Saturday, January 30, 2010

Battery Cut-Outs and Spar Installation

I again used a dremel cutter to remove foam for the two battery locations. The 1050 mAh battery location only extended 1/2 way through the center wing section. The 2150 / 2200 mAh battery location, on the other hand, requires a full depth removal of foam. I'll have to create a "floor" for the battery compartment with lite-ply or 1/4" foam. The dremel works, but it is messy and time consuming. I think I'll be building or obtaining a small hot wire cutter to make future foam cuts.


After cutting the battery compartment holes it was very obvious the wing needed some sort of wing spar. I was hoping the prototype wouldn't need them, but after the cuts the wing had very low flexural rigidity. I chose to use some 1/8" x 1/2" scrap to fashion spars rather than carbon. I'll save the expensive carbon for the real high speed machine. 

I used my soldering iron to cut the spar channels rather than the dremel. This worked, but the slots were a little too wide. I would have preferred tight-fitting channels. To fill the gap, rather than heavy epoxy or hot-glue I used white Gorilla Glue. I soaked the spars in water, wiped the excess off with a towel, then set them in the channels. I tried three techniques to apply the glue, one for each spar section:
  1. Apply gorilla glue to each side of the spar, then insert in the channel
  2. Place spar in channel, squirt glue on each side of spar
  3. Squirt glue into channel first, then place spar.
After the glue is cured it should be obvious which technique is best and will be used for future aircraft.

Once the spars were in place I put a stripe of "extreme" 3M packing tape over the top, to keep the Gorilla glue in place and to add additional strength.


  1. Did it foam all over, or did the tape keep the glue in place?

  2. The tape kept the glue in place. It worked pretty well. I could have actually added a little more Gorilla glue to have the foam completely fill the cut cavity. Next time I'll use a smaller tip on the soldering iron.

  3. You should borrow my hot wire cutter for the battery box etc.