Back in the shop finally. Tonight I'll start by laminating the wing spars. Anticipating a question about why I use tapered laminated spars, I'll tell you I've done this going back to Music in the 80's. It had to do with trying to get the most strength where it was wanted but pare off whatever unneeded weight I could. I long ago forgot the equations and parted with my engineering manuals (and it doesn't matter) but I was considering span loading. The types here are supported and unsupported spans. Our planes are sort of both. In the air the wings are not resting on static points or a fulcrum so it would be called unsupported. BUT to a greater or lesser degree it IS supported along the span on a blanket of air pressure. From an engineering standpoint there are separate formula for both to figure structure requirements. Since I try to think worst case scenario I consider the airplane in a hard bottom corner at 10 Gs. Not sure how good that number is but it's been used as a basis for our discussions for years. That would then equate to resting your 65 ounce airplane between two chairs on the wing tips or last rib then applying 40 lbs on the fuselage! WOW! What is obvious is that the highest stress is right in the center, tapering to zero at the extreme tip. (Remember that airborne those tips have no pressure point- no chairs). So to put spar requirements in line with where loads are imposed one would beef it in the center and taper it to zilch at the tips where next to nothing is needed. Common structure here might be 1/4 square spars. Given our criteria I'd think 1/4 sq. is two light in the center for, say 5000 load flexes before failure and surely too heavy at the tips. So my spars taper in steps along the span in the horizontal ( constant vertical) from 3/8" square at the root to 1/8"x 3/8" at the tip. It's always worked so I continue the practice without further thought.
Topic: Build threads look fun (Read 60010 times)
