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

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?e...08X06203&key=1

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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://w.../3_0_2_1_2.asp

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

Mike
MU-2


wrote in message
...
In rec.aviation.owning Mike Rapoport
wrote:
About the size of the Caravan 900hp+

Mike
MU-2

According to the Cessna website, the current Caravan is 675hp.

--
Jim Pennino

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"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

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

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

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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

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

"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

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...

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.