Auto conversions & gear boxes

On Tue, 09 Mar 2004 03:18:59 GMT, Peter Dohm
-KNOW wrote:

At the moment, the Geshwender drive (which is back in production despite Mr G's
death) looks like the most reliable scheme for much more than 100 horsepower,
any may still be the best value in the long run.

I agree, but add that this psru was originally designed for high
output engines, engines that start with around 400 horsepower.

For those interested, the reason Fred designed the psru in the first
place was to provide a less expensive engine alternative for crop
dusters. The engine he used was a Ford big block V8. I think that
smaller psru's may be available now but I haven't checked for a while.

When I called him to talk about his psru a year before he died, he
talked me out of using it because it was overkill to use that psru on
an engine putting out only 190 or so hp.

Corky Scott

Corky Scott wrote:

On Tue, 09 Mar 2004 03:18:59 GMT, Peter Dohm
-KNOW wrote:

At the moment, the Geshwender drive (which is back in production despite Mr G's
death) looks like the most reliable scheme for much more than 100 horsepower,
any may still be the best value in the long run.

I agree, but add that this psru was originally designed for high
output engines, engines that start with around 400 horsepower.

For those interested, the reason Fred designed the psru in the first
place was to provide a less expensive engine alternative for crop
dusters. The engine he used was a Ford big block V8. I think that
smaller psru's may be available now but I haven't checked for a while.

When I called him to talk about his psru a year before he died, he
talked me out of using it because it was overkill to use that psru on
an engine putting out only 190 or so hp.

Corky Scott

I agree about it being overkill. An it is not cheap either. However, it looks
like something you can trust.

It's really an interesting dilemma that I will have to face when I get ready to
build. If you don't require true short field capability, and only need a two
seater; you can give up a little power and thrust, and build a v6 version of
Steve Wittman's Tailwind installation.

I admit that I am willing to give up a lot of "utility" for the few features
that I think I need. I really don't consider landing speed very important, but
want adequate cabin width at my own elbows and shoulders.

The basic point is that I believe that I can power my first project with direct
drive. Probably an engine in the 3.8 to 4.3 liter displacement range turning a
56 to 60 inch diameter prop and developing 130 to 150 horsepower. That should
be enough for a cruising speed of about 130 kts tas.

To be really blunt about it, I could probably design a better airplane with
similar performance around a 110 hp corvair engine--if I knew of a source for
*new* heads and crank cases.

I also recognize that such an installation won't work on a Christavia MK4, which
needs a longer prop. Therefore, you really don't have a choice. You are
building the airplane that those 2400 to 2500 rpm engines were designed for! If
you use an automotive conversion, you need a psru. Hypothetically, you could
get about 170 hp from a 350 cid v8 turning a 72 inch prop at crankshaft rpm; but
you would be lugging the engine, so the smaller engine with the psru would last
longer and would still be at least 50 pounds lighter after allowing for the
drive shaft and thrust bearing adapter on the v8.

Peter

On Wed, 10 Mar 2004 01:27:46 GMT, Peter Dohm
-KNOW wrote:



I also recognize that such an installation won't work on a Christavia MK4, which
needs a longer prop. Therefore, you really don't have a choice. You are
building the airplane that those 2400 to 2500 rpm engines were designed for! If
you use an automotive conversion, you need a psru. Hypothetically, you could
get about 170 hp from a 350 cid v8 turning a 72 inch prop at crankshaft rpm; but
you would be lugging the engine, so the smaller engine with the psru would last
longer and would still be at least 50 pounds lighter after allowing for the
drive shaft and thrust bearing adapter on the v8.

Peter

I'm building a Christavia Mk4 and have the Ford 3.8 installed in it
right now. The psru I'll be using was one of the products put out by
NW Aero before Johhny Lindgren acquired the business. Johhny made the
psru for the Ford V6's available for a while but does not do so any
longer because very few people seem interested in it.

He does have psru's for Chevy V6's and V8's though and I bought all
the things I need for my engine from him. Things like the camshaft,
distributer, alternator and brackets, and the proper sized pulleys to
drive everything. He can still get them.

The original psru has undergone considerable modification and looks
like a very nice unit. The top and outer drive cog bearings are now
lubricated by an enclosed oil bath, rather than by grease that must be
injected periodically by the owner.

