Auto conversions & gear boxes

On Fri, 20 Feb 2004 16:27:38 GMT, "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

Dave, this is kindof the Auto Conversion 101 question no. 1. The
answer is pretty much all of the above.

Auto crankshafts aren't designed for bending loads, so if you bolt a
prop to one, you are taking a big chance that the prop loads
transferred directly to the hub of the crankshaft you bolted the prop
to, could fail the crankshaft, just behind the prop hub.

Many of the early VW direct drive engines did fail in this manner.
This resulted in a lot of changes to the VW engine when used as an
airplane engine, one of the changes was to redesign the crankshaft.
Not all VW engines get so modified though, even today.

Props have an rpm range in which they are most effective. There are
an incredible number of variables, but diameter, shape, cord, pitch,
thickness all play a part in prop design. A bitty prop turning very
fast just isn't as effective as a large prop turning slower. The
smaller prop, with it's smaller diameter has less thrust because much
of the prop is blowing air against the nose of the airplane. It's a
lot more complicated than that but that's the gist.

Auto engines are tiny when compared to direct drive airplane engines.
Take a 180 hp Lycoming. It's cubic inch displacement is 360. They
turn the prop at around 2600 to 2700. The Ford V-6 in airplane trim,
puts out 180 hp also. It displaces 232 inches and makes it's power at
4800 rpm. No prop will work at that rpm. To harness the power, it
needs to be turned slower. Enter the prop speed reduction unit.

The psru takes care of keeping the bending loads off the crankshaft
and reduces prop speed to a more useable rpm.

Yes there are motorcycles that are being used in airplanes, the BMW
comes to mind.

Corky Scott

On Fri, 20 Feb 2004 18:08:35 GMT,
(Corky Scott) wrote:


Auto engines are tiny when compared to direct drive airplane engines.
Take a 180 hp Lycoming. It's cubic inch displacement is 360. They
turn the prop at around 2600 to 2700. The Ford V-6 in airplane trim,
puts out 180 hp also. It displaces 232 inches and makes it's power at
4800 rpm. No prop will work at that rpm. To harness the power, it
needs to be turned slower. Enter the prop speed reduction unit.

Speaking of Fords! How's your project coming?

__________________
Note: To reply, replace the word 'spam' embedded in return address with 'mail'.
N38.6 W121.4

On 20 Feb 2004 14:19:16 -0600, Barry S. wrote:

On Fri, 20 Feb 2004 18:08:35 GMT,
(Corky Scott) wrote:


Auto engines are tiny when compared to direct drive airplane engines.
Take a 180 hp Lycoming. It's cubic inch displacement is 360. They
turn the prop at around 2600 to 2700. The Ford V-6 in airplane trim,
puts out 180 hp also. It displaces 232 inches and makes it's power at
4800 rpm. No prop will work at that rpm. To harness the power, it
needs to be turned slower. Enter the prop speed reduction unit.

Speaking of Fords! How's your project coming?

__________________
Note: To reply, replace the word 'spam' embedded in return address with 'mail'.
N38.6 W121.4

Slowly. I have the engine assembled and is currently mounted in the
airframe. But there's everything else to do. The airframe has yet to
be blasted and painted. I think that can happen this summer. On the
other hand, we are planning some major kitchen redo's and trust me,
ALL of my attention had better be on that.

I've built an engine test stand that will allow me to wheel the engine
outside and run it, with the prop installed. I'd like to get some 30
or so hours on the engine before it gets it's final installation onto
the airframe. I decided this after listening to a crusty old DAR
speak at a local EAA meeting. It sounded to me like he'd be REALLY
unhappy with such an engine unless I could show him that it had been
thoroughly tested.

At this point, I'm being educated about headers. I was going to just
bend up a bunch of tubes, weld them to be what I need, get them jet
coated and call it good. Then I started doing some research.

It turns out that the diameter of header tubing is critical to the
performance of the engine. Larger diameter is not necessarily better.
In fact in almost all aircraft type applications, bigger is virtually
for sure not better. The exhaust header flange has openings that are
1.75" in diameter. This matches the exhaust port opening in the head.
But the tubing diameter should be 1.5", or possibly even 1 3/8" in
diameter. Also, the length of the runners should be at least over 30
inches, and 36 would be better. In addition, each tube should be as
close in length to each other as possible. Finally, the collector
needs to be about 1 78" diameter and it should be 18" long.

Reality is rearing it's ugly head. The lengths I mentioned literally
won't fit without welding the headers into loops. Not going to
happen.

