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NOSE WHEEL SHIMMY/FAILURE
(From CP33, Page 6, July, 1982)
We have heard of three more nose wheel fork failures. This is a part of our airplanes we seldom see; it is retracted when parked and we are usually in the seat when the gear is extended. Do not neglect to check your nose wheel during your preflight. Pay particular attention to the friction damper. You should grab the tire as far aft as possible and swing the fork left and right. It should take 2 to 4 lbs. of force to do this. If you are not certain how much 2 to 4 lbs is, use a spring scale to calibrate yourself. If you have less than 2 lbs., it is possible for the nose wheel to shimmy. This shimmy or flutter instantly goes divergent and in only a fraction of a second the fork will fail. due to side loads. The nose wheel/fork, can then bounce back and go through the prop. The nose wheel fork is designed with more than enough integrity to take the maximum expected landing loads and has been tested to over 80% above the FAR Part 23 requirement without failure (see CP #18). This type of failure caused by shimmy generally occurs with very little load on the nose wheel, usually at the very moment of a nose wheel touch down, or even at the moment of nose wheel lift off during a take off. The new shimmy damper spring called out in CP 30. page 4, MUST be installed and correctly adjusted. Also check to see you have no ovalizing or bending of the NG17 steel tube and that the thick-wall (0.125+ wall) NG17 is installed.