COZY: PISS (Pilot Induced Speed Shimmy)
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Del Schier
Andy, I have recently had nosewheel shimmy on landing and I think there are a couple of causes. I had cleaned and lubed and set the shimmy damper and after it got too loose causing the first two incidents. I was using white grease on the friction discs and switched to graphite which I think was a bad idea. Both times re-tightening the nut fixed it. Most recently I was heavy at 2/3 fuel, 3 aboard and with a forward CG. I think on landing the nose gear spring compressed and took the caster out. No damage was done except my new nose tire now has noticeably less tread than it did. The plans spec of 0-8 deg positive caster should be more like > 8 deg positive fully loaded. A friend with an EZ talked to Jack about this recently and he indicated you can’t have too much only too little. Del Schier Cozy IV N197DL Cannon Creek Airpark 15FL
From: 'Andrew Anunson' via COZY Builders Mailing List <cozy_builders@...>
Sent: Friday, March 10, 2023 1:47 PM To: Cozy Builder Google List <cozy_builders@...>; Canard Aviators List <canard-aviators@canardzone.groups.io> Subject: COZY: PISS (Pilot Induced Speed Shimmy)
I was up flying this past Sunday in my Cozy MKIV with buddy, we were at front seat weight of 390 and a CG of 99.3. Final landing for the day, did my GUMPS check and watched the electric nose gear extend through the little plans built windows in the wheel well.
Good approach to landing, planted the mains, and the nose gear touched firmly. The nose wheel came back up off the runway just a bit, and once back down a nose shimmy started. It sounded like driving on the highway rumble strips and felt like a flat tire/rumble strip combination. Tried to keep weight off the nose gear using back pressure on the stick but it didn't come up again, we gently slowed and the shimmy stopped at perhaps 45 kias.
I said something like "Man, that was a nosewheel shimmy! WTF?" I looked down at the panel, and my nosegear switch was in the middle (off) position (no longer in the down/extend position). We taxied to the hangar and did a post flight inspection. I don't know how the switch got to that position.
I haven't ever noticed my NG mechanism back driving, but I never taxi, takeoff, or land with it in the off position. I have an old Wilhelmson unit with the manual backup system and it doesn't have the electric brake system. I have installed small belleville washers per Jack's instructions, and it never (noticeably) back drives.
I found the nose gear leg slightly loose in the MKNG6. The flox bond had broke loose. Just a slight wiggle but it needed to be re-done. It took about 15 minutes to get the nose gear leg out, and less than an hour to clean it up and reflox the assembly at home.
Cause: Perhaps the nose gear switch in the "OFF" position Effect: Shimmy, and loss of the flox bond at MKNG6
Prevention: Any ideas?
I have a Nose Gear warning system that alerts me when landing and the nose gear is up. I need to see if it alerts me when I'm landing and the switch is in the OFF position. If not, I'll change it so that it does.
NOTES: 1.) My nose tire did very well. No damage. 2.) The nose fork and attachment did very well. I attached my nose fork to the gear leg using the "bulb and clamp method". Thats what I call it. I think Marc Zetilin recommended it. 3.) Check closely for damage after anything unusual like this.
Andrew Anunson Cozy MKIV #1273 Pound, VA
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James Russell
Hi all:
Del said: > I was using white grease on the friction discs and switched to graphite which I think was a bad idea. What is the consensus on what grease to use on the shimmy damper? I'm getting ready to lube it for the first time. Thanks! Regards, James |
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Del Schier
For more info here is some detail. When it is time for a new nose tire, I take apart everything and clean with mineral spirits. There is usually some galling of the metal so I re-surface the discs and the aluminum with 600 grit on a surface plate. I used to use white grease on everything which seemed to work but after many hours the damper would get tighter or a bit sticky. The last service I used grease on the pivots and graphite on the discs. The graphite seemed to get looser with time causing the shimmy and needing re-tightening. I doubt it is a good idea to put it together dry so next time I will go back to the white grease. I try to set the Belville tension to 8-10 pounds pulling on the axle nut with a fish scale. The kick test on pre-flight should have made me aware it was getting loose but it didn’t. The other issue is my positive caster is barely positive and probably goes away loading the nose on landing. I am sure that Lithium grease is OK. Del Schier Cozy IV N197DL Cannon Creek Airpark 15FL
From: canard-aviators@canardzone.groups.io <canard-aviators@canardzone.groups.io> On Behalf Of James Russell
Sent: Saturday, March 11, 2023 11:42 AM To: canard-aviators@canardzone.groups.io Subject: Re: [c-a] COZY: PISS (Pilot Induced Speed Shimmy)
Hi all: |
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