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Nose Gear Issue (Long Gospel)

s24789

Well Known Member
Patron
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
 
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.
 
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.
 
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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.
 
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.
 
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.
 
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????
 
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/nose-wheel-bearing-mod

The sealed bearings are far superior. I have not encountered this oscillation since buying the mod.
 
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.
 
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
 
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.

Ha. Well, I taxied out behind Van yesterday. I can definitively say, while on the ground, he has the stick all the way back, and on takeoff, he lifts the nose wheel ASAP and flies it off on the mains.

Doesn?t get much more definitive than that!
 
Amazing!!
Well....thanks for your note.
I?m beyond disappointed, I would have expected a better effort by everyone.
And now the pilots have got to cover for the engineers.
?Nothing more than a parking dolly? they write.
Embarrassing.

R
 
Amazing!!
Well....thanks for your note.
I’m beyond disappointed, I would have expected a better effort by everyone.
And now the pilots have got to cover for the engineers.
“Nothing more than a parking dolly” they write.
Embarrassing.

R

Funny, when I learned to fly about 40 some years ago in a C150 they all seem to have a wicked nose gear shimmy, guess what the instructors told me... keep the yoke back after landing and when taxing, which took care of the shimmy, a habit that has served me well.
Guess the Cessna engineers weren't any better than Van's.
 
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Funny, when I learned to fly about 40 some years ago in a C150 they all seem to have a wicked nose gear shimmy, guess what the instructors told me... keep the yoke back when taxing, which took care of the shimmy, a habit that has served me well.
Guess the Cessna engineers weren't any better than Van's.

Haha I remember on my first solo in a 150 it happened to me on my first landing of the flight and I thought the plane was about to self destruct!
 
Amazing!!
Well....thanks for your note.
I?m beyond disappointed, I would have expected a better effort by everyone.
And now the pilots have got to cover for the engineers.
?Nothing more than a parking dolly? they write.
Embarrassing.

R


Maybe the new changes are the engineers covering for the pilots.

Simple, light, and effective aren?t for everyone I guess. There are plenty of heavier, slower, more expensive planes that will be more tolerant of somebody who doesn?t wish to put too much effort into flying and taxiing them properly.

RVs are built light for a reason - performance. You can?t treat it like a Cherokee or skyhawk and expect it to hold up the same.
 
Funny, when I learned to fly about 40 some years ago in a C150 they all seem to have a wicked nose gear shimmy, guess what the instructors told me... keep the yoke back when taxing, which took care of the shimmy, a habit that has served me well.
Guess the Cessna engineers weren't any better than Van's.

Seriously, I see your resume under your name and this is your answer?
All an easy joke. You need to remember that Vans sells to everybody, most of which do not have your experience. And many who simply want to fly.
Anti-splat, $2200+ gear mods, dozens of threads, years of concerns....vs. overhauling the shimmy damper is equal to you?
I?m not down on Vans, I just wonder what made them give up. How could they create a remarkable line of aircrafts and accept owners calling their nose gear a ?parking dolly? or others selling improvement mods.
That is the question.
Peace

R
RV-14
C-150 ????????????????????????????-B747-8
C-172
C-182
SH Discus 2b
SH Ventus 2cxT
36,000+ hours..no drips, no runs, no errors.
 
Gosh folks, even Van's can't design an aircraft that makes up for poor piloting habits. Maybe some training is in order...

Flame suit on and I don't even care!

Bob
 
Interesting Thread

(quote) "Maybe the new changes are the engineers covering for the pilots."

and the winner is...

Walt and Chris for the most obvious and simple solution.
 
Anti-splat, $2200+ gear mods, dozens of threads, years of concerns....vs. overhauling the shimmy damper is equal to you?

Appropriate piloting technique for the aircraft being flown makes that entire list obsolete.

...I just wonder what made them give up.


"Giving up" takes many forms. I'm not sure I'd agree that "Devoting substantial engineering, development, and testing time to new A-model nose gears, resulting in an aircraft more tolerable of pilot abuse" is one of them.
 
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.

I experienced the same issue as the OP. Observers confirmed the shimmy was in the vertical plane. Problem was that the Aeroclassic tubeless tyre that came with my Beringer nose wheel was out of round. Replaced it with a new Aeroclassic tubeless tyre that turned out to be even more out of round than the first one and excited a more severe shimmy. Third tyre lucky and no more shimmy. Shouldn?t have been so difficult to obtain a tyre that is round.
 
I had anti-splat mod my nose wheel and have never had any shimmy problems!

What I would do is.
1. Send nose wheel out to anti splat and get the mod done
2. Replace and install new squish washers on nose wheel.
3. Take lessons on how to keep stick in your lap during taxi, takeoff and landing.
4. Convert to tail dragger If all else fails
 
Problem apparently has been solved

Here is the epilogue to the nose bounce issue. We did the following anD the problem appears to be gone.

1. Replaced the main tires. They only had about260 landing but we decided to do it.

2. Rebuilt right brake cylinder.

3. Replace brAke pads on both sides

4. Replaced both main landing gear to weldment attach bolts.

Replacing nose tire had no effect (done first)

Thanks for all the great suggestions. We will most likely do the anti splat bearing mod in the near future.

Kevin
 
It sounds like your vibration issue was related to one of the main gear legs and not the nose gear. Some of the same influences apply there as well ( roundness and balance of tire,etc)
Glad you resolved it.
 
A mild shimmy is not the end of the world. I practice due diligence to dial in breakout force, maintain proper tire pressures, balance wheel/tire assemblies, etc., but sometimes the shimmy will reappear...if only slightly. I'd rather fly and enjoy my RV than spend additional time trying to eradicate it completely.

Perfection being the enemy of good enough, and all that...

And keep the weight off that nose wheel! I had a fun landing on the way back from Osh at Borger, TX. I landed on 17 well short of the FBO, so once the mains touched I added little power and carried the nose for more than a quarter mile. Good practice.
 
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