Differences between automotive & airplane engines

"Alan Baker" wrote in message
...
In article .com,
wrote:


I don't know. But whatever rotational speed it turns at, you can convert
that into any other rotational speed and still be getting 40 hp.

You can't say the same about torque.


Right. Horsepower is equal to torque multiplied by RPM times a constant.
For any given horsepower if torque goes up the RPM must go down and vice
versa.

Of course, if you know any two of HP, torque, or RPM you can easily find the
third.

Gearing adds weight and wear points. However, many aircraft engines have
been geared. It does get a little tricky, since the prop serves as the
flywheel, so you are putting your gears inbetween the crankshaft and the
flywheel. That is not a good place for gears if you hope for reasonable
service life!

Highflyer
Highflight Aviation Services
Pinckneyville Airport ( PJY )

"stol" wrote in message
oups.com...

Philippe Vessaire wrote:

An automotive engine burn the same amount of gas than an airplane one

Bull****....

Any engine that burns gasoline will burn very close to the same amount of
gasoline per horsepower hour. Conservatively figure .5 pounds per
horsepower per hour. The best you are likely to get is .43 or so. The
worst is probably not more than .6. To get much better than that you would
have to be able to use your exhaust stacks to make ice cubes.

An automobile engine burns the same amount of gas an an aircraft engine per
horsepower hour.

Is that better!


Is automotive engines cheaper than a 2000h core of airplane engine? (with
the PSRU).

This answer doesn't make sense....


The folks I have seen who go out and buy a converted automobile engine for
their airplane have spent around $15,000 by the time they got it flying.
That is about the price of a field overhauled Lycoming or Continental of
similiar horsepower.
That is what he just said. I bought a midtime Lycoming O-290-D 135HP engine
for my Cavalier 102.5. I paid $1200 for the engine ready to run. All I
have to do to it is bolt it into the airplane and put a prop on it, which I
bought from the same gentleman for $400. I am going with an aircraft
engine. :-)

Highflyer
Highflight Aviation Services
Pinckneyville Airport ( PJY )

"Chris Wells" wrote in message
...

I'm well aware of the purpose of the PSRU, I'd like to know if it's
feasible to convert an automobile (or other) engine to run at an RPM
low enough so that a PSRU wouldn't be necessary. I'm thinking a custom
camshaft would be needed, and different ignition timing, what else?



If the cam in the engine is pretty mild it is probably OK. Ignition timing
depends on the RPM and most aircraft engines run a fixed timing advance of
around 25 degrees. Plus or minus about 5. Not a big deal. You can trash
the advance stuff on the engine.

Then just work out a decent way to attach a prop hub to the crankshaft. One
easy way is to machine up an adaptor that bolts onto the crankshaft instead
of the flywheel. If you do it that way you can use ordinary aircraft
props, which is a plus. Then just pick a prop so that you can't pull more
than about 2700 RPM. You will get right around 1/2 horsepower for every
cubic inch if everything else is fine. Actually you probably want the
engine to lug down to about 2400 RPM static at full throttle. The RPM will
pick up some when you start to move and the horsepower will go up with it.

For best efficiency put in a cam that gives you max torque at around 2400
RPM. That will give you the best specific fuel consumption, because you
will be cruising at about torque peak.

Highflyer
Highflight Aviation Services
Pinckneyville Airport ( PJY )

In article , "Highflyer"
wrote:

"Alan Baker" wrote in message
...
In article .com,
wrote:


I don't know. But whatever rotational speed it turns at, you can convert
that into any other rotational speed and still be getting 40 hp.

You can't say the same about torque.


Right. Horsepower is equal to torque multiplied by RPM times a constant.
For any given horsepower if torque goes up the RPM must go down and vice
versa.

Of course, if you know any two of HP, torque, or RPM you can easily find the
third.

But the point is that if you know torque, you *must* also know RPM if
you're going to know what kind of performance to expect.

With horsepower, you instantly know whether or not an engine offers
enough performance for the application you are considering.


Gearing adds weight and wear points. However, many aircraft engines have
been geared. It does get a little tricky, since the prop serves as the
flywheel, so you are putting your gears inbetween the crankshaft and the
flywheel. That is not a good place for gears if you hope for reasonable
service life!

