REFLECTOR: Shimmy and Nose Gear Pivot Bushings

Chuck Jensen cjensen at dts9000.com
Fri Nov 18 07:16:47 CST 2005


Ronnie,

The photo wasn't a detailed as one would like but I'm estimating that's
a $50,000 to $75,000 military mod.  Of course, if the bolts that hold it
on weren't bought at Home Depot, then it's probably more.

Alex had a good question about whether it's a trailing or leading mass,
though it may not make a difference.  If trailing works, and if a 6" rod
with a 2-3 pound mass of lead on the end of it would do the trick,
wouldn't that be great.  If it's out front, a person would have to do
some measuring and calculation for dog house clearance, but in the
trailing position, it would look better and have lots of clearance.

Do we have any guinea pigs in the house?

Chuck

 

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Ron Brown
Sent: Thursday, November 17, 2005 6:13 PM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Shimmy and Nose Gear Pivot Bushings

Brian,

I did a Google on "nose wheel shimmy" and got the following article on 
F-15's and a fix for their long standing problem.  See 
http://engineering.wpafb.af.mil/success/F-15_Nose_Wheel_3_08_01.pdf

It involves what looks like a mass weight attached such that the center
of 
mass is shifted forward.  Looks like something worth trying assuming
there 
is room for the bar when the gear is up - I think there is.

It sure would be nice to be able to reduce the shimmy nut torque to 
something like 5-10 ft lbs instead of the difficult to steer 20 ft lbs.

Ronnie

----- Original Message ----- 
From: "michalk" <michalk at awpi.com>
To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
Sent: Tuesday, November 15, 2005 11:19 AM
Subject: Re: REFLECTOR: Shimmy and Nose Gear Pivot Bushings


>I always wondered why there hasn't been an example where a
counterbalance 
>was used?
>
> The problem is that the CG is aft of the pivot point.  If one needs to
use 
> ballast anyway, place a counterbalance to get the CG closer to the
pivot 
> point.
>
> Might be a problem with RG's, maybe easier with fixed gear.  Get the 
> center of lift to be aft of pivot as well and have self centering 
> nosewheel, with a very light easy to steer friction system.
>
> Ron Brown wrote:
>> I discovered how destructive nose wheel shimmy can be.
>>
>> On a half dozen or so occassions, I have had nose wheel shimmy after 
>> landing.  The last time, I smelled hot epoxy.  After shut down I did
some 
>> investigating and found that the right side pivot bushing had worked 
>> loose from its mounting in the keel. It had worn the hole into an egg

>> shape with most of the wear toward the lower front of the bushing 
>> mounting.
>>
>> I have epoxied a new bushing into place using the Aeropoxy structural

>> adhesive.
>>
>>> From now on, I am going to keep my bellville washers clean and
tighter 
>>> to
>>
>> minimize - or rather prevent nose wheel shimmy.  (sure makes steering

>> tougher - especially on take off)
>>
>> Has anybody else had this problem?  I am guessing there is a problem
in 
>> that there is a new and improved mounting for these bushings.
>>
>> Do I also need to go ahead and plan to replace these with the new 
>> bushings and plates that are shown in the latest on-line plans?
>>
>> Ronnie
>> 173 Elite RG
>>
>>
>>
>> (173 Elite RG).
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