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Nose-wheel Vibration?

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Nose-wheel Vibration?

Postby PKnight » Thu Apr 16, 2015 9:31 am

I recently replaced the nose wheel on my J430. (Puncture in grubby hanger!) I now notice a vibration through the rudder pedals. The vibration seems to be dependent on airspeed as it starts to come in at 100+ Knts and will slowly drop of if I reduce airspeed. I cannot feel any vibration through the console or the firewall. My best theory is the the nose-wheel is starting to rotate in the air-stream and is slightly out of balance, hence the sensation through the rudder pedals. The vibration is mild but I have a nervous disposition in relation to any change in the characteristics of the aircraft. Any one experienced the same effect?
Peter
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Re: Nose-wheel Vibration?

Postby diablo » Fri Apr 17, 2015 6:03 am

Hi peter,

Do you have spats ? I had a similar issue when I replaced by nose wheel tire with one that was Slightly larger and had a nobly profile. I had removed the spats for the winter as the airfield can get muddy. It turned out that the tire was causing the wheel to spin while in flight.

It does sound like you have a wheel balance problem and airstream is causing wheel to spin. Have you opted for a rib tread profile ? Some tires are more prone to inducing wheel spinning in flight. Best to use a rib profile rather than one which has a more prominent presence.

If you are using a rib tire, the I suppose balancing may go some way to reducing vibration.
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Re: Nose-wheel Vibration?

Postby PKnight » Fri Apr 17, 2015 6:58 pm

An easy test will be to see if the vibration goes away if the spat is taken off. When I remove it I can also try a simple balance of the front wheel but I think I may only change one factor at a time. So spat off, does vibration go away? If it does balance tyre before spat returned.
Peter
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It's not as simple as I thought...

Postby PKnight » Sat Apr 18, 2015 4:52 pm

I had an opportunity to look carefully at the behavior of the nose-wheel to determine the cause of the vibrations that I was feeling through the rudder pedals above a certain air speed.

I put the aircraft on its tail and spun the nose-wheel up using an electric drill as a drive. At low and medium rotational speeds there was no vibration. The wheel rotated smoothly and nothing could be felt on the nose leg. However above a certain speed (quite fast but not quantified) there was suddenly the on-set of significant vibration. The nose-leg appeared to be pivoting about either the front bush suspension pivot or the glycodur bush at the base of the rubber dampers. There is no doubt that this is what I was feeling through the rudder pedals. Further speeding up of the wheel caused the vibration to cease.

It is clear that there is a resonant frequency in the nose-leg and it is triggered at a particular rotational speed of the nose-wheel. I suspect this is caused by wear or movement in one of the bearings rather than any inherent lack of balance in the nose-wheel. I will have to investigate further to see if there is any undue movement in the bearings. (I hope it is not a lack of umph from the rubber damper)

The problem can be made to "go away" by flying with the back half of the front spat removed as that stops the nose-wheel speeding up in the air stream but that is only a short term fix rather than a cure. I will report findings in due course.
Peter
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Re: Nose-wheel Vibration?

Postby diablo » Sat Apr 18, 2015 8:19 pm

bearings are a bummer to change. they are cheap enough though. I suggest you source them from a bearings supplier. You are likely to save significantly. I purchased 3 sets (6 bearings) from a supplier for less than the cost of one set from the approved supplier. No difference in quality, just price !

Happy to share details if required.
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