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Strange occurance.

NYTOM

Well Known Member
Only have a few dozen landings on my 6-A and still mastering the technique.
Today while landing at a neighboring hard surface airport and with a touch down at about 65 mph I encountered a quick and short tremendous noise I can’t even describe when I let the nose wheel down. Felt like the tire was missing. Tried to keep the nose off and it did it again. I was committed to land and and on the third nose wheel touch down everything was fine.
Fully expected to find a damaged nose gear when I shut down. No visible damage. Everything looked fine. It’s a Grove wheel and had the bearings and balance job done by Antisplat. Pressure was at 50 psi. and the breakout was recently checked at 22lbs. I’m thinking it was short bursts of imbalance when the tire touched and came up to speed. Take off was normal but I was really puckered up landing at my home field on my return. Everything fine again.
I’m going to pull everything apart and check anyway but does anyone have any thoughts of what may have happened? It really got my attention when it happened.:eek:
 
6A's land slightly nose up actually. so it shouldn't have been a far drop especially since you kept the nose off. I was thinking you should get the sealed bearings from Nimmo but looks like that's done. Check to make sure the nose gear is firmly in the engine mount.

If you are used to something like a Cessna oleo strut on the nose, the RVA's will be interesting at first. Maybe that is what you are experiencing. I've had a 6A and a 7A. Keep that nose off. A long time ago someone said it was a taxi aid and that's about it.
 
Hi Tom,
One possible reason might be the nosewheel stayed cocked before touchdown. Did you slip it on final? It’s very hard to duplicate I had it three or for times through the years. The noise and vibration were horrifying.
 
Shimmy?

Hard to diagnose without seeing or feeling it, and I’ve never raised a screwdriver at a nosegear equipped RV, but Cessna and Grumman nosegears can shimmy and make a godawful racket when they do. A couple of causes for the shopping cart nosegear leg shimmy are tire/wheel combination out of balance or the steering pivot is too loose. So, I’d check that the steering preload is within spec, and while the nose is off the ground, just do a poor boy balance check... loosen the wheel bearings until they spin as freely as possible, then give the wheel a bit of a spin and watch where it stops. Do several of those spins and if the balance is far off, it will consistently stop at the same place. Easy way to fix it is with stick-on weights from the auto parts store. Or you can replace the tire and tube, and then check again. Again, while the snoot is up in the air, grab the gear leg and give it a good wiggle. ANY movement at all is cause for closer inspection. And yeah, as my first flight instructor taught me, always protect the nose wheel. My CFI wife tells her students it’s for taxiing, not landing. But still, it should run smooth.
 
and with a touch down at about 65 mph I encountered a quick and short tremendous noise I can’t even describe when I let the nose wheel down. Felt like the tire was missing. Tried to keep the nose off and it did it again. I was committed to land and and on the third nose wheel touch down everything was fine.

Just a general comment. True for most all airplanes, but especially true for the RV: Keep the nose off the runway for as long as possible. Since you had 3 nose gear touchdowns you clearly let it down at a higher than minimum speed. And, once down, keep the stick aft. As others said, these nose wheels are really just for taxiing. All that said, check the breakout force on the nose wheel.
 
I've seen evidence of the spinner making contact with the forward cowl when the gap is too tight and the engine flexes on the mounts. Flying small piston twins you can really be amazed at seeing how much some engines can flex up and down on their mounts. The cowl itself could be a massive woofer amplifying a horrible racket and disguise the direction the sound seems to be coming from.
It could also be the sidewall of the nose tire flexing and making contact with the edge of the nose pant if the gap is too tight.
 
Have a ground observer closely watch and capture video of your next landing. Seems likely you have a shimmy problem, pretty common. Check the sidewalls of your nose wheel tire closely to make sure it didn’t rub on the wheel pant.

Erich
 
It's really simple to mount a cheap video camera ($49 at Amazon) in the tail tie-down ring with a couple of large washers. Helps improve your landings too :)
 
I don’t have much experience with -A model RVs, but 50psi in the nose sounds high to me.. is that what they call for? I’ve found that a Cessna may have nose shimmy st published air pressure.. and dropping the psi to 20 in a Cessna will usually stop the shimmy..
 
