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We have to keep the two dampers apart, torque oscillation damper and
torsional vibration damper. Most every piston engine has a torsional vibration
damper, the rotary does not. Don't have enough room to elaborate.
The issue on the rotary is torque oscillation. In the case of a single rotor,
it is twice as much as in the two rotor. It can be a problem if not dealt with
it in the proper way.
Why is my single rotor running right? I believe, mainly because all the
single rotor Wankels I know of, did run right or are running right. Starting
with the NSU Spider, which I have personal experience with, through all the
F&S models, including the ones in the Sirius motor glider, and many more.
Never ever did anyone, anywhere mention a problem with torque reversal or
vibration.
How things can be misinterpreted was demonstrated by PowerSports years ago,
when they had torsoinal vibration problems with the 13B PP engine on the test
stand. It turned out to be test stand installation problems.
It is certainly imperative to do some research when you do a new setup.
Especially since there is not sample of a single rotor, based on the MAZDA
engine, on the market one could lean on.
I certainly had some run-ins with nature(of engineering that is) on drive
coupling. The first coupler I used on the direct drive load prop, disintegrated
in less than 5 min. of running because I ignored my own philosophy of not taking
short cuts. From that time on, it was never less then what I am using
now.
My whole set up can certainly be modeled, and analyzed why it works the way
it does. Unless I run into a problem, there is no room for any academic effort,
and at the same time getting the engine into the air. It is only me working on
it.
FWIW
Richard Sohn
N2071U
----- Original Message -----
Sent: Tuesday, December 04, 2007 3:46
PM
Subject: [FlyRotary] Re: Giving up on
single rotor
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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