TMann Posted September 15, 2009 Share Posted September 15, 2009 It is interesting to read the latest posts by AirNico & Bob Setzer regarding the way a perceived substandard part can gnaw on you. I was not happy with either the exterior shape or weight of my center section spar. I also was very dissatisfied with the technique to construct it. After several nights of staring at the ceiling, I decided to rebuild it....... from the outside in. After drawing out the 'jig' in AutoCad, it became clear that a mold could be constructed in much the same way as the jig is fabricated by finishing out the last side (that creates the bottom) in 3/4 MDF and lining it with Vacuum Bag film followed by peel ply. The slight twist in the top exterior leg was formed in the mold using plaster and the 1/2 inch x 1 inch wedge was added to simulate the cutouts for the leading top and bottom tapers. I started my layups 8/30 and should have a finished product and weight this week. I started with the outside skin, followed by the top and bottom spar cap. Then I installed the shear web. All of these layups were vacuum bagged. The 1 inch foam was installed in two stages. I ripped a piece to cover the spar cap area (2 3/4 inch) back buttered with micro and installed and vacuum bagged the part. The other piece of 1 inch foam was ripped to 2 3/4 inches and then the 1/2 inch x 1 inch wedge was cut out and again it was fitted and bagged until the micro cured. After the cure, I used the Fein to cut the lower foam flush with the upper (forward) foam. The offset is due to the thickness of the spar cap. For the infinity retracts there is a mod that comes into play here. The shear web is left exposed (outboard 19 inches) and the foam is tapered in a gentle slope to the shear web. Later in the process a layup of 13 plies of UND will cover the three internal faces (bottom, forward and top). NOTE: This is the technique used as a retrofit vs. the new construction technique. It ends up with a much cleaner finished product and it is sure a lot easier to shape the internal foam while it's open like this. I was trying to install the inside BID layup with 1/8 inch hard points and all the additional associated layups last Friday after work but I could see I was running out of time. In order to make the best use of my remaining time, I made all of the Multi UND and various BID layups on vacuum bag film and stored them in the freezer for the night. Saturday AM, I started the internal layup (layup #2 per plans) and then pulled out my previous nights work, cut to the proper dimensions and fit into place. The layup was in the bag by noon. Sunday I fabricated the 1/4 inch forward face foam. Because I am using the infinity retracts, I incorporated the crush plate (16 plies of BID) that I had previously fabricated into the foam and installed the BID on both sides of the outboard pieces. The inboard piece and the interior bulkheads were fabricated and skinned last night. As long as I had everythig was still open, I fabricated some 1/2 inch PVC Conduit to run along what will be the bottom aft corner from about BL 8.0 and extending about 10 inches outboard of the bulkheads. I made a layup of two plies of BID on a piece of Vacuum Bag film & Peel Ply and installed it over the conduit. It went back into the vacuum bag for the last time to compress the layup over the conduit shape and into the corner. When I remove this part tonight, (and remove the PVC conduit). I'll be cutting this into two pieces to strattle the bulkhead and flox in place tonight. To this point, all layups have been vacuum bagged. I substituted West 703 Carbon Fiber tapes for the standard glass tapes. My target weight is 30 lbs or less. The first attempt came in at 42 lbs. I attribute the weight to lack of experience, the construction technique and the glass roving type tapes. I should have a final product as well as a final weight by Thursday. Quote T Mann - Loooong-EZ/20B Infinity R/G Chpts 18 Velocity/RG N951TM Mann's Airplane Factory We add rocket's to everything! 4, 5, 6, 7, 8. 9, 10, 14, 19, 20 Done Link to comment Share on other sites More sharing options...
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