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  #1  
Old 08-02-2019, 12:57 PM
s24789 s24789 is offline
 
Join Date: Jan 2009
Location: Hobe Sound, Florida
Posts: 302
Default Nose Gear Issue (Long Gospel)

Late last year we developed what we thought was a nose gear shimmy on our RV-7A. The aircraft has 1000 flight hours. It started as a light amplitude shaking noticed on roll out when we were going slow prior to exiting the runway. We had a friend watch us land and roll out. He noted that the motion of the nose wheel was vertical (nose strut bending along the longitudinal axis) and not horizontal (shimmy). We then jacked the aircraft and inspected and found the nose landing gear attach bolt near the firewall had lost torque. We replaced the bolt and retorqued. The joint seemed tight.

We were planning a panel upgrade so we went down then for the next five months. While we were down we removed and repacked the nose wheel bearings and conducted the pull test. All was well.

Fast forward post panel up ? Things got worse. If we did not consciously hold the nose off on landing roll out, we would get a violent motion that shook the entire plane on landing deceleration at slow speed. We then conducted taxi tests and determined that at 24 knots ground speed while decelerating we would get the vertical motion/shake. This vibration never happens on take-off most likely due to off-loading of the nose gear during acceleration.

Last night we tied the tail down (nose off the ground) and banged the nose strut both vertically and horizontally. Horizontally it is extremely well damped. Vertically it looks like a tuning fork that eventually damps but rings noticeably for a period of time. Obviously, we have looked for a cracked engine mount and cracked gear leg with no findings. Additionally, we have the AntiSplat nose job installed however, we operate from hard surface runways and only have about 10 grass field landings in 1000 hours.

Things we had done in an attempt to remedy the situation;

Replaced nose tire with new one ? No change
Reduced nose tire pressure to 30 psi ? No change
Rechecked the pull test on the fork ? No change
Replaced main tires, rebuilt right brake caliper (it appeared to be sticking a little, repacked main wheel bearings, replaced brake pads ? Have not flown this configuration yet.

Has anyone experienced this and more importantly what is the corrective action? The new nose gear damper appears promising but is a big job.

Thanks
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  #2  
Old 08-02-2019, 01:15 PM
WingsOnWheels WingsOnWheels is offline
 
Join Date: Mar 2009
Location: Plano, TX
Posts: 2,244
Default

Sounds like the nose wheel bearing is binding under load. I machined my wheel for ball bearings, it is much better now, with very little rolling resistance. If you have access to a lathe, you can do it yourself, or send it to antisplat.
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  #3  
Old 08-02-2019, 01:24 PM
F1R F1R is offline
 
Join Date: Nov 2010
Location: ____
Posts: 912
Default A Whole lot of shakin going on!

There are many past threads with sage advice on nose gear health and maint. tips. ( See the excellent link in post#5 below )

Assuming the castor bushing is in good condition and break out force is correct, balance the MAIN wheels AND the NOSE wheel.

Please report back after you have tried balancing the 3 wheels/tires.


Your own words "If we did not consciously hold the nose off on landing roll out"

As with any trike gear light single I can't imagine not wanting to do this on every landing and take off even if everything else is perfect and with no shimmy.
The nose wheel is only a parking dolly.

https://youtu.be/xraIf_cYRQE?t=47
Since the OP mentioned the Gospel, Jerry Lee Lewis was thrown out of seminary for hamming up the hymns. As a result he was able to reach millions of people through his music.
This one fits the thread. Enjoy.

Last edited by F1R : 08-02-2019 at 06:37 PM.
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  #4  
Old 08-02-2019, 01:43 PM
Mike S's Avatar
Mike S Mike S is offline
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Join Date: Sep 2005
Location: Dayton Airpark, NV A34
Posts: 16,110
Default

The antisplat nose reinforcement will add mass to the leg------no idea how much this effects the vibration, but I suspect there is some.

