PSRU design advantages

Richard Lamb wrote:
ADK wrote:

IF you had to design a PSRU, to drive a pusher propellor via shaft,
what would your experience dictate? Thinking along the lines of a
gearbelt, chain or gear. Please, I would appreciate the collective
experience available on this group. I have decided on the aircraft,
but want to make it the most reliable and safest it can be.

"ADK" wrote in message
news:X6TXf.28774$%H.11944@clgrps13...

This is probably going to open old wounds. What I would like is
experienced input on the advantages, for economic, efficiency and
longevity etc. of different types of redrives.

I am leaning towards a cog-belt reducer in a 6 cylinder, liquid
cooled, configuration driving a long drive shaft to the prop.




The collective experience is zilch = nada = squat = undefined.

THAT is what everybody had been trying to tell you.

Wait a second. Look around the airport.

How many shaft driven propellers do you see?

Have you ever seen?

If you are heart set on doing it, I sincerely wish you luck.

But I can't offer any further advice - 'cuz they ain't none...



Richard


Richard,

Didn't the military do this once?? Seems there was the P-39 Aircobra,
shaft driven from a rear mounted engine?? Are the gray cells working
that far back??

Not that it would be applicable to an experimental, but at least It was
once done?

George

My friends who flew the P-39, always said they worried about the drive
shaft running between their legs, breaking loose )

Big John
`````````````````````````````````````````````````` ``````````

On Wed, 05 Apr 2006 13:23:05 GMT, George wrote:

Richard Lamb wrote:
ADK wrote:

IF you had to design a PSRU, to drive a pusher propellor via shaft,
what would your experience dictate? Thinking along the lines of a
gearbelt, chain or gear. Please, I would appreciate the collective
experience available on this group. I have decided on the aircraft,
but want to make it the most reliable and safest it can be.

"ADK" wrote in message
news:X6TXf.28774$%H.11944@clgrps13...

This is probably going to open old wounds. What I would like is
experienced input on the advantages, for economic, efficiency and
longevity etc. of different types of redrives.

I am leaning towards a cog-belt reducer in a 6 cylinder, liquid
cooled, configuration driving a long drive shaft to the prop.




The collective experience is zilch = nada = squat = undefined.

THAT is what everybody had been trying to tell you.

Wait a second. Look around the airport.

How many shaft driven propellers do you see?

Have you ever seen?

If you are heart set on doing it, I sincerely wish you luck.

But I can't offer any further advice - 'cuz they ain't none...



Richard


Richard,

Didn't the military do this once?? Seems there was the P-39 Aircobra,
shaft driven from a rear mounted engine?? Are the gray cells working
that far back??

Not that it would be applicable to an experimental, but at least It was
once done?

George

Big John wrote:
My friends who flew the P-39, always said they worried about the drive
shaft running between their legs, breaking loose )

Big John
`````````````````````````````````````````````````` ``````````

On Wed, 05 Apr 2006 13:23:05 GMT, George wrote:

Richard Lamb wrote:
ADK wrote:

IF you had to design a PSRU, to drive a pusher propellor via shaft,
what would your experience dictate? Thinking along the lines of a
gearbelt, chain or gear. Please, I would appreciate the collective
experience available on this group. I have decided on the aircraft,
but want to make it the most reliable and safest it can be.

"ADK" wrote in message
news:X6TXf.28774$%H.11944@clgrps13...

This is probably going to open old wounds. What I would like is
experienced input on the advantages, for economic, efficiency and
longevity etc. of different types of redrives.

I am leaning towards a cog-belt reducer in a 6 cylinder, liquid
cooled, configuration driving a long drive shaft to the prop.



The collective experience is zilch = nada = squat = undefined.

THAT is what everybody had been trying to tell you.

Wait a second. Look around the airport.

How many shaft driven propellers do you see?

Have you ever seen?

If you are heart set on doing it, I sincerely wish you luck.

But I can't offer any further advice - 'cuz they ain't none...



Richard


Richard,

Didn't the military do this once?? Seems there was the P-39 Aircobra,
shaft driven from a rear mounted engine?? Are the gray cells working
that far back??

Not that it would be applicable to an experimental, but at least It was
once done?

George

Sounds like a legitimate concern to me

George wrote:
Richard Lamb wrote:

ADK wrote:

IF you had to design a PSRU, to drive a pusher propellor via shaft,
what would your experience dictate? Thinking along the lines of a
gearbelt, chain or gear. Please, I would appreciate the collective
experience available on this group. I have decided on the aircraft,
but want to make it the most reliable and safest it can be.

