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Main gear attachment location theory

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geosnooker2000

Well-Known Member
Joined
Mar 30, 2019
Messages
196
Location
Somerville, TN
I'm looking at different main gear ideas for my design. I think I have settled on what I want to do, but would love it if you guys could critique this thought.
(4 place all aluminum, total gross of as far under 2200lbs as I can get)
I don't like the idea of spring gear because I DO like the idea of offering a retractable gear option.
So for simplicity's sake, I'm thinking of mounting a rotating tube attached along the longitudinal axis of the plane.
The front of the weldment would be bolted through the main spar. The rear of this weldment would be bolted through the rear spar (flap attachment zone)
The main gear strut would be welded to this. Retract version rotates down, fixed gear version is just fixed in the down position with fairings.
.... first question, is there an advantage torque-wise with the angle that the strut is welded to the rotating tube weldment?
.... I know Piper (PA-28) has had problems with this as far as a really hard landing busting up through the top skin of the wing, and I suspect that is also the source of their cracked main spar problem.
All of their landing force is on the main spar. The strut is literally bolted to the top and bottom flanges of the spar (back-side).
My proposal is to divide the load between the main spar and the rear spar. But I would be bolting through the webs, so they would need to be reinforced with doublers.
Anyway, I know that a moment will be caused by force x distance. wherever the wheel is relative to the main spar, contacting the ground at the particular range of landing angles will apply torque to the main spar, but it just seems logical to me that if the strut were raked forward, as opposed to straight, or even raked aft, it would be (somewhat) less of a twisting force, and more of a "pulling aft" force on the main spar. Or maybe it is the fact that if you rake forward, you must contact/connect to the horizontal piece closer to the rear spar to keep the tire in the correct position relative to CG and CL. Obviously that will put more load on the rear spar.
.... Second question, is it a bad idea to have an actual rear spar carry-through in order to carry some of this landing gear load through the cabin? There is plenty of room under the rear seats.
....Third question, it sure would be nice to get away with a 5" wide tire in stead of the traditional 6" due to the possibility of retracts. Are there weight restrictions/recommendations to aircraft tires? because I can't find them if there are.

Wing Landing Gear.jpg
 
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