I think the best I can do is get the runners as long as I can make
them and make sure they are of equal length, and get the proper
collector as that also has a huge affect on engine operation.

Why is it so important to have the runners be the same length?
Because different length runners cause different scavenging effects
within the combustion chamber. You will end up with an engine that
does not respond to ignition adjustments nor mixture adjustments as
some combustion chambers will run rich and some lean. "A series of
single cylinder engines flying loosely in formation." Quote from John
Deakin.

Many builders of the Ford V6 have complained that their engine ran
rough at maximum power. Huge effort was made to modify the intake
manifold to correct the problem. But I have not seen a single picture
of an exhaust manifold where the effort was made to create equal
length exhaust headers of the proper diameter.

I talked with a header manufacturer who told me he had heard of Dave
Blanton because a bunch of builders had asked him about headers. He
told me they all wanted to ignor his advice about tubing diameter.
They all wanted to use bigger tubing than was dictated, because they
all thought bigger was better. It's not.

Why is it so important to have the proper diameter tubing? Because
the bigger the diameter the slower the velocity of the gasses inside
it, and visa versa, up to a point. Eventually you can have exhaust
tubing in a diameter too small such that exhaust flow is restricted.
Large diameter tubing tends to cause the engine's power to peak at
extreme rpms. The smaller the diameter of the tubing, the more low to
midrange power you have.

But everyone wanted to use 1.75" tubing because that's what the
exhaust port was. 1.75" tubing would be what you would use if you
wanted flash horsepower from the engine at 8,000 rpm, like at the
dragstrip.

The header manufacturer also had a lot to say about "Zoomie" type
headers. These are headers without collectors, basically straight
pipes. Not only are these tubes also usually too large a diameter,
they leave off the collector which is crucial to the proper design of
the header system.

So with all this information, I'm taking my time with the header
design. Obviously something so important to the proper running of the
engine is not something I'm going to throw together without using
proper design criteria.

Corky Scott

Corky,

Do you have any details available about your engine test stand, such as how you restrain it, instrumentation, cooling?

Also, a buddy of mine was talking about an engine build he did, and how he used water to match each header tube volume,
old news I'm sure...

--
Dan D.



..
"Corky Scott" wrote in message ...
On 20 Feb 2004 14:19:16 -0600, Barry S. wrote:

On Fri, 20 Feb 2004 18:08:35 GMT,
(Corky Scott) wrote:


Auto engines are tiny when compared to direct drive airplane engines.
Take a 180 hp Lycoming. It's cubic inch displacement is 360. They
turn the prop at around 2600 to 2700. The Ford V-6 in airplane trim,
puts out 180 hp also. It displaces 232 inches and makes it's power at
4800 rpm. No prop will work at that rpm. To harness the power, it
needs to be turned slower. Enter the prop speed reduction unit.

Speaking of Fords! How's your project coming?

__________________
Note: To reply, replace the word 'spam' embedded in return address with 'mail'.
N38.6 W121.4

Slowly. I have the engine assembled and is currently mounted in the
airframe. But there's everything else to do. The airframe has yet to
be blasted and painted. I think that can happen this summer. On the
other hand, we are planning some major kitchen redo's and trust me,
ALL of my attention had better be on that.

I've built an engine test stand that will allow me to wheel the engine
outside and run it, with the prop installed. I'd like to get some 30
or so hours on the engine before it gets it's final installation onto
the airframe. I decided this after listening to a crusty old DAR
speak at a local EAA meeting. It sounded to me like he'd be REALLY
unhappy with such an engine unless I could show him that it had been
thoroughly tested.

At this point, I'm being educated about headers. I was going to just
bend up a bunch of tubes, weld them to be what I need, get them jet
coated and call it good. Then I started doing some research.

It turns out that the diameter of header tubing is critical to the
performance of the engine. Larger diameter is not necessarily better.
In fact in almost all aircraft type applications, bigger is virtually
for sure not better. The exhaust header flange has openings that are
1.75" in diameter. This matches the exhaust port opening in the head.
But the tubing diameter should be 1.5", or possibly even 1 3/8" in
diameter. Also, the length of the runners should be at least over 30
inches, and 36 would be better. In addition, each tube should be as
close in length to each other as possible. Finally, the collector
needs to be about 1 78" diameter and it should be 18" long.

Reality is rearing it's ugly head. The lengths I mentioned literally
won't fit without welding the headers into loops. Not going to
happen.