A lot of excellent imput

I like the idea of mounting a camera to capture this phenomena. I was very careful and followed the advice gleaned off this site to try to avoid any problems with the nose wheel. The last thing I want is to be featured on the local news.
Probably over did it in most RVer’s minds. Grove wheel , Antisplat bearings and balance job, the Nose Job, skid plate, extra wide clearance around the tire. There’s some conflicting info here on tire pressures, some like 40 and others 50.
In the last 10 hours I had checked and readjusted breakout to the suggested 22lbs. Was doing some air work before the landing and Vlad’s mention of slips might be a factor. Like I said I’m still trying to master the 6A and my hundreds and hundreds of landings in my old Ercoupe ( with rudder pedals for slips) probably didn’t help. You could land that thing like a F-18 slamming onto the deck and stopping in a few hundred feet and everything would still be attached. Going to mount the camera and go practice, practice, practice. Heard somewhere that you should treat the gear of a 6A like it was made of glass and you’d be fine. I guess my plane is trying to talk to me. Thank you for your help Gentleman and have a safe and Merry Christmas. :)
 
I just removed and tossed an AS modified nose wheel, bearings were toast, this is the second one I've seen.
IMO modifying the Grove was a mistake.
 
I just removed and tossed an AS modified nose wheel, bearings were toast, this is the second one I've seen.
IMO modifying the Grove was a mistake.

What were the indications that you notice, Walt? I just had the AS mod done to my stock (non-Grove) nosewheel mod done by AS...seems to be smoother, plus sealed bearings so I don't have to mess with them, but if there's a failure mode and symptoms, sure do want to know what those are! Thx!
 
2 thoughts - maybe, maybe not.
-lift the nosewheel & see how freely it rolls. Hi rolling resistance will show up more on pavement than grass operations.
-remove the front cover on the front wheel pant. If there are recent skid marks in the cover paint, than the story is told.
Land on mains & let the nose down Gently!
 
I just removed and tossed an AS modified nose wheel, bearings were toast, this is the second one I've seen.
IMO modifying the Grove was a mistake.

Walt, failure caused by roller bearing side loading? I always thought this might be an issue with roller bearings in this application.
 
Reminds me of other bearings that have failed

I just removed and tossed an AS modified nose wheel, bearings were toast, this is the second one I've seen.
IMO modifying the Grove was a mistake.

Interesting observation Walt. Do you recall if the bearings actually failed ?
I’ve seen bearings on other pieces of machinery reach a point where they will vibrate violently for a second or two in certain situations. And to think about it, that’s kinda what it sounded like. Now I’m wondering about the manufacturers of bearings used on my wheel. I will definitely check .
UPDATE: turns out that this is a real thing. Just did some research and there’s a condition called violent radical oscillation. Happens when bearings and the balls are not ground perfectly. I guess there is the potential for it to happen with any bearing regardless of source . If it happens again with mine , I’ll at least replace the bearings with the best brand I can find. It’s always something.
 
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Where are you located? Snow / ice inside the wheel pant?
Loose wheel pant making contact with pavement?
Just tossing out suggestions
 
Just a tip!
Once your main gear touch and your nose gear is off the runway lower the flaps. This will help you keep the nose wheel off the pavement much longer than with flaps extended
 
Shake test

Interesting observation Walt. Do you recall if the bearings actually failed ?
I’ve seen bearings on other pieces of machinery reach a point where they will vibrate violently for a second or two in certain situations. And to think about it, that’s kinda what it sounded like. Now I’m wondering about the manufacturers of bearings used on my wheel. I will definitely check .
UPDATE: turns out that this is a real thing. Just did some research and there’s a condition called violent radical oscillation. Happens when bearings and the balls are not ground perfectly. I guess there is the potential for it to happen with any bearing regardless of source . If it happens again with mine , I’ll at least replace the bearings with the best brand I can find. It’s always something.

I would shake the wheel and see if there is any slop in the wheel/ bearing assembly. The center spacer between the two bearing’s inner races may need a slight length adjustment.
 
They say the hardest part about flying a 6A is landing. I’m going to try everything you folks have suggested. I’m sure a big part of it is my inexperience. First thing is to pull everything apart and check pressure, bearings, clearances, breakout adjustment, gear attach and overall condition. Unless I find something definitely wrong,I’m going to assume the problem is with the guy flying the plane. :rolleyes:
 
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