"ADK" wrote in message
news:X6TXf.28774$%H.11944@clgrps13...

This is probably going to open old wounds. What I would like is
experienced input on the advantages, for economic, efficiency and
longevity etc. of different types of redrives.

I am leaning towards a cog-belt reducer in a 6 cylinder, liquid
cooled, configuration driving a long drive shaft to the prop.




The collective experience is zilch = nada = squat = undefined.

THAT is what everybody had been trying to tell you.

Wait a second. Look around the airport.

How many shaft driven propellers do you see?

Have you ever seen?

If you are heart set on doing it, I sincerely wish you luck.

But I can't offer any further advice - 'cuz they ain't none...



Richard


Richard,

Didn't the military do this once?? Seems there was the P-39 Aircobra,
shaft driven from a rear mounted engine?? Are the gray cells working
that far back??

Not that it would be applicable to an experimental, but at least It was
once done?

George

Wasn't the gub'ment, George, but Bell Aircraft.
P-39 not only had a drive shaft but a cannon firing thru the psru gearbox.

layout of engine, gearbox and cannon at:
http://www.home.earthlink.net/~tp-1/p392.jpg


So it *can* be done.
(The cannon firing thru the prop! )

I was curious to see if Bell had reduced the shaft RPM between the engine
and gearbox, but it looks like 1:1 there.

That might have been of interest to the OP, since his setup will likely
drive the shaft at prop rpm (after the psru).

Gonna take one tough (probably spelled h.e.a.v.y) shaft for that service...


Are there any others?


Richard

-----------snip------------

Wasn't the gub'ment, George, but Bell Aircraft.
P-39 not only had a drive shaft but a cannon firing thru the psru gearbox.

layout of engine, gearbox and cannon at:
http://www.home.earthlink.net/~tp-1/p392.jpg


So it *can* be done.
(The cannon firing thru the prop! )

-------------snip-----------

IIRC, the Messerschmidt ME-109 (a/k/a BF-109) was similar--except that the
long driveshaft was omitted, the engine was in the "normal" location, and
the canon was located in the valley area of the engine.

Peter

"Richard Lamb" wrote

So it *can* be done.
(The cannon firing thru the prop! )

I was curious to see if Bell had reduced the shaft RPM between the engine
and gearbox, but it looks like 1:1 there.

Yep. The normal speed reduction unit for the prop is taken off, and put at
the end of the shaft.

That might have been of interest to the OP, since his setup will likely
drive the shaft at prop rpm (after the psru).

Gonna take one tough (probably spelled h.e.a.v.y) shaft for that
service...


Are there any others?

There are numerous dual rotar sling wings that have an interconnected rotor
shaft, but they are usually turbine engines. One example is the Osprey.

The normal Allison AC engine also had an active fluid torsional resonance
reducer at the non driven end of the crankshaft on the engine, and a
torsional reducer coupling (rubber) on the drive end. I could not find
that info about the aircobra, but I'll bet they are there on that
application, also.
--
Jim in NC

"George" wrote in message
m...
Richard Lamb wrote:
ADK wrote:

IF you had to design a PSRU, to drive a pusher propellor via shaft, what
would your experience dictate? Thinking along the lines of a gearbelt,
chain or gear. Please, I would appreciate the collective experience
available on this group. I have decided on the aircraft, but want to
make it the most reliable and safest it can be.

"ADK" wrote in message
news:X6TXf.28774$%H.11944@clgrps13...

This is probably going to open old wounds. What I would like is
experienced input on the advantages, for economic, efficiency and
longevity etc. of different types of redrives.

I am leaning towards a cog-belt reducer in a 6 cylinder, liquid cooled,
configuration driving a long drive shaft to the prop.




The collective experience is zilch = nada = squat = undefined.

THAT is what everybody had been trying to tell you.

Wait a second. Look around the airport.

How many shaft driven propellers do you see?

Have you ever seen?

If you are heart set on doing it, I sincerely wish you luck.

But I can't offer any further advice - 'cuz they ain't none...



Richard


Richard,

Didn't the military do this once?? Seems there was the P-39 Aircobra,
shaft driven from a rear mounted engine?? Are the gray cells working that
far back??

Not that it would be applicable to an experimental, but at least It was
once done?