I think the best I can do is get the runners as long as I can make
them and make sure they are of equal length, and get the proper
collector as that also has a huge affect on engine operation.

Why is it so important to have the runners be the same length?
Because different length runners cause different scavenging effects
within the combustion chamber. You will end up with an engine that
does not respond to ignition adjustments nor mixture adjustments as
some combustion chambers will run rich and some lean. "A series of
single cylinder engines flying loosely in formation." Quote from John
Deakin.

Many builders of the Ford V6 have complained that their engine ran
rough at maximum power. Huge effort was made to modify the intake
manifold to correct the problem. But I have not seen a single picture
of an exhaust manifold where the effort was made to create equal
length exhaust headers of the proper diameter.

I talked with a header manufacturer who told me he had heard of Dave
Blanton because a bunch of builders had asked him about headers. He
told me they all wanted to ignor his advice about tubing diameter.
They all wanted to use bigger tubing than was dictated, because they
all thought bigger was better. It's not.

Why is it so important to have the proper diameter tubing? Because
the bigger the diameter the slower the velocity of the gasses inside
it, and visa versa, up to a point. Eventually you can have exhaust
tubing in a diameter too small such that exhaust flow is restricted.
Large diameter tubing tends to cause the engine's power to peak at
extreme rpms. The smaller the diameter of the tubing, the more low to
midrange power you have.

But everyone wanted to use 1.75" tubing because that's what the
exhaust port was. 1.75" tubing would be what you would use if you
wanted flash horsepower from the engine at 8,000 rpm, like at the
dragstrip.

The header manufacturer also had a lot to say about "Zoomie" type
headers. These are headers without collectors, basically straight
pipes. Not only are these tubes also usually too large a diameter,
they leave off the collector which is crucial to the proper design of
the header system.

So with all this information, I'm taking my time with the header
design. Obviously something so important to the proper running of the
engine is not something I'm going to throw together without using
proper design criteria.

Corky Scott

On Tue, 24 Feb 2004 11:46:41 GMT, "Blueskies" wrote:

Corky,

Do you have any details available about your engine test stand, such as how you restrain it, instrumentation, cooling?

Also, a buddy of mine was talking about an engine build he did, and how he used water to match each header tube volume,
old news I'm sure...

--
Dan D.

I fabricated the engine stand using a lot of OTLAR measurements.

I pulled some 1 1/4" tubing out of the pile (I bought a pile of tubing
for a Skybolt kit years ago and still have at least half of it left.
I always seem to find enough of what I need for projects like this. I
think the cost for the tubing worked out to something like 10 cents on
the dollar.) and welded a large rectangle. Then I welded plates on
each of the corners and scrounged up four casters from around my shop
and drilled bolt holes in the plates and bolted them on. It has two
swiveling and two that don't. They are largish,solid rubber
commercial casters and I have no idea where I found them originally
but I've had them in the shop for years. I didn't pay anything for
them, I remember that.

Then I duplicated the engine mount rails and bolted them to the
engine. I suspended the engine over the base and fitted and welded
support legs from the rails to each corner of the base. Removed the
engine and welded everything.

Then I added 3/4" diagonal tubing fore and aft between the support
legs so that the engine could not shift or sway. That REALLY
solidified things.

What I'd **like** to do is remove the instrument panel from the
cockpit and mount it on the stand and use what instruments are
necessary to monitor engine performance. That way I don't have to
fabricate two instrument panels. I have not cut any holes for
instruments yet so that's in the near future. Actually buying some
instruments is also in the near future. ;-)

I'll need: Oil pressure, oil temperature, tachometer, water pressure,
water temperature and an EGT guage. It probably wouldn't hurt to have
a cylinderhead temperature guage too. I'm leaning towards digital for
the tach and possibly the temps as well but have not made up my mind
on which of the numerous choices to use.

Or I could just use some scrap plywood since I only need the
instruments that monitor engine performance so the test stand panel
could be smallish. Or I could cut up some of the 1/8" sheet aluminum
from the huge panel I scored for free. Using that stuff takes a lot
more work than using plywood though.

The radiator is sitting below the engine at present, but I think I'm
going to have to move it a bit so that the exhaust system can clear
it. The plan is for the exhaust to wrap under and behind the engine
and tuck right behind the Griffin radiator, when I get it. But for
now, the radiator I picked up from the auto parts place will do the
job. It's a Ford Taurus radiator so I know it's adaquate for the
task. If I pick up the custom radiator before all is installed back
on the airframe, I'll likely fabricate the entire cooling duct system,
including the exhaust augmentation, just to make sure the system cools
properly.

