WING TIPS Page 2
I joined the two halves with a coat of Bondo Glass. This is a polyester resin based material with glass fibers mixed in. Over that I put one layer of 3" fiberglass tape with resin brushed on. When the resin cured I removed the aluminum tape. I marked the material that needs to be removed to align the trailing edge with the trailing edge of the aileron with masking tape (at right above). I removed the material and sanded the tip back to round (no photo).
The right tip is done for now. Time to start on the left. First thing to do is cut it in half. This time I decided to make the honeycomb insert in one piece.
Above left is a photo of the left upper half of the wing tip ready for resin lay-up. Above right is the upper tip half in the vacuum bag.
After the resin set up or hardened if you prefer, I pulled the tip out of the bag. Do wonder why I didn't put weights on this side on a flat table? Above right shows a photo of what I did instead. I taped a piece of plywood to the outside of the tip. I let the vacuum bag do the work of the weights.
I cleco'd the tip to the wing like I did on the other tip. The photos above show two views of the left upper tip half cleco'd to the wing.
I added the lower half and taped the two halves together with aluminum tape.
Here is a picture of the Bondo Glass. As the can says, this is polyester resin with short fiberglass strands added. At right is a picture of the inside of the tips bonded back together.
Above left is a different view of the inside of the finished tip. At right I have started to enlarge the fastener holes to number 30. They will end up at number #27 for 6-32 screws eventually.
Here is one of the aluminum strips used to re-enforce the nutplate attach area of the tip. I decided to use miniature nutplates on the tip. This was a mistake. As you can see from the photo above right the rivets are very close to the screw holes.
Ultimately, I decided to switch to normal pattern floating nutplates (MS21059L06). These made much more sense in this application.
packed. Why do manufacturers use polyester resin then? The answer is that it is cheaper and easier to use. The % of hardener is not critical so you don't have to be a rocket scientist to use it. The "Cheap and easy" theory has its rewards but also has its problems. These problems can be overcome with some effort.
I cut the re-enforcements along the tape line on the bandsaw. I did not install them yet. That will come later when all of the bodywork is completed on the tips. Above right is a tub of fiberglass bubbles sometimes referred to as micro-balloons. These are used to thicken resin while not adding weight. Actually they reduce the weight of resin because they weigh nothing.
I still had low spots on the tips even after my efforts to stiffen them up. I mixed some polyester resin with glass bubbles, added hardener and filled a low spot on one of the tips (above left). Bondo would probably have done just as well but I wanted to try this (Education!). Above right is a photo of a gap on the right tip at the leading edge. It will need filler to make it look right.