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From: David Jones
Hmmm. The first thing Mike Dehate did when he came to check out my IV, was
to put more pressure in the tires.
In my IV, I use 50 lbs in the nose and 55 in the mains.
( I use McCreary tires because the cutouts in the fuselage were originally
made for that brand, and other profiles might bind on retraction--but that is
no consequence to ES builders)
I suspect that your tire pressure is too low, causing some harmonics that
result in shimmy.
I assume that you have adjusted your oleo pressure using a nitrogen bottle.
If I had nose shimmy on a new plane, and all other remedies failed, I would
switch tire brands, especially on an ES, where tire profiles make no
difference in retraction--buying a different brand of tire is relatively
inexpensive, and you can always reuse or sell the old ones if they are in
good shape. A different brand with higher pressure than you have now (which
I think is too low a pressure) may solve your problem.
A final thought--lift your nose and recheck the tightness in the axle of the
nose wheel. If that has not loosened and seems ok, you should check the
tightness on the mains as well--jack the entire plane, remove the cotter pins
and rotate the axle nut until it seems to bind the wheel when you spin it by
hand. Then back off the nut to the next castle flute, allowing the wheel to
spin a little more freely.
Ohh, and one last suggestion. All tires have a light side and a heavy
side--marked by a red dot. McCreary tires come with a sheet that tells where
the red dot should be placed to keep the thing best in balance. (but at 2:00
AM I'll be darned if i can remember where the spot goes)
Good Luck,
David Jones, Pecatonica, Illinois
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