Highflyer
Highflight Aviation Services
Pinckneyville Airport ( PJY )

--
Alan Baker
Vancouver, British Columbia
"If you raise the ceiling 4 feet, move the fireplace from that wall
to that wall, you'll still only get the full stereophonic effect
if you sit in the bottom of that cupboard."

An automotive engine burn the same amount of gas than an airplane one

Bull****....

Any engine that burns gasoline will burn very close to the same amount of
gasoline per horsepower hour. Conservatively figure .5 pounds per
horsepower per hour. The best you are likely to get is .43 or so. The
worst is probably not more than .6. To get much better than that you
would
have to be able to use your exhaust stacks to make ice cubes.

An automobile engine burns the same amount of gas an an aircraft engine
per
horsepower hour.

Is that better!

If you are saying that an air cooled aircraft engine burns the same amount
of gas as a water cooled engine (auto or aircraft), then I say you are
wrong.

The water cooled engine is able to burn less fuel per HP produced because of
many factors, major ones being the cooler cylinder, non tapered bore, and
ability to run leaner with less danger of preignition and detonation.
Backing that up is the fact that air cooled engines disappeared from
automobiles, primarily because they could not meet emission standards.
Wasted gas, unburned, going out with the exhaust is one of the things that
could not be improved on enough. Also, it is interesting that the Scaled
Composite's around the world piston engine was to be liquid cooled,
primarily to improve on fuel economy.

There are too many examples of water cooled airplane engines that are
flying, and reporting lower fuel burns compared to the air cooled examples,
to argue that water cooled engines are not superior (in fuel burn) to air
cooled engines. The difference is even greater for the conversions using a
computer to control fuel mixtures.

There is no arguing that converting and working out the bugs in an auto
conversion is a tricky, and expensive proposition. Some people thrive on
that, just like people who drag race and build hot rods. If the person is
not in to that kind of thing, then they should stick to the proven,
standard, aircraft engine.

It is a shame that Lycoming and Continental (and others) are not making
faster progress on creating easy to substitute water cooled engines, and jet
fuel burning piston engines for the GA fleet. Small tubojet and turboprop
engines would be nice, too. It could open up options that would be
beneficial to many people, and many designs.
--
Jim in NC

Not quite "Bull****"

An aircraft engine is normally either run full rich, or "leaned" to max RPM-
that's usually an air fuel ratio of around 10:1. An auto engine (at least a
fuel injected auto engine) is kept right at the stoichiometric point of 14.7
to 1 air fuel ratio. It makes a little less power there, but not much, and
burns 30% or so less fuel.

For an auto engine, BSFC of 0.45 lb/hp/hr is expected, but I have seen
figures as low as 0.39. Some ECU's even run very lean (~17:1 or so)
returning to stoich every now and then just to make sure they know where
it's at (the Oxygen sensor puts out a characteristic sawtooth pattern at
stoich). An aircraft engine running full rich is lucky to see 0.55.

Anyway - anyone with much experience with an auto conversion will tell you
it burns much less fuel than a Lycosaur of the same HP. That's one reason
why.

Another is the pattern of torque pulses. A geared V6 or V8 has a lot of
overlap on the torque pulses. A direct drive 4 does not. If you plot torque
vs time, you see a series of BIG spikes, that drop way down between piston
firings. A prop does completely different things when twisted with a series
of jerks, than it does with a smooth twisting force. I'll leave you to guess
which is more efficient, even if both are getting the same average
horsepower.



An automotive engine burn the same amount of gas than an airplane one

Bull****....

Any engine that burns gasoline will burn very close to the same amount of
gasoline per horsepower hour. Conservatively figure .5 pounds per
horsepower per hour. The best you are likely to get is .43 or so. The
worst is probably not more than .6. To get much better than that you
would have to be able to use your exhaust stacks to make ice cubes.

An automobile engine burns the same amount of gas an an aircraft engine
per horsepower hour.

Is that better!


Is automotive engines cheaper than a 2000h core of airplane engine? (with
the PSRU).

This answer doesn't make sense....


