Sunday, September 18, 2011

The weather was bad on Saturday and I took it as a chance to try to reduce the friction in the rudder system and reduce nose gear shake on landing.

For the shake I fabricated a new lower nylon bearing. This one has a tighter fit than the original, so the forward\back motion is limited.

To install it the old lower bushing had to be removed. This was an incredible pain. Reaching the bolts is complicated by the nose strut and the muffler. While the nose bearing was out I removed the v-notch channels and machined them down to create a smoother ride. the new shape is a semi-circle instead of t notch.

I also experimented with the strut cap. New pieces were fabricated out of nylon and phenolic to attempt to reduce the nose gear friction. Once all the pieces were re-installed some reduction of friction was made, but not much. In addition new friction was added by the new lower bearing. The lower nose gear needs to be removed again as I found the new machining of the notches allows for full left rudder deflection, but not full right deflection.

There is still too much friction in the rudder system. After much experimentation I can say the friction is mostly from the nose strut. The rudder by itself is free of perceivable friction. Some friction is being added by the rudder pedal assembly bearings. Grease, teflon, lithium, ect does not seem to reduce the pedal friction.

With the nose gear push rods removed, it obvious that the nose gear is the cause of my troubles. By placing washers under the nose strut cap, I tried lowering the nose strut to allow the cross tube to rub the newly machines angle. This was more friction than the strut cap, despite having less contact surface. The addition of a nylon or phenolic piece under the strut cap adds some reduction in friction, but not as much as expected. One idea I have is to place a matching nylon piece on the firewall shelf so the bearing is nylon to nylon. This would require removing\accessing the bolts holding the upper nylon bearing and may be impossible with the nose strut in place.

The final attempt will be to perform the roller bearing mod. Adding the bearings will require removal of the nose strut or the exhaust system. It will also require some way of adding additional material on top of the lower nylon bearing to allow for full deflections.

The roller bearing mod was originally found here:

The proper bolt length appears to be AN3-37 and the bearings are "DPP4-FS464" from ACS.

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