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.

"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.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Warning,Warning, Danger, Danger, Will Robinson!

Yep, that is a really big can of worms.

The redrive is not as big a problem as you think. You get into a mess when
you start talking about long drive shafts.

Torsional resonance has brought many of the great minds of the flying
industry to their knees. No joke. I don't have all of the links at hand,
but someone here does. Start by googling torsional resonance.

Then, be afraid. Be very afraid.
I you don't get afraid, keep looking, until you get afraid, because you need
to get afraid, or you don't understand the problem.
--
Jim in NC

Morgans wrote:
> "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.
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> Warning,Warning, Danger, Danger, Will Robinson!

LOL :)

> Yep, that is a really big can of worms.
>
> The redrive is not as big a problem as you think. You get into a mess
> when you start talking about long drive shafts.

I'd recommend (ADK) research on the BD-5 drivetrain (redrives and long
driveshafts). Not unsurmountable, but a certainly a big can of worms as
you (Jim) state.

Efficiency isn't directly affected. Weight may be affected. Longevity
will be either good or very short (vibration), but not in between.

("Morgans" wrote)
> Torsional resonance has brought many of the great minds of the flying
> industry to their knees. No joke. I don't have all of the links at hand,
> but someone here does. Start by googling torsional resonance.
>
> Then, be afraid. Be very afraid. I you don't get afraid, keep looking,
> until you get afraid, because you need to get afraid, or you don't
> understand the problem.


I'm not skeer't AND I don't understand the problem.

I thought the (rubber?) (toothed?) (cog?) belt redrives absorb? dampen? out
a lot of those problems - even, to some extent, the slightly longer shaft
kind of problems. Add a three bladed wooden prop, and you're golden. <g>

No?

Next I tackle Mu-1 issues...


Montblack
"Get out of the house. Now! That [post] came from your basement."
Fooled them. We don't have a basement. Ha!
"Then get out of your house, an F5 twister is coming down the street! Now be
afraid..."

"Morgans" > wrote in message
...
>
> "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.
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> Warning,Warning, Danger, Danger, Will Robinson!
>
> Yep, that is a really big can of worms.
>
> The redrive is not as big a problem as you think. You get into a mess
when
> you start talking about long drive shafts.
>
> Torsional resonance has brought many of the great minds of the flying
> industry to their knees. No joke. I don't have all of the links at hand,
> but someone here does. Start by googling torsional resonance.
>
> Then, be afraid. Be very afraid.
> I you don't get afraid, keep looking, until you get afraid, because you
need
> to get afraid, or you don't understand the problem.
> --
> Jim in NC
>
Yes, Sir! Lots of old wounds, etc, etc ...

Actually, I believe that a driveshaft can be part of the problem, solution,
or both--although, in and of itself, I agree that a long driveshaft is far
more likely to be a problem than a solution. Also, don't forget that all
resonance applied through the engine mount to the airframe will still
apply--there is a famous "Contact!" magazine article describing some of both
problems during the [attempted] development of the BD-5. The point here is
that, although a loss of power is the most obvious

And keep in mind that, although the redrive is not a source of torsional
resonance, the redrive is not inherently dampening. However, many redrives
can be a source of considerable shear and bending loads applied to the
crankshaft. I don't know how much is too much in either case.

As additional food for thought: I was a long time advocate of automotive
conversions, but I am now leaning away from them--as well as from many of
the more modern engine packages now available. I believe that they can be
just about as reliable in service, and that the probable weight penalty is
acceptable--if a slightly heavier airplane does the same job, burns a little
more fuel, and has a lower initial cost; it may still be the best value,
especially if you enjoy the education that you will achieve through the
development work. However, I am now leaning back toward the "traditional"
type certified engines because it may be much easier to get approval for IFR
operation. For some time to come, at least in the US, TFRs are going to
continue as a fact of life; and an IFR flight plan gives that greatest
assistance in staying out of difficulty on cross country flights. Just my
$.02, and YMMV.

Peter

How would one of the composite props, such as an IVO or Warp drive fair in
an application such as I have described? Especially using a 3 or 4 blade
prop.
Also I want to use a segmented drive shaft so that each of two sections are
reduced in length over a single long shaft.
Would not using a 6 cylinder higher reving engine also be an advantage over
a lycoming for torsional vibration or would the concern only change in
frequency?
"Peter Dohm" > wrote in message
...
>
> "Morgans" > wrote in message
> ...
>>
>> "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.
>> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>>
>> Warning,Warning, Danger, Danger, Will Robinson!
>>
>> Yep, that is a really big can of worms.
>>
>> The redrive is not as big a problem as you think. You get into a mess
> when
>> you start talking about long drive shafts.
>>
>> Torsional resonance has brought many of the great minds of the flying
>> industry to their knees. No joke. I don't have all of the links at
>> hand,
>> but someone here does. Start by googling torsional resonance.
>>
>> Then, be afraid. Be very afraid.
>> I you don't get afraid, keep looking, until you get afraid, because you
> need
>> to get afraid, or you don't understand the problem.
>> --
>> Jim in NC
>>
> Yes, Sir! Lots of old wounds, etc, etc ...
>
> Actually, I believe that a driveshaft can be part of the problem,
> solution,
> or both--although, in and of itself, I agree that a long driveshaft is far
> more likely to be a problem than a solution. Also, don't forget that all
> resonance applied through the engine mount to the airframe will still
> apply--there is a famous "Contact!" magazine article describing some of
> both
> problems during the [attempted] development of the BD-5. The point here
> is
> that, although a loss of power is the most obvious
>
> And keep in mind that, although the redrive is not a source of torsional
> resonance, the redrive is not inherently dampening. However, many
> redrives
> can be a source of considerable shear and bending loads applied to the
> crankshaft. I don't know how much is too much in either case.
>
> As additional food for thought: I was a long time advocate of automotive
> conversions, but I am now leaning away from them--as well as from many of
> the more modern engine packages now available. I believe that they can be
> just about as reliable in service, and that the probable weight penalty is
> acceptable--if a slightly heavier airplane does the same job, burns a
> little
> more fuel, and has a lower initial cost; it may still be the best value,
> especially if you enjoy the education that you will achieve through the
> development work. However, I am now leaning back toward the "traditional"
> type certified engines because it may be much easier to get approval for
> IFR
> operation. For some time to come, at least in the US, TFRs are going to
> continue as a fact of life; and an IFR flight plan gives that greatest
> assistance in staying out of difficulty on cross country flights. Just my
> $.02, and YMMV.
>
> Peter
>
>

ADK

Look up Molt Taylor and his Aerocar system. He used a pusher
arrangement and seemed to have most of the problems solved with long
shaft back to prop.

