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notchy feel to nosewheel castoring

david.perl

david.perl

Well Known Member
Yesterday a maintenance engineer noted that when towing the plane (RV7A) , the castering nosewheel felt notchy as compared to other castering nose wheel aircraft he had towed. (DA40 and AA5's)

With the load off the wheel by adding weight to the rear the breakout force is set to the recommendations (I think something just over 20 pounds pull force) and the action is smooth.

Is this a quirk of the design or is there something deeper amiss here?

Plane is due a annual check next month so i'll take the assembly apart to check for wear / grit/ corrosion just in case

Thanks for any input
 
I would say normal. When I am maneuvering my 6A from the prop, I would describe the steering as "notchy." The fork doesn't want to move from it's position until enough force is attained to allow it. The moment it allows the movement, it moves easily and the cycle repeats. Watch your fish scale next time you test. You'll see the force drop off aggressively as it "breaks out."

I assume this is a design choice Van made that Diamond didn't. The stronger breakout force helps to hold direction a bit better at the cost of less smooth turning moment. However, the "notchy" resistance is only noticeable at very slow speeds. Taxiing on a gusty day, you can really appreciate the choice.

The Van's setup doesn't provide linear drag, as I described. It is also possible that Diamond uses a more advanced arrangement that provides a linear drag on the fork joint to achieve the same goal without the "notchy" feel at slow speeds.

Larry
 
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At the moment I'm pushing/pulling both a -6A and a Tiger in and out of my hangar.

With both planes correctly set on the break-out force, the -6A definitely has the "notchy" effect when you want to turn. It is very noticeable, the Tiger is much smoother turning.

Not sure why, the Tiger has about 400 lbs on the nose wheel and the RV has about 300 lbs. Perhaps the small wheel diameters, longer "castor arm" on the Tiger and overall dimensions have an effect?

The Tiger is set for essentially the same breakout force and has identical Bellville washers, but uses three instead of two.
 
Hand packed grease worked for me

My nosewheel pivot was notchy and noisy, despite adding grease through the zerk. So I removed the fork to inspect and it was apparent the grease wasn't getting to where it needed to be. After cleaning everything up, repacking the voids in the fork with fresh grease and adding a smear to the contact surfaces (but not the cupped washers) prior to re-installing, the pivot is now noise and notch free.

I'll take note of how it lasts and if necessary will add nose fork pivot re-pack to my annual inspection checklist.
 
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BobTurner said:
Since the Bellvilles are cupped and go concave to concave, how do you use the third one?
Click to expand...

Belleville washers are very handy from a design standpoint since you can customize a spring assembly.

They dont have to be "paired". The third can be small to small as long as the rest of the nosegear design is done to accomodate. Doing it as Vans did increases spring travel and reduces spring rate (if my statics corpuscle is working right). :) One could put them together in a nested fashion to reduce travel but double the spring rate (or spring "stiffness")


ALSO to the OP. Take a look at this post. Maybe it applies to you.

Nosegear Pivot descrepancy
 
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nose wheel swivel

The swivel plate with the stops on it is not welded squarely on the sleeve which is bolted to the strut. It causes the fork to not contact it all the way around and causes high pressure points which just pushes the grease out and causes the jerky movement. The sleeve/plate weldments need to be put in a lathe and trued up to allow equal pressure all around... Also greasing at the zerk does not get grease where it needs to be... Loosen the nut and put grease under the swivel plate where the fork bushing contacts it, retorque to proper tension and replace cotter key with new one..
 
nose wheel swivel

The swivel plate with the stops on it is not welded squarely on the sleeve which is bolted to the strut. It causes the fork to not contact it all the way around and causes high pressure points which just pushes the grease out and causes the jerky movement. The sleeve/plate weldments need to be put in a lathe and trued up to allow equal pressure all around... Also greasing at the zerk does not get grease where it needs to be... Loosen the nut and put grease under the swivel plate where the fork bushing contacts it, retorque to proper tension and replace cotter key with new one..
 
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