This is the start of the construction of my seat bottom.  I used 1/2" styrofoam with 2 layers of 8 oz fiberglass on each side.  On the edges of the seat I used a dremel to cut out the foam and floxed the edges all around.  I have also added two I beams 1/2" foam and fiberglass to the bottom of the seat running front to back.

The seat is supported on the main and aft spars by 5/8" spruce blocks. I did an engineering calc. to check this out; the weakest point is actually the 5/8" spruce and not the seat itself. I still have a pretty good safety factor in the design.  The seat back is also 1/2" styrofoam with 1 layer of fiberglass each side.  The seat back is attached to the rear spar with a piano hinge so it will fold forward.

Initial design load testing of seat with 40-pound son Sean.  Inital test was passed and more testing has since been conducted.

I added a forward lip at the main spar to give the seat a better appearance. The lip is two layers of fiberglass.  Then I painted the seat white.

Update 2006, The seat bottom started to demalinate after about 30 hours of flight testing.  For a quick fix I relaced it with a sheet metal pan across the two spars.