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

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

In rec.aviation.owning Stefan wrote:
wrote:

Now granted these are turbojets, not turboprops, but it appears to me
that making small turbines is possible...

Nobody ever said that it's not possible. It's just not economical and
will never be.

Stefan

Several people have said that but I've yet to see any analysis (with
numbers) to back up that contention.

Since (current) turbines are terribly inefficient at low throttle, I can
see the problem with an aircraft that spends most of the time doing
touch and goes.

But where is the crossover point as dictated by the physics of turbines?

C-182? C-209? Caravan? Whoops, that last one is already a turbine.

--
Jim Pennino

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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

In rec.aviation.owning Mike Rapoport wrote:

wrote in message
...

While not quite a .049, here's a 3.7" in diameter, 2.6 lb turbine
that produces 16.5 lb of thrust.

http://jetcatusa.sitewavesonline.net/p70.html

Their biggest turbine is 5.12", 5 lb, and produces 45 lb of thrust.

Here's another outfit that sells a 3.5" diameter, 7.25" long, 1.9 lb
turbine with 11.4 lb of thrust.

http://www.swbturbines.com/model_turbines.htm

Now granted these are turbojets, not turboprops, but it appears to me
that making small turbines is possible...


--
Jim Pennino


You are missing the point. Everyone agrees that small turbines can be
built, the issue is fuel consumption. What is the specific fuel consumption
per lb of thrust?

Not quite "everyone" has signed on to that notion and you are one of few
that has wanted to talk about numbers as opposed to making sweeping
statements.

For the 16.5 lb thrust engine it is 1.8 lb/hr-lb thrust, but I doubt fuel
efficiency is a design criteria in a model airplane engine.

The question remains, at what HP level, based on the physics of the engines,
does the crossover from piston to turbine occur?

As additional criteria, assume specific fuel consumption is the most
important parameter and that the A/C spends the majority of its time in
flight not doing touch and goes.


--
Jim Pennino

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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

Remove -spam-sux to reply.

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.

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

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


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

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

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

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

C,

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

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

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


Huh? Same fuel burn? Hardly.

--
Thomas Borchert (EDDH)