another poor man's car engine conversion

Yesterday I was talking to a friend who plans to power his single-seat
slow flyer with an engine from a Citroen Visa. I suppose this engine (a
linear descendant from the famous Citroen 2CV) is not well known in the
US, it is an air-cooled 2-cylinder boxer, in this particular application
it would produce some 45 HP.

My friend absolotely wants it in the plane as it is in the car, i.e.
with the clutch side rearward (the plane is a traditional "puller"), and
wants to take power from the clutch side. His idea is to have a belt
reduction "behind" the engine, then a transmission axle above the engine
to drive the prop. Now I'm sceptical 'cause I heard all kind of bad
things about transmission axles driving propellers, vibration not the
least. But he answers the axle needn't be long, as the engine is only a
2-cylinder.

Any thoughts / ideas / comments / experiences?
TIA,

On Feb 14, 6:38*am, jan olieslagers
wrote:
Yesterday I was talking to a friend who plans to power his single-seat
slow flyer with an engine from a Citroen Visa. I suppose this engine (a
linear descendant from the famous Citroen 2CV) is not well known in the
US, it is an air-cooled 2-cylinder boxer, in this particular application
it would produce some 45 HP.

My friend absolotely wants it in the plane as it is in the car, i.e.
with the clutch side rearward (the plane is a traditional "puller"), and
wants to take power from the clutch side. His idea is to have a belt
reduction "behind" the engine, then a transmission axle above the engine
to drive the prop. Now I'm sceptical 'cause I heard all kind of bad
things about transmission axles driving propellers, vibration not the
least. But he answers the axle needn't be long, as the engine is only a
2-cylinder.

Any thoughts / ideas / comments / experiences?
TIA,

Not a bad concept. I've spent some time thinking about the same
layout with larger engines. It has several advantages and a few
disadvantages.

Some advantages are that it moves the weight of the PSRU to the rear
of the engine and raises the propeller hub for better prop ground
clearance. It puts the radiator at the front of the engine with the
water pump mounted fan right behind it.

I think the key is that the shaft has to be thin and flexible to get
its resonance well below that of any other part of the drive train.
Going the other way to make a very stiff shaft raises its natural
resonance frequency so it's likely to match some other component
resulting in destructive resonance.

bildan wrote:
On Feb 14, 6:38 am, jan olieslagers
wrote:
My friend absolotely wants it in the plane as it is in the car, i.e.
with the clutch side rearward (the plane is a traditional "puller"), and
wants to take power from the clutch side. His idea is to have a belt
reduction "behind" the engine, then a transmission axle above the engine
to drive the prop.

I think the key is that the shaft has to be thin and flexible to get
its resonance well below that of any other part of the drive train.
Going the other way to make a very stiff shaft raises its natural
resonance frequency so it's likely to match some other component
resulting in destructive resonance.

You should model that sometime...

Charles

On Feb 14, 8:41*am, Charles Vincent wrote:
bildan wrote:
On Feb 14, 6:38 am, jan olieslagers
wrote:
My friend absolotely wants it in the plane as it is in the car, i.e.
with the clutch side rearward (the plane is a traditional "puller"), and
wants to take power from the clutch side. His idea is to have a belt
reduction "behind" the engine, then a transmission axle above the engine
to drive the prop.
I think the key is that the shaft has to be thin and flexible to get
its resonance well below that of any other part of the drive train.
Going the other way to make a very stiff shaft raises its natural
resonance frequency so it's likely to match some other component
resulting in destructive resonance.

You should model that sometime...

Charles

It's been done many times - and examples built. If the propeller/
shaft resonance is well below the lowest fundamental frequency of the
engine/PSRU, you're probably OK. If it's above the lowest fundamental
frequency, you're probably not OK.

The neat thing is that the most successful solution is also likely to
be the lightest.

As an example, look at the ridiculously skinny half shafts on the rear
of a Honda CRV.

