PSRU design advantages

"George" wrote in message m...
JP wrote:
"George" kirjoitti gy.com...
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.



http://www.prime-mover.org/Engines/T.../contact1.html

".Blueskies." wrote

http://www.prime-mover.org/Engines/T.../contact1.html

Thanks, so much, for posting that link. It was the one the OP needed to
read, but I did not remember enough about it, to find it. It is now on my
hard drive.

To the OP; did this scare you enough? My best advise? Change the design,
so it does not involve a long driveshaft.

It is doubtful (from reading your questions) that you have the expertise to
solve a problem of that magnitude. It is doubtful that you even know anyone
capable of solving such a problem. Even if you or someone you know has
enough "mojo" to solve the problem, you probably will spend a fortune
getting the application to be safe and reliable. Remember, it kicked Burt
Rutan's arse. That is really saying something!
--
Jim in NC

"Bill Daniels" bildan@comcast-dot-net wrote

I suppose...you could use a hydro drive. Turn a pump with the engine and
use a hydraulic motor to turn the prop. Some type of pressure regulator
could smooth the pressure to the prop motor. Might work for a really slow
turning prop.

One word. HEAVY ! ! !
--
Jim in NC

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

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

The 9 cylinder 1820 and 1840 CID radials used on B-17's were geared
approximately 16:9. However, your point is well taken, and I also am
unable
to name any 4 or 6 cylinder engines that have stood the test of time with
reduction drives.


Continental GO-300 (Cessna 175).
Lycoming GO-435 (Navion).
--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
Spell checking is left as an excercise for the reader.

Peter Dohm wrote:

"Bill Daniels" bildan@comcast-dot-net wrote in message
...

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.


The 9 cylinder 1820 and 1840 CID radials used on B-17's were geared
approximately 16:9. However, your point is well taken, and I also am unable
to name any 4 or 6 cylinder engines that have stood the test of time with
reduction drives.

I also believe that tuning any drive system, including a PSRU, is a
science--when fully understood. And therein lies the rub: There's plenty
left to learn--especially if it must also be light. So, in practice, you
are right--it is still an art. :-(

Peter




Rotax - the 912/914

Jabaru - (but the 6 cylinder will be a better seller - IMHO)

Believe it or not, a few VW's with belts.

And a couple of Subes with Rotax B boxes scabbed on.

The one that DIDN'T work was the Geo Metro 3-banger (broke the crank).

But that issue was already known - don't cut off any flywheel on 3 holers.
With the full flywheel, the 3 cylinder runs fine.


Richard

Ian Stirling wrote:

Peter Dohm wrote:
snip

The 9 cylinder 1820 and 1840 CID radials used on B-17's were geared
approximately 16:9. However, your point is well taken, and I also am unable
to name any 4 or 6 cylinder engines that have stood the test of time with
reduction drives.

I also believe that tuning any drive system, including a PSRU, is a
science--when fully understood. And therein lies the rub: There's plenty
left to learn--especially if it must also be light. So, in practice, you
are right--it is still an art. :-(


I suspect that electronics help.
Instrumenting the shaft, to measure resonances in real time is no longer
prohibitively expensive.
I suspect a belt PSRU - if properly configured could act to decouple the
prop from the engine/shaft somewhat.
Add one or more rotational vibrational dampers - fill the shaft with
oil? And trim.



Best tool available to the amateur is a variable speed strobe - Party Light!

That way you can actually look and SEE what's happening.


Richard

There is nothing that eliminates a long shaft from the design of a
PSRU. Nonbelievers might be advised to consider ship propulsion; long
shafts, low cylinder counts, propellers operating in uneven flow, often
via a gearbox. Sound familiar?

The important issue is torsional stiffness of the shaft, not
length. A long shaft can be torsionally stiff or soft, depending on
diameter and material. The engineering process will tailor torsional
stiffness of the shaft (along with a number of other factors) to adjust
natural frequency.

The information you need is found in engineering texts, not on RAH.
The subject can be complicated, but there are no unknowns. You will
find most of the torsional vibration classics listed in the
bibliography of Taylor's "Internal Combustion....". Some texts, like
Wilson's "Practical Solution.." (the ultimate reference) will be
difficult to locate. Try a large university library. The best readily
available text (sort of the ultimate primer on all matters vibrational)
is JP DenHartog's "Mechanical Vibrations". You can buy it for less
than $15 at Amazon. Here is a short list:

CF Taylor, "The Internal-Combustion Engine in Theory and Practice",
1966 (vol. 1), 1968 (vol. 2), MIT Press

W Ker Wilson, "Practical Solution of Torsional Vibration Problems", 3rd
Ed, 5 Vols., 1956, 0412091100, Chapman & Hall

JP Den Hartog, "Mechanical Vibrations", 1956, 070163898, McGraw-Hill

My compliments to Mr. Christley, whose comment (re frequency) was a
sole beacon of accuracy.


Dan Horton

-----------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