It was miserable weather today so I did a full days work on the plane and decided to tackle one of the jobs that seemed likely to be tricky - the fabrication of the fuel tank. First job was to cut out form blocks to shape the end panels of the tank and the centre baffle. First a paper template was made to fit into the space under the combing from the firewall back to the tank support cross member. The vertical dimension of the tank is determined by the need to get the pilot's feet onto the rudder pedals with good clearance - which needs about 12" from the floor to the bottom of the tank. Then the template was glued to one piece of particle board which was then bolted to a second. The two pieces were then cut to the template on the bandsaw. Next two blank end panels were cut from 0.050" thick 5052 alumium - each 1/2" bigger than the form block in each dimension. 5052 is a fairly soft material which can be successfully welded unlike some of the other aluminium alloys used in aircraft construction. Drill holes in the blanks were made at each of the the corners of the form block and at 1" centres along the curve of the shape and 
filets of material removed to allow the flanges to bend round the form block. The blanks were then thoroughly deburred. Then the first blank was bolted between the two form blocks and the flanges hammered down against the block. Once removed the top edge was folded to 45 degrees to create a relief in the shape of the top of the tank visible in the last picture to clear the engine mount bolts. The second blank was then shaped to form the opposite end of the tank.Then started the process of forming the skin of the tank. A flange was folded at right angles where the horizontal join in the skin will take place - visible in the third picture, using the bending brake. Then the curve of the tank was created using small bends every 1/2". Every few bends the skin was drilled and clecoed to the end panels to check fit and make sure that the position of each bend was correct. The third picture shows the tank with just the last two bends waiting completion. Once the final bends were made the final section of the skin was trimmed to fit in behind the flange created at the beginning. Next the top of the form blocks were trimmed to fit the final tank shape ( taking into account the impact of the 45 degree bend) and a third blank prepared and folded. This fits in the centre of the tank and is drilled with 7 off 3/4" holes three at the bottom and four 2" up. This piece forms a centre baffle to stop the fuel surging in the tank as the aircraft banks. A centre line was drawn on the flanges of the baffle and holes drilled in the skin around its centre line in the same position as the end plates. Then it was a question of manouevering the baffle into position centering the line through the holes and match drilling and using clecos to fasten it into position. Finally we have the world's largest bread bin.