I ran the models several times on a V8 with a simple flex-plate PTO on
the flywheel housing driving an overhead shaft via a cog belt. It
didn't look as if there would be any problems at all if the propeller
shaft was thin enough.

The V8 sat low in the nose, water pump forward with the radiator in
front of that just like in a car. The prop shaft went forward over
the engine. It would fit perfectly in a 3/4 scale P-40 or a Piper
Pawnee glider tug.

On 14 Feb, 14:26, bildan wrote:
On Feb 14, 6:38*am, jan olieslagers
wrote:





Yesterday I was talking to a friend who plans to power his single-seat
slow flyer with an engine from a Citroen Visa. I suppose this engine (a
linear descendant from the famous Citroen 2CV) is not well known in the
US, it is an air-cooled 2-cylinder boxer, in this particular application
it would produce some 45 HP.

My friend absolotely wants it in the plane as it is in the car, i.e.
with the clutch side rearward (the plane is a traditional "puller"), and
wants to take power from the clutch side. His idea is to have a belt
reduction "behind" the engine, then a transmission axle above the engine
to drive the prop. Now I'm sceptical 'cause I heard all kind of bad
things about transmission axles driving propellers, vibration not the
least. But he answers the axle needn't be long, as the engine is only a
2-cylinder.

Any thoughts / ideas / comments / experiences?
TIA,

Not a bad concept. *I've spent some time thinking about the same
layout with larger engines. *It has several advantages and a few
disadvantages.

Some advantages are that it moves the weight of the PSRU to the rear
of the engine and raises the propeller hub for better prop ground
clearance. *It puts the radiator at the front of the engine with the
water pump mounted fan right behind it.

I think the key is that the shaft has to be thin and flexible to get
its resonance well below that of any other part of the drive train.
Going the other way to make a very stiff shaft raises its natural
resonance frequency so it's likely to match some other component
resulting in destructive resonance.

You might like this.
http://ibis.experimentals.de/downloa...lvibration.pdf

bod43 wrote:

You might like this.
http://ibis.experimentals.de/downloa...lvibration.pdf

That URL would do well to be presented to any engine developer.
Moreover, it's not only engines with jack shafts or quill shafts
that are affected. I read a comparable piece that was - perhaps
still is - available on the net about the historical development
of some Pratt & Whitney engines.
The P&W work also mentioned pendulum crankshaft dampers, one
of the methods not mentioned in bod43's reference.

The automobile clutch friction plate torsion springs mentioned
in the URL aboveremind me of a feature of the first motorbike
I owned; a 1936 BSA 250 CC side valve model with girder forks
and unsprung rear end.
The drive side of the crank was splined. Over the splines,
a chainwheel was free to rotate, but outboard of its hub
was a wavy edged cylinder. On this a splined drive hub with a
complementary wavy cylinder was fitted, and a stiff spring
pressed the driven hub to the chain wheel via those wavy edges.
If the crank wished to move, while the chainwheel stayed fixed,
the driven hub would slide outwards against spring force.
This provided a soft drive characteristic always useful in a
single cylinder engine.

Brian W

You might like this.http://ibis.experimentals.de/downloa...lvibration.pdf

I've read this several times in the past. What strikes me is the
absence of test equipment like wireless load cell torque sensors on
the shafts. If used, any torsion oscillations could be seen on an
oscilloscope long before they became destructive.

High speed shafting is as old as the industrial revolution. Solutions
to torsion oscillations are just as old. Yes, there are potential
problems but there are also well tested solutions. The trick is
knowing what they are and how to use test instrumentation.

The other thing that jumps out about the Bede saga is that fact that
they were trying to put an experimental engine/prop drive into an
experimental airplane before it was de-bugged and they were doing it
under a deadline.

That's snakebite country. Even things that work everywhere else are
almost certainly going to bite you under those conditions.

