REFLECTOR: wheel shimmy

Andy Millin amillin at sbcglobal.net
Thu Feb 19 12:56:29 CST 2009 

I'm sorry guys.  This is killing me.  I held off as long as I could.

They are Belleville washers.  http://en.wikipedia.org/wiki/Belleville_washer

Whew...



-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Scott Derrick
Sent: 02-19-2009 1:33
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: wheel shimmy

The point about the bellevue washer system and difficulty in keeping it
straight on the runway is that the bellevue system requires a higher brake
pressure to get the washer to release than to turn the wheel after it has
released, since your standing hard on the brake to correct a few degrees,
once it releases it over steers in the direction you want to go, then you
have to brake in the opposite direction to correct for the over steer and so
the zigzag ride down the runway begins!

If the anti-shimmy device does not have such a high breakout force you could
gently tap the brake and steer straight down the runway with ease.  Well,
relative ease!

A hydraulic damper like Cessna airplanes use, also like Sid installed on his
V,  does not have this high break out force.  The force is the same to pivot
the wheel from a stop as it does after it has started moving. 

So the Cessna style damper does solve a lot of the problems associated with
the bellevue system.

I agree its not as positive as a steerable nose wheel.  

I personally don't like the locking nose wheel.  I think its a system that
inherently sets you up for an incident as scary or damaging than the problem
it is supposed to cure.  Kinduv like prescription medications!  Forget to
unlock it before landing and you could have an experience much more
memorable than a nose wheel shimmy. 

Scott

Velocity wrote:
> :it's difficult to get the plane exactly straight with the runway
>
> So the dampener idea really would not solve this problem of steering
right?
> Sounds like steerable nose wheel is what is really needed. I remember 
> some one had made a steerable nose wheel once using a servo motor.
> Any idea on how it worked out?
>
> Also there is the locking nose wheel which looks good . That way the 
> tension can be quite low making steering easier?
> Still have to stab the brakes to get it to turn though.
>
> Any one played with changing the caster amount?
>
> Ron
>
> ----- Original Message -----
> From: <aminetech at bluefrog.com>
> To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
> Sent: Thursday, February 19, 2009 10:49 AM
> Subject: Re: REFLECTOR: wheel shimmy
>
>
>   
>> Another issue with the tension at 14 lbs or so, is that it's 
>> difficult to get the plane exactly straight with the runway and that 
>> results in the need for braking during takeoff.  Not a good thing if 
>> takeoff distance is critical.
>>
>> John
>>
>> --- scott at tnstaafl.net wrote:
>>
>> From: Scott Derrick <scott at tnstaafl.net>
>> To: Velocity <velocityxl at fastmail.fm>,        Velocity Aircraft Owners
and 
>> Builders list <reflector at tvbf.org>
>> Subject: Re: REFLECTOR: wheel shimmy
>> Date: Thu, 19 Feb 2009 09:30:19 -0700
>>
>> Ron,
>>
>> I have about 450 hours of flying on my V.  With the bellevue washer 
>> system.
>>
>> It is adequate, but certainly not optimal.  The problems for me are,
>>
>> 1.)  Hard to turn. Specifically hard to break into a turn, once the 
>> wheel breaks free it turns fairly easily, leading to the next problem.
>> The tighter you have teh bellevue washers the harder to initiate a turn.
>>
>> 2.) In tight situations, its easy to over turn so that the wheel is 
>> now near 90 degrees and then its tough to get it to straighten out.
>> Sometimes I've had to get out and kick the nose tire straight before 
>> continuing a taxi.
>>
>> 3.) Bellevue's continuing tendency to loosening up.  Even though I 
>> check it before every flight I have had it loosen up to much and then 
>> get a bit of shimmy on landing, not a good feeling, especially for 
>> passengers who imagine the worst.  As some have mentioned,  how you 
>> land and how much weight on the nose can influence if you get a shimmy or
not.
>>
>> A system that did not require constant maintenance/attention and 
>> provided easier turning would be a great addition.  The bellevues 
>> have simplicity and proven performance on their side, which in 
>> airplanes is a big big plus.
>>
>> Scott
>>
>> Velocity wrote:
>>     
>>> Now being on this list for over 10 years now I know this issue keeps 
>>> coming up. It seems the answer usually goes to set the tension on 
>>> the front wheel to 14 lbs of pull or something like that and you 
>>> should not have a problem. Is this not true? I have heard that this 
>>> should be on the preflight check list. Does this number change and 
>>> really need to be adjusted regularly?
>>> If so maybe  we just need to find the way to get the tension to stay 
>>> within a range that works.
>>> Or perhaps  there are people that feel that there is a better mouse 
>>> trap out there and are working toward a simpler/ better design for 
>>> the front wheel which is great. So is there a steering Issue?
>>> Or is there a real problem that needs to be addressed? Just 
>>> wondering because I have not had the joy yet of being in the front 
>>> seat and seeing for my self. One of these days, One of these days.
>>>
>>> Ron
>>>
>>>
>>>
>>>
>>>
>>> ----- Original Message -----
>>> From: "Sid Knox" <sbjknox at earthlink.net>
>>> To: "Velocity Aircraft Owners and Builders list" 
>>> <reflector at tvbf.org>
>>> Sent: Wednesday, February 18, 2009 11:56 PM
>>> Subject: Re: REFLECTOR: wheel shimmy
>>>
>>>
>>>
>>>       
>>>> From: "Scott Derrick" <scott at tnstaafl.net>
>>>>
>>>>         
>>>>> Sid,
>>>>> Can you give an update on the damper? Working well?
>>>>>
>>>>>           
>>>> Working great.  Never a hint of shimmy.  The big nut is tight only 
>>>> enough to take up any slack.  With damper disconnected, completely 
>>>> free of friction.
>>>>
>>>>
>>>>         
>>>>> How many landings on the system?
>>>>>
>>>>>           
>>>> Several dozen since install in Spring of 2006.
>>>>
>>>>
>>>>         
>>>>> Did you ever put external stops on it so the damper wouldn't 
>>>>> bottom out?
>>>>>
>>>>>           
>>>> No.  I can make the sharp 120 degree turn on the narrow taxiway 
>>>> leading to my ramp no problem.
>>>>
>>>>
>>>>         
>>>>> Ever miss not having a fulling castoring nose wheel?
>>>>> Scott
>>>>>
>>>>>           
>>>> Not yet.  I simply pick up the nose and walk it around if needed.  With

>>>> no
>>>> passenger(s) inside of course... its too heavy for me otherwise. 
>>>> Pushing
>>>> backwards is easier too without the tendency for the wheel to caster
>>>> around
>>>> backwards.
>>>>
>>>> Sid
>>>>
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>>>>         
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>>
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>>     
>
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