DXB Posted November 12, 2019 Report Posted November 12, 2019 I've read about this issue in the other threads, including the wear of the steering horn, need to shim, need to replace/upgrade bushings etc. I have a focused inquiry. The scenario: I flew the other day after the first cold snap without checking tire pressures first. Upon landing and braking lightly after the nose wheel touched, I noticed a violent shimmy on the nose - it was pretty alarming, and I initially assumed that I'd had popped the tire. I landed slightly downhill, perhaps with a slight tailwind, and just a tad fast, but it was not a terrible landing, and I was not going ridiculously fast when I braked. The issue did not recur on the return home flight - I deliberately braked firmly after I landed and could not reproduce it. I subsequently noted my nose wheel pressure to be at 23psi and reinflated it to just above the normal 30 for the C model. The issue has not recurred on my two subsequent flights. I've never had any steering controllability issues or nose wheel shimmy before in >650 hours of operating the plane. There was no excess play in the nosewheel noted when the gear preload AD was recently completed. My rudder does not have excess play in it. My nose wheel tire is nearing the end of its tread life but still has a little tread left with no flat spots. My questions: I will have the steering mechanism inspected at annual next month. Assuming there is no obvious issue identified, is any preventive maintenance warranted on it? If not, I just plan to replace the aging tire/tube and pay more close attention to my tire pressures - The Michelin Airstop tubes have made me a little complacent maybe. Or at this point is there clear indication something must be wrong besides an underinflated and worn tire?
carusoam Posted November 12, 2019 Report Posted November 12, 2019 Expect that low air pressure starts to mess with geometry of the gear... The nose wheel is pretty sensitive to its geometry... It is quite possible that low air pressure is exacerbating the situation... inflate the tire, note any looseness, or play in the gear... Check the geometry at annual when it is up on jacks... Any additional concern, put it up on jacks sooner... PP thoughts only, not a mechanic... Best regards, -a-
KB4 Posted November 12, 2019 Report Posted November 12, 2019 If unable to duplicate issue, I am going with under inflated tire that had a flat spot. Get up on jacks asap to verify as @carusoam said. 1
Prior owner Posted November 12, 2019 Report Posted November 12, 2019 +1 on jacking the plane- grab the wheel and move it side to side...
TTaylor Posted November 14, 2019 Report Posted November 14, 2019 Key statement may have been "cold snap". How old are your gear pucks? Old pucks can contribute to shimmy and cold conditions make it worse. 2
DXB Posted November 15, 2019 Author Report Posted November 15, 2019 (edited) 18 hours ago, TTaylor said: Key statement may have been "cold snap". How old are your gear pucks? Old pucks can contribute to shimmy and cold conditions make it worse. Pucks are only 5 years old - I changed the originals as soon as I got the plane. I’d kinda expected for folks to say it can’t be tire pressure alone that is the issue here, but I’m starting to feel like it might be just the tires. The issue hasn’t recurred after inflating the tires back up to normal pressure in the cold. Edited November 15, 2019 by DXB
Prior owner Posted November 15, 2019 Report Posted November 15, 2019 Every aircraft tire I have put up on a spin balancer has been well out of balance, whether new or worn.... if you believe it's the tire, then pull it off and get it balanced- that would be an easy fix! 1
Romer Posted November 15, 2019 Report Posted November 15, 2019 In all my years of working as an a&p over 75% of nose wheel shimmy are caused by a bad nose wheel tire. Always put the best tire you can buy and it will most always cure the shimmy problem. 3
David Lloyd Posted November 15, 2019 Report Posted November 15, 2019 Nosewheel misbehavior could be summed up in three areas: Shimmy, sloppy and marginal control/darting. Shimmy could be caused by a worn or imbalanced nose tire or worn and improperly adjusted parts. Most likely caused by a combination a couple of otherwise marginal problems. Sloppy steering; worn or improperly adjusted parts. Marginal control and darting is most likely caused by improper caster of the nose gear as so well described by Don Maxwell as the 8 second ride. Most Mooneys that are actively flying either have not experienced this problem or have already complied with the service bulletin. The stress of attempting to control either a shimmy or darting will wear other parts rapidly, and sometimes outright break things. 1
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