Drilled Fuel Caps and Drains

Time: 4 Hours

Today I took care of some office items and played 2 hours of drop-in hockey at the local ice rink. I used to play a lot but had taken a few years off since my divorce. It feels really good to get back out on the ice and realize how old I am while playing with much younger and faster players. It was fun nonetheless and I’m hoping to get in the ice at least twice a week if not more. When I got home I jumped in the Hangar to carry the momentum I had from this weekend. First up is to mark and drill the fuel caps. I decided to go with upgraded lockable caps just cause they look much better and the stock ones have a history of being difficult to open. The ones I relieved are from Newton Equipment and are great looking and operate very smoothly.

I drew a line on the face of the cap flange that marked center so I had a reference point and clamped them to the skin as they were centered.

Once happy with the placement I secured them with vise-grip’s for match drilling.

The next step is to countersink the flange so that it could accept the dimples from the tank skin.

20140127-174304.jpgI got three done and my #40 countersink broke the pitot off, so a tool order is in order.

So I just moved on to the fuel drains. They come already drilled and countersunk, you just need to align it up with the hole in the skin and match drill it. I drew a center line on the skin and lined up the top and bottom holes. With everything looking good I clamped it down and drilled the holes. I placed a clecko in each hole as I drilled to help hold everything in position.

One other task I wanted to start today was the fuel tank trap doors. There are holes at the lower aft end of the tank ribs that are approximately 1.5″. These allow fuel to flow between the ribs and as the fuel moves. When doing acrobatics such as a knife edge (the plane flys with one wing pointing towards the sky and the other towards the ground) fuel on the lower wing try’s to move to the outboard of the tank. This isn’t good as the fuel pickup is at the inboard of the tank. So to help with this problem you fabricate a check valve of sorts called a trap door. The idea is to allow fuel to flow freely towards the fuel pickup and not the opposite. The trap door is simply a square piece of aluminum on a hinge that swings open as fuel enters the pickup area and covers the hole as fuel try’s to escape. I got the parts cut and shaped and will rivet them when I’m back in the Hangar on Friday.

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