Bill Freeman wrote:

If the bolt problem is guitar string type of vibrations (lateral

vibrations), then

providing an elastomeric doughnut (sleeve, tube, whatever) in the

middle which is

snug on the bolt and in the hole will dramatically detune the system

and provide

substantial damping.  Both are good.

If the bolt hole size is consistent, I'd use a sleeve in the middle

portion. Sounds

like what the 20B has.  It needs to be a snug fit in the hole, does not

need to

cover the whole bolt, does need to be in the middle, at least

approximately.

Actually, from a purely off-the-cuff harmonics point of view, the damper

should *not*

be *exactly* in the center.  Near, but slightly off, center is optimal;

it forces the

vibrating object (bolt shaft in this case) to seek out much higher order

harmonics,

which have proportionately lower energy.

Russell Kent

Good point, I was thinking of forcing a shift from first mode to second,
which is
typically much higher freq and of course the magnitude of the motion is much
less,
which is what is driving the fatigue.  Not sure if you would get an odd order
vibration with the longer section vibrating at a lower freq in your
assymetric case.  Probably have to force the short end to match the freq, so
force it higher like you
said.

Bill

The AirCraft Rotary Engine NewsLetter.              Powered by Linux.

http://home.earthlink.net/~rotaryeng/            http://www.linux.org