> I tell ya Frank - if I could just get my mind around this dissimilar > stiffness thing. According to at least one reputable composite guy, > this is a problem. I am sure there is an answer /solution, but in the > mean while it really worries me.
I'm not sure exactly what the previous paragraph is about, but I do remember the subject of carbon fiber in spars came up a few weeks ago, and it says something to the WAF question asked earlier. >From AN-18, paragraph 4.82, Behavior of Dissimilar Materials Working Together: "When materials of different rigidities, such as normal wood, compreg, or metal fittings, are fastened together for a considerable distance and are under high stress, consideration should be given to the fact that the fastening causes the total deformation of all materials to be the same. A typical example is a long metal strap bolted to a wood spar flange for the purpose of taking the load at the wing joint. In order that the load be uniformly distributed among the bolts, the ratio of the stress to the modulus of elacticity should be the same for both materials at every point. This may be approximated in practical structures by tapering the straps and the wood in a such a manner that the average stress in each (over the length of the fastening) divided by its modulus of elasticity gives the same ratio." Of course, fastened joint design is also a large consideration in the case of WAFs. I am certainly not an expert on this sort of thing, but I'm sure the information is out there somewhere if somebody wants to do the homework. I probably even have that sort of thing in my personal collection of aircraft design stuff, but right now I want to finish up my plane. The time for design and testing is long over for THIS airplane...I just need to get N56ML flying. Yesterday I finished up the tailwheel and rudder cables, and will do shoulder belts today. The seat is now lowered, and canopy latches are in the works, so my list of excuses is on the decline. My list of 30 things that needed to be done is now down to "only" 24, so there's still a ways to go, but things should be slowing down a little at work soon, so maybe I'll actually get to finish it soon. I should be very close to taxiing around the neighborhood, and blowing the leaves out of the yard... Mark Langford, Huntsville, Alabama N56ML "at" hiwaay.net see KR2S project at http://home.hiwaay.net/~langford
