Most airplanes that utilize landing gear bungees also have STC'd modifications available to eliminate them. Must be a message in there somewhere! With that in mind, I have been designing a modification which eliminates the bungees but avoids conventional springs as well. The design utilizes commercially available polyurethane die "springs". Preliminary tests indicate that 6 springs 1-3/4" tall will do the job. I have selected polyurethane springs of the appropriate diameter, length, and durometer to give the equivalent of 300#/in. spring rate.
Referring to the CAD image, the silver tube is the lower strut tube which attaches near the axle while the red tube is the upper strut tube which attaches to the gear strut/flying wire attach point. The green split clamp collar represents a method of adjusting the bottom spring perch position. It can be adjusted up or down on the lower strut to change the spring pre-load. The polyurethane die springs carry the load by being compressed between the green Clamp collar and the red flange .
Note that there is one urethane die spring above the flange on the red tube. This provides a cushion for when the strut is fully extended.
Others have done similar modifications using steel die springs. I anticipate that the urethane will offer beneficial dampening (damping ?) compared to the steel springs. Another potential advantage is elimination of the total collapse failure mode of the bungee. It will likely take more than one try to arrive at the correct combination of variables. The urethane springs are interesting in that the effective spring rate decreases with compression. I have ordered enough polyurethane springs to mock up a test strut. You can see them at http://www.polyprod.com/
