PSRU design advantages

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

Richard Lamb wrote:
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.

That'll spot ordinary vibrations.
Torsional ones are a little bit harder.

Especially if you want, as you probably should, a graph of maximum stress
anywhere in the shaft/PSRU/Prop system vs RPM.

Ian Stirling wrote:

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

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


That'll spot ordinary vibrations.
Torsional ones are a little bit harder.

Especially if you want, as you probably should, a graph of maximum stress
anywhere in the shaft/PSRU/Prop system vs RPM.

A few fine white lines down the length of the shaft will clear up that
problem.

--
This is by far the hardest lesson about freedom. It goes against
instinct, and morality, to just sit back and watch people make
mistakes. We want to help them, which means control them and their
decisions, but in doing so we actually hurt them (and ourselves)."

Ernest Christley wrote:
Ian Stirling wrote:

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

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


That'll spot ordinary vibrations.
Torsional ones are a little bit harder.

Especially if you want, as you probably should, a graph of maximum stress
anywhere in the shaft/PSRU/Prop system vs RPM.

A few fine white lines down the length of the shaft will clear up that
problem.

Will they?
It'll obviously show huge torsional movement, but many, especially
shorter shafts may fail before it becomes visible.

"Richard Lamb" wrote in message
k.net...

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


I used to use a tool called a "Strobotach" which was a variable speed strobe
unit used for a non-contact tachometer.
Very useful for analyzeing periodic motions. :-)

Highflyer
Highflight Aviation Services
Pinckneyville Airport ( PJY )

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

"Richard Lamb" wrote in message
k.net...
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

OK, you caught me fair and square on poor phrasing. I tend to think of
higher power applications, but you are right that some of the more
conservative and lower powered systems with flywheels still in place and a
little looser coupling seem to run quite reliably. I don't know how much
power is lost to friction, but some of the v-belt reduction drives even seem
to work quite reliably without any external crankshaft support!

Peter

Peter Dohm wrote:
"Richard Lamb" wrote in message
k.net...

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


OK, you caught me fair and square on poor phrasing. I tend to think of
higher power applications, but you are right that some of the more
conservative and lower powered systems with flywheels still in place and a
little looser coupling seem to run quite reliably. I don't know how much
power is lost to friction, but some of the v-belt reduction drives even seem
to work quite reliably without any external crankshaft support!

Peter



You didn't follow the link that blueskies posted, didja Peter.

The BD-5 story - in all it's glory! And a few other odds and ends,
That was not a high powered setup, but kicked a bunch of engineers around.

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


Richard

"Richard Lamb" wrote in message
nk.net...
Peter Dohm wrote:
"Richard Lamb" wrote in message
k.net...

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


OK, you caught me fair and square on poor phrasing. I tend to think of
higher power applications, but you are right that some of the more
conservative and lower powered systems with flywheels still in place and
a
little looser coupling seem to run quite reliably. I don't know how
much
power is lost to friction, but some of the v-belt reduction drives even
seem
to work quite reliably without any external crankshaft support!

Peter



You didn't follow the link that blueskies posted, didja Peter.

The BD-5 story - in all it's glory! And a few other odds and ends,
That was not a high powered setup, but kicked a bunch of engineers around.

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


Richard

Actually I did, some months ago following an earlier post, and subsequently
also learned that the Contact! article is quite famous. One of the more
interesting points was that trying to make the shaft and/or transfer drive
more rigid was not helpful on the BD-5. Softening the system eventually did
resolve the breakage problem within the drive train; but IIRC the drive
system to airframe resonance (evidenced initially by loosened rivets) was
not fully resolved during the author's tenure. That was the article that
really convinced me that I didn't necessarily know enough to design a
clutchless system with a high degree of confidence--even by leaving the
flywheel in place.

However, the set of books mentioned elsewhere in this thread, by Mr. Horton,
could prove to contain the necessary formulas and explanations to reduce
this problem to a cookbook science. A quick web search confirmed his belief
that one of the books may now be virtually unobtainable.

I am willing to entertain his book suggestion because, in my earlier career
as an electronic technician, a technical tome entitled "Shielding and
Grounding Techniques in Instrumentation" made previously insurmountable
grounding problems easy to solve. It is probable that work on mechanical
resonance, done for World War II, may have been covered in books published
during the succeeding quarter century.

Peter