His bird may still be flying some place to exhibitions?

Am sure someone will jump in here and give data on his bird and how he
coupled shaft to engine with a "power glide" clutch or some such. It
allowed a small amount of slippage at each power stroke to prevent the
pulse being transmitted to drive shaft and prop as I recall.

Best of luck with a difficult problem.

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

On Sun, 02 Apr 2006 16:39:19 GMT, "ADK" > wrote:

>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.
>

ADK wrote:
> How would one of the composite props, such as an IVO or Warp drive fair in
> an application such as I have described? Especially using a 3 or 4 blade
> prop.

My cure the problem. May create it.

> Also I want to use a segmented drive shaft so that each of two sections are
> reduced in length over a single long shaft.

May solve the problem. May create it.

> Would not using a 6 cylinder higher reving engine also be an advantage over
> a lycoming for torsional vibration or would the concern only change in
> frequency?

The concern is about frequency. Not power. Not absorbtion. Not
dampening. Not anything except frequency. If the power pulses
generated by the engine or turbulence around the propeller (the ONLY
excitation sources available in flight), or any of the harmonics of the
two matches the natural frequency of the prop/drivetrain combination,
you'll have a short useful life for the drivetrain.

--
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)."

("Big John" wrote)
> Look up Molt Taylor and his Aerocar system. He used a pusher arrangement
> and seemed to have most of the problems solved with long shaft back to
> prop.
>
> His bird may still be flying some place to exhibitions?


http://www.airventuremuseum.org/collection/aircraft/Taylor%20Aerocar.asp
EAA site with links at the bottom:
*Taylor Aerocar Design and Construction
*Taylor Aerocar Manufacturers History
*Taylor Aerocar Specifications
*Taylor Aerocar Virtual Exhibit

http://www.goldenwingsmuseum.com/Aircraft.html
Golden Wing's Museum Collection

http://www.goldenwingsmuseum.com/Aircraft%20Pages/Aero%20Car.html
1954 Taylor Aero Car/Aerocar.

http://www.goldenwingsmuseum.com/Photo's/Aero%20Car-2.jpg
Bigger pic


Montblack
It would fly tomorrow - after some minor touch ups and an annual. Don't know
when it's scheduled to go up again. They take the car out and run around the
airport from time to time. School kids love the Aero Car during their tours.
It last flew maybe 5 years ago. Maybe 6?

"Montblack" > wrote

> It would fly tomorrow - after some minor touch ups and an annual. Don't
> know when it's scheduled to go up again. They take the car out and run
> around the airport from time to time. School kids love the Aero Car during
> their tours. It last flew maybe 5 years ago. Maybe 6?

I'm almost positive that I have seen it fly at OSH, within the past 3 years.
Last year, perhaps?

It was in the 1:00 PM showcase.
--
Jim in NC

Resonance.

God's gift of humility.



* Jim Bede, of course, with the BD-5 drive train.
Hard times and heartache...
That engine and drive ran flawlessly 24/7 for months without a single problem.
It looked goooood!

But bolted into the airframe, it would come apart in minutes.

Back on the test stand (concrete block!) it ran and ran and ran.
(the energizer bunny hadn't been born yet)

But in the airplane... pure bad news.

Now you tell me. Where's the logic in that???

As it turned out, all we needed to do to solve the drive problem on the -5
was to fill the belly of the airplane with a few inches of concrete.
(well, it's not a *great* solution, but it would fix the drive problem!)



* Molt Taylor and his AeroCar. 1950's chic!
Here is a really *good* long drive shaft problem.
I say good because it has a happy ending.

The patented "Flexodyne"(sp?) drive shaft damper.


* Tail rotor drive shafts on almost any rotary winged beast.
(Shudder)


As for engines on experimental aircraft?
My attitude parallels Peter's.

I used to see it as a way to get airborne for a few dollars less.
And in some (small) cases, VW, simple Subes, Geo, and the like, it may
still be a valid way to go.
A-65's don't grow on trees anymore.

But I too have come back to the olde timy 1930's tractor engines as the
solution for fast iron (or wood or plastic as the case may be).

Those engines evolved(?) to be the way they are because that's what does
the job best. Long stroke, slow turning, light weight, reliable.


My personal reason is weight.
Pure and simple.

Our (small experimental) airplanes are - for the most part - simply too small
to carry the extra weight *well*.

Lighter is better.
Hey!
It's a freekin airplane!
(chant mantra - lighterisbetteroooommmm...)


There is, also, that old saw about not mixing experimental engines with
experimental airframes. I wonder what nut came up with that one?



But then the topic is resonance, isn't it.
And?
With the exception of combinations which are known to have engine/prop/AIRFRAME
resonance issues (hint, hint, hint), certified engines avoid that trap entirely
(well, mostly?).


That's not my $.02,
It's my bunch of thousand bucks...
And?
In the end, my ass, and maybe yours?


Richard

for what it's worth

Big John wrote:

> ADK
>
> Look up Molt Taylor and his Aerocar system. He used a pusher
> arrangement and seemed to have most of the problems solved with long
> shaft back to prop.
>
> His bird may still be flying some place to exhibitions?
>
> Am sure someone will jump in here and give data on his bird and how he
> coupled shaft to engine with a "power glide" clutch or some such. It
> allowed a small amount of slippage at each power stroke to prevent the
> pulse being transmitted to drive shaft and prop as I recall.
>
> Best of luck with a difficult problem.
>
> Big John

Ok,

I think it's also used on the Imp and Mini-Imp.


