We assumed a 1" x >1" piece of spruce with 4000 pounds (pilot and passenger) of force out in >the middle of that 32" span, neglecting the upper cap, and the vertical >members and plywood connecting them to the "subject" lower cap (somewhat >conservative). >Mark Langford, ++++++++++++++++++++++++++++++++++++++++++++++++++++++
Mark, In my case, and most KR's, two brackets are attached near the vertical fuselage sides. That should cut the load in the center by one half. My brackets, as you stated, span both spar caps. Also I don't think the entire load is horizontal to the spar but some load would carry a vertical angle. The seat back where my sholder belts are attached has two pieces of 5/8" spruce with a piece of 3/32" ply on the top and a piece of 1/4" ply on the bottom and a spruce block between the two where the bolt goes through. My question: how big of a tree can I hit? :-) :-) Seriously, from what you stated and considering the KR design, I'd guess the simplest and lightest weight way to strengthen the spar for crash forces from the belts would be to run two steel tubes or wood structures from near center of the rear spar to the forward spar at the fuselage sides. Thoughts? Larry Flesner
