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That Dancin' Nosegear

Anti Splat Nose Wheel Mod

Had the same issue as your having with my 9A.
Send your nose wheel to Allen at Anti Splat and have them put their bearing mod on and true your tire and you will be a very happy camper.
It was a daylight to dark difference with mine.
Worth every penny.:)
 
Mine did the exact same thing until I changed to the sealed bearing setup by Allan at Antisplat Aero. Smooth as silk now! No brainer not to change that nose wheel bearing to sealed free wheeling.
 
CharlieMike said:
The issue I see with landing is letting the nose gear touch down at almost the time as the mains! I hold the nose off until the elevator will not allow it to be held off.

Just an observation.
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Does it on takeoff too...

I hold it off as long as I can without letting it thud down, you can see the oscillation gets worse at 30-40 knots actually. I don't know about your plane but I can't hold the nose wheel off at 30 knots at idle power (geared engine, 400 rpm prop). This was a flapless landing BTW.

I have seen other As do this on landing so I suspect they all do it. The leg has a natural frequency and little damping. I don't see how bearings would affect this. Does someone have video with the modded parts doing a takeoff and landing? I can machine the parts for a better bearing setup if need be as I did on my RV10, if that really solves it.
 
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CharlieMike said:
To me in all of the videos the nose is not held off as much as it could be just by looking at how fast the runway is passing by in the videos. With my aircraft configuration the weight on the nose wheel is light from what I hear, 254 lbs empty weight (RV-6A with an O-320 and a wood prop), which allows me to keep the wheel off as much as possible. I know I begin and end each takeoff and landing with the elevator at full up stop, which allows the nose to be held off before I am able to measure the airspeed, my indicator starts at 40 mph.

I know that there have been a lot of talk about issues with the nose gear so any time my plane is on the ground I try to make sure I have full nose up on the elevator at all times when I'm moving, whether on concrete, asphalt, or grass.
Click to expand...

I believe most of us have full up elevator at all times on the ground but few would have as little as 254 lbs. on the front gear. If the front tire is off the ground, you can't have shimmy or longitudinal oscillation.
 
CharlieMike said:
The issue I see with landing is letting the nose gear touch down at almost the time as the mains! I hold the nose off until the elevator will not allow it to be held off.

Just an observation.
Click to expand...

rv6ejguy said:
I hold it off as long as I can without letting it thud down
Click to expand...

I agree Ross... I only took one quick look at the video, but it looked like a 3 point touch down to me. Not good technique in a tri gear anything...
If it was a no flap landing, that concerns me even more, because with no flaps the touch down AOA should be even higher at any given airspeed. A flat touch down would then possibly indicate that the airplane is either excessively nose heavy, such that there is not enough elevator authority when touching down slow, or the touch down was actually very fast (at least much more than it needed to be).

Sorry for the thread drift, but an on-line video like this has the potential of teaching good as well as bad information / technique.

Back on track... Two factors that have a significant effect on the performance of the nose wheel and interaction with the gear leg are tire roundness and balance.
 
love the scoop!

nice work Ross,
now that you see some of the flow characteristics, are you considering any mods, or will you just try to improve it with some subtle adjustments; VG's here and there or fences to keep the airflow attached where desired?

another data point is needed on the nosegear.....maybe some guys just land on much smoother asphalt!?
how does the oscillation respond to a wood or fibreglas stiffener?
Does the ASA brace change the 'tuck' by limiting the travel?...most guys say it never touches the gear in normal ops.

I do not like the 'action', so am just trying to learn the best way to eliminate it....(shipping my nosewheel to Alan is not cheap or easy.)
 
rvbuilder2002 said:
I agree Ross... I only took one quick look at the video, but it looked like a 3 point touch down to me. Not good technique in a tri gear anything...
If it was a no flap landing, that concerns me even more, because with no flaps the touch down AOA should be even higher at any given airspeed. A flat touch down would then possibly indicate that the airplane is either excessively nose heavy, such that there is not enough elevator authority when touching down slow, or the touch down was actually very fast (at least much more than it needed to be).

Sorry for the thread drift, but an on-line video like this has the potential of teaching good as well as bad information / technique.

Back on track... Two factors that have a significant effect on the performance of the nose wheel and interaction with the gear leg are tire roundness and balance.
Click to expand...

Well, I can see the mains touch a couple seconds before the nose gear and I have 314 lbs. on the nose gear which is pretty typical on C/S equipped aircraft. Got about 800 landings on this plane now as it is used for testing and training primarily and I've never touched down on the nose gear first. Touchdown is at 55-60 knots IAS and I almost always land clean, sometimes with half flap, almost never with full flap. My setup does not have the residual thrust of a Lycoming at idle either.

Anyway, the vid was just to show this phenomenon. Since the worst oscillations occur well below touchdown speeds, I really don't see the point in this part of the discussion. You can see the main gear also goes through a tremor at around 25-30 knots.

I do agree that tire roundness and balance could be a big factor in this and I'm going to look into that. I've seen some vids which show some pretty out of round nose tires which could really make this worse.
 
rv6ejguy said:
I found this on YouTube and some others: http://www.youtube.com/watch?v=xhthU9nhDgo

I don't see any difference in behavior.

I have not had any lateral fork shimmy for many years using 15-22lbs breakout on the bearing there.

I only feel the flexing when I hit a bump on the runway.
Click to expand...

The video you linked shows the antisplat brace, not the sealed bearing mod.