The "clutch" consists of two (wavy surfaced) plates with lead shot
loaded between them.

As the thing spun up, centrifugal force packed the shot solid, but
there was enough "give" with the shot to absorb the "jerk" (4th derivative?).


Richard

no idea why that came out in past tense...

The aircraft I am interested in is the G802 Orion, designed in France in the
80's. It had problems with a long drive shaft and so I am interested in how
others have solved a similar problem. It also incorporated a Flexidyne type
coupler but it still had problems.
I work in aviation but there isn't a lot of good suggestions (printable)
from the people and engineers I work with.


"Richard Lamb" > wrote in message
ink.net...
> Big John wrote:
>
>> ADK
>>
>> Look up Molt Taylor and his Aerocar system. He used a pusher
>> arrangement and seemed to have most of the problems solved with long
>> shaft back to prop.
>>
>> His bird may still be flying some place to exhibitions?
>>
>> Am sure someone will jump in here and give data on his bird and how he
>> coupled shaft to engine with a "power glide" clutch or some such. It
>> allowed a small amount of slippage at each power stroke to prevent the
>> pulse being transmitted to drive shaft and prop as I recall.
>>
>> Best of luck with a difficult problem.
>>
>> Big John
>
> Ok,
>
> I think it's also used on the Imp and Mini-Imp.
>
>
> The "clutch" consists of two (wavy surfaced) plates with lead shot
> loaded between them.
>
> As the thing spun up, centrifugal force packed the shot solid, but
> there was enough "give" with the shot to absorb the "jerk" (4th
> derivative?).
>
>
> Richard
>
> no idea why that came out in past tense...

---------------snip-----------------
>
The point here is
> that, although a loss of power is the most obvious
---------------snip-----------------

I don't know how I inadvertantly edited out part of the point that I was
trying to make, but the sentence and paragraph should have continued to read
as follows:


The point here is that, although a loss of power is the most obvious outcome
of a torsional resonance problem, it is not the only failure mode and may
not even be the worst. For example, the same "Contact!" article also
mentioned severe flexing of a bulkhead in the fusalage due to a resonance
between the complete engine and drive system and the fusalage at critical
speed(s). That caused me to be even more afraid than the driveshaft and
redrive problems.

Peter

"Peter Dohm" > wrote

> The point here is that, although a loss of power is the most obvious
> outcome
> of a torsional resonance problem, it is not the only failure mode and may
> not even be the worst. For example, the same "Contact!" article also
> mentioned severe flexing of a bulkhead in the fusalage due to a resonance
> between the complete engine and drive system and the fusalage at critical
> speed(s). That caused me to be even more afraid than the driveshaft and
> redrive problems.

That is along the lines of what I wrote. The more a person reads about
torsional resonance, the more one understands how much there is that can go
wrong.

I am convinced not to use a long driveshaft, for my personal use. <g>
--
Jim in NC

Richard Lamb wrote:

> But then the topic is resonance, isn't it.
> And?
> With the exception of combinations which are known to have
> engine/prop/AIRFRAME
> resonance issues (hint, hint, hint), certified engines avoid that trap
> entirely
> (well, mostly?).
>

I'm glad to add the "(well, mostly?)", because I could read that as "not
at all". What you do have with a certified engine is a situation where
the prop manufacturer has tested their prop with that engine. It's a
well studied combination that everyone knows how to work with.

For instance, you can't cut a metal prop down but so far. Why? Because
everyone knows where that resonant point is, and cutting the prop down
to 70" will land you smack-dab in the middle of patooky when one of the
blades comes off.

But build a new prop of your own design, sufficiently different from the
typical prop...then it doesn't matter if you put it on a certified
powerplant or the front of your Oldsmobile. Unless you have the
facilities to test it, its longevity is just guesswork.


--
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)."

> Richard Lamb wrote:
>
> > But then the topic is resonance, isn't it.
> > And?
> > With the exception of combinations which are known to have
> > engine/prop/AIRFRAME
> > resonance issues (hint, hint, hint), certified engines avoid that trap
> > entirely
> > (well, mostly?).
> >

"Ernest Christley" > wrote in message
...
>
> I'm glad to add the "(well, mostly?)", because I could read that as "not
> at all". What you do have with a certified engine is a situation where
> the prop manufacturer has tested their prop with that engine. It's a
> well studied combination that everyone knows how to work with.
>
> For instance, you can't cut a metal prop down but so far. Why? Because
> everyone knows where that resonant point is, and cutting the prop down
> to 70" will land you smack-dab in the middle of patooky when one of the
> blades comes off.
>
> But build a new prop of your own design, sufficiently different from the
> typical prop...then it doesn't matter if you put it on a certified
> powerplant or the front of your Oldsmobile. Unless you have the
> facilities to test it, its longevity is just guesswork.
>
>
> --
> 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)."

I think that the point of "(well mostly)" may have been that even the tried
and true combinations, such as certain Lycoming engines with approved
constant speed props, failures can occur long after the design appears to be
mature, and some of the failures may yet prove to be related to resonance.
The moral may be that everything is experimental, but some things are less
experimental than others.

At least, that would have been my point...

Peter

"Peter Dohm" > wrote

> I think that the point of "(well mostly)" may have been that even the
> tried
> and true combinations, such as certain Lycoming engines with approved
> constant speed props, failures can occur long after the design appears to
> be
> mature, and some of the failures may yet prove to be related to resonance.
> The moral may be that everything is experimental, but some things are less
> experimental than others.

