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

"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.

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)

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
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In rec.aviation.owning Mike Rapoport wrote:

wrote in message
...
In rec.aviation.owning Mike Rapoport
wrote:
The Caravan has a 940hp engine flat rated to 675hp. Turbines are
typically
flat rated so that the engine can make rated power to reasonable
altitudes
and temperatures without having to design the gearbox for the full
thermodynamic horsepower. To keep the comparison with piston engines
apples
to apples you need to use thermodynamic ratings.


http://www.pwc.ca/en/3_0/3_0http://w.../3_0_2_1_2.asp

OK, that explains that.

To put some numbers on things, the engines in my MU-2 have a specific
fuel
consumption of .55lb/hp/hr and a piston engine is about .45 and
diesels
can
be under .40. Huge (ship) diesels can be under .30. Compare your
model
aircraft engines with the TFE731-60 used on the Falcon 900EX which
uses
.405lb/lb thrust/hr

Aha, numbers!

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

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


--
Jim Pennino

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

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

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


--
Jim Pennino

Remove -spam-sux to reply.

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
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"Roy Smith" wrote in message
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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

"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

"C Kingsbury" wrote in message
om...
wrote in message
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In rec.aviation.owning Mike Rapoport
wrote:

wrote in message
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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

wrote in message
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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

"Peter Duniho" wrote in message
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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

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

http://www.tc.faa.gov/its/cmd/visito...30/turbine.pdf

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


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Bowie, MD, USA | Tablet and Inkle bands, and other stuff
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