Differences between automotive & airplane engines

Lou wrote:

I'll agree with the automotive engine with PSRU being heavier, but are
you sure about your other statement "the lighter the better"?
I'm currently looking at an engine that is 100lbs lighter than the one
recommended for my plane. Although cutting 100lbs from the total
weight is a dream come true, it brings up the question of weight and
balance. I can move the engine forward to make up the difference in
balance, but I don't know how far or how to find out.
Lou


Googling this group for weight and balance yields 25 pages...
So I picked up one of mine here (Dec 10, 2002) and included
Brian's note at the bottom...
(Unfortunately, there was no link attached, so here is the text).



There is a lot of smoke and mirror magic around weight and balance
because so many people understand it so poorly.

At the heart of all of it, though, is a rotational force about a
reference point. the rotational force is called a MOMENT, and
the reference point is called the DATUM.

Sometimes the datum is located at the tip of the spinner.
Sometimes it's located at the main gear axles.
Sometimes its located at the leading edge of the wing.
It doesn't particularly matter where it is located, as long
as you use the same location to work the problem.

You'll often see the term STATION. This is the distance from the
datum to a particular place on the aircraft. Say, for instance,
the instrument panel?

The station numbers change according to where the datum is placed.
But the instrument panel stays in the same physical location.
It's all an offset from a zero point.

One reason to place the datum at the tip of the spinner is because
all the station numbers are positive. No negative distances to
confuse things.

One reason to place the datum at the axles is because the datum
is station zero.zero. Multiply the weight on the wheel times
zero (the ARM is zero at the datum) and the moments for that
wheel come out to zero. Makes the arithmetic a little easier?

And, the reason to place the datum at the leading edge of the wing
it because that's where we are going to wind up anyway. The results
of our CG calculations will finally boil down to a point some given
distance aft of the leading edge.

CG range is often refereed to in terms of a percentage of the wing
chord. Say 25% would be the forward CG limit, maybe 33% would be the
aft limit. So our end number actually refers to a distance aft of
the leading edge. The actual numbers will be different, depending
on where the datum is located, but they all (hopefully) come out
at the same place on the airplane.

First rule:

weight x distance = moments pounds x inches = pound inches (!)
So,
moments / inches = pounds
and
moments / pounds = inches

Practical example:

A bowling ball, held at the chest, has a certain weight.
Held at arms length, it has exactly the same weight!

But due to the longer distance (called ARM) it has a much higher moment.
\
THAT's what feels so heavy.
That rotational force.

So, to solve your little weight and balance question.

The only distance from anything. that matters, is the
distance from the CG of the instrument to the DATUM
specified for that aircraft.

If you have a "before" weight and balance already done,
multiply the weight of the instrument times the distance
from the datum given in the "before" problem.

Then add that moment to the airplane's moment,
and the instrument weight to the airplane's weight.

Divide the new moments by the new weight and you get the
new CG location.

Does that help?

Or do you maybe feel like I sometimes do after some
of your answers???


From: Brian Anderson - view profile
Date: Tues, Dec 10 2002 12:22 am

Jim,

EE's are the brightest of the lot - - - they can measure and calculate
things you can't even see.

The revised CG calculation is straightforward, but you need to calculate the
original moment first, i.e. the total weight [W] x the arm from the datum
[D]. Add to this the additional moment for the instrument, i.e. 8 lbs x the
distance of the instrument CG from the datum [d]. The resulting moment is
[W*D] + [8*d]. Divide this by the new total weight [W+8], and the result is
the new CG location from the datum.

Hence, new CG location = [[W x D] + [8 x d]]/[W+8]

I know even an elderly EE can follow that. After all, I is one too.

Brian

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?

Also level the plane as it would fly though the air.Only my $0.02.
LJ

Richard Lamb wrote:
Lou wrote:

I'll agree with the automotive engine with PSRU being heavier, but are
you sure about your other statement "the lighter the better"?
I'm currently looking at an engine that is 100lbs lighter than the one
recommended for my plane. Although cutting 100lbs from the total
weight is a dream come true, it brings up the question of weight and
balance. I can move the engine forward to make up the difference in
balance, but I don't know how far or how to find out.
Lou


Googling this group for weight and balance yields 25 pages...
So I picked up one of mine here (Dec 10, 2002) and included
Brian's note at the bottom...
(Unfortunately, there was no link attached, so here is the text).



There is a lot of smoke and mirror magic around weight and balance
because so many people understand it so poorly.

At the heart of all of it, though, is a rotational force about a
reference point. the rotational force is called a MOMENT, and
the reference point is called the DATUM.

Sometimes the datum is located at the tip of the spinner.
Sometimes it's located at the main gear axles.
Sometimes its located at the leading edge of the wing.
It doesn't particularly matter where it is located, as long
as you use the same location to work the problem.

You'll often see the term STATION. This is the distance from the
datum to a particular place on the aircraft. Say, for instance,
the instrument panel?

The station numbers change according to where the datum is placed.
But the instrument panel stays in the same physical location.
It's all an offset from a zero point.

One reason to place the datum at the tip of the spinner is because
all the station numbers are positive. No negative distances to
confuse things.

One reason to place the datum at the axles is because the datum
is station zero.zero. Multiply the weight on the wheel times
zero (the ARM is zero at the datum) and the moments for that
wheel come out to zero. Makes the arithmetic a little easier?

And, the reason to place the datum at the leading edge of the wing
it because that's where we are going to wind up anyway. The results
of our CG calculations will finally boil down to a point some given
distance aft of the leading edge.

CG range is often refereed to in terms of a percentage of the wing
chord. Say 25% would be the forward CG limit, maybe 33% would be the
aft limit. So our end number actually refers to a distance aft of
the leading edge. The actual numbers will be different, depending
on where the datum is located, but they all (hopefully) come out
at the same place on the airplane.