I will leave the engine installed in the fuselage for the moment, so I
can fabricate the exhaust and make sure that it fits the airframe
properly, then the exhaust will be removed from the engine and the
engine transferred to the test stand and the exhaust system
re-installed.

I'll route hoses to the radiator as necessary and weld on a pan to
hold the battery. I'll also have a "gas tank" somewhere on the base
of the stand and will have to use a fuel pump to get the gas up to the
carburetor, probably a submerged type, or something that goes in-line
and I'll just bond on a fuel line out of the gas tank.

I've built the stand tall enough that the prop can be mounted to the
engine.

When I get ready to fire it up, I'll literally have to chain the stand
down so that it does not try to hurtle off into the woods like some
demented woods buggy run amuck.

I may lift the whole thing into the back of the pickup and drive up
into the woods to do the extended running so that the neighbors don't
complain. I'll strap it down for the trip, and for running it, of
course.

I'll probably pitch the prop so that the engine can run to it's
maximum rpm while on the test stand. This will be necessary because
I'll need to make sure the engine can manage full power for extended
periods, plus there may be some tuning and adjustments required that
show up only at full power.

The test stand is roughly patterned after the engine test stands I
worked with while training as an auto mechanic at the Rhode Island
Trades Shops. Those engines did not have props bolted to them though.

If anyone would like to see what the test stand looks like, send me an
e-mail and I'll enclose a picture and send it to you. It's in rough
form right now, not completed, but I have some shots of the engine
bolted in place so you'll get a good idea of what I'm trying to
accomplish. Plus, since it's in the unpainted stage, I can still make
lots of modifications to it, should anyone have any ideas.

Corky Scott

Corky Scott wrote:

On 20 Feb 2004 14:19:16 -0600, Barry S. wrote:

On Fri, 20 Feb 2004 18:08:35 GMT,
(Corky Scott) wrote:


Auto engines are tiny when compared to direct drive airplane engines.
Take a 180 hp Lycoming. It's cubic inch displacement is 360. They
turn the prop at around 2600 to 2700. The Ford V-6 in airplane trim,
puts out 180 hp also. It displaces 232 inches and makes it's power at
4800 rpm. No prop will work at that rpm. To harness the power, it
needs to be turned slower. Enter the prop speed reduction unit.

Speaking of Fords! How's your project coming?

__________________
Note: To reply, replace the word 'spam' embedded in return address with 'mail'.
N38.6 W121.4

Slowly. I have the engine assembled and is currently mounted in the
airframe. But there's everything else to do. The airframe has yet to
be blasted and painted. I think that can happen this summer. On the
other hand, we are planning some major kitchen redo's and trust me,
ALL of my attention had better be on that.

I've built an engine test stand that will allow me to wheel the engine
outside and run it, with the prop installed. I'd like to get some 30
or so hours on the engine before it gets it's final installation onto
the airframe. I decided this after listening to a crusty old DAR
speak at a local EAA meeting. It sounded to me like he'd be REALLY
unhappy with such an engine unless I could show him that it had been
thoroughly tested.

At this point, I'm being educated about headers. I was going to just
bend up a bunch of tubes, weld them to be what I need, get them jet
coated and call it good. Then I started doing some research.

It turns out that the diameter of header tubing is critical to the
performance of the engine. Larger diameter is not necessarily better.
In fact in almost all aircraft type applications, bigger is virtually
for sure not better. The exhaust header flange has openings that are
1.75" in diameter. This matches the exhaust port opening in the head.
But the tubing diameter should be 1.5", or possibly even 1 3/8" in
diameter. Also, the length of the runners should be at least over 30
inches, and 36 would be better. In addition, each tube should be as
close in length to each other as possible. Finally, the collector
needs to be about 1 78" diameter and it should be 18" long.

Reality is rearing it's ugly head. The lengths I mentioned literally
won't fit without welding the headers into loops. Not going to
happen.

I think the best I can do is get the runners as long as I can make
them and make sure they are of equal length, and get the proper
collector as that also has a huge affect on engine operation.

Why is it so important to have the runners be the same length?
Because different length runners cause different scavenging effects
within the combustion chamber. You will end up with an engine that
does not respond to ignition adjustments nor mixture adjustments as
some combustion chambers will run rich and some lean. "A series of
single cylinder engines flying loosely in formation." Quote from John
Deakin.

