Discussion:
PSRU...Belt or gear
(too old to reply)
RDR
2004-07-24 01:25:07 UTC
Permalink
Without (hopefully) opening another debate on the pros and cons of auto
conversions in aircraft I would like opinions regarding the choices between
a belt or gear driven PSRU in the 150 HP range.
Me thinks a belt driven unit would somewhat dampen the piston pulses and
also be lighter. Yet most of the firewall forward "packages" seem to offer
gear driven PSRUs.
Is it a reliability issue? Aren't modern cog belts almost indestructible
with proper alignment, cooling and tension?
How about some of you flying behind either one. Comments?
Roland
Ben Haas
2004-07-24 13:26:17 UTC
Permalink
Post by RDR
Without (hopefully) opening another debate on the pros and cons of auto
conversions in aircraft I would like opinions regarding the choices between
a belt or gear driven PSRU in the 150 HP range.
Me thinks a belt driven unit would somewhat dampen the piston pulses and
also be lighter. Yet most of the firewall forward "packages" seem to offer
gear driven PSRUs.
Is it a reliability issue? Aren't modern cog belts almost indestructible
with proper alignment, cooling and tension?
How about some of you flying behind either one. Comments?
Roland
All the things you mentioned are true plus if ya get a prop strike the
belt absorbs the impact along with the prop, no engine teardown...

I am running about three times your HP requirments through a Belted
Air redrive and wouldn't think of using a gear drive in my plane. Here
is a link to a few pics of my set up..
Loading Image...

Loading Image...

Ben Haas N801BH
UltraJohn
2004-07-24 17:25:12 UTC
Permalink
Nice job Ben!
John
Post by Ben Haas
I am running about three times your HP requirments through a Belted
Air redrive and wouldn't think of using a gear drive in my plane. Here
is a link to a few pics of my set up..
http://www.zenithair.com/stolch801/builder-pics/bh2.jpg
http://www.zenithair.com/stolch801/builder-pics/bh1.jpg
Ben Haas N801BH
Blueskies
2004-07-25 01:56:53 UTC
Permalink
That looks great...
--
Dan D.
http://www.ameritech.net/users/ddevillers/start.html


.
Post by Ben Haas
Post by RDR
Without (hopefully) opening another debate on the pros and cons of auto
conversions in aircraft I would like opinions regarding the choices between
a belt or gear driven PSRU in the 150 HP range.
Me thinks a belt driven unit would somewhat dampen the piston pulses and
also be lighter. Yet most of the firewall forward "packages" seem to offer
gear driven PSRUs.
Is it a reliability issue? Aren't modern cog belts almost indestructible
with proper alignment, cooling and tension?
How about some of you flying behind either one. Comments?
Roland
All the things you mentioned are true plus if ya get a prop strike the
belt absorbs the impact along with the prop, no engine teardown...
I am running about three times your HP requirments through a Belted
Air redrive and wouldn't think of using a gear drive in my plane. Here
is a link to a few pics of my set up..
http://www.zenithair.com/stolch801/builder-pics/bh2.jpg
http://www.zenithair.com/stolch801/builder-pics/bh1.jpg
Ben Haas N801BH
RDR
2004-07-25 02:33:29 UTC
Permalink
Nice looking installation! How many hours flying time on this configuration?
What is the firewall forward weight?
Roland
Post by Ben Haas
Post by RDR
Without (hopefully) opening another debate on the pros and cons of auto
conversions in aircraft I would like opinions regarding the choices between
a belt or gear driven PSRU in the 150 HP range.
Me thinks a belt driven unit would somewhat dampen the piston pulses and
also be lighter. Yet most of the firewall forward "packages" seem to offer
gear driven PSRUs.
Is it a reliability issue? Aren't modern cog belts almost
indestructible
Post by Ben Haas
Post by RDR
with proper alignment, cooling and tension?
How about some of you flying behind either one. Comments?
Roland
All the things you mentioned are true plus if ya get a prop strike the
belt absorbs the impact along with the prop, no engine teardown...
I am running about three times your HP requirments through a Belted
Air redrive and wouldn't think of using a gear drive in my plane. Here
is a link to a few pics of my set up..
http://www.zenithair.com/stolch801/builder-pics/bh2.jpg
http://www.zenithair.com/stolch801/builder-pics/bh1.jpg
Ben Haas N801BH
Daniel
2004-07-25 02:30:34 UTC
Permalink
RDR wrote ...
...
Me thinks a belt driven unit would somewhat dampen the piston pulses ...
Might. Then again it might make them worse. Trick is proper design.
Go get a big heavy rubber band. Hang something heavy on one end.
Grab hold of the other & start bobbing the weight up & down. Do it at
the right frequency & it will indeed dampen the "pulses". Do it at
the wrong frequency & it will magnify them.

