Larry, The "added weight" is so negliable that for the extra margin of safety, it's the choice I'd make. To put this into perspective, the US Navy requires all equipment inside a cockpit to be able to withstand a 40 G impact load, and only yeild, not break. The thought here is that they don't want to make a survivable crash, un-survivable by having some piece of equipment dislodge and impact the pilot. One bolt size up gives me another 5+ G's? OK, it's quarters for me. Also, remember because of the angle of the belt, you can expect one bolt to be loaded higher than the other(asymetric loading, so using 60%/40% is fairly conservative.
Another conservative sizing approach would be to compare the belt anchor bolt size area, to the attachment bracket bolts. Combined areas of the attachment bolts need to be roughly 100% of the input. Thus a 3/8 bolt diameter area=.110 in sq. compared to 3/16=.028 in sq. A 1/4 inch bolt =.049 in sq, combined it's closer in area to the 3/8 inch bolt area than the 3/16. I use this rough sizing method more often than I care to admit, and find that by the time the strength department does their FEM, and sizing, They usually ask me how I came up with the bolt size. They usually say things like: "Looks like you ran some numbers, because they're exactly what we need...." Then I usually "beat" on them and complain, you're asking for quarters, can I go down to 3/16ths instead? I mean I used a consrvative approach at sizing the fasteners, can't we get some weight out and go with 3/16ths? They usually give me a look that tells me not to push my luck! OK quarters it is! --- larry flesner <fles...@midwest.net> wrote: > Scott, > I have two bolts holding each bracket, two brackets > per > occupant = 4 each 3/16" bolts holding each occupant. > > I have 3/8" bolts holding each end of the lap belt. > > Would you still think I need 1/4" bolts through the > spar? > If each 3/16" bolt holds 1000 pounds that would give > it a 20 G rating at my 200 pounds. > > Larry Flesner > > > > _______________________________________________ > see KRnet list details at http://www.krnet.org/instructions.html ===== Scott Cable KR-2S # 735 Wright City, MO s2cab...@yahoo.com __________________________________ Do you Yahoo!? Free Pop-Up Blocker - Get it now http://companion.yahoo.com/