This video shows the difference in nosegear flexing between the standard and the new sealed bearings:

http://youtu.be/W0kHXOIop5Y
 
flyboy1963 said:
nice work Ross,
now that you see some of the flow characteristics, are you considering any mods, or will you just try to improve it with some subtle adjustments; VG's here and there or fences to keep the airflow attached where desired?

another data point is needed on the nosegear.....maybe some guys just land on much smoother asphalt!?
how does the oscillation respond to a wood or fibreglas stiffener?
Does the ASA brace change the 'tuck' by limiting the travel?...most guys say it never touches the gear in normal ops.

I do not like the 'action', so am just trying to learn the best way to eliminate it....(shipping my nosewheel to Alan is not cheap or easy.)
Click to expand...

I am pretty happy with the scoop flow, a little separation at the aft few inches but this seems to be caused by the higher pressure at the exit as it goes away when the door is opened a bit more. The big thing is we recover a large percentage of the lost momentum so hoping it will prove faster despite the drag of the scoop. I had a lot of other inlets and exits before which added up to more frontal area than I have now.

This part of runway 26 is fairly smooth. Runway 17 is really bad near the touchdown point so I try to land long whenever possible. That video would be more scary I think.

I used to have wood dampers on main and nose legs years ago and those cured a big, big shake I had at about 20 knots. With new legs, these went away without the dampers so I always suspected alignment issues with the original legs but never checked it.

I never fly off grass or even taxi on it.
 
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rvbuilder2002 said:
Two factors that have a significant effect on the performance of the nose wheel and interaction with the gear leg are tire roundness and balance.
Click to expand...

Agree with Scott. When the rotation rate matches the natural frequency of the leg assembly it's really gonna oscillate.

Somebody please tell me the point of the wheel bearing mod. A once per rotation bearing drag?
 
bearing mod

Dan, In my review of the nose gear it appears that the bearings tend lock up due distortion of the fork. The timken bearings do not have a spacer between them and have a lot of drag when the axle bolt or fork is flexed.On some of the nose gear failures the outer aluminum spacers were galled into the sides of fork. The only reason the spacer would turn is because the bearing is dragging it. The fork seams pretty rigid but if you mount it in a vice it does need a lot of force to flex it enough to get tight bearings with timken bearings. The ball bearings with a spacer between them is a huge improvement as the ball bearings will tolerate a lot more misalignment. Ron
 
868RM said:
Dan, In my review of the nose gear it appears that the bearings tend lock up due distortion of the fork. The timken bearings do not have a spacer between them and have a lot of drag when the axle bolt or fork is flexed.On some of the nose gear failures the outer aluminum spacers were galled into the sides of fork. The only reason the spacer would turn is because the bearing is dragging it. The fork seams pretty rigid but if you mount it in a vice it does need a lot of force to flex it enough to get tight bearings with timken bearings. The ball bearings with a spacer between them is a huge improvement as the ball bearings will tolerate a lot more misalignment. Ron
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We've modded some forks and I've looked at the stock design. They are not going to flex to any significant degree with 50, 100, 200 or even 300 lbs. on them. I suspect the main reason you'd be seeing rotation of the aluminum spigots is that the bolt is not tight enough to establish proper pre-load on the bearing.

The original design is not good with the rubber seal touching metal but there is nothing wrong with tapered roller bearings in this application if done right. I already did a mod to correct what the factory did on my RV10.

I just don't see a switch in bearing design alone fixing the intrinsic problem here which is the leg vibrating at its natural frequency. Now fixing an out of round or severely out of balance tire could change how the leg is excited in the first place.
 
So, I'm at the hangar greasing bearings right this very moment. I used to have fun wallering (southern term) around in grease in my younger years, but I guess I'm getting old and lazy... I would give a few hundred bucks to never have to pack another bearing. My 100K+ mile Toyota has never had its wheel bearings serviced and it still seems to run fine :).
 
Flex

Ross, I agree 100% if the 400 lbs. is a nice straight on load but it is not as simple as that.Do some research on high speed wobble of motorcycles and they have very stiff forks attached to a somewhat rigid frame. The nose fork is attached to a spring. Does not take much flex to skew the taper rollers of a timken bearing and create a lot of drag. As the drag occurs the fork moves rearward and centers removing the drag, the fork goes forward, skews slightly, loads and cycles again. Luckily not as bad as grocery cart front wheel. Caster wheels are strange beasts. Ron
 
rv6ejguy said:
I just don't see a switch in bearing design alone fixing the intrinsic problem here which is the leg vibrating at its natural frequency. Now fixing an out of round or severely out of balance tire could change how the leg is excited in the first place.
Click to expand...

Do you know for sure that the problem spotted in the video is that the gear leg is vibrating at its natural frequency? What is the natural frequency of the gear leg? I suppose it would be easy to test by lowering the tail such that the nosewheel is off the ground and exciting (whacking) the nosegear leg like a tuning fork. However the fact that the tire is interacting with the runway during the vibration incidents could certainly be expected to play into the equation of natural frequency. For that matter so could the age/condition/brand of the tire, inflation pressure, runway surface, you name it.

Perhaps that is indeed the root of the problem. However tens (or more?) of VAF posters so far have reported that the wheel bearing mod completely solved any problem of excessive gear leg vibration. Likewise no-one to date has come out and said that they had the wheel bearing mod done and it didn't solve the problem. Together, that speaks volumes to me.
 
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Quoting Scoot:
So, I'm at the hangar greasing bearings right this very moment. I used to have fun wallering (southern term) around in grease in my younger years, but I guess I'm getting old and lazy... I would give a few hundred bucks to never have to pack another bearing.
Click to expand...


I'm happy with my Beringer nosewheel. No more bearings to pack, and no more cheap, hard to find tube.
 
I found a video last month on YouTube showing a before and after with only a wooden stiffener on the leg (stock bearing setup). Pretty much stopped the leg dancing. Looks like there are a couple ways to address the problem.
 
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