Daniel
Ben Haas
2004-07-25 22:56:03 UTC
Permalink
Post by Daniel
RDR wrote ...
...
Me thinks a belt driven unit would somewhat dampen the piston pulses ...
Might. Then again it might make them worse. Trick is proper design.
Go get a big heavy rubber band. Hang something heavy on one end.
Grab hold of the other & start bobbing the weight up & down. Do it at
the right frequency & it will indeed dampen the "pulses". Do it at
the wrong frequency & it will magnify them.
Daniel
WOW,,,,, Perpetual motion.. You are gonna be a RICH man soon....
Remember to keep all of us homebuilders in your will so we can develop
other kool stuff.
Pete
2004-07-26 19:56:33 UTC
Permalink
Ben,

what would this have to do with perpetual motion??

RDR's analogy is essentially correct, in that he is adding energy to the
system with every bounce with his hand. All that is happening is that the
energy is added at the correct time to super impose and add to the motion,
rather than cancel it out. Trampoline jumpers use the same theory all the
time, either go higher or quickly stop.

It appears to be simple wave-type theory.... why the sarcasm?

Whether belt, gear, or chain, the effect is the same, just with different
number/frequencies. Gears and chains add a slop to the system making the
dynamics that much more complicated however.

Cheers,
Pete
Post by Ben Haas
Post by Daniel
RDR wrote ...
...
Me thinks a belt driven unit would somewhat dampen the piston pulses ...
Might. Then again it might make them worse. Trick is proper design.
Go get a big heavy rubber band. Hang something heavy on one end.
Grab hold of the other & start bobbing the weight up & down. Do it at
the right frequency & it will indeed dampen the "pulses". Do it at
the wrong frequency & it will magnify them.
Daniel
WOW,,,,, Perpetual motion.. You are gonna be a RICH man soon....
Remember to keep all of us homebuilders in your will so we can develop
other kool stuff.
hjarrett
2004-07-26 21:57:37 UTC
Permalink
We need to cut Ben some slack here. Vibration theory is confusing when you
haven't figured it out yet and ISN'T intuitive. Once you start to
understand it it's hard to see why it is confusing to those that don't. I
have had a number of people that confused perpetual motion with an unstable
amplified vibration. When you don't understand it it looks like free energy
just shakes the parts to pieces. Most of my experience was with flutter but
it's the same concept and formulas as a belt drive with the belt receiving
amplifying pulses at the natural frequency..
Hank J
And by the way, NO, I DON'T fully understand flutter. It's a specialized
area of structures and dynamics and I had a specialist that did the
analysis. He was a little "strange" but really good at it.
Post by Pete
Ben,
what would this have to do with perpetual motion??
RDR's analogy is essentially correct, in that he is adding energy to the
system with every bounce with his hand. All that is happening is that the
energy is added at the correct time to super impose and add to the motion,
rather than cancel it out. Trampoline jumpers use the same theory all the
time, either go higher or quickly stop.
It appears to be simple wave-type theory.... why the sarcasm?
Whether belt, gear, or chain, the effect is the same, just with different
number/frequencies. Gears and chains add a slop to the system making the
dynamics that much more complicated however.
Cheers,
Pete
Post by Ben Haas
Post by Daniel
RDR wrote ...
Post by RDR
...
Me thinks a belt driven unit would somewhat dampen the piston pulses
...
Post by Ben Haas
Post by Daniel
Might. Then again it might make them worse. Trick is proper design.
Go get a big heavy rubber band. Hang something heavy on one end.
Grab hold of the other & start bobbing the weight up & down. Do it at
the right frequency & it will indeed dampen the "pulses". Do it at
the wrong frequency & it will magnify them.
Daniel
WOW,,,,, Perpetual motion.. You are gonna be a RICH man soon....
Remember to keep all of us homebuilders in your will so we can develop
other kool stuff.
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Kevin Horton
2004-07-27 03:26:29 UTC
Permalink
Post by hjarrett
And by the way, NO, I DON'T fully understand flutter. It's a specialized
area of structures and dynamics and I had a specialist that did the
analysis. He was a little "strange" but really good at it.
I don't think anyone fully understands flutter, and I wouldn't want anyone
working on my project who thought they did. I am reminded of the modified
707 that Boeing did for a Navy TACAMO mission, a few years ago. I'm not
sure what the design changes were, but they had to do the flutter
clearance again. Boeing is known as a very conservative company, so I
suspect they did all the analysis and ground test that they would normally
do.