First rule:

weight x distance = moments pounds x inches = pound inches (!)
So,
moments / inches = pounds
and
moments / pounds = inches

Practical example:

A bowling ball, held at the chest, has a certain weight.
Held at arms length, it has exactly the same weight!

But due to the longer distance (called ARM) it has a much higher moment.
\
THAT's what feels so heavy.
That rotational force.

So, to solve your little weight and balance question.

The only distance from anything. that matters, is the
distance from the CG of the instrument to the DATUM
specified for that aircraft.

If you have a "before" weight and balance already done,
multiply the weight of the instrument times the distance
from the datum given in the "before" problem.

Then add that moment to the airplane's moment,
and the instrument weight to the airplane's weight.

Divide the new moments by the new weight and you get the
new CG location.

Does that help?

Or do you maybe feel like I sometimes do after some
of your answers???


From: Brian Anderson - view profile
Date: Tues, Dec 10 2002 12:22 am

Jim,

EE's are the brightest of the lot - - - they can measure and calculate
things you can't even see.

The revised CG calculation is straightforward, but you need to calculate
the
original moment first, i.e. the total weight [W] x the arm from the datum
[D]. Add to this the additional moment for the instrument, i.e. 8 lbs x the
distance of the instrument CG from the datum [d]. The resulting moment is
[W*D] + [8*d]. Divide this by the new total weight [W+8], and the
result is
the new CG location from the datum.

Hence, new CG location = [[W x D] + [8 x d]]/[W+8]

I know even an elderly EE can follow that. After all, I is one too.

Brian

Richard Lamb wrote:
Lou wrote:

I'll agree with the automotive engine with PSRU being heavier, but are
you sure about your other statement "the lighter the better"?
I'm currently looking at an engine that is 100lbs lighter than the one
recommended for my plane. Although cutting 100lbs from the total
weight is a dream come true, it brings up the question of weight and
balance. I can move the engine forward to make up the difference in
balance, but I don't know how far or how to find out.
Lou


Googling this group for weight and balance yields 25 pages...
So I picked up one of mine here (Dec 10, 2002) and included
Brian's note at the bottom...
(Unfortunately, there was no link attached, so here is the text).



There is a lot of smoke and mirror magic around weight and balance
because so many people understand it so poorly.

At the heart of all of it, though, is a rotational force about a
reference point. the rotational force is called a MOMENT, and
the reference point is called the DATUM.

Sometimes the datum is located at the tip of the spinner.
Sometimes it's located at the main gear axles.
Sometimes its located at the leading edge of the wing.
It doesn't particularly matter where it is located, as long
as you use the same location to work the problem.

You'll often see the term STATION. This is the distance from the
datum to a particular place on the aircraft. Say, for instance,
the instrument panel?

The station numbers change according to where the datum is placed.
But the instrument panel stays in the same physical location.
It's all an offset from a zero point.

One reason to place the datum at the tip of the spinner is because
all the station numbers are positive. No negative distances to
confuse things.

One reason to place the datum at the axles is because the datum
is station zero.zero. Multiply the weight on the wheel times
zero (the ARM is zero at the datum) and the moments for that
wheel come out to zero. Makes the arithmetic a little easier?

And, the reason to place the datum at the leading edge of the wing
it because that's where we are going to wind up anyway. The results
of our CG calculations will finally boil down to a point some given
distance aft of the leading edge.

CG range is often refereed to in terms of a percentage of the wing
chord. Say 25% would be the forward CG limit, maybe 33% would be the
aft limit. So our end number actually refers to a distance aft of
the leading edge. The actual numbers will be different, depending
on where the datum is located, but they all (hopefully) come out
at the same place on the airplane.

First rule:

weight x distance = moments pounds x inches = pound inches (!)
So,
moments / inches = pounds
and
moments / pounds = inches

Practical example:

A bowling ball, held at the chest, has a certain weight.
Held at arms length, it has exactly the same weight!

But due to the longer distance (called ARM) it has a much higher moment.
\
THAT's what feels so heavy.
That rotational force.

So, to solve your little weight and balance question.

The only distance from anything. that matters, is the
distance from the CG of the instrument to the DATUM
specified for that aircraft.

If you have a "before" weight and balance already done,
multiply the weight of the instrument times the distance
from the datum given in the "before" problem.

Then add that moment to the airplane's moment,
and the instrument weight to the airplane's weight.

Divide the new moments by the new weight and you get the
new CG location.

Does that help?

Or do you maybe feel like I sometimes do after some
of your answers???





Thanks Rich,
This information does help quite a bit, and I'm happy that I could
make you feel a little smarter everytime I answer one of your posts.
Lou

On 10 Feb 2006 05:55:48 -0800, "Lou" wrote:

I'll agree with the automotive engine with PSRU being heavier, but are
you sure about your other statement "the lighter the better"?
I'm currently looking at an engine that is 100lbs lighter than the one
recommended for my plane. Although cutting 100lbs from the total
weight is a dream come true, it brings up the question of weight and
balance. I can move the engine forward to make up the difference in
balance, but I don't know how far or how to find out.
Lou
That is simple to determine. Get a good book on aircraft design and do
the math. multiply the weight times the distance in inches from the
genter of gravity of the plane to the center of mass on the original
engine. Then devide that number by the weight of the new
powerplant.The answer is the distance in inches to the center of mass
of the engine.

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


Bull****....

It can, too. The volumetric efficiency of a high-RPM engine
suffers at that higher RPM, and I have experience with a Soob to prove
it.

Dan

"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 )

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 )

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

"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