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  #1  
Old 05-09-2021, 01:30 PM
texdog texdog is offline
 
Join Date: Jan 2013
Location: Fredericksburg, Tx.
Posts: 369
Smile Shimmy, not what you think

RV6A, very nice airplane that we have maintained and flew about 150 hrs. a year for the last 9 years. We have not had any problems but a main gear shimmy that seemed to go away except for 22 to 23 knots, no matter what tire pressure we used and we always balanced the tires. At the condition inspection last month we replaced the tire and tube on the left side. We just touched one of the four nuts holding the axle on with a wrench and it moved. They were lock nuts, but they were not tight. All four were about a quarter turn from proper torque. Four flights now and no shimmy at all, at any speed. CHECK THOSE NUTS.
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  #2  
Old 05-09-2021, 02:11 PM
Mike S's Avatar
Mike S Mike S is offline
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Location: Dayton Airpark, NV A34
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I had a similar issue with the wheel pants brackets on the RV 10.

Due to the heat generated from braking action, that area should use all metal lock nuts IMHO.
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Last edited by Mike S : 05-09-2021 at 02:41 PM.
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  #3  
Old 05-09-2021, 02:45 PM
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Janekom Janekom is offline
 
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I can only agree with that. I have also seen more than enough of those nuts loosening due to heat down there.
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  #4  
Old 05-09-2021, 09:13 PM
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rvbuilder2002 rvbuilder2002 is offline
 
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Location: Hubbard Oregon
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I don't usually go public with info prior to a design change being issued but will in this case because it is rather minor to describe.

The looseness is not because of heat on nylon lock nuts.

Yes, the brake disks do get hot but the disks are conductivity isolated quite a bit from the brake mount flanges. If it were a problem we would have seen serious issues by now with the airplanes that use bolts and nylon lock nuts to attach the axle to a flat gear leg.

The looseness is caused by the spacer bushings being made of 6061-T6 aluminum. It is just not a hard enough material to take the shaking / pounding of the wheel fairings. Over time the bushings suffer plastic deformation and reduce in length slightly. Once that happens, the bolts get loose and the wear process gets accelerated until the bolts are re-torqued.

A change is in the works to switch to steel bushings. The ones for the RV-10 will likely be all one piece in steel instead of the current steel reducer bushing and aluminum extension bushing.

Please don't call the office asking for the new parts. It will be a while until the change makes its way through the internal process. Once it has, they will then be available. In the mean time,it would be very simple for someone to substitute the same dimension steel tubing on a 6A, 7A, 8A, or 9A.
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  #5  
Old 05-10-2021, 05:06 AM
s24789 s24789 is offline
 
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Location: Hobe Sound, Florida
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I saw the original post and the speed of 22-24 knots ground speed caught my eye. We had the exact same issue and after replacing many items replaced the right main tire and the world has been better ever since.
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  #6  
Old 05-10-2021, 02:19 PM
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bjdecker bjdecker is offline
 
Join Date: Jun 2005
Location: Georgetown, TX
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Quote:
Originally Posted by rvbuilder2002 View Post
I don't usually go public with info prior to a design change being issued but will in this case because it is rather minor to describe.

The looseness is not because of heat on nylon lock nuts.

Yes, the brake disks do get hot but the disks are conductivity isolated quite a bit from the brake mount flanges. If it were a problem we would have seen serious issues by now with the airplanes that use bolts and nylon lock nuts to attach the axle to a flat gear leg.

The looseness is caused by the spacer bushings being made of 6061-T6 aluminum. It is just not a hard enough material to take the shaking / pounding of the wheel fairings. Over time the bushings suffer plastic deformation and reduce in length slightly. Once that happens, the bolts get loose and the wear process gets accelerated until the bolts are re-torqued.

A change is in the works to switch to steel bushings. The ones for the RV-10 will likely be all one piece in steel instead of the current steel reducer bushing and aluminum extension bushing.

Please don't call the office asking for the new parts. It will be a while until the change makes its way through the internal process. Once it has, they will then be available. In the mean time,it would be very simple for someone to substitute the same dimension steel tubing on a 6A, 7A, 8A, or 9A.
Scott,

Thanks for the heads up; just to confirm we're all thinking about the same thing, I've attached a screen-grab of the plans -- you're referring to U-408, correct??

Thanks tons!

B
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  #7  
Old 05-10-2021, 02:29 PM
jrs14855 jrs14855 is offline
 
Join Date: Apr 2008
Location: Lake Havasu City AZ
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Default Axle

As shown in the drawing in post 6 the bolts do not "hold the axle on" The axles on the round Wittman Landing gear are part of the machined one piece gear leg. The drawing shows the single bolt attaching the brake flange to the gear leg. The bolts described are used to attach the wheel pant bracket to the brake flange.
The RV8 uses the flat Wittman Gear and does have bolt on axles. Except for the 8, RV3 thru RV9 all use the round Wittman gear.
Wittman invented and patented the flat spring gear around 1935 and the round gear around 1950. That would be the Steve Wittman that Oshkosh Airport is named for.
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  #8  
Old 05-10-2021, 02:51 PM
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bjdecker bjdecker is offline
 
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Thanks for the factoid...

The OP has an RV-6A, and I *think* he was referring to the 4 AN365-428A nuts that hold the U-403-PC to the U-810-L/R.

Scott was referring to the 3 bushings that stand-off the U-810-L/R from the U-403-PC.

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  #9  
Old 05-10-2021, 04:28 PM
jrs14855 jrs14855 is offline
 
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Default Bolts

OP clearly stated main gear.
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  #10  
Old 05-10-2021, 04:47 PM
bjdecker's Avatar
bjdecker bjdecker is offline
 
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Quote:
Originally Posted by jrs14855 View Post
OP clearly stated main gear.
I don't understand.
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