The folks I have seen who go out and buy a converted automobile engine for
their airplane have spent around $15,000 by the time they got it flying.
That is about the price of a field overhauled Lycoming or Continental of
similiar horsepower.
That is what he just said. I bought a midtime Lycoming O-290-D 135HP
engine for my Cavalier 102.5. I paid $1200 for the engine ready to run.
All I have to do to it is bolt it into the airplane and put a prop on it,
which I bought from the same gentleman for $400. I am going with an
aircraft engine. :-)

Highflyer
Highflight Aviation Services
Pinckneyville Airport ( PJY )

"Morgans" wrote in message
news

An automotive engine burn the same amount of gas than an airplane one

Bull****....

Any engine that burns gasoline will burn very close to the same amount
of
gasoline per horsepower hour. Conservatively figure .5 pounds per
horsepower per hour. The best you are likely to get is .43 or so. The
worst is probably not more than .6. To get much better than that you
would
have to be able to use your exhaust stacks to make ice cubes.

An automobile engine burns the same amount of gas an an aircraft engine
per
horsepower hour.

Is that better!

If you are saying that an air cooled aircraft engine burns the same amount
of gas as a water cooled engine (auto or aircraft), then I say you are
wrong.

The water cooled engine is able to burn less fuel per HP produced because
of
many factors, major ones being the cooler cylinder, non tapered bore, and
ability to run leaner with less danger of preignition and detonation.
Backing that up is the fact that air cooled engines disappeared from
automobiles, primarily because they could not meet emission standards.
Wasted gas, unburned, going out with the exhaust is one of the things that
could not be improved on enough. Also, it is interesting that the Scaled
Composite's around the world piston engine was to be liquid cooled,
primarily to improve on fuel economy.

There are too many examples of water cooled airplane engines that are
flying, and reporting lower fuel burns compared to the air cooled
examples,
to argue that water cooled engines are not superior (in fuel burn) to air
cooled engines. The difference is even greater for the conversions using
a
computer to control fuel mixtures.

There is no arguing that converting and working out the bugs in an auto
conversion is a tricky, and expensive proposition. Some people thrive on
that, just like people who drag race and build hot rods. If the person is
not in to that kind of thing, then they should stick to the proven,
standard, aircraft engine.

It is a shame that Lycoming and Continental (and others) are not making
faster progress on creating easy to substitute water cooled engines, and
jet
fuel burning piston engines for the GA fleet. Small tubojet and turboprop
engines would be nice, too. It could open up options that would be
beneficial to many people, and many designs.
--
Jim in NC

I am not really sure which side of some of these issues I really want to be
on; for a lot of reasons.

First, I too, was instructed in the mythology of *real* airplane engines.
However, I have come to doubt much of what I was taught, and the two
examples which I can think of at the moment a
1) Full rich on take-off, except at high altitude airports, to cool the
engine. Wrong! The real reason is far more important, and failure to
follow the directive is far more destructive. We *really* do it to prevent
detonation, because we can't retard the spark. The obvious defense of the
procedure is that it works, and will continue to work as long as we use
fuel(s) with a radical change of performance number between lean and rich
operation.
2) Dual magneto ignition makes them ultra-reliable. Well, yeah, sort-of,
assuming that you keep them e-gapped correctly, and timed correctly, and
understand mag-drop, and ...

My point is that the ECM for a modern automotive controls mixture and intake
temperature far better than I ever could or ever will, handles timing quite
nicely as well, and provides pretty good early warning of most failure modes
as well. That is not to say that the redundancy of dual magnetos, if fully
maintained, can't provide better reliability for a long flight than a single
ignition ECM; but I strongly suspect that a single ignition ECM with a coil
per cylinder (as is now typical) may provide equal or better reliability
than a typical dual mag installation in the real world--at least in the real
world that I saw years ago.

I also have doubts whether the emissions problems that we saw 30 years ago
with air cooled automotive engines would be true today. We can now meter
fuel and airflow, and measure temperature and residual oxygen levels quite
reliably. Therefore, air cooled engines might be capable of the same fuel
efficiency as liquid cooled engines--or slightly better if I correctly
understand the Carnot Cycle. OTOH, I doubt there is any real motivation for
any automotive manufacture to bother.