There was a failure written up by a guy who had a Chevy V-8 in his
Lancair. The drive cog bearing seized and the belt broke. He landed
short and the airplane flipped over when the wheels dug into the soft
ground but the guy was ok. Saw some pictures of it in Contact!
magazine. The drive cog bearing had overheated and seized and the guy
admitted he did not really know how much to grease it, or how much to
put in while greasing and apparently hadn't for a while.

I'd call those bearings pretty critical parts and I'd want to have
maintenance logs telling me exactly when they were last greased.

The engine, by the way, continued to run fine and the owner was
planning to get the updated psru, which he felt was a better design.

The Chevy V6 is a pretty good engine and has a good track record when
used in airplanes but it's considerably heavier than the Ford V6
because it has cast iron heads, intake manifold and timing chain
cover. All the afore mentioned parts are aluminum in the Ford, which
makes it the lightest V6 of that type of design in the US.

You can buy all kinds of aluminum parts for it (the Chevy) to lighten
it up, but the aluminum heads are competition models and the intake
valves and air passages are designed for max power at high rpm and
they don't adopt very well to moderate output levels. You can also
buy aluminum intake manifolds for it and probably aluminum oil pans
too. It's just that each purchase takes you beyond the cost of the
original engine. I've said this before but if money were no object,
or if I had no mechanical background, I would not be converting an
auto engine. I'd just bite the bullet and spend the $10,000 to
$15,000 it takes to get a reasonable, well maintained Lycoming or
Continental. I still think it's incredible that engines can cost that
much, but they do.

Corky Scott

On Wed, 10 Mar 2004 14:29:29 GMT,
(Corky Scott) wrote:



He does have psru's for Chevy V6's and V8's though and I bought all
the things I need for my engine from him. Things like the camshaft,
distributer, alternator and brackets, and the proper sized pulleys to
drive everything. He can still get them.

Clarification: Sorry, this paragraph is confusing. What I meant to
say is that Johnny does not offer the psru for the Ford anymore, but
he does still offer some parts for it. Or at least I was able to get
them from him.

The distributer is machined for him and he installs dual sensors so
that you can run two electronic ignition systems. The distributer is
set up with advance weights so that the engine can be started at zero
degrees BTDC and then advances to it's running timing setting after
the start. This makes for easy starting.


You can buy all kinds of aluminum parts for it (the Chevy) to lighten
it up, but the aluminum heads are competition models and the intake
valves and air passages are designed for max power at high rpm and
they don't adopt

Adopt should be adapt.

very well to moderate output levels. You can also
buy aluminum intake manifolds for it and probably aluminum oil pans
too. It's just that each purchase takes you beyond the cost of the
original engine. I've said this before but if money were no object,
or if I had no mechanical background, I would not be converting an
auto engine. I'd just bite the bullet and spend the $10,000 to
$15,000 it takes to get a reasonable, well maintained Lycoming or
Continental. I still think it's incredible that engines can cost that
much, but they do.

Corky Scott

Corky Scott wrote:

On Wed, 10 Mar 2004 14:29:29 GMT,
(Corky Scott) wrote:


He does have psru's for Chevy V6's and V8's though and I bought all
the things I need for my engine from him. Things like the camshaft,
distributer, alternator and brackets, and the proper sized pulleys to
drive everything. He can still get them.

Clarification: Sorry, this paragraph is confusing. What I meant to
say is that Johnny does not offer the psru for the Ford anymore, but
he does still offer some parts for it. Or at least I was able to get
them from him.

The distributer is machined for him and he installs dual sensors so
that you can run two electronic ignition systems. The distributer is
set up with advance weights so that the engine can be started at zero
degrees BTDC and then advances to it's running timing setting after
the start. This makes for easy starting.

You can buy all kinds of aluminum parts for it (the Chevy) to lighten
it up, but the aluminum heads are competition models and the intake
valves and air passages are designed for max power at high rpm and
they don't adopt

Adopt should be adapt.

very well to moderate output levels. You can also
buy aluminum intake manifolds for it and probably aluminum oil pans
too. It's just that each purchase takes you beyond the cost of the
original engine. I've said this before but if money were no object,
or if I had no mechanical background, I would not be converting an
auto engine. I'd just bite the bullet and spend the $10,000 to
$15,000 it takes to get a reasonable, well maintained Lycoming or
Continental. I still think it's incredible that engines can cost that
much, but they do.

Corky Scott

It looks like you've made the right choices for the type aircraft, and
I'm eager to read about the flight experiences.