It was noted (I think it was here) that when engine mount bushings wear out,
the properties of the mount/engine/airframe combination may have changed
enough that the resonance may become a factor again, where it was not - when
the mount bushings were fresh.
--
Jim in NC

"Ernest Christley" > wrote in message
...
<...>
> I'm glad to add the "(well, mostly?)", because I could read that as "not
> at all". What you do have with a certified engine is a situation where
> the prop manufacturer has tested their prop with that engine. It's a well
> studied combination that everyone knows how to work with.
>
> For instance, you can't cut a metal prop down but so far. Why? Because
> everyone knows where that resonant point is, and cutting the prop down to
> 70" will land you smack-dab in the middle of patooky when one of the
> blades comes off.
>
> But build a new prop of your own design, sufficiently different from the
> typical prop...then it doesn't matter if you put it on a certified
> powerplant or the front of your Oldsmobile. Unless you have the
> facilities to test it, its longevity is just guesswork.

That was a problem on some of the early T-18's that were using cut down
propellers - resonance was fatiguing the propeller which would then shed a
blade, which would then encourage the engine to attempt to part company with
the airframe...

--
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.

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.
>

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 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

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.
>>
>
>

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

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 :o)
>
> 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

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.
>>>>
>>>> "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
>
>
>
> The P-39/P-63 examples can't probably be compared directly with this matter
> in question. These designs both have a large reduction gear casing in front
> of the plane. The support structure for this PSRU looks very firm. Perhaps
> the safety cage type center fuselage structure has something to do with the
> lack of severe resonance problems? Any known resonance problems with these
> aircrafts?
>
> JP
>
>
I find myself wondering if, even though the P-39/63 can't be directly
applicable to experimental class aircraft, isn't there a lesson to be
learned here.

The primary shart turns at engine speed, the PSRU is located remotely
and the propeller is not transmitting torsional resonant frequency
pulses to the shaft. At least not directly. Would a pulse absorbing
coupling, such as Molt used, totally eliminate the resonant frequencies
in the shaft??

Since the OP was thinking of a remote mounted engine and a long shaft,
is this worth considering, since he seems bent on exploring this
possibility??

Just my mental ruminatings. YMMV

"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

On Wed, 05 Apr 2006 13:56:26 GMT, George > wrote:

>Big John wrote:
>> My friends who flew the P-39, always said they worried about the drive
>> shaft running between their legs, breaking loose :o)
>>
>> 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
If it EVER did, it was a legitimate concern. Did they have quill shaft
failures???
*** Free account sponsored by SecureIX.com ***
*** Encrypt your Internet usage with a free VPN account from http://www.SecureIX.com ***

"Peter Dohm" > wrote in message
...
>
> "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
>
You're right. I forgot that there were some successful 9 cyl geared
engines. The radials used planetary gears in the nosecase. I like
planetaries since there's a lot of tooth engagement to carry the power yet
they tend to be compact and light.

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.

Bill D

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.

"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/Torsional/contact1/contact1.html

".Blueskies." > wrote

> http://www.prime-mover.org/Engines/Torsional/contact1/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

"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

"Dan Horton" > wrote in message
ups.com...
> 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
>
You are very probably right--and it won't be the first time that I believed
that something was still a "black art" until I found out otherwise. For
years after I first became an electronic technician, I believed that about
grounding problems--and then I read a book titled "Sheilding and Grounding
Techniques in Instrumentation." Even 20 years ago, that book was long out
of print; but could still be obtained by special order from University
Microfilm. Almost miraculously, the problems went away!

After reading your post, I decided to look for the books you mentioned and
found that you were correct about the difficulty of locating W Ker Wilson's
book. That could indicate that it is the true source, as the dates
mentioned for earlier editions suggest, and therefore a custom reprint could
be worth every penny and more if a source is known.

The other two books seem to still be available, although I have no idea when
I might find time to read them...

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/Torsional/contact1/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/Torsional/contact1/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

"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

"Dan Horton" > wrote

> 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?

I think you will find that they do it on ships, with pure weight. A big,
heavy, solid steel shaft. Very heavy! That is how they get the stiffness.

Also, the shaft turns very slowly, so there are many pulses per revolution;
more than you will get with a 4 or 6 cylinder, 4 cycle airplane engine, in
most cases.

I agree with the rest of your post; dig into the engineering text books.
--
Jim in NC

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.

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.
>

For the sake of Peter, IT DOESN'T MATTER!!

For the energy to transfer to the prop, you have to attach the engine to
the prop. The engine doesn't produce smooth even power. It produces a
series of pulses. If the frequency of the pulses resonates with the
prop or shaft, it will store a little bit of each pulse as "spring
energy". This type of energy is stored by deflecting (ie, bending) the
prop or shaft. The prop stores it and then immediately tries to release
it by unbending. If the next engine pulse comes along at just the right
time, the new "spring energy" will be added to the previous "spring
energy" and the prop will bend a little more. This continues until the
prop or shaft has as much "spring energy" as it can phyiscally hold, and
then the element just vibrates. Eventually, the prop or shaft gets
tired of all the bending and unbending and just gives up (ie, breaks).

Making the pulses smaller doesn't help for the most part. All that does
is cut down on the amount of "spring energy" added with each pulse. A
smaller pulse will take 2000 pulses to fill the prop with "spring
energy" vs 1000 with a unmodified pulse. Whoop-te-do! What difference
will that make with the engine turning 2000RPM and four pulses per round.

Any one of the gearboxes you mentioned made to work safely, and each has
a set of advantages and disadvantages that are well known and easily
engineered around. The type of gearbox has nothing to do with torsional
resonance. Will not mitigate torsional resonance. Will not
cure/alleviate/lesson or bypass torsioanl resonance. Torsional
resonance is a totally different issue.

You didn't tie gearbox type and torsional resonance together directly,
but many people have in the past, and it's just self-deception. Any of
the gearboxes you mentioned can be as safe and dependable as any of the
others, if engineered properly.


--
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)."

