REFLECTOR: wheel shimmy
KMis178813 at aol.com
KMis178813 at aol.com
Thu Feb 19 15:57:10 CST 2009
After this last post (So many negative words) I thought I might need to
inform some as to the operation of the nose lock. It was designed not as a shimmy
damper but to keep the wheel pant straight in flight. A wheel pant, even at
a slight angle, will alter level flight and cruise speeds. The side effect of
the lock, is that it stops the front wheel/tire assembly from starting the
oscillation that becomes the shimmy that some of us know so well. The lock is
engaged when lined up with the runway for take off. Steering is not a problem
on take off roll and does not give you the over steer that you get with
factory set up. The lock remains engaged for entire flight including the landing.
The mains are supposed to touch first on a landing and will straighten the
plane before the nose ever touches. (Anyone landing nose gear first will have
other problems besides a shimmy). Disengage the lock when down to taxi speeds
and turning becomes normal. Turning can be made easier by loosening the
tension nut, just Don't forget to engage lock for flight. CHECKLIST!
The operation does require pilot to engage and disengage at the proper
times. Similar to putting the gear up or down. Failure to put the gear down
usually ends up with a bad outcome. Failure to disengage the lock should not
hurt anything. I have gone through several tests trying to break these parts.
In the severest case the lock should break it's mounting screws according to
computer generated stress analysis. If it's any stronger it breaks the gear
leg-any weaker and it just keeps breaking off. It's a fine line for sure.
Approximately 45 locks were sold, I don't know how many are flying?
There have been 2 failures both of which were failure to disengage for taxing
which led to other issues after the initial problem. Taking the pilot out of the
loop would require a automatic engagement and make the system way
complicated. The lock was only designed as a band aid for a problem that some of us
already have. If anyone comes up with a better mouse trap, I'm all for it.
Weight and looks were also important to me in the design.
Some specs for anyone who cares. On a retract model, with the lock
disengaged, the nose gear is full castoring as it is now. On a fixed gear, the
wheel pant limits the gear to 60 degrees in each direction (120 total). On a SE,
This angle will let you turn a 180 on a 17ft wide taxiway. Turning that hard
pivots on the inside main tire without it even turning.
Ken Mishler
N2087M SUV FG 200hp 750hrs
N173EX 173 SE RG 300hp 165hrs
N872KM XLRG-5 Turbo 300hp Still Under Construction
Things I don't do never seem to get done??? :)
In a message dated 2/19/2009 1:33:56 P.M. Eastern Standard Time,
scott at tnstaafl.net writes:
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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