C172 Shimmy

wrxpilot

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One of the 172s I rent has a tendency to shimmy on T/O and landing rollout. It's much more pronounced on T/O, but I can get it to settle out by adding back pressure until I hit a high enough a/s to get rotation (or adding back pressure on rollout until I've slowed past the "critical" shimmy speed). Nonetheless, it is annoying. I've squawked this on the maintenance sheet before, but it always seems to re-appear on this a/c. What is the typical cause of nosewheel shimmy? Is it ever dangerous? Are there any long term effects such as early fatigue on nose gear components?
 

erj-145mech

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Causes for nose wheel shimmy in Cessna's (partial list)

a) Shimmy dampener requires servicing and/or resealing
b) Shimmy dampener attaching hardware/bushings worn
c) Nose tire out of balance
d) Nose wheel bearings and races worn
e) Nose gear torque links (scissors) bolts/bushings worn
f) Nose wheel fairing (if installed) cracked/broken
g) Spring bungees from rudder pedal torque tube to nose gear horn worn
f) Nose gear to firewall fitting clearance too great, requires reshimming

these are some things that I would normally check, not in this order, and this is just shooting from the hip without examining the aircraft.
 

RipCurl

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Sounds like some of the Cessnas I've rented. I used to do soft field TOs with those ones...

However, I did abort one TO because the 182 was shaking so bad my teeth were chattering.

Seems (to me) to be a combination of Cessna design and less-than-stellar maintenance. However, I'm not an A&P (unlike erj-145mech).
 
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JimG

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erj-145mech said:
Causes for nose wheel shimmy in Cessna's (partial list)

a) Shimmy dampener requires servicing and/or resealing
b) Shimmy dampener attaching hardware/bushings worn
c) Nose tire out of balance
d) Nose wheel bearings and races worn
e) Nose gear torque links (scissors) bolts/bushings worn
f) Nose wheel fairing (if installed) cracked/broken
g) Spring bungees from rudder pedal torque tube to nose gear horn worn
f) Nose gear to firewall fitting clearance too great, requires reshimming

these are some things that I would normally check, not in this order, and this is just shooting from the hip without examining the aircraft.

I'm guessing one, or all of the above also.

My first airplane was a 1966 C172 and I had more problems with that shimmy dampener than just about anything else on the airplane, which is why I've never had the desire to own another Cessna single.
 

avbug

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ERJ already hit the high points. Most of those problems are due to pilot error, either one time or over time. Airplanes would generally do just fine if we could just bump off the pilots...

From your perspective, keeping the weight off the nosewheel is important. Is it dangerous? It can be. But usually it's just annoying.

Keep pressure on both rudder pedals, just like you should in a tailwheel airplane.

If the rental facility can't be bothered to maintain their aircraft, don't you think you might be better served elsewhere?
 

cougar6903

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RipCurl said:
Seems (to me) to be a combination of Cessna design and less-than-stellar maintenance. However, I'm not an A&P (unlike erj-145mech).
I've seen a direct cuase/effect relationship between pilots (student and otherwise) landing flat time and time again and nosewheel shimmy in cessna singles.
 

troy

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Keep the nosewheel off the ground with backpressure and watch the speed. Most of our Skydogs do the same thing.
 

say again

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shimmy shimmy ya, shimmy yo, shimmy yey
 

DJS

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The 172SP at the place I rent does that periodically. I (and others, based on the logs) squawk it, the mechanic tightens something, it goes away for a few months, then returns. I'd assume some design defect causes one of the previously listed items to repeatedly get out of whack.

When that happens on takeoff, I simply pop the nose early (soft-field) and try to remember to soft-field it on landing (and taxi with the yoke back to remove as much weight as possible from the nosewheel). Write up the notes when I return the plane and it is generally "fixed" the next time I rent it.
 

mattpilot

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Coming in for landing once, i set off the ELT because the freakin nosewheel vibrated so bad. It was otherwise a smooth touchdown on the mains and the nosewheel was lowered at a normal rate. I guess the speed was just to fast for the shimmy damper ... but i nearly got a heart attack hearing the ELT in the cockpit. :)
 

Len

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Just land and keep the nose wheel in the air... Its good training for when your A320 nose gear cocks 90 degrees!
 

a&p cfiguy

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As an A&P who's worked on 172 flight school aircraft for over three years, I can tell you exactly what's wrong. Most likely the steering collar is worn out and needs to be shimmed. Cessna makes three different size shims to accomplish this. This requires the whole nose strut to be removed the steering collar slid off, shims installed as required to get a tight fit, but not too tight that you can't steer the airplane, steering collar and nose strut reinstalled.

This is one of the most common complaints of 172s and one that usually goes unfixed for years because no one wants to do the job right! Everyone thinks they'll just service the shimmy dampener and it'll be okay. Or I'll just shim the torque links and that outta do it. Or maybe I'll replace the nose tire cause it may be out of balance. ALL of which do absolutly NOTHING! The shimmy dampener on a 172 is a joke! That tiny little thing couldn't stop a shopping cart from shimming. All the other things may make it a little better, but until you take out all the play in that worn out steering collar, it'll shimmy.

And NO, holding the nose off as long as possible is not the answer. That's just ignoring the problem. The more it shimmies, the more it's wearing out that firewall and eventally it'll just shimmy right off the plane (although I've never seen this happen, but it could). Tell your mechanic to do the job right.
 

CutEmUp

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I've seen that happen. It was a 172RG and the nose gear had a shimmy. The mechanics tried all the usual things and the problem was mostly fixed. The next day, the plane came back in after it started to shimmy REALLY bad. One of the mounts actually started to tear itself apart. A vibration of any sort should be fixed ASAP or it will lead to something worse.
 
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