Peter

longer is better not only applies to propellers, i'll wager!
"Richard Lamb" wrote in message
...
Dave Covert wrote:

I notice that most auto engine conversions use a gear box between the
engine
and the prop. Why is that? Is it because an auto engine's peak HP is too
high for a prop to swing? Is it because auto engines weren't designed to
be
pulled around by their crankshafts and don't have proper thrust
bearings?
Both?

Are there any auto/motorcycle conversions that don't require gear boxes?

Dave

Some people think aircraft engines are "old fashioned technology"
and have not kept up with developments in auto engine field.

They point out that aircraft engines haven't changed much in
over 50 years.

Some people feel that auto engines can be used to power airplanes.

To some extent, all three of these ideas are true.

Aircraft engine do not run like car motors.

Aircraft engines run at much higher sustained power settings and
constant rpm for long periods of time.

And then there is the propeller...
Turning the propeller is what it's all about.

The propeller converts the engine's power into thrust.
As always, when energy is converted, there are losses.

Moving through the air at very high speeds, the propeller
makes lift (thrust, which is power successfully converted into
forward motion) and drag (pure conversion losses).

So, propeller efficiency is extremely important.

If the propeller is only 50% efficient, half of the
power generated by the engine is wasted in losses.
Yes, literally.

Only one hard rule for propellers - longer is better.

But longer blades mean lower RPM because the tips of the
propeller blades MUST stay below the speed of sound (yep,
Mach 1, really) for any efficiency at all.

Part of the reason for this is the huge increase in drag
as the tip enters the transonic (speed) region.

It takes TORQUE to turn that propeller - not horsepower.

A given propeller needs to turn at a given RPM, which
will require a given amount of torque.

If the engine makes enough torque to turn the propeller at
that RPM, a direct drive set up may be possible.

There are a lot of other minor details that may get in the way -
Harmonic Resonance is a big one.
But, it may be possible to run this combination direct drive.

If the engine needs to turn at a higher RPM to make adequate
power, some kind of gearing would be necessary to reduce engine
RPM to propeller RPM. Notice that reducing RPM will increase
torque proportionally. Seems like a nice trade off.

Now the engine should be running at an RPM near the peak of its'
torque curve. This is for best engine operating economy.

And the (longer) propeller is running at a comfortable (lower)
RPM for good efficiency. Life is wonderful.

Except for the weight.
Auto engines are seldom as light as possible.
Then we add more weight in the form of a gearbox and such.
Radiators full of heavy (hot!) fluids.
External oil sump?
Mounting?
Propeller gyroscopic forces operating on the crankshaft?

Weight is critical to any flying machine.
(Go back and look at how birds are built)

So...
Think of it as evolution in action.

The reason our old antique Lycosourus engines are the way they
are is that they evolved into a very narrow niche.

They turn propellers to pull airplanes.

They make very high torque
at very low RPM,
and are as light as possible.
They are tremendously reliable and fairly efficient.

Prices are high because of limited production and high demand.
Simple economics.

But the economics of engine development (and risk assesment) are
anything but simple.

I have a big bore VW (2180cc) on my parasol.
That's a converted car motor.

There is a weatlh of prior art using VW engines for small airplanes
(if one is inclined to use it).

What works, and what doesn't. (eg: breaking cast crankshafts)

Mine is a very simple conversion, using high quality (GPAS) parts
built by a little German perfectinist.
I trust it - so far.

I also don't push it beyond conservative limits.

All VW engines are 40 hp engine (IMHO).
Some can make more power than that - for a while.
This one is _rated_ at 70 hp.
But will reach thermal limits of the fin area and overheat
if not throttled back (to roughly 40?)

It's a fairly expensive motor.
The jugs and pistons are standard parts, but the crank (!) and
accessories and machine work are all specialty items.
A new 2180 can easily go over $5000 with a few bells and whistles.

But the weight, power, reliability, and operating cost are all within
reason for this particular airplane.

The airplane itself can land slowly, around 35 mph.

The chances of getting down safely if the engine quits are a lot better
at 35 than they are at 53.

To me, it seems like a reasonable risk for the potential rewards.

But...

Your milage may vary.

Richard

http://www.flash.net/~lamb01


PS: I've read of a Curtiss Hawk replica that uses a direct drive Chevy
350.
It's supposed to make roughly 190 hp?
It would obviously be a heavy motor.
Not something you'd hang on a glass slipper.
But on a big old biplane with a looong prop
it seems to be just the ticket.

I think longer is only better in terms of static thrust, not
necessarily top aircraft speed.


"wes marso" wrote in message ...
longer is better not only applies to propellers, i'll wager!