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Message
I don't have any expertise on this subject. But I
do play around with harmonic vibrations all the time in physics lab. I
understand aspects from statistical point of view too. Here's my wild
theory:
Apply torque wrench to the damper. Also measure the
angle of that wrench as you apply torque. You would end up with chart that says:
at 1 degree, you have 5 lbs. At 3 degrees you have 18 lbs. Etc. If you change
the durometer of ONE of your dampers, you change the above numbers AND the
frequency response of the unit. Using above numbers you should be able to
predict effect and test a whole bunch of frequency responses. That would allow
you to tune the device to optimize the damping. It gets you away from the "Aha!"
approach of experimenting. Converts your ideas into numbers.
Just an idea. I could be totally full of
it.
-al wick
----- Original Message -----
Sent: Sunday, December 02, 2007 3:05
PM
Subject: [FlyRotary] Re: Giving up on
single rotor
Al,
It sounds like you might be right - but I wish I
had an idea of what your talking about in regard to torque V angle of
deflection.
I do my best but you have me beat on this
one.
George ( down under)
----- Original Message -----
Sent: Monday, December 03, 2007 1:19
AM
Subject: [FlyRotary] Re: Giving up on
single rotor
Instead of using durometer in this case. I
think it would be better to measure torque vs. angle of deflection. Using
torque wrench and simple angle measure device. If you graphed this, you
would end up with a chart that defines frequency response of the damper.
Goal to have damper frequency response that's out of phase with the worst
torsional pulses.
Once you've measured frequency response, you
could then tune it with durometer tweaks. So you might end up with 2 dampers
at 50 durometer, 2 at 40, to obtain your ideal frequency response of
system.
I've always been drawn to having damper that
has more than one frequency response. You never see designs like that. So
with mild TV, it would respond one way. Suddenly it would have different
response with larger TV. Both responses out of phase. They use this method
with electronics and I've seen a few auto clutch dampers utilizing the
concept.
FWIW
al wick
----- Original Message -----
Sent: Saturday, December 01, 2007
10:46 PM
Subject: [FlyRotary] Re: Giving up on
single rotor
Righ-t-o Rusty!
Thanks
George ( down under)
So what durometer is your gut feeling
now that you went this far?
Hi George,
I don't think you can compare the durometer of one
damper to another, because the physical size is as important as the
hardness of the rubber. The Autoflight drive uses a stock
Centaflex coupler that's only available in 50 and 60 durometer.
It's a fairly large diameter, and thick coupler. 50 was better
than 60, but two 50's (effectively 25) in series was way too
soft. Maybe a 40 would be good, but it doesn't
exist.
Richard seems to be having better luck with
the Hirth drive. Two strokes are rough at low rpms, so
perhaps they already have the right damper for the job. I
also suspect his engine has softer power pulses at low rpms. It's
a 12A for one, and PP for another. PP is great at high rpms, but
not know for good power down low. It's the best theory I
have.
Cheers,
Rusty
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