My company used to make prepreg parts. For any who don't know what I'm talking about. We purchased fiberglass cloth and carbon fiber uni cloth that already had epoxy resin in it. We could through testing determine how much resin we wanted in the cloth and order it that way. The percentage of resin to cloth as compared to wet hand layup is considerable. Much weight can be saved in the manufactured parts as compared to hand laid up. These rolls of prepreg cloth had to be kept refrigerated. If you did not the resins could melt/soften enough to stick together throughout the roll. If that happened then you were left with a log of glass or carbon. A very expensive mistake! We cured our parts above 225 degrees F. If we needed to soften a cured part (which we did occasionally) we had to raise the temperature above or hotter than the original curing temperature. The point to this is the hotter you can cure your parts the better it will be for your wings for example sitting out in the hot summer. I say this because of a situation I saw many years ago at Oshkosh during the EAA Convention. I was with a friend of mine from Anchorage Alaska during the afternoon air show. While sitting, standing, guarding his airplane from careless lookers/tire kickers he had stood up placed his elbows on top of his canard leaning over with his hands holding his head as we stood there watching the airshow. After a little while he turned to talk to me and moved his elbows. I was a couple feet to his left and two indentions were left in the top of his canard on his Rutan Defiant. I immediately knew what had happened. His plane or at least his canard had been built during the cooler temperatures in Alaska and then during that hot year in Wisconsin the temperatures had caused his wing skins to get hotter than they were originally cured so the resin began to soften. His plane was built with Safety Poxy which most Long Ezes and Defiants were built with up until the change to the new version of Safetypoxy. A common practice that was used for post curing composite structures back in the day was to build a temporary wood structure over your work table and fiberglassed parts, cover the frame with black plastic, roll the table out into the sun. An option is to do the same thing but put a heater under the plastic if you are in cool temps or cant go outside with your table. This would cause the temps inside to get very hot like an oven which was good. Curing hotter than the finished painted product will see or reach later out in the elements is the goal in a 100% composite structure. Wings are not as critical in a KR2 because it has wooden structure spars unlike a LongEze that has resin and S glass spars that you don't need or Want to soften. My company made prepreg carbon fiber tubular spars that went into the Quickie Q200 canards for one reason. The reason is as described above. Those little planes were all hand layup structures. When sitting out in the hot sun that canard wing was also the landing gear. There were cases when the hand laid up resins softened just enough while holding the 0-200 Continental, fuselage, fuel etc that they sagged down enough to cause major problems. That was when we were asked to remedy the problem with stiff carbon fiber spars for them. Another thing I have seen happen on the S glass Eze landing gear is melting of the resins by the axle. This usually happens when a new Eze pilot spends too much time doing high speed taxi tests. The pilot has to use brake steering to drive or steer a Vari or Long Eze. Those brake disks get very hot when under high speed stops then steering back to do it again. Get the picture? When the brake disk axle transfer enough heat to the fiberglass landing gear, the resin melts, the whole thing gives up and the outer end of axle goes up the end of the gear drops down or twists. I have seen two of these in my area. What a mess to attempt to repair. Just my experience with this subject.
Larry Howell