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 in message
...
> 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.
>>
>
> For the sake of Peter, IT DOESN'T MATTER!!
>
> For the energy to transfer to the prop, you have to attach the engine to
> the prop. The engine doesn't produce smooth even power. It produces a
> series of pulses. If the frequency of the pulses resonates with the prop
> or shaft, it will store a little bit of each pulse as "spring energy".
> This type of energy is stored by deflecting (ie, bending) the prop or
> shaft. The prop stores it and then immediately tries to release it by
> unbending. If the next engine pulse comes along at just the right time,
> the new "spring energy" will be added to the previous "spring energy" and
> the prop will bend a little more. This continues until the prop or shaft
> has as much "spring energy" as it can phyiscally hold, and then the
> element just vibrates. Eventually, the prop or shaft gets tired of all
> the bending and unbending and just gives up (ie, breaks).
>
> Making the pulses smaller doesn't help for the most part. All that does
> is cut down on the amount of "spring energy" added with each pulse. A
> smaller pulse will take 2000 pulses to fill the prop with "spring energy"
> vs 1000 with a unmodified pulse. Whoop-te-do! What difference will that
> make with the engine turning 2000RPM and four pulses per round.
>
> Any one of the gearboxes you mentioned made to work safely, and each has a
> set of advantages and disadvantages that are well known and easily
> engineered around. The type of gearbox has nothing to do with torsional
> resonance. Will not mitigate torsional resonance. Will not
> cure/alleviate/lesson or bypass torsioanl resonance. Torsional resonance
> is a totally different issue.
>
> You didn't tie gearbox type and torsional resonance together directly, but
> many people have in the past, and it's just self-deception. Any of the
> gearboxes you mentioned can be as safe and dependable as any of the
> others, if engineered properly.
>
>
> --
> 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)."

Let me try a different idea.

Suppose the prop shaft is to be just long enough for the gear belt pulley
and the neccessary bearings - say 10 inches. But the engine flywheel pulley
is to be 4 - 6 feet below the prop shaft. The idea is to use a very large
multi-blade carbon fiber prop turning 800 - 1000 RPM driven by a 4 cyl Soob
turning at best power RPM. The idea is to get best thrust in the 0 - 60
knot range. The airframe configuration is a prop over tail boom pusher - an
ultralight on steroids. (BTW, I'm not looking for a long engine life under
these conditions. I'll treat the Soob as a throwaway power plant.)

I'm thinking there isn't too much torsional vibration concern with very
short shafts, high reving engine and a stiff carbon fiber prop. The prop
will be seeing 6 - 7 power pulses per rev from the high reving Soob.

Bill

Peter Dohm wrote:
> "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/Torsional/contact1/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
>
>

My pardon, sir!

Richard

"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

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

> Suppose the prop shaft is to be just long enough for the gear belt pulley
> and the neccessary bearings - say 10 inches. But the engine flywheel
> pulley is to be 4 - 6 feet below the prop shaft. The idea is to use a
> very large multi-blade carbon fiber prop turning 800 - 1000 RPM driven by
> a 4 cyl Soob turning at best power RPM. The idea is to get best thrust in
> the 0 - 60 knot range. The airframe configuration is a prop over tail
> boom pusher - an ultralight on steroids. (BTW, I'm not looking for a long
> engine life under these conditions. I'll treat the Soob as a throwaway
> power plant.)

Strange, but I am considering a system, very much like that. Flying boat,
with the engine in the fuselage, instead of on a pylon.

> I'm thinking there isn't too much torsional vibration concern with very
> short shafts, high reving engine and a stiff carbon fiber prop. The prop
> will be seeing 6 - 7 power pulses per rev from the high reving Soob.

On that, I would agree. I believe you will have a new problem, though.

I believe that you will have a problem with the belt vibrating, like a
guitar string. At some speeds, it will get to the same resonance of the
belt, and slap like the devil. I have a 20" band saw that does this every
time, as it slows down, right before it stops.

One way to deal with this is to make the string (belt) shorter, with some
idler pullies. At least that is my plan. It would be a good idea to make
the distances between the plies a little different, or it will have a strong
tendency to vibrate as a complete string, at a higher fundamental (lowest)
frequency.

It is the same (in a way) as muffler design. The volume in the different
chambers is a little different, so when the frequency is resonating in one
chamber, it will not be resonating in the other chamber, thus more
frequencies are muffled.
--
Jim in NC

"Morgans" > kirjoitti
...
>
> "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

The Bell P-39 Airacobra V-1710 engine does have a direct drive from the
crankshaft to the 8 foot extension-shaft. This coupling certainly may have
some kind of a damper unit? The rotation speed reduction is done in the nose
section PSRU unit. The extension-shaft does have a support bearing unit in
the middle of the shaft.

Here's some nice pictures about the powerplant/driveline combo
http://www.aviation-history.com/engines/allison.htm

"However, there were problems with the complex nose-mounted reduction gear,
which caused reliability problems and resulted in fairly low serviceability
rates as compared with other fighters"
(http://home.att.net/~jbaugher1/p39_1.html).

JP

("Richard Lamb" wrote)
[150+ lines of quoted text snipped]

> My pardon, sir!


Speaking of reduction units ...! <g>


Montblack :-=)
Franz Liebkind: Der Führer does not say, "Achtung, baby."
The Producers (1968)

