Carrying on with the tank, next jobs were to
create a sump in the bottom which will take the fuel outlet and to install the filler tube. The sump was created by cutting a 6" diameter hole in a piece of 3/4" particle board, springing open the tank and then hammering. This seemed a little crude so I tried it on a scrap piece of the same sheet first and it worked well creating a smooth depression about 1/2" deep in the centre. So the exercise was repeated on the real thing with the same result. Then the tank was temporarily fastened into the fuselage to establish the location and angle for the filler tube 35 degrees from vertical and 4 inches from the front and right side of the tank seemed to work well so the tube was cut to the correct angle and used as a template to mark the hole to cut. A small cutting disk on the Dremel cut the hole reasonably accurately and the end of the pipe was cut into a turret shape to create four tabs which were bent over and match drilled to the top of the tank to support the tube ready for welding. Then it was a case of deburring and trimming the edges of the tank wrap. Next its just a case of mounting the fuel level sender and the tank outlet and the tank is ready for welding. I haven't tried to make the tank the maximum possible size but was interested to know what it should hold - but how to measure it before welding? Inspiration was at hand and I weighed the form block used to make the central baffle. I then weighed a square piece of the same wood. Using the ratio of the weights and the measured area of the square section gave me the cross sectional area of the tank - 1201 sq cm. Multiplying this by the length gives a volume of 106339 cc or 106 litres or 28 USG or 23.4 Imperial gallons. This will give me a duration of about 5 hours to empty with for example a Jabiru 3300 engine - that should do OK.
Carrying on with the tank, next jobs were to 
create a sump in the bottom which will take the fuel outlet and to install the filler tube. The sump was created by cutting a 6" diameter hole in a piece of 3/4" particle board, springing open the tank and then hammering. This seemed a little crude so I tried it on a scrap piece of the same sheet first and it worked well creating a smooth depression about 1/2" deep in the centre. So the exercise was repeated on the real thing with the same result. Then the tank was temporarily fastened into the fuselage to establish the location and angle for the filler tube 35 degrees from vertical and 4 inches from the front and right side of the tank seemed to work well so the tube was cut to the correct angle and used as a template to mark the hole to cut. A small cutting disk on the Dremel cut the hole reasonably accurately and the end of the pipe was cut into a turret shape to create four tabs which were bent over and match drilled to the top of the tank to support the tube ready for welding. Then it was a case of deburring and trimming the edges of the tank wrap. Next its just a case of mounting the fuel level sender and the tank outlet and the tank is ready for welding. I haven't tried to make the tank the maximum possible size but was interested to know what it should hold - but how to measure it before welding? Inspiration was at hand and I weighed the form block used to make the central baffle. I then weighed a square piece of the same wood. Using the ratio of the weights and the measured area of the square section gave me the cross sectional area of the tank - 1201 sq cm. Multiplying this by the length gives a volume of 106339 cc or 106 litres or 28 USG or 23.4 Imperial gallons. This will give me a duration of about 5 hours to empty with for example a Jabiru 3300 engine - that should do OK.