proppastie
Well-Known Member
Now I are an Enganeer but before that I was a Tool Designer, and had the pleasure of working at McDonnell Douglas on the tooling for the prototype AV8-B. At the time this aircraft was the largest Graphite Epoxy assembly ever made. I thought the site might like to see how the spars were designed. They were a modified I Beam but instead of a flat web they were in a corrugation pattern. They did not glue the wing together but used steel or titanium fasteners (I can not remember which). The molds all had “K” factors for the differences between the coefficient of expansion at temperature of either steel or aluminum molds. The wing skin used a steel mold, NC machined to the proper mold line, and the spars had aluminum molds. The unit was bagged and put in a large autoclave. The parts came out of the oven distorted, and twisted, and had to be bent back into shape in the assembly tools. Now as I understand it if you make a carbon wing you make a carbon mold to eliminate the expansion problems. When taking the composite design night course there they brought in someone to talk about the strength of the various sub-assemblies. Some assemblies were 25 times as strong as they needed to be. I raised my hand and asked “were they therefore lots heavier than they needed to be?” He looked like I punched him but recovered nicely and said it was designed for “stiffness”. I am not sure I understand that but these War Machines do carry lots of bombs and fuel, so what do I know? 
