Jan 032013

Now it should be obvious to anyone that when doing something important, like for instance landing a large scale sailplane, that one needs to pay attention to what one is doing. These lessons often have to be relearned, sometimes at great effort – and embarrassment. Such was the case when I stalled while landing my TopModel ASG29E at the 2012 SKSS Aerotow. And to make it worse this was the flight after I had bragged to my SKSS colleagues that I had just “made the best landing of my life”. At least I was saved the embarrassment of having to carry the wreckage to my car by Charlie and Gunny who rescued me with the Ranger – thanks.

Now a few months have gone by and with the help of some epoxy and carbon fiber I’m feeling good about the 29 again. I’m glad I resisted the urge at the time to find a can of gasoline and a match …
The major damage was the break in the tail boom in front of the fin, there was some damage to the nose but those repairs were straight forward. The canopy hinge broke loose as did the brass latches –my goal was that the repair should keep the original capability of opening and latching the canopy. The wing on this sailplane is very stout and had only slight damage where the outer panel joins the main.
This repair log will focus on the repair of the tail boom. My goal here was to repair the boom to full structural integrity while making the repair as invisible as possible. I needed a tapered splice to join the two pieces together. First though there were some breaks to the fin which had to be repaired from the inside. Breaks were repaired with glass cloth and epoxy, gel coat injuries with no glass fiber breaks were just CA’d.
My first thought was to use the tail boom as a mold to make a tapered splice but my first attempt/proof of concept even with liberal mold release wax the piece was very hard to remove even while the piece was still green. So I decided to make a cylindrical joiner (using a bottle as a mold), cut a wedge in it to accommodate the difference on diameters (boom is 42mm at the break). I made a prototype out of epoxy glass that was too big in diameter but was helpful in figuring out how it all would work. So the second was made using a bottle 42mm in diameter using 3 layers of 5.7 oz carbon fiber one layer of 8oz glass cloth tape 100mm long (joiner was 1.7mm thick – very light but of course I forgot to weigh it). The glass cloth was on the outside and would be the layer to be sanded smooth.

Photo 2 and 3 are of the joiner before and after sanding, still on the mold/bottle. The next step was to make a length-wise cut and insert into the fuse to determine how to modify the cylinder to make it into a tapered joiner. I forgot to take a picture of the joiner but you can see it in the fuse in #4. Photos 5-8 shows the alignment devices. Photo 9 shows right after the epoxy went off and the bracing removed, photo 10 after some sanding and filling. Next step priming and painting.