Wednesday, February 22, 2012

Get Smart use to say: "Missed it by that much."

When you make mistakes, you just find solutions. As I build a piece or build a part, I always try to anticipate how this step is going to effect things down the road. Sometimes you understand the cause and effect, and sometimes you don't. I built my fuel tank about a year ago.  There has been some modifications to the tank plans and I have 3 plan revisions to work from. The original tank was only 9.5 gallons, but that wasn't large enough for some builders, so Dave Thatcher created a 10.5 gallon drawing for someone and I got a copy of this. Then when the Europe equivalent of the FAA didn't like how Dave had installed his tank, Dave modified the tank and how it was installed/mounted. At about the same time, Dave developed the floor mounted rudder pedals; again in response to a Europe request. The fuel tank dimensions changed with these modifications, but remained a 10.5 gallon tank. I had bought the hanging rudder pedals and after reviewing the floor mounted version, decided to stick with the hanging pedals. My plan was to use version 1 of the 10.5 gallon tank but use the new mounting method which involved side to side straps that would cradle the tank from underneather. The tank cover would be sandwiched between 2 gaskets at the fuel filler flange. Everything was going to plan until I rasied the tank top to be level with the flanges where the tank cover would be attached. That's when "I missed it by that much." I found my tank corners sticking out beyond edge of the fuselage.

click on image to enlarge

So, in a panic I called Dave and then a local friend, Steve Bennett who stopped by to see what could be done. Between the conversations I had with these two, a "plan B" was developed. I would simply buy longer bolts to lower the tank and I would create a strap to go over the top of the tank to hold it in place. I would then create a fuel access door for the tank cover. This seems to be working out and no snags have presented themselves.

First, I came up with a paper pattern for the top strap that I liked and transfered it to some scrap .020 aluminum. I cut out the perimeter using my band saw. Then I clamped the piece to a scrap board, drilled a hole in the interior and cut the circle out using a jig saw. The .020 aluminum is a little flimsy so I used the board to help with filing the edges.

Once the piece was cut and filed, I mark the locations where I wanted bends and proceeded to make the bends one at a time. I would trial fit the piece after every bend and mark the next bend location. The bottom photo is the final product. I drilled & tapped two holes on each side in the upper longeron for 8-32 screws. To help spread the load, I created two 1/16th inch thick plates to go on top of the strap on each side (as shown in the above photo).

This photo shows the top strap installed. I plan to install aluminum tubing over the 4 bolts that hold the lower straps on so that the nuts can be tighten. The tubes would serve as spacers and this would essentially trap the tank in place.

I'm thinking about creating a cup of some sort to go under the fuel cap flange to catch any drops of fuel so they don't spill inside the cockpit. Look for an update describing what I came up with.  I have an automotive gas cap door on order as I felt this might make a more "professional" installation than me making one myself.

In concert with the installation of the tank, comes the installation of the hanging rudder pedals, but that's the topic for my next post.

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