They lost half the vertical tail during the flutter testing. They got the
aircraft back on the ground, and you can be sure they really took the
microscope out on the analysis and ground testing, and made whatever
changes in the design or flight envelope were required. Then they went up
on another flutter flight test and promptly lost half the vertical tail
again.

If a company with the resources and smarts of Boeing can have such an
event happen, then no one should have the hubris to think that they fully
understand flutter.
--
Kevin Horton
Ottawa
e-mail: khorton02(_at_)rogers(_dot_)com
Cam
2004-07-28 00:02:53 UTC
Permalink
Excuse my ignorance, but what is flutter?

Cam.
Post by Kevin Horton
Post by hjarrett
And by the way, NO, I DON'T fully understand flutter. It's a specialized
area of structures and dynamics and I had a specialist that did the
analysis. He was a little "strange" but really good at it.
I don't think anyone fully understands flutter, and I wouldn't want anyone
working on my project who thought they did. I am reminded of the modified
707 that Boeing did for a Navy TACAMO mission, a few years ago. I'm not
sure what the design changes were, but they had to do the flutter
clearance again. Boeing is known as a very conservative company, so I
suspect they did all the analysis and ground test that they would normally
do.
They lost half the vertical tail during the flutter testing. They got the
aircraft back on the ground, and you can be sure they really took the
microscope out on the analysis and ground testing, and made whatever
changes in the design or flight envelope were required. Then they went up
on another flutter flight test and promptly lost half the vertical tail
again.
If a company with the resources and smarts of Boeing can have such an
event happen, then no one should have the hubris to think that they fully
understand flutter.
--
Kevin Horton
Ottawa
e-mail: khorton02(_at_)rogers(_dot_)com
Kevin Horton
2004-07-28 02:00:12 UTC
Permalink
Post by Cam
Excuse my ignorance, but what is flutter?
Cam.
http://www.dfrc.nasa.gov/Education/OnlineEd/Intro2Flight/nasflut.html

--
Kevin Horton

A. Because it forces people to start at the bottom and read towards the
top, which is not natural.
Q. Why is top posting bad?

A. Top posting.
Q. What is the greatest frustration when reading a news group?
Blueskies
2004-08-01 12:42:45 UTC
Permalink
http://www.dfrc.nasa.gov/DTRS/1995/PDF/H-2077.pdf
--
Dan D.
http://www.ameritech.net/users/ddevillers/start.html
Richard Lamb
2004-07-28 02:10:16 UTC
Permalink
Post by Cam
Excuse my ignorance, but what is flutter?
Cam.
Aeroelastic excitation at or near resonant frewuency of the airframe.
hjarrett
2004-07-29 01:24:18 UTC
Permalink
Why do I think that isn't going to answer Cams question (correct as
everything you wrote except the spelling of frequency is). ;-)
Cam,
This could be a LONG explanation and the group isn't the right place to do
it. If you want to get together off group I will "try" to explain it, but
it could take a while. Like Kevin said, very few people really understand
it, but several have died trying to figure it out as amateurs. If you get
flutter, SLOW DOWN AND LAND, NOW! I have seen some incredible damage to the
primary structure of aircraft after a flutter incident and done several
crash investigations where crews were brought back in numerous small plastic
bags. Don't join them. If you are flying and the controls "buzz" or a
surface starts to oscillate back and forth SLOW DOWN AND LAND! Don't try
and figure out why it happens and CERTAINLY DON'T TRY AND REPRODUCE IT! A
friend did on a Taylorcraft wing strut vibration and I am real happy he is
still alive. When the jury strut was properly positioned and tightened the
flutter disappeared but a FULL inspection of the wing and controls was in
order. His second "amateur test flight" was a real test of the Grim Reapers
patience.
Hank
Post by Richard Lamb
Post by Cam
Excuse my ignorance, but what is flutter?
Cam.
Aeroelastic excitation at or near resonant frewuency of the airframe.
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Orval Fairbairn
2004-07-29 02:39:41 UTC
Permalink
Post by hjarrett
Why do I think that isn't going to answer Cams question (correct as
everything you wrote except the spelling of frequency is). ;-)
Cam,
This could be a LONG explanation and the group isn't the right place to do
it. If you want to get together off group I will "try" to explain it, but
it could take a while. Like Kevin said, very few people really understand
it, but several have died trying to figure it out as amateurs. If you get
flutter, SLOW DOWN AND LAND, NOW! I have seen some incredible damage to the
primary structure of aircraft after a flutter incident and done several
crash investigations where crews were brought back in numerous small plastic
bags. Don't join them. If you are flying and the controls "buzz" or a
surface starts to oscillate back and forth SLOW DOWN AND LAND! Don't try
and figure out why it happens and CERTAINLY DON'T TRY AND REPRODUCE IT! A
friend did on a Taylorcraft wing strut vibration and I am real happy he is
still alive. When the jury strut was properly positioned and tightened the
flutter disappeared but a FULL inspection of the wing and controls was in
order. His second "amateur test flight" was a real test of the Grim Reapers
patience.
Hank
Post by Richard Lamb
Post by Cam
Excuse my ignorance, but what is flutter?
Cam.
Aeroelastic excitation at or near resonant frewuency of the airframe.
Flutter test are usually performed with the airplane pointed somewhat
upward, so it is slowing down when the test pilot excites the controls,
thus limiting exposure.

