- Apr 7, 2020
Anybody looked at the MLG on the Ercoupe lately?
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I get that you want rubber, but McMaster Carr and others have a whole variety of die springs with varying spring ratesOk, to streamline the responses, and ideas, for this thread:
I am using an existing strut. Unloaded, the area the die spring, or rubber doughnut assembly, will be installed is 6 1/4", and has a 7/8" center tube. At rest, empty, the gap is 5 5/8", and I do not know what the compressed (Loaded aircraft, and thumping the runway) gap is, at present. The gross weight of the airplane is 750#.
I intend to use the existing strut, not fabricate a new one.
The existing strut was originally designed to use 1/2" x 2 1/2" rubber disks. The builder of this particular airframe opted to use die springs, instead. The die springs from Aircraft Spruce proved to be too soft for the OB's liking, and he installed a spring from another source (a cut down oilfield down-hole service tool).
When the aircraft is at rest, and empty, there is very little compression left in the spring, and she bottoms-out rather easily. I wish to change this.
But, if using springs, the strut will still need some sort of damping.I get that you want rubber, but McMaster Carr and others have a whole variety of die springs with varying spring rates
McMaster-Carr 6 inch long, would give you a little gap when completely unloaded, which you COULD pack out with a spacer - a LITTLE pre-load is a good thing, a LOT makes assembly a fight like getting a wet cat into a paper bag. Or you can get cut to length, but cutting this stuff down and grinding the ends is a Bee-Yatch you might best leave to a Spring Shop, if any such still exist in your area. McMaster-Carr only one rate per shaft size, and it looks a little low to me.
You're not wrong. But if the shock strut is splayed away from the fuselage at an angle, you'll get some damping from the scrubbing of the tire sideways as the gear deflects. This is the ONLY damping in a Wittman style landing gear, whether bar or rod. Trailing link gear, all bets are off, and you'll have to find some other source of damping.But, if using springs, the strut will still need some sort of damping.
McMaster-Carr Polyurethane rod in the right OD. Punch the center holes as previously described. 40A or 60A durometer to start? A bandsaw with metal cutting blade without much tooth set should turn this bar into disks with little difficulty, but I'd freeze it first.The existing strut was originally designed to use 1/2" x 2 1/2" rubber disks.
That's a very good point, and I think is a good argument for molding them.And add polishing the "cut" edges. Must get rid of the stress risers.
This is, also, an area I have explored, and is in the running.
Probably durometer about Shore A 70. Pretty stiff, and the cord makes them more so, but stack stiff springs on top of each other (in "series") and you get a soft spring, so...One original drawing for the Jodel d9 shows undercarriage rubbers of 30mm x 30mm cut from truck tyres.
this should cut round rubber washers cleanly....
lots of various rubber sheet materials from the same source also... search 'rubber sheet and strip'