WING TIPS Page 2

 

Joining the two halves Area to be trimmed to right of masking tape

 

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 left tip split in two halves Honeycomb work progressing

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.

Lay-up sandwich ready for resin Sandwich in the bag

 

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.

 

Completed lay-up after resin cured Plywood used to take out warp

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. 

 

The lower half added Aluminum tape

I added the lower half and taped the two halves together with aluminum tape.

Bondo Glass Two halves joined

 

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.

 

Another view inside the finished tip Upping the holes to number 30

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. 

Nutplate re-enforcements Rivets too close to screw countersink area

 

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.

 

MS21059L06 floating nutplate Strip installed with floatin nutplates

Ultimately, I decided to switch to normal pattern floating nutplates (MS21059L06).  These made much more sense in this application.

To keep the tips from collapsing while I worked on the nutplate strip installation I used the internal contour board.  My fear was that if I didn't try to help the tips keep their shape that I could have another problem with warping.  If I ever do another project like this I will certainly wait until I am ready for installation before the wing tips are received.  That goes for any other fiberglass as well.  Parts made with polyester resin do not hold their shape over long periods without help.  That is what why my wingtips were distorted when they came out of the box, they were not supported for shipping and I did not open the box for nearly a year after they were

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. 

 

OK. enough about the theory of resin.  I decided that while I was mixing resin and using honeycomb I would make the trailing edge stiffeners from honeycomb.  I made a honeycomb "plate" by cutting 4 oz. cloth and laminating it to a waxed aluminum sheet.  I put the honeycomb over the cloth  and laminated another piece of 4 oz. fiberglass cloth over the top of the honeycomb.  I put another waxed aluminum sheet over the whole sandwich and weighted it down with some tubs filled with water.  I forgot to take any photos of the process.  In the photo at right I am using the aluminum trailing edge as a pattern to mark the honeycomb to be trimmed.

 

Cutting the honeycomb on the bandsaw Glass bubbles

 

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.

 

Filling a low spot in the tip Leading edge needs filling

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.