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Thomas,
You are certainly not "full of it". Lyc uses a similar damper in most of their counterbalanced cranks. Weather it would help the single rotor depends on finding the frequency that is causing the problem and designing for it.
Bill Jepson
-----Original Message-----
From: Thomas Jakits <rotary.thjakits@gmail.com>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Sent: Tue, 4 Dec 2007 1:16 pm
Subject: [FlyRotary] Re: Giving up on single rotor
To quote Al,
"I might be full of it", .... but:
A couple of years ago, when I started to read up on all the fantastic aftermarket gadgets available and legal to the US folks (I am from Europe and modifying vehicles is a PITA MAJOR), I read about a vibration/torque pulse damper that consisted of a rather massive ring with holes (don't remember if they where evenly spaced or not...) the holes where filled with rolls (cylindrical), with what seemed of different sizes. The rolls where free to roll around inside their specific hole.
obviously once the crank started to turn the rolls would be drawn to the outside, but depending on the torque pulses they would roll back and forth inside the holes, supposedly dampening (?) vibration/torque pulses. Supposedly a development from WW II aircraft engines.
Usable only with even number cylinder engines and even firing order engines..
On the site below this thing is called a pendulum absorber??
See:
http://www.tciauto.com/Products/Rattler/
Lynn, Bill, George, Richard - anyone knows what I am talking about? Any possible application for the 1-rotor?
Am I full of it??
TJ
On 12/4/07, George Lendich <lendich@optusnet.com.au> wrote:
Ok Al,
I can understand that now that you have explained it further.
All we have to do is marry up the frequency of the single rotor, one pulse per shaft rotation, to that of a known damper.
We know that the more outward (to the edge of the flexplate) and the softer the damper the better for the 2 rotor, 2 pulses per shaft rotation .
I believe that Richard's suggestion that the damper for the single be closer to the centre of the flexplate.
George (down under)
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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