"Morgans" > wrote in message
...
>
> "Bill Daniels" <bildan@comcast-dot-net> wrote
>
>> Suppose the prop shaft is to be just long enough for the gear belt pulley
>> and the neccessary bearings - say 10 inches. But the engine flywheel
>> pulley is to be 4 - 6 feet below the prop shaft. The idea is to use a
>> very large multi-blade carbon fiber prop turning 800 - 1000 RPM driven by
>> a 4 cyl Soob turning at best power RPM. The idea is to get best thrust
>> in the 0 - 60 knot range. The airframe configuration is a prop over
>> tail boom pusher - an ultralight on steroids. (BTW, I'm not looking for
>> a long engine life under these conditions. I'll treat the Soob as a
>> throwaway power plant.)
>
> Strange, but I am considering a system, very much like that. Flying
> boat, with the engine in the fuselage, instead of on a pylon.
>
>> I'm thinking there isn't too much torsional vibration concern with very
>> short shafts, high reving engine and a stiff carbon fiber prop. The prop
>> will be seeing 6 - 7 power pulses per rev from the high reving Soob.
>
> On that, I would agree. I believe you will have a new problem, though.
>
> I believe that you will have a problem with the belt vibrating, like a
> guitar string. At some speeds, it will get to the same resonance of the
> belt, and slap like the devil. I have a 20" band saw that does this every
> time, as it slows down, right before it stops.
>
> One way to deal with this is to make the string (belt) shorter, with some
> idler pullies. At least that is my plan. It would be a good idea to
> make the distances between the plies a little different, or it will have a
> strong tendency to vibrate as a complete string, at a higher fundamental
> (lowest) frequency.
>
> It is the same (in a way) as muffler design. The volume in the different
> chambers is a little different, so when the frequency is resonating in one
> chamber, it will not be resonating in the other chamber, thus more
> frequencies are muffled.
> --
> Jim in NC

A low RPM high thrust prop on a high thrust line would be ideal for a
seaplane.

Actually this is not too different than some motorgliders with the engine
buried in the fuselage and the prop on a retractable pylon. The tooth belts
have only one or two idler pulleys. I figgured on at least two idlers to
maintain belt tension and to damp belt vibrations.

I want the engine in an external conformal pod below the fuselage for
accessability and to locate it below the pilot for survivability reasons.
I'd want the whole engine/cooling system in this pod so it could be removed
as a unit. The prop and drive belt would remain with the airframe.

Bill D

Montblack wrote:
> ("Richard Lamb" wrote)
> [150+ lines of quoted text snipped]
>
>> My pardon, sir!
>
>
>
> Speaking of reduction units ...! <g>
>
>
> Montblack :-=)
> Franz Liebkind: Der Führer does not say, "Achtung, baby."
> The Producers (1968)


Resonance, dude!

Morgans wrote:

>
> "Bill Daniels" <bildan@comcast-dot-net> wrote
>
>> Suppose the prop shaft is to be just long enough for the gear belt
>> pulley and the neccessary bearings - say 10 inches. But the engine
>> flywheel pulley is to be 4 - 6 feet below the prop shaft. The idea is
>> to use a very large multi-blade carbon fiber prop turning 800 - 1000
>> RPM driven by a 4 cyl Soob turning at best power RPM. The idea is to
>> get best thrust in the 0 - 60 knot range. The airframe configuration
>> is a prop over tail boom pusher - an ultralight on steroids. (BTW,
>> I'm not looking for a long engine life under these conditions. I'll
>> treat the Soob as a throwaway power plant.)
>
>
> Strange, but I am considering a system, very much like that. Flying
> boat, with the engine in the fuselage, instead of on a pylon.
>

Curious...
Tell me why?
What is the advantage?
(not argumentative, please - just curious)

If I absolutely *had* to do that, I'd think two stages.

HTD belt on the first stage from the engine, and either HTD, or Vopar type
chain for the final. Come to think of it, probably have to be chain for the
final drive due to the length of the thing...

But I'm back to the original question - why?

Wouldn't that put the engine where you would want to put people?

Richard

Bill Daniels wrote:

> "Morgans" > wrote in message
> ...
>
>>"Bill Daniels" <bildan@comcast-dot-net> wrote
>>
>>
>>>Suppose the prop shaft is to be just long enough for the gear belt pulley
>>>and the neccessary bearings - say 10 inches. But the engine flywheel
>>>pulley is to be 4 - 6 feet below the prop shaft. The idea is to use a
>>>very large multi-blade carbon fiber prop turning 800 - 1000 RPM driven by
>>>a 4 cyl Soob turning at best power RPM. The idea is to get best thrust
>>>in the 0 - 60 knot range. The airframe configuration is a prop over
>>>tail boom pusher - an ultralight on steroids. (BTW, I'm not looking for
>>>a long engine life under these conditions. I'll treat the Soob as a
>>>throwaway power plant.)
>>
>>Strange, but I am considering a system, very much like that. Flying
>>boat, with the engine in the fuselage, instead of on a pylon.
>>
>>
>>>I'm thinking there isn't too much torsional vibration concern with very
>>>short shafts, high reving engine and a stiff carbon fiber prop. The prop
>>>will be seeing 6 - 7 power pulses per rev from the high reving Soob.
>>
>>On that, I would agree. I believe you will have a new problem, though.
>>
>>I believe that you will have a problem with the belt vibrating, like a
>>guitar string. At some speeds, it will get to the same resonance of the
>>belt, and slap like the devil. I have a 20" band saw that does this every
>>time, as it slows down, right before it stops.
>>
>>One way to deal with this is to make the string (belt) shorter, with some
>>idler pullies. At least that is my plan. It would be a good idea to
>>make the distances between the plies a little different, or it will have a
>>strong tendency to vibrate as a complete string, at a higher fundamental
>>(lowest) frequency.
>>
>>It is the same (in a way) as muffler design. The volume in the different
>>chambers is a little different, so when the frequency is resonating in one
>>chamber, it will not be resonating in the other chamber, thus more
>>frequencies are muffled.
>>--
>>Jim in NC
>
>
> A low RPM high thrust prop on a high thrust line would be ideal for a
> seaplane.
>
> Actually this is not too different than some motorgliders with the engine
> buried in the fuselage and the prop on a retractable pylon. The tooth belts
> have only one or two idler pulleys. I figgured on at least two idlers to
> maintain belt tension and to damp belt vibrations.
>
> I want the engine in an external conformal pod below the fuselage for
> accessability and to locate it below the pilot for survivability reasons.
> I'd want the whole engine/cooling system in this pod so it could be removed
> as a unit. The prop and drive belt would remain with the airframe.
>
> Bill D
>
>

Ok, that was the quick answer :)

Ricahrd

"Morgans" > wrote in message
...
>
> "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
>
Sounds like a pretty sure bet to me. BTW, Thanks--I had wondered what
Allison did to eliminate resonance.

