PSRU design advantages

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 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)."

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

---------------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