Many builders of the Ford V6 have complained that their engine ran
rough at maximum power. Huge effort was made to modify the intake
manifold to correct the problem. But I have not seen a single picture
of an exhaust manifold where the effort was made to create equal
length exhaust headers of the proper diameter.

I talked with a header manufacturer who told me he had heard of Dave
Blanton because a bunch of builders had asked him about headers. He
told me they all wanted to ignor his advice about tubing diameter.
They all wanted to use bigger tubing than was dictated, because they
all thought bigger was better. It's not.

Why is it so important to have the proper diameter tubing? Because
the bigger the diameter the slower the velocity of the gasses inside
it, and visa versa, up to a point. Eventually you can have exhaust
tubing in a diameter too small such that exhaust flow is restricted.
Large diameter tubing tends to cause the engine's power to peak at
extreme rpms. The smaller the diameter of the tubing, the more low to
midrange power you have.

But everyone wanted to use 1.75" tubing because that's what the
exhaust port was. 1.75" tubing would be what you would use if you
wanted flash horsepower from the engine at 8,000 rpm, like at the
dragstrip.

The header manufacturer also had a lot to say about "Zoomie" type
headers. These are headers without collectors, basically straight
pipes. Not only are these tubes also usually too large a diameter,
they leave off the collector which is crucial to the proper design of
the header system.

So with all this information, I'm taking my time with the header
design. Obviously something so important to the proper running of the
engine is not something I'm going to throw together without using
proper design criteria.

Corky Scott

Another trick that was popular on cars years ago, to bring a broad band
of peak torque into the "mid range" of 2500 to 4000 rpm; was to bring
the shortest practical header pipes which could be long enough to converge
at a reasonable included angle into collectors in groups of 3 which
would fire 240 degrees apart on six and twelve cylinder engines, or in
pairs which would fire 360 degrees apart on 4 and 8 cylinder engines.

On a V6, that would be be end of the story, and a collector having
about the same diameter as the header pipes should continue the same
inertial effect out to the exit or muffler. On V8 and in-line 4
cylinder engines, the resulting initial collectors were about as long
as the header pipes before converging into a final collector.

My expectation is that "tubing headers" made this way for V8 engines
with 90 degree cranks should be only marginally useful. However, they
should work well for all V6 engines, as well as V8 engines with single
plane cranks.

I am still (at a minimum) a couple of years away from testing this
recollection on any project. My own goal would be to achieve the
desired torque curve with an exhaust system length of 4 feet or less.

However, it appears from your post that you have found a competent
exhaust fabricator who can give you some additional guidance.

Peter

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

The Corvair engine operates successfully in direct drive configuration.
See http://www.flycorvair.com/

But with the stock Corvair engine having its peak torque at 3000 (or
4000-4500 for a modified unit) it would still be best to gear it down
for a prop speed around 2500 right?

Dave

Tom Cummings wrote:
Are there any auto/motorcycle conversions that don't require gear boxes?


The Corvair engine operates successfully in direct drive configuration.
See http://www.flycorvair.com/

For props, bigger is better for static thrust (look at a helecopter)
but what about for top speed, a more desireable figure of merit for
fixed wing aircraft? I seem to remember hearing somewhere that for
top speed there is an optimal prop length that is not infinite. You
need to generate a stream of air that is going faster than the speed
that you want to fly.

I think it relates to why you see high bypass jet engines on sub sonic
airliners but no-bypass engines on supersonic jet fighters.

On 23 Feb 2004 09:32:01 -0800, (Jay) wrote:

For props, bigger is better for static thrust (look at a helecopter)
but what about for top speed, a more desireable figure of merit for
fixed wing aircraft? I seem to remember hearing somewhere that for
top speed there is an optimal prop length that is not infinite. You
need to generate a stream of air that is going faster than the speed
that you want to fly.

You just described the reason no piston engined WWII fighter ever flew
faster than the speed of sound. The prop needed to produce enough
thrust to pull the airplane into supersonic speed, but the prop was
running into the wall of drag as the tips neared supersonic speed and
the fuselage was producing enormous drag too.

The prop tips would have to go supersonic if the airplane was to go
that fast too, and props of that era were not designed for supersonic
speeds.

Even going straight down at full power, just too much drag. They went
fast enough to scare the bajeebers out of a number of pilots though.
:-) They also went fast enough to lock up the controls and in some
cases, cause the destruction of the airplane... and the pilot.

Corky Scott