It's vital to work one problem at a time. If it's an experimental
engine and prop drive, work on that until it's been running sweetly
for a long time. Then, maybe, think about designing an airframe
around it.

bildan wrote:
You might like this.http://ibis.experimentals.de/downloa...lvibration.pdf

I've read this several times in the past. What strikes me is the
absence of test equipment like wireless load cell torque sensors on
the shafts. If used, any torsion oscillations could be seen on an
oscilloscope long before they became destructive.

You must have missed the fact that this all took place in the early
sixties and seventies. Even if they had practical wireless sensors for
this, they didn't have the compute power available economically to
process it. Having said that, you still have to account for the effects
of the sensor. For that matter I think that wireless sensors and
attendant equipment are still not practical for the average modern
homebuilder.

High speed shafting is as old as the industrial revolution. Solutions
to torsion oscillations are just as old. Yes, there are potential
problems but there are also well tested solutions. The trick is
knowing what they are and how to use test instrumentation.

The other thing that jumps out about the Bede saga is that fact that
they were trying to put an experimental engine/prop drive into an
experimental airplane before it was de-bugged and they were doing it
under a deadline.

That's snakebite country. Even things that work everywhere else are
almost certainly going to bite you under those conditions.

It's vital to work one problem at a time. If it's an experimental
engine and prop drive, work on that until it's been running sweetly
for a long time. Then, maybe, think about designing an airframe
around it.

Sometimes an experimental airframe demands an experimental engine.
Engineering is seldom one dimensional, which is why I was poking at the
use of a long flexible shaft as a guaranteed solution. As far as
deadlines go, thats may not be a factor for a homebuilder, as many
projects get completed post mortem, but it is a factor form commercial
endeavors (Moller notwithstanding)

Charles

On Feb 15, 11:43*am, Charles Vincent wrote:
bildan wrote:
You might like this.http://ibis.experimentals.de/downloa...lvibration.pdf

I've read this several times in the past. *What strikes me is the
absence of test equipment like wireless load cell torque sensors on
the shafts. *If used, any torsion oscillations could be seen on an
oscilloscope long before they became destructive.

You must have missed the fact that this all took place in the early
sixties and seventies. * Even if they had practical wireless sensors for
this, they didn't have the compute power available economically to
process it. *Having said that, you still have to account for the effects
of the sensor. *For that matter I think that wireless sensors and
attendant equipment are still not practical for the average modern
homebuilder.

I didn't miss it. I did tests like this in the early 1960's. Load
cells are just Wheatstone Bridges and the wireless tech WAS available
then - it just used discrete components instead of IC's. It needs no
computer power whatsoever since it's an analog signal. If you don't
like wireless tech, slip rings are available.

The sensors are very light and have little or no effect on the shaft
under test - if they did, no one would use them. In any event, you
can put an accelerometer on a shaft bearing housing and see if it's
output changes when you remove the torque sensor.

The only reason they didn't use instrumentation must have been that
Bede was cheap and in a hurry. It was definitely available and not
expensive.

Torsional resonance instrumentation is absolutely practical for home
builders and it doesn't cost all that much. The oscilloscope is
probably the most expensive thing and you could probably borrow one.

If I were going to do the auto engine shaft drive thing, I'd buy a
cheap running engine from a junk yard. If it ran rough, so much the
better. I'd build up the firewall forward drive system on a trailer
with a club prop. Then I'd run it to find and eliminate resonances.
Only then would I build an exact replica of the flight article using
new components and run that on the test stand.

jan olieslagers schrieb:
Yesterday I was talking to a friend who plans to power his single-seat
slow flyer with an engine from a Citroen Visa. I suppose this engine (a
linear descendant from the famous Citroen 2CV) is not well known in the
US, it is an air-cooled 2-cylinder boxer, in this particular application
it would produce some 45 HP.

In Germany we have some microlights on this engine.

http://www.ulf-2.de/

Under "Bilder" on the left you will see details of the engine.

KH