Peter

"Richard Lamb" > wrote in message
k.net...
> Peter Dohm wrote:
> > "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/Torsional/contact1/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
> >
> >
>
> My pardon, sir!
>
> Richard
>
No appology needed - I manage to miss plenty!

Peter

"Morgans" > wrote in message
...
>
> "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.
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> Warning,Warning, Danger, Danger, Will Robinson!
>
> Yep, that is a really big can of worms.
>
> The redrive is not as big a problem as you think. You get into a mess
> when you start talking about long drive shafts.
>
> Torsional resonance has brought many of the great minds of the flying
> industry to their knees. No joke. I don't have all of the links at hand,
> but someone here does. Start by googling torsional resonance.
>
> Then, be afraid. Be very afraid.
> I you don't get afraid, keep looking, until you get afraid, because you
> need to get afraid, or you don't understand the problem.
> --
> Jim in NC


The long driveshaft is a problem. Unlike a car, in an aircraft you put the
driveshaft in between the crankshaft and the flywheel. Not the place for a
driveshaft. My recommendation is to couple the driveshaft to the
engine/reduction unit with one of the shot filled fluid couplings. They
kill any feedback and pretty well damp the reinforcement that makes the
driveshaft go totally bonkers. Then use the largest diameter tubular
driveshaft you can fit into the space available. That will tend to put the
resonant frequencies into a range you won't pass through or run in normally.

Highflyer
Highflight Aviation Services
Pinckneyville Airport ( PJY )

>

"Capt. Geoffrey Thorpe" <The Sea Hawk at wow way d0t com> wrote in message
...
>snip<

> That was a problem on some of the early T-18's that were using cut down
> propellers - resonance was fatiguing the propeller which would then shed a
> blade, which would then encourage the engine to attempt to part company
> with the airframe...
>

That used to happen so frequently with Formula air racers where they chopped
the props for the O-200's to get the RPM up to get additional HP out of that
little engine that they started using a safety cable around the engine.
That way when the prop shed a blade and the engine jumped out of the engine
mount the cable held it somewhere near where it was supposed to be so you
could get the airplane on the ground in a survivable fashion!

Not something you want to play with normally.

Highflyer
Highflight Aviation Services
Pinckneyville Airport ( PJY )

"Richard Lamb" > wrote in message
ink.net...
> Big John wrote:
>
>> ADK
>>
>> Look up Molt Taylor and his Aerocar system. He used a pusher
>> arrangement and seemed to have most of the problems solved with long
>> shaft back to prop.
>>
>> His bird may still be flying some place to exhibitions?
>>
>> Am sure someone will jump in here and give data on his bird and how he
>> coupled shaft to engine with a "power glide" clutch or some such. It
>> allowed a small amount of slippage at each power stroke to prevent the
>> pulse being transmitted to drive shaft and prop as I recall.
>>
>> Best of luck with a difficult problem.
>>
>> Big John
>
> Ok,
>
> I think it's also used on the Imp and Mini-Imp.
>
>
> The "clutch" consists of two (wavy surfaced) plates with lead shot
> loaded between them.
>
> As the thing spun up, centrifugal force packed the shot solid, but
> there was enough "give" with the shot to absorb the "jerk" (4th
> derivative?).
>
>
> Richard
>
> no idea why that came out in past tense...


It is indeed used on the Imp and the MiniImp. Molt used it on most of his
designs and spent quite a few years getting the bugs worked out of it. It
is NOT "two wavy surfaced plates" but just a little different.

The driven part is a cylindrical case with a charge of shot in it. When the
case is driven the "fluid" shop is packed tightly against the outer diameter
of the spinning cylinder. The output shaft has a single "wavy" plate on the
end of it. This plate is enclosed in the cylinder with the shot. As the
shot gets packed into the rim of the case it grips the plate and transmits
the power to the output shaft. If you try to drive it backwards all the
plate does it turn in the loose shot and warm it up a bit. Like a "sprague
clutch" from a helicopter, it only transmits power in one direction. By
varying the load of shot in the cylinder you can vary the coupling
coefficient and "set" the breakaway torque for the unit. It cannot transmit
damaging torques from torsional vibration back through the coupling because
the output shaft "breaks away" before a crippling torque is reached. You
don't want it to break away at too low a torque either, or you will
basically have a "slipping" clutch in your drive train.

Highflyer
Highflight Aviation Services
Pinckneyville Airport ( PJY )

"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 )

"Peter Dohm" > wrote in message
...
>> 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.
>

GO-300, GO-435, GO-480, etc. There are lots of geared flat aircraft
engines. Note that all of the ones I mentioned are sixes. Fours are
tougher and twins are about impossible. Gearbox design is pretty critical.
Also, all of these engines got a bad reputation from pilots who didn't know
how to fly them. You never want to unload the gears. Put them is an
unloaded situation and the gears will lash with each power pulse and quickly
eat the gearbox.

Highflyer
Highflight Aviation Services
Pinckneyville Airport ( PJY )

"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 )

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.

