nosewheel shimmy - shadow

[merlin]

Anyone here have know what could cause a nosewheel to start to shimmy and therefore what remedial action could be taken.

[Steve Brown]

Several things can cause this including:
Incorrect pivot (castor) angle ?
Is this
a new build problem (spec wrong? or
was it ok but is now an ongoing problem - heavy landing permanently altered the angle/damaged the fork?) or
intermittent ie when a certain weight is on it the castor angle changes sufficiently to cause shimmy.

Insufficient friction? - my free swivelling nose wheel has 3-5lbs force at the tyre damping friction.

Wheel out of balance?

Loose wheel bearing?

Loose pivots?

Tail wheel steering cable/spring tensions?
Regards
Steve

[J.C.]

"Tail wheel steering cable / spring tensions?"
Cause nose wheel shimmy????

Can't think of too many aircraft with a steerable nose wheel and a steerable tailwheel, come to think of it I can't think of too many with non steerable nose and tailwheel iether.
Certainly no shadows...is this an approved mod?

[Steve Brown]

Oops - you're right - while compiling my response I started thinking generally rather than the specifics of the question. At least someone with tail wheel shimmy might benefit since the other causes listed affect both!
Regards
Steve

[Nigel Ramsay]

Having owned two Shadows and a Streak in the past (!!) I seem to remember that nose-wheel shimmy was simply a matter of tightening up the wire strop that retained the movable nosewheel tube inside the bonded mounting tube. This was a highly technical procedure.... you simply leave the aircraft sitting on it's tail-skid and twist the nosewheel one full turn! Too tight and it becomes obvious that it is (too tight), but if it's 'loose' then it will shimmy!

[chrismk260]

one very simple thing you could try is the tyre pressure if you have not already ?