Before I started fitting my Diehl wing skins, I went over the instructions many times as well as looked at his video. My concern was always the sealing the top of the wing tanks when the top wing skin goes on.
Well, you guessed it, the wing tanks would not hold light air pressure. ( test method, balloon on the fuel out let, cap on, air pressure in the breather, and inflate the balloon) After much head scratching and lost sleep and dreams of cutting holes in the tank, I did the following, without cutting holes in the tank, and it worked. ( At least they will hold air pressure now, fuel test soon) Note, my tanks start just outward of the WAF. and finish at the 3rd rib, and 11inches behind the main spar. I resealed all inside top sides of the tank, even if they were not leaking. My tanks have two baffles each, that sealed at the top corners, and cut out to allow fuel past the front and rear corners. Method With the wing upside down, fuel cap off and fuel out let and fuel drains removed, We will start with sealing the 3rd rib, or outboard end first, Place some padding on the workshop floor to sit the wing tip on, raise the inboard end of the wing to 45 dec. or more and support. Have a look in the fuel filler hole with a small mirror, to see if you are able to find the top edge ( which is now the bottom edge because the wing is inverted) Note: As my wing is not painted as yet, I could shine a light on the outside of the tank, and this would allow me to see in through the filler, drain, or fuel outlet holes to light the inside of the tank.) I used a 60cc syringe and 1/4" I/D plastic tubing, I mixed some Vinyl Ester resin with Cotton flox, and mixed till it was runny enough to pour into the syringe, I tilted the wing to one side and injected the flox into one corner, about 50cc. (Clean out the syringe with rag and wipe the plunger after each use first before continuing or you will need a new syringe every time you put resin in it. also a small amount of Vaseline on the plunger rubber.) Now tilt the wing and allow the flox to run to the opposite corner. you can place you finger in the filler or use the small mirror and wire to check the flox as reached the other corner. Now support the wing back to a level position ,to allow the flox to sit and dry, the wing needs to stay at a steep angle to allow the flox to dry and make a nice 45 Dec. finger fillet. That's the easy one. Now the fuel out let end. Reverse the wing position so the out let end is now at the bottom. this time you will need a plastic tube that will fit into the fuel outlet or into the fuel drain hole. ( 1/4" I'D) ??? Now do the same as you did for the other end. The long sides of the tank are a bit more of a problem. Stand the wing safely on the leading edge and lean the wing to allow the top of the main spar edge to be done next. ( lean the wing over again about 45 dec.. with the bottom facing up. and lift at the tip end to allow the flox to run backwards to get into the closest corner first. Sealing the top edge of main spar side of the tank. This will depend on you tank design, number and type of baffles. My baffles were cut to allow fuel to get past the front and rear lower corners of the baffle, but not at the top front and rear corners ( Wish I had it done now) I used a piece of welding wire and entered the fuel outlet to measure the distance to the first baffle, then allowed about 4 inches more to allow the plastic tube to enter and fall into the 2nd chamber I wanted to seal. ( I used the wire inside the tube, to keep it straight to reach the 1st baffle) I did the 1st & 2nd chambers at the same time. First I injected about 60cc of flox into the 1st chamber, then injected the same amount of flox into the 2nd chamber past the baffle, through the cut away corner of the baffle. I picked up the tip to ensure the flox flowed back to the closest corner, then picked up the inboard end and lifted it high enough to allow the flox to run along the inside edge to the next corner. Then packed the wing so the spar is level and the flox will now stay in the same position to dry. The 3rd chamber, I had the reverse the wing and inject the flox into the filler hole and run it back the baffle. The aft or rear edge of the tank, this was were my tanks were leaking the worst. I had to find a way to sit the wing or support the wing on it's trailing edge with out damage. I ran flox in through the outlet , and between the baffles as I did in the last paragraph. After it dried, I used a hole saw and cut a hole in the rib BEHIND the tank,I used a smaller hole saw and a arrow shaft and cut a hole in the next rib as well, this allowed me to see the full length of the back outside wall of the fuel tank. As this was the main area of the leak , I wanted to run some flox along the out side edge of the top skin and rear wall .(as well as inside the tank.) I use the a piece of dowel long enough to reach through the inspection holes to the very far end of the tank. I taped a small plastic cup to the dowel as a pouring device, I mixed up the Flox as before and poured it along the entire edge of the tank, this was the easiest part, as you can see what you are doing. ( you may have to left the ends of the wing again to get the flox along the entire length) I made a nice finger fillet along the rear edge of the tank, left the wing supported in that position until dry. It now hold air pressure. That's how I did it, you may have some improvements, but it worked for me, and I did not have to cut any holes in the tanks, thus no repairs to the outside finish of the wing skin. My 2 cents worth. Phil Matheson mathe...@dodo.com.au Australia 61 3 58833588 See our VW Engines and home built Parts and Kits at: http://www.vw-engines.com/ www.homebuilt-aviation.com
