I banged out the dents and patched the tears on the rudder. There were no bent flanges or spars on the rudder. The Stabilizer is a complete re-built. The spar caps are significantly thicker and the spar is thicker with stiffeners. A major problem was a basic lack of understanding that a yield failure in buckling is an ultimate failure. The FAA Basic Glider Criteria calls for 12#/sq ft. minimum limit for our gliders including gust loading on the tail. I had designed for 18# ultimate with 12 # limit. What I failed to understand was 12# is an ultimate failure in buckling. The spar was also weak for even this number. I have now designed ultimate of 27#/sq ft. with yield of 18#/sq ft. That 18# number is really an ultimate failure in buckling. I will still test to 12 # and I hopefully will have met the Spec. for minimum limit load. If it is over designed so be it.
Except for about 8 extra long rivets on order the vertical tail is assembled, and it weighs in at 7.04 # Original wood/cf vertical tail was 5 # but I am a little gun shy because of my load test failure. Also we do not know what the design loads were for the original.
Load test passed. Several problems encountered, the 3 hinges did not line up after riveting, so I eliminated the middle one. I checked the stress but the hole where it was needs to be patched. One problem with using a tractor for a fixture base is the rubber tires move when the weight is added. I ended up having to jack up the near axle to get the tail clear of the table.
The rudder was tested first with the stabilizer spar blocked. The all the rest of the weight was added, and the tractor jacked up until there was light under the tip.
The weight was 201 lb total with 83 lb on the rudder. 12 lb/ft sq. minimum limit load.
The distribution was approximately as page 28 Fig 1-XII Faa Basic Glider Criteria. The revised vertical tail with 4 attach fittings is 7.23 Lb.. The original wood one is reported to be 5 lb. and I do not know if that includes fittings. It is not as bad as all that because the original had a large wrench bonded to the boom at the tail for weight and balance.
Been working on detail design of the Pod/Boom, it is very different than the wood version. I was able to obtain at a local scrap yard 4 "x .12 wall 7075-T6 for my Boom and structure. Calculations are about 40-45 lb for the Pod/Boom vs the 60 lb wood version. It is a single tube air-chair type structure with just enough support for a fabric pod covering. The design requires that I over lap smaller wall tube. I had to restore a lathe, make a steady rest, make an expanding mandrel (very out of round tubes) and do lots of dancing but it looks like I will be finished one of the Boom tubes soon.
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