The analysis of the failure mode of the KR WAFs done by Don Reid starts on page 46 of the set of newsletters located at http://www.krnet.org/newsletter/nl5.pdf . He practically wrote the whole newsletter that month.
In another analysis he sent to the list in 1998, Don made the following comment in answering a similar question about the roll of clamping force in holding the WAFs in contact with the spars: "The frictional load can not be used in the structural analysis. The wood will expand and contract due to weather, the metal in the fittings and bolts will expand and contract with temperature. The ONLY way to calculate the stresses is to assume that they are transferred in the bolts bearing on the wood." This is steel on wood, of course, rather than the steel to steel joint that we were talking about, but shows that neglecting friction is not uncommon. The page before Don's article (page 45) was Jim Hill's KR2. He passed away several years ago now, but this plane was my first KR ride, and Jim turned out to be one of my very best friends. I now own his hangar. A lesson learned was that he hooked up ram air to the front of the carb and went for a test flight. On climbout the more speed he picked up, the leaner it ran, until it finally quit on downwind. Problem was the airport was one-way due to high trees on the end, so he landed very long and ended up in the cotton field off the end of the runway, breaking the tail off the plane. This was about the time I'd done the tail airfoils, so we outfitted his plane with the new horizontal and vertical stabs, rudder, and elevator, and added another bay to it to make it "almost" a KR2S. He reported the difference was amazing. My point though is that even a simple change like ram air can make a huge difference. Our theory was that pressurizing the carb without pressurizing the float bowl reduced the gravity fuel flow to a level the engine could no longer run on. There was a little tube hanging around that should probably have been connected to the ram air source. At least I think that was a float carb...if not, the tube was an overflow or something...that was a long time ago. But the fact remains that even something as simple as adding ram air can be a serious matter with unintended consequences. For those who haven't looked through the newsletters, you don't know what you're missing. Time spent reading these things will save you more time than it takes to read them, and probably answer a lot of questions that you didn't know you had. The rest are at http://www.krnet.org/newsletter . See y'all in McMinnville...arriving early Thursday afternoon... Mark Langford ML at N56ML.com http://www.n56ml.com