And, I second the prior comment about keeping the nose wheel off the ground during take off and landing.
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  #5  
Old 08-02-2019, 01:55 PM
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AlexPeterson AlexPeterson is offline
 
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Location: Ottertail, MN
Posts: 2,462
Default

Please read post #1 of this thread before you fly it again. Pay particular attention to the wheel bearing design discussed in "3. Nose Wheel" of the post. It is possible for the nose wheel to lock up, making for a very bad day.
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  #6  
Old 08-02-2019, 02:30 PM
Discus2b Discus2b is offline
 
Join Date: Mar 2016
Location: Willis Gliderport
Posts: 186
Default

Quote:
Originally Posted by Mike S View Post
The antisplat nose reinforcement will add mass to the leg------no idea how much this effects the vibration, but I suspect there is some.

And, I second the prior comment about keeping the nose wheel off the ground during take off and landing.
Bull....Vans would not have his engineers do such a poor job as to require all his
?A? s rolling out or taxing around with the yoke in the gut and the tie down ring dragging on the ground.

Pilot A ?Hey , there?s a Van!?
Pilot B ?How can you tell??
Pilot A ?Look at the elevator, it?s all the way up?
Pilot B ?Why??
Pilot A ?It?s to prevent the nose gear from ripping off?
Pilot B ? Wow, that ain?t good!?

The thread ops said his problem just started, so his original install worked.
It is very apparent that the design while adequate for the test pilot, not so for the masses. Risk a prop strike or perform the upgrade for those with marginal skill set. Those who feel they have the touch, wisdom, ...steady as she goes.
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  #7  
Old 08-02-2019, 03:14 PM
Mike S's Avatar
Mike S Mike S is offline
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Location: Dayton Airpark, NV A34
Posts: 16,110
Default

Bull???

Mike Seager, over (IIRC, 10000 hours instruction) of RV time and the go to guy for transition training is who told me to always get the nose up asap on takeoff, hold it off as long as I can on landing, and taxi with the stick in my gut.

Your quals as an RV instructor????
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VAF 909

Rv-10, N210LM.

Flying as of 12/4/2010

Phase 1 done, 2/4/2011

Sold after 240+ wonderful hours of flight.

"Flying the airplane is more important than radioing your plight to a person on the ground incapable of understanding or doing anything about it."
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  #8  
Old 08-02-2019, 04:43 PM
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scrollF4 scrollF4 is offline
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Join Date: Jan 2010
Location: Flower Mound, TX
Posts: 1,632
Default Nose wheel needs mod

Kevin,
Previous commenters pointed out the apparent drag on wheel rotation being caused by your nose wheel bearings. I ASSUME you have the stock unsealed ?pack?em yourself? bearings.

Here?s what?s happening. Stock bearings don?t allow the wheel to spin freely enough, creating drag on the wheel which pulls it back, thus bending the nose strut back. Then the strut?s spring forward overpowers the bearing drag. Repeat. Now you have this oscillatory vibration that feels like a shimmy. It usually happens at speeds you described. Looks like:
https://youtu.be/Cxoa_t0NJ6s

I had it too, and ordered Antisplat?s nose wheel mod:
https://antisplataero.com/products/n...el-bearing-mod

The sealed bearings are far superior. I have not encountered this oscillation since buying the mod.
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Catch her on YouTube's "Because I Fly!" channel

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  #9  
Old 08-02-2019, 04:54 PM
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rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,667
Default

Not saying that it couldn't be a bearing problem but assuming that automatically could be missing the real cause.
As already mentioned, an out of balance wheel/tire can excite a motion, but an out of round tire will as well.
That is the very first thing I would check.
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  #10  
Old 08-02-2019, 05:38 PM
NewbRVator NewbRVator is offline
 
Join Date: Jul 2018
Location: CA
Posts: 280
Default

Quote:
Originally Posted by Mike S View Post
Bull???

Mike Seager, over (IIRC, 10000 hours instruction) of RV time and the go to guy for transition training is who told me to always get the nose up asap on takeoff, hold it off as long as I can on landing, and taxi with the stick in my gut.

Your quals as an RV instructor????
In other words fly it like a tailwheel
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