I have had several landing gear failures since going to the spring "bush gear". I have been researching the subject and have noted quite a few similar failures of that type gear, all in about the same location and of the same nature, Inward bending of the forward strut leg. I have been reluctant to re enforce that leg for fear of promoting a more serious failure elsewhere. The gear is a Chinese copy of the gear used by Piper from the 1930s onward but the Piper gear does not seem to suffer the same failure. Today I made a cardboard model of the gear geometry and I believe I have located the problem. The bottom anchor bolt for the spring leg on the "bush gear" is fastened to a metal plate welded between the front leg and the axle. When the spring strut is fully extended and bottoms out, or the spring becomes coil bound, that point then becomes a rigid fulcrum with the axle as a lever. The upward motion or the axle is then translated into an inward rotary motion on the front gear leg. The failure always seems to occur at the point halfway between the axle and the fuselage, which makes sense. I have never bent a rear strut, nor the spring strut, always the front one.

Looking at photographs and real life examples of Piper, Hatz, and Pietenpol gear shows that the anchor point on those gear is at the inboard end of the axle. My model shows a significant difference in the movement of the middle of the forward gear leg when the anchor point is moved to the end of the axle. As a matter of fact, the farther inboard the pivot is, the lesser the rotary movement at the front gear leg center.

I have yet to figure a force analysis on the gear, but I think i am onto something. I'll post more as I find more. On a positive note, my welding is getting better.

Bob McCaa