When testing in the flutter range, you test in 1-2 kt increments, until
you get signs of oscillation, then quit and thoroughly examine the
structure for damage. Flutter can literally rip the surfaces off within
2 seconds, so it is not something to trifle with.
Richard Lamb
2004-07-29 04:35:42 UTC
Permalink
Post by hjarrett
Why do I think that isn't going to answer Cams question (correct as
everything you wrote except the spelling of frequency is). ;-)
Post by Richard Lamb
Aeroelastic excitation at or near resonant frewuency of the airframe.
speech impediment :^)
Ron Wanttaja
2004-07-29 05:13:50 UTC
Permalink
Post by Richard Lamb
Post by hjarrett
Why do I think that isn't going to answer Cams question (correct as
everything you wrote except the spelling of frequency is). ;-)
Post by Richard Lamb
Aeroelastic excitation at or near resonant frewuency of the airframe.
speech impediment :^)
And here I thought it was just your regimental accent. :-)

Ron "Fwashman, I say, Fwashman..." Wanttaja
Cam
2004-07-29 06:09:21 UTC
Permalink
Thanks Guys, I get the jist of it, can see the problem but hadn't heard
the term before.
Does flutter apply to rotor blades?
(Please say no.)

Cam.
Stealth Pilot
2004-07-29 12:13:39 UTC
Permalink
Post by Cam
Thanks Guys, I get the jist of it, can see the problem but hadn't heard
the term before.
Does flutter apply to rotor blades?
(Please say no.)
Cam.
flutter can occur to any aerodynamic surface in motion.

cg in front of the cp will help dampen it out/prevent it.
(actually, if the spar is at the cp -centre of pressure then having
the section cg in front of the spar is what helps.)

Stealth Pilot
Bill Daniels
2004-07-29 13:07:57 UTC
Permalink
Post by Stealth Pilot
Post by Cam
Thanks Guys, I get the jist of it, can see the problem but hadn't heard
the term before.
Does flutter apply to rotor blades?
(Please say no.)
Cam.
flutter can occur to any aerodynamic surface in motion.
cg in front of the cp will help dampen it out/prevent it.
(actually, if the spar is at the cp -centre of pressure then having
the section cg in front of the spar is what helps.)
Stealth Pilot
I've read of another technique which to add small dampers that look like
shock absorbers to the control surfaces during flight test. These are loose
enough to allow just enough flutter to be detected but tight enough to
hopefully prevent damage.

Bill D
hjarrett
2004-07-29 22:16:20 UTC
Permalink
Sorry, but yes, flutter in rotor blades is one of the worst. I did fixed
wing crashes but the "rotor heads" said a bad rotor flutter would tear the
crews heads off in a split second before the structure broke up (don't know
first hand if it is true but sure put the "scrunchies" in our seat cushions
when they described it). At least it was quick. I get nervous around
anything that is SUPPOSED to shake that much.
Only helicopter crash I was involved in was a dynamic roll over. Lots of
injuries there too. Them things just ain't safe.
Hank J
Post by Cam
Thanks Guys, I get the jist of it, can see the problem but hadn't heard
the term before.
Does flutter apply to rotor blades?
(Please say no.)
Cam.
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Orval Fairbairn
2004-07-30 01:13:57 UTC
Permalink
Post by hjarrett
Sorry, but yes, flutter in rotor blades is one of the worst. I did fixed
wing crashes but the "rotor heads" said a bad rotor flutter would tear the
crews heads off in a split second before the structure broke up (don't know
first hand if it is true but sure put the "scrunchies" in our seat cushions
when they described it). At least it was quick. I get nervous around
anything that is SUPPOSED to shake that much.
Only helicopter crash I was involved in was a dynamic roll over. Lots of
injuries there too. Them things just ain't safe.
Hank J
Post by Cam
Thanks Guys, I get the jist of it, can see the problem but hadn't
heard
Post by Cam
the term before.
Does flutter apply to rotor blades?
(Please say no.)
Cam.
Any time you have an ultra-high aspect ratio airfoil, it can flutter.
That is what did in the infamous Tacoma Narrows Bridge, back in the late
1930s. Helocopter blades are ultra-high aspect ratio and are usually
extremely stiff, and done with symmetric airfoil sections to avoid extra
moment generation.
Bruce A. Frank
2004-07-28 05:56:43 UTC
Permalink
I will recommend the cog belt type PSRU over most gear type, but for
destructive harmonic vibration, there are no PSRUs that are immune to
it. The solution is to design so that those destructive harmonics are
outside the operating envelope of the engine, prop and belt combination.
The cog belt PSRUs, as developed for auto conversions by Dave Blanton,
have been well refined by both Belted Air Power and Northwest Aero. The
belt, sprockets and bearings have been found to survive for the life of
the engine in V-6 and V-8 applications. When installed correctly, belt
not too tight, they show virtually no wear and several have run to 2000
hours with no repairs necessary.

