The thrust duct

First step to the thrust duct was the plywood disk. 2 lengths of a sheet were cut to 330mm width and placed good face down. A single layer of 6oz cloth was used to glue the halves together. Once dry I placed the ply in the pool for 2 days to help with bending.

One end of The ply was screwed to the plywood jig then bent around and the joint glued with 6oz cloth.

Next was the foam
Firstly I created the shape of the thrust duct foam on the computer and calculated exactly where to cut and join the 2 inch peices together to make the overall length required. In total it took 3 peices of 1200 x 2400 sheets. The sheets were cut to the correct angle and glued.

Once dry I needed to mark the 2 radius. To do this I used a 6m length of pvc pipe with 5 holes drilled into it. Hole 1 was for a screwdriver to go through so the pipe can pivot on the grass, hole 2-5 were the inside radius, outside radius, 9 inch taper mark and 1 inch mark for fiberglassing. A pencil was placed in the holes and the pvc pipe was dragged across the foam to make the markings.

Once marked I used a hand saw to cut out the foam. Next a 9 inch long taper was required so I used my trusty foam cutter which made it very easy work, it only needed a small amount of sanding after cutting.

Now the underneeth needed a layer of 6oz cloth....Well this wasn't fun. Newish to fiberglassing I coated the whole surface with epoxy first then tried to lay the cloth down. I found doing it this way made it very hard to pull the cloth tight as the glue is very grippy. Also I mixed the whole 1kg of epoxy at the same time so the glue hardened quicker. This left a badly wrinckled surface once dry. Next time I'll be laying the cloth down and applying glue over the cloth and mixing in only 200gms of epoxy at a time.

So sadly I had to spend 3 hours sanding the fibreglass down and reapply a 3oz layer.

Now I needed to make cuts into the foam so it will bend around the plywood disk. I chose to make a cut every inch which ment 190 cuts! I welded steel square onto the saw so it could only cut 1.75 inch deep.

Now this curved foam peice had to be bent around the ply disk. This was definently a 2 person job. Prior to gluing I practiced bending the foam several times to get the correct procedure. Once happy I applied glue to both surfaces and bent around the disk. I temporarily screws the foam in place until I could get the 2 sachet straps around. To stop them slipping I used multiple peices of blue tack which worked well. Once tight and in place clothes pegs were used to hold the trailing edge in place.
Once dry I needed to add foam fill in peices at the front. I cut the peices to the correct angle using the foam cutter, a total of 12 peices were made to fill in.

Now the front edge needed to be shaped to an airfoil. I made the shape out of coathanger wire and initially I was going to use it for a hot wire. As I found out coat hanger wire does not have much resistance so when I connected the wire to my hot wire cutter it blew up. So I used plan 2 which involved sanding the shape bit by bit using the coat hanger shape as a guide. This method took about 4 hours.

After shaping I glassed the inlet and the trailing edge. Thrust duct complete until it's installed on the hull.