning Robert Briggs > wrote:
> wrote:
> > Dean Wilkinson wrote:

> > > The probability of an ETOPS plane losing both engines in a single
> > > flight due to unrelated failures is extremely remote. That doesn't
> > > mean it can never happen, but it is less likely than winning the
> > > lottery.
> >
> > Not quite; the probability of all engines failing decreases with the
> > number of engines if all engines have the same probability of failing.

> That looks fair enough at first sight, but, as you go on to say, it
> is "highly dependent on the probability of the individual engine
> failing".

> The whole point of ETOPS is that the *requirements* for the engines
> are rather stricter than those for airliners with three or more
> engines, since once you've got a single failure the other fan had
> jolly well better keep turning.

> With three or more engines, a second failure during diversion is
> much less likely to be catastrophic.

> Of course, if you take two pairs of ETOPS engines, fit them to a
> four-motor aeroplane, and maintain them to ETOPS standards then
> the probability of losing all of them from unrelated failures is
> exceedingly small - *way* down in the noise of multiple failures
> with a *common* cause.

After posting it occured to me that the above was an incorrect statement.

It should be, the probability of all engines failing decreases with the
number of engines.

While the probability of all engines failing will increase with the
probabilities of individual enginge failure, that number will always
be less than any individual probability.

This is a consequence of the laws of probability and nothing else.

In the real world, we attempt to keep those probability numbers low
so that such an occurance becomes highly unlikely.

The probability of getting 3 jackpots in a row on a Vegas slot machine
is a number greater than zero, but does not form a valid basis for a
retirement plan, for example.

--
Jim Pennino

Remove -spam-sux to reply.

[Robert Briggs]

wrote:
> Robert Briggs wrote:

> > The whole point of ETOPS is that the *requirements* for the
> > engines are rather stricter than those for airliners with
> > three or more engines, since once you've got a single failure
> > the other fan had jolly well better keep turning.

> While the probability of all engines failing will increase with
> the probabilities of individual engine failure, that number will
> always be less than any individual probability.
>
> This is a consequence of the laws of probability and nothing else.

There is more than simple "the laws of probability" at work here.

In pre-ETOPS days, three or more engines were required for, say,
transatlantic airliners because the risk of multiple engine
failures was deemed to be too high.

ETOPS certification requires engines which are *demonstrated* to
be more reliable than those on 707s, early 747s, and the like.

It is by no means impossible for four independent engine failures
on an older aeroplane to be more likely than two on an ETOPS kite.

Of course, now that manufacturers are building ETOPS-certified
engines there's not a great deal of point in deliberately making
*less reliable* versions for airliners with three or more engines,
so it is rather likely that *newer* 747s are less prone to losing
all four engines independently than twins are to losing both.

[Matt Whiting]

Dean Wilkinson wrote:

> Jim,
>
> Please don't reply in such a way as to make it appear that I said something
> that I did not. It was Matt Whiting that made the comment about losing all
> engines on a twin being more likely than losing all four. I didn't say
> that, and I know that is not true.

How do you know this is not true? If I recall correctly, the
probability of independent events occuring simultaneously is equal to
the product of the probabilities of each event occurring. If we rule
out common cause failures such as fuel exhaustion and look at only
random failures, the the probability of all engines failing
simultaneously is the product of the probability of failure of each
engine separately. Assuming that each engine has the same probability
of failure, means that with two engines the probability of both failing
is P^2 whereas with four engines the probability of all failing is P^4.
Since 0=<P<=1, P^4 will be less than P^2.

As someone else said, the probability of having AN engine fail on any
given flight is higher with more engines, but I believe the probability
of ALL engines failing on a given flight is less with more engines.


Matt

[[email protected]]

In rec.aviation.owning Robert Briggs > wrote:
> wrote:
> > Robert Briggs wrote:

> > > The whole point of ETOPS is that the *requirements* for the
> > > engines are rather stricter than those for airliners with
> > > three or more engines, since once you've got a single failure
> > > the other fan had jolly well better keep turning.

> > While the probability of all engines failing will increase with
> > the probabilities of individual engine failure, that number will
> > always be less than any individual probability.
> >
> > This is a consequence of the laws of probability and nothing else.

> There is more than simple "the laws of probability" at work here.

> In pre-ETOPS days, three or more engines were required for, say,
> transatlantic airliners because the risk of multiple engine
> failures was deemed to be too high.

> ETOPS certification requires engines which are *demonstrated* to
> be more reliable than those on 707s, early 747s, and the like.

> It is by no means impossible for four independent engine failures
> on an older aeroplane to be more likely than two on an ETOPS kite.

> Of course, now that manufacturers are building ETOPS-certified
> engines there's not a great deal of point in deliberately making
> *less reliable* versions for airliners with three or more engines,
> so it is rather likely that *newer* 747s are less prone to losing
> all four engines independently than twins are to losing both.

Mathematics doesn't care about certifications or maintenance
programs. Programs are based on the mathematics.

If the probability of an engine failing is 0.1, the probabilities for
all engines failing are:

1 0.1
2 0.01
3 0.001
4 0.0001

If the probability of an engine failing is 0.7, i.e. really ratty engines,
the probabilities for all engines failing are:

1 0.7
2 0.49
3 0.34
4 0.24

Things like ETOPS exist because the numbers say getting the probabilities
low is a good thing.


--
Jim Pennino

Remove -spam-sux to reply.

[PaulH]

Ernest Gann in "Fate is the Hunter" described one event in which he
lost nearly all power on 3 of 4 out of LGA once, and another time that
all 4 quit simultaneously with a load of passengers over the Pacific.
The first event was caused by the mechanics testing a new type of
spark plug, which they "unfortunately" had time to install on 3
engines. The second was a glitch in the fuel system.