George

Yep. And Molt Taylor did it on several different airplanes and with several
different engines. There have been several pushers with engines mounted
near the CG and the props back on the tail with long drive shafts. Several
of them worked very well. There is a gain in efficiency when you do that.
Unfortunately the increased weight of the drive train and the additional
cost and complexity of the requisite drive train generally overcame any
efficiency gain and none of them has ever gone into "production."

The P-39 was a special case. It had an aft mounted engine and a big
driveshaft that passed between the pilots legs! It scared a lot of pilots
thinking about what they would lose if the drive shaft pickled on them.
They also used the drive shaft for a gun barrel for a large bore cannon so
that it could fire straight ahead through the spinner and be easy for the
pilot to aim. Just point the airplane at your target and cut loose. The
additional weight of the complex drive train raised hob with the performance
and our pilots didn't like them at all. The Russian pilots loved them.
They could aim the whole airplane fairly well and when you ran out of cannon
shells they would just ram the enemy fighter. That brought down both of
them, but the russians didn't mind. They were fighting in their own
backyard and the German's were not.

Highflyer
Highflight Aviation Services
Pinckneyville Airport ( PJY )

Actually I do work in aviation. I am an aviation machinist and aircraft
mechanic, I also work on Allison turbines (hercs and convairs) that drive a
gearbox via a shaft. My experience is mostly helicopters but being a fixed
wing pilot I want to have my own plane for cross country flights. I don't
believe any one person can ever learn everything there is to know about a
subject and therefore I am was soliciting usefull information on this
subject.
Thank you!

"Richard Lamb" wrote in message
.net...
ADK wrote:

IF you had to design a PSRU, to drive a pusher propellor via shaft, what
would your experience dictate? Thinking along the lines of a gearbelt,
chain or gear. Please, I would appreciate the collective experience
available on this group. I have decided on the aircraft, but want to
make it the most reliable and safest it can be.

"ADK" wrote in message
news:X6TXf.28774$%H.11944@clgrps13...

This is probably going to open old wounds. What I would like is
experienced input on the advantages, for economic, efficiency and
longevity etc. of different types of redrives.

I am leaning towards a cog-belt reducer in a 6 cylinder, liquid cooled,
configuration driving a long drive shaft to the prop.




The collective experience is zilch = nada = squat = undefined.

THAT is what everybody had been trying to tell you.

Wait a second. Look around the airport.

How many shaft driven propellers do you see?

Have you ever seen?

If you are heart set on doing it, I sincerely wish you luck.

But I can't offer any further advice - 'cuz they ain't none...



Richard

"ADK" wrote in message
news:WlXYf.4880$4S.2741@edtnps82...
Actually I do work in aviation. I am an aviation machinist and aircraft
mechanic, I also work on Allison turbines (hercs and convairs) that drive
a gearbox via a shaft. My experience is mostly helicopters but being a
fixed wing pilot I want to have my own plane for cross country flights. I
don't believe any one person can ever learn everything there is to know
about a subject and therefore I am was soliciting usefull information on
this subject.
Thank you!

Good for you. Read all you can, talk to some others that have been there,
done that. They are not on this group, though. Find the author of the link
that was posted on the subject. Then, if your heart is set on it, start
experimenting, and be prepared to experiment, a bunch! g

Good luck!
--
Jim in NC

The basics:

Piston engines produce more power per pound if they rev higher. (HP = RPM x
torque/5252)
Propellers are MUCH more efficient if they turn slow.
This begs for a PSRU.
BUT, a PSRU adds weight, cost and complexity.
Resonances, particularly torsional resonances are a real problem.
Lots of examples of PSRU's on 12, 14 and 18 cyinder engines
Few workable examples with fewer cylinders suggesting PSRU's don't like
power pulses.
If a shaft has a strong resonant fundamental, don't excite it or lower the
fundamental below the input frequency.
Tuning a PSRU/shaft/propeller system is like tuning a piano - it's an art
not a science.

"ADK" wrote in message
news:3pGYf.26105$Ph4.10950@edtnps90...
IF you had to design a PSRU, to drive a pusher propellor via shaft, what
would your experience dictate? Thinking along the lines of a gearbelt,
chain or gear. Please, I would appreciate the collective experience
available on this group. I have decided on the aircraft, but want to make
it the most reliable and safest it can be.

"ADK" wrote in message
news:X6TXf.28774$%H.11944@clgrps13...
This is probably going to open old wounds. What I would like is
experienced input on the advantages, for economic, efficiency and
longevity etc. of different types of redrives.

I am leaning towards a cog-belt reducer in a 6 cylinder, liquid cooled,
configuration driving a long drive shaft to the prop.