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Old 04-01-2012, 06:00 PM
  #254  
Ron Stahl
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Default RE: Enlarged Zirioli Turbinator 125% size

Skinned the second stab today. The pictures will show the layout of the sheeting as it should be done with the grain following the leading and trailing edges. I used about 1.5 fluid oz of epoxy and find that the three hour NHP is just right in viscosity so that it does not soak into the balsa and give you plenty of time to complete the process without rushing; also you do not have to put any epoxy onto the foam just the wood skins. I tape the sheets together and do not glue them as most people do and find it is not needed since the vacuum bagging process drives the adhesive into the joints and the tape prevents it from coming through to the outside of the balsa. I have been doing it this way for over twenty years and have never had a loose skin once the process is complete. The vacuum equipment is from ACP sales and I have used it for over the last ten years bagging things at home. If you use EPS ( White Beaded foam) DO NOT go over 6" of vacuum as it will crush the foam cores. The setup I have at home is preset for white foam from ACP and I use it when ever I am skinning with balsa no matter what type of foam I am using. I have been using the pink insulation foam from HD as it is easy to get 2" x 24" x 98" blocks and most of what I built will fit this size. The wing will have to get cut from thicker foam as it is 3" think at the root. As you will see the sheeting it sized to fit just a little over the edges of the foam since the bagging process puts about 4 PSI of pressure from the atmosphere on the cores and if you let it over hang to much it will break it off For those of you worried about only having 4 PSI on the bag surface this would mean that your work bench would have to be able to not bow in any direction with 750 -800 lbs on it for a core this size. The wing will be in the tons of weight that you would have to put onto it to get the same pressure mother nature gives us for free. I mark the skins and place the foam 1/4 inside the trailing edge and tape the two skins together face to face so that they touch each other at the last 1/4" to form the trailing edges. Once inside the bag I clamp the straight edges together at the trailing edges just until the vacuum gets pulled down good and tight. I then place the skinned cores back into their sucks for the cure cycle. Also you will see a piece of paper towel inside the bag between the two stabs and this is to allow the bag to remove all of the internal air otherwise it could close off and trap air inside and not allow good pressure to be applied to the skins. Next the wings will get cut, but first i have to build the cordinate file to fit Nicks ribs. He thought that he used a RITZ 2-12 airfoil but we cut a test piece and it was not even close. Once we get it right I will pass on the files to anyone who wants to cut cores with a CNC foam cutter.
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