There are theories that the rubber/polymer in the construction (the
belts have no give or stretch) of the belt helps to damp pulses from
both the engine and the prop and thus reducing the likelihood of a
harmonic getting started. But, Blanton found harmonic problems at
certain tooth counts on his sprockets.

Some gear units seem to hold up well when designed with good
lubrication systems...the cog belt type need only a few squirts of
grease in the bearings every few hundred hours or so. There are no gear
lash adjustments or spring loaded clutches to care for. A cog tooth belt
on a correctly machined sprocket wears imperceptibly for years...its
only enemy is sunlight.
Post by Daniel
RDR wrote ...
...
Me thinks a belt driven unit would somewhat dampen the piston pulses ...
Might. Then again it might make them worse. Trick is proper design.
Go get a big heavy rubber band. Hang something heavy on one end.
Grab hold of the other & start bobbing the weight up & down. Do it at
the right frequency & it will indeed dampen the "pulses". Do it at
the wrong frequency & it will magnify them.
Daniel
--
Bruce A. Frank, Editor "Ford 3.8/4.2L Engine and V-6 STOL
***@worldnet.att.net Homebuilt Aircraft Newsletter"
| Publishing interesting material|
| on all aspects of alternative |
| engines and homebuilt aircraft.|
*------------------------------**----*
\(-o-)/ AIRCRAFT PROJECTS CO.
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/ \ for homebuilt aircraft,
0 0 TIG welding

While trying to find the time to finish mine.
geo
2004-07-25 15:04:09 UTC
Permalink
http://homepage.mac.com/rotarycoot/
Post by RDR
Without (hopefully) opening another debate on the pros and cons of auto
conversions in aircraft I would like opinions regarding the choices between
a belt or gear driven PSRU in the 150 HP range.
Me thinks a belt driven unit would somewhat dampen the piston pulses and
also be lighter. Yet most of the firewall forward "packages" seem to offer
gear driven PSRUs.
Is it a reliability issue? Aren't modern cog belts almost indestructible
with proper alignment, cooling and tension?
How about some of you flying behind either one. Comments?
Roland
B2431
2004-07-25 19:37:26 UTC
Permalink
Date: 7/25/2004 10:04 AM Central Daylight Time
http://homepage.mac.com/rotarycoot/
Did the girl come with the kit? Autopilot?

Dan, U.S. Air Force, retired
karel
2004-07-25 20:01:00 UTC
Permalink
Post by B2431
Date: 7/25/2004 10:04 AM Central Daylight Time
http://homepage.mac.com/rotarycoot/
Did the girl come with the kit? Autopilot?
nay, too shaky for that ...
geo
2004-07-25 20:39:15 UTC
Permalink
Post by B2431
Date: 7/25/2004 10:04 AM Central Daylight Time
http://homepage.mac.com/rotarycoot/
Did the girl come with the kit? Autopilot?
Dan, U.S. Air Force, retired
Dan, you need to scroll down, so to speak.
George A. Graham
2004-07-30 21:04:06 UTC
Permalink
Post by RDR
a belt or gear driven PSRU in the 150 HP range.
Both work, the belt offers/needs offset which you may want (to raise
the prop shaft). I've been flying for six years in second gear.

When I was looking at belts (maybe 10 years ago) they were rated at less
than 100 hp. All the WWII birds used gears.

Perhaps a more important question might be "what engines have the
most/least destructive torsionals. The Mazda wankle motor has some
similar to a six cylinder piston engine -eg. no reversals.

George Graham
RX-7 Powered Graham-EZ, N4449E
Homepage <http://bfn.org/~ca266>
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