"Highflyer" > wrote in message
...
>
> "Richard Lamb" > wrote in message
> ink.net...
> > Big John wrote:
> >
> >> ADK
> >>
> >> Look up Molt Taylor and his Aerocar system. He used a pusher
> >> arrangement and seemed to have most of the problems solved with long
> >> shaft back to prop.
> >>
> >> His bird may still be flying some place to exhibitions?
> >>
> >> Am sure someone will jump in here and give data on his bird and how he
> >> coupled shaft to engine with a "power glide" clutch or some such. It
> >> allowed a small amount of slippage at each power stroke to prevent the
> >> pulse being transmitted to drive shaft and prop as I recall.
> >>
> >> Best of luck with a difficult problem.
> >>
> >> Big John
> >
> > Ok,
> >
> > I think it's also used on the Imp and Mini-Imp.
> >
> >
> > The "clutch" consists of two (wavy surfaced) plates with lead shot
> > loaded between them.
> >
> > As the thing spun up, centrifugal force packed the shot solid, but
> > there was enough "give" with the shot to absorb the "jerk" (4th
> > derivative?).
> >
> >
> > Richard
> >
> > no idea why that came out in past tense...
>
>
> It is indeed used on the Imp and the MiniImp. Molt used it on most of his
> designs and spent quite a few years getting the bugs worked out of it. It
> is NOT "two wavy surfaced plates" but just a little different.
>
> The driven part is a cylindrical case with a charge of shot in it. When
the
> case is driven the "fluid" shop is packed tightly against the outer
diameter
> of the spinning cylinder. The output shaft has a single "wavy" plate on
the
> end of it. This plate is enclosed in the cylinder with the shot. As the
> shot gets packed into the rim of the case it grips the plate and transmits
> the power to the output shaft. If you try to drive it backwards all the
> plate does it turn in the loose shot and warm it up a bit. Like a
"sprague
> clutch" from a helicopter, it only transmits power in one direction. By
> varying the load of shot in the cylinder you can vary the coupling
> coefficient and "set" the breakaway torque for the unit. It cannot
transmit
> damaging torques from torsional vibration back through the coupling
because
> the output shaft "breaks away" before a crippling torque is reached. You
> don't want it to break away at too low a torque either, or you will
> basically have a "slipping" clutch in your drive train.
>
> Highflyer
> Highflight Aviation Services
> Pinckneyville Airport ( PJY )
>
>
>
I can really only agree with part of that. I did not reread the entire
brochure, but the clutch itself does not appear to be unidirectional, and it
is not intended to be a torsional dampener. However, the soft start
certainly would have eliminated resonance at srating motor speed, which
proved to be the most vexing problem in the Contact! article regarding the
BD-5. It could have made that other problems a lot easier to solve as well.

I have never personally seem any of Molt Taylor's aircraft, and I don't know
which specific parts he used, but a Dodge Flexidyne brochure is available
at: http://www.dodge-pt.com/pdf/brochures/pt_components/dmr_1513.pdf

Peter

JP wrote:

>
> The P-39/P-63 examples can't probably be compared directly with this matter
> in question. These designs both have a large reduction gear casing in front
> of the plane. The support structure for this PSRU looks very firm. Perhaps
> the safety cage type center fuselage structure has something to do with the
> lack of severe resonance problems? Any known resonance problems with these
> aircrafts?
>
> JP

I doubt any such information would be of value here since the those
PSRU has a gun barrel through it. Assuming any contact between the gun
and the PSRU any resonance solutions would be different.

Dan, U.S. Air Force, retired

Dan Horton wrote:
> 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?

Yes, but they use mass for damping like solid shafts. Weight is
nowhere near the issue it is for aircraft.

Dan, U.S. Air Force, retired

Ian Stirling wrote:
> 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.
>

Ian, if it won't stay together long enough to turn on the strobe,
it probably needs a little more work... ;)

Richard

Jim in NC writes:
<<I think you will find that they do it on ships, with pure weight. A
big,
heavy, solid steel shaft. Very heavy! That is how they get the
stiffness.>>

Sheesh. Shaft weight is not a factor. And more stiffness may or
may not be desired.

Shaft stiffness is one of the parameters that may be adjusted (up OR
down) so that the system has a natural frequency not matched by a
significant exciting frequency. If the system is driven by internal
combustion, identifying the most significant exciting frequency is dead
simple. It is (RPM x #cyls)/120 = hertz for a 4-stroke and (RPM x
#cyls)/60 = hertz for a two stroke. Designing a system with a natural
frequency that does not match the exciting frequency identified by this
equation is easy IF the engine runs at one RPM only. It gets a lot
harder if you expect to use a wide RPM range.

<<Also, the shaft turns very slowly, so there are many pulses per
revolution;
more than you will get with a 4 or 6 cylinder, 4 cycle airplane engine,
in
most cases.>>

Sheesh again. Shaft rotational speed alone is not a factor.

Shaft speed AND number of propeller blades may be of interest if
disturbed flow is the source of an exciting frequency. "Pulses per
revolution" sort of defines the term ''order" as it is used in
rotordynamics (the number of times anything happens per revolution). A
handy term, nothing more. For example, a ship's shaft at 90 RPM turns
1.5 times per second. If it has a four-blade prop and a single source
of disturbed flow (perhaps a strut supporting the shaft), then the
disturbance is a 4th order event. Order times rotational speed per
second (4 x 1.5) means an exciting frequency of 6 hertz. In this case
let us hope the engineer designed a system with no natural frequencies
between 4 and 8 hertz.

Wnat another example of speed x order? Consider the cardan joint.

<<I agree with the rest of your post; dig into the engineering text
books.>>

I wish you well with them.

Dan

Ian Stirling wrote:
> Richard Lamb > wrote:
>
>>Ian Stirling wrote:
>>
>>>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.
>>>
>>
>>Ian, if it won't stay together long enough to turn on the strobe,
>>it probably needs a little more work... ;)
>
>
> :)
>
> I suspect you know what I mean.
> But to clarify in any case, any shaft will have a given torque/torsional
> bending ratio.
> Say a half a degree at maximum safe load (or whatever) per 10 diameters.
> If the shaft is half a diameter long, it's going to be much harder to
> observe, than if it's 100.

The discussion was about long shafts. Rear mounted engine on tractor
airplane. No, it won't do much good on a 6" shaft.


--
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)."

ADK wrote:
> 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.

If it means anything, having the redrive and the >4 cyclinder ahead of
the drive shaft probably helps. This means the system would be seeing
a large number of small impulses rather than the small number of large
impulses with a direct drive 4.

On the other hand, the longer that drive shaft is, the lower its
natural frquency, and the larger the gear reduction of your redrive,
the higher the impulse frequency, so those might be coming into range
of each other.