REFLECTOR: Shimmy and Nose Gear Pivot Bushings

Ron Brown romott at adelphia.net
Sat Nov 19 08:11:59 CST 2005


Yeah, but did it shimmy?

As Chuck suggests, perhaps it doesn't have to be totally balanced, just 
reduce some of the tendency to shimmy - along with a 5-10 ft lb shimmy 
washer/nut setting.

My Velocity is very easy to steer with 10-15 ft lb.  Unfortunately, it takes 
more like 20-25 ft lb to keep it from shimmying.  Now we are sliding in the 
grass.  Or difficult keeping it lined up with the center line on take off 
without dragging a brake.

Ronnie

----- Original Message ----- 
From: "Wayne" <wowens at darientel.net>
To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
Sent: Friday, November 18, 2005 10:55 AM
Subject: Re: REFLECTOR: Shimmy and Nose Gear Pivot Bushings


>I actually balanced mine with the lead weight in the front of the wheel 
>pant . I think I remember holding  the fork horizontal and balanced it like 
>an aileron The moment arm was short and it took about 17 lbs of lead. It 
>sucked.
> Wayne
> ----- Original Message ----- 
> From: "Ron Brown" <romott at adelphia.net>
> To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
> Sent: Friday, November 18, 2005 9:14 AM
> Subject: Re: REFLECTOR: Shimmy and Nose Gear Pivot Bushings
>
>
>> I'm pretty certain the rod projects forward - to counterbalance the 
>> weight behind the pivot that the fork, wheel and tire has.
>>
>> Any body who hasn't installed their nose wheel and tire - could you weigh 
>> the wheel and tire to give me an idea of how much mass needs to be placed 
>> out front.
>>
>> I'm guessing that nose wheel shimmy is similar to control surface 
>> flutter. The likelihood of shimmy would be reduced/eliminated by having 
>> the counterbalance equal or heavier than the tire and wheel.
>>
>> Ronnie
>>
>> ----- Original Message ----- 
>> From: "Chuck Jensen" <cjensen at dts9000.com>
>> To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
>> Sent: Friday, November 18, 2005 8:16 AM
>> Subject: RE: REFLECTOR: Shimmy and Nose Gear Pivot Bushings
>>
>>
>> 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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>
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