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

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.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

--
Jim Pennino

Remove -spam-sux to reply.

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".

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.

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.

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

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.

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.

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