As to liquid cooling in airplanes, there are not only a considerable number
currently flying; many were quite well developed long ago and played a roll
roughly equal to their air cooled counterparts in WWII. And they did so on
behalf of the US, UK, Germany, USSR, Japan and probably others.

Everything is a compromise. Speed and drag (induced plus equivalent flat
plate area) pretty much dictate the size of propeller disk area required.
Propeller disk area defines diameter. Propeller diameter strongly
influenced RPM. And so forth.

One size does not fit all. Just as an example, a VW powered STOL with a
cruising speed around 60 kts requires a larger diameter prop (and probably a
redrive) than does a KR-2. We do not all need 84 inch props turning 2000
rpm. There really are designs that perform much better with 48 to52 inch
props. And most homebuilts fall in between those figures.

Peter

It is a shame that Lycoming and Continental (and others) are not making
faster progress on creating easy to substitute water cooled engines, and jet
fuel burning piston engines for the GA fleet. Small tubojet and turboprop
engines would be nice, too. It could open up options that would be
beneficial to many people, and many designs.

Liability issues. Better stuff means the old stuff was
defective, or so a lawyer will argue and a jury will swallow.
R&D costs. Everybody wants at least $100K a year. The
governments want big certification fees, at least here in Canada.
The old stuff is making money. For how long yet, no one can
guess, but it's probably a shortsighted strategy, seeing that the
Europeans are building certified diesels that drop into existing
airframes. See http://www.centurion-engines.com/c17/c17_start.htm
Small turboprops and jets are inefficient because of the
very small diameter/area of the compressors and turbines, similar to
the low efficiencies of very small propellers. Rule of thumb says that
anything below 400 HP is going to get too thirsty for the power it
produces. Converted APUs like the one I saw at Arlington a few years
ago generated 150 hp but burned 18 GPH, which is at around 50% worse
than an O-320 running at full throttle at sea level and producing the
same 150 HP. And that's 18 GPH of diesel or jet, which has more energy
per gallon than gasoline and weighs more.

Dan

On Mon, 13 Feb 2006 02:48:12 -0500, "Morgans"
wrote:

The water cooled engine is able to burn less fuel per HP produced because of
many factors, major ones being the cooler cylinder, non tapered bore, and
ability to run leaner with less danger of preignition and detonation.
Backing that up is the fact that air cooled engines disappeared from
automobiles, primarily because they could not meet emission standards.
Wasted gas, unburned, going out with the exhaust is one of the things that
could not be improved on enough. Also, it is interesting that the Scaled
Composite's around the world piston engine was to be liquid cooled,
primarily to improve on fuel economy.

I used to think so too, but after reading about the physics of fuel
economy I've come to the conclusion that aircraft engines, under very
specific circumstances, usually beat out auto engines in terms of
BSFC.

When properly leaned for best economy, aircraft engines will turn in a
BSFC of under .40. Auto engines normally run in the range of .50,
even during cruise.

So why do auto engine conversions seem to get a better fuel burn in
real life? Mostly because most pilots do not lean their engines as
much as is possible. Plus, they do not lean on the ground, or during
climb. I'm generalizing here, some pilots do lean on the ground and
during climb of course.

With a auto conversion, even one that's carburated, the fuel mixture
setting is normally much closer to ideal than the overly rich initial
setup the aircraft engine is set to.

So even during full power takeoffs, the auto conversion is not running
as rich as the aircraft engine becuase it does not need to do so in
order to prevent overheating or detonation.

Most aircraft engines have fixed timing, which requires that they run
excessively rich during full power takeoffs in order to prevent
overheating and detonation. Auto engines have variable timing so they
do not need to run excessively rich mixtures in order to reduce
detonation and overheating.

So it may seem that the auto engines are getting better fuel economy
when used as aircraft power plants, but their BSFC usually is not as
good as that of a properly leaned aircraft engine.

Corky Scott

I'm rather curious, considering the current fuel situation,

What would a healthy dose of alcohol do the the BSFC and power
output?

I'm a little familiar with some of the handling and corrosion
issues from a friend that races quarter midgets.

Richard