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Wings

Inverted flight fuel tank mods

Today I decided to go back through the fuel tank plans to double check if I had missed anything. It seemed like I had everything covered except I couldn’t find any mention in the instructions on how the fuel lines need to be modified to allow for inverted flight. However, the drawings do have some info on them. After reviewing the drawings for a while to think things through, I decided on a plan of attack.

I didn’t have the piano hinge or 0.020″ Alclad for the trap door, so I sent an email off to the local supplier to get these for me. I did however, have some 0.025″ Alclad to make the anti-hang up brackets for the flop tubes. I marked out four 0.5″ strips and cut these using my band saw.

Alclad strips

I then marked a line on the inboard tank rib that was 1 1/16″ down from the forward tip. I marked the centre of the rib on this line initially, but it looked to be too close to the upper flange. I decided to make a second mark that was directly underneath the point of the nose rib, which was roughly evenly spaced from closest points of the upper and lower flanges.

Fuel hose rib hole mark

After drilling a #40 pilot hole, I used my Unibit to carefully drill the pilot hole out to 9/16″ size. This is how big the hole needs to be to fit the fuel line elbow fitting.

Fuel hose hole drilled out

I then clecoed the reinforcing angle in place and marked out the hole onto the angle. I then removed the angle from the rib and drilled out the hole to 9/16″ also.

Fuel hose mark angle

I then clecoed on the reinforcing plate and marked and drill out the hole again.

Doubler fuel hose mark

I then deburred the new holes and clecoed the rib, angle and plate together. Next I picked out the fuel line elbow fitting and checked it for fit. It was nice and snug.

Fuel line elbow fit

In order to figure out how high the anti-hang up bracket needed to be, I screwed the fuel sender plate onto the rib with a single crew and attached the flop tube to the fuel line elbow. I then measured how far the flop tube needed to be to remain clear of the screw. I figured 0.5″ would be plenty.

Flop tube height test

I then rounded and deburred two of my Alclad strips and bent them to shape so that they were the required height. I used my Sharpie pen to provide nice bends with no creases. I then drilled a #40 hole in each end of the strip and marked these holes on the tank rings.

Anti hang up mark

Next I drilled the tank ring and countersunk the side of the rib where the gasket will be seated. I also deburred the hole on the other side.

anti hang up hole counter

Finally, I riveted the anti-hang up brackets into position. I only have one flop tube but here are both ribs with the brackets riveted on.

anti hang riveted

Build time 2.5 hours

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About gstrack

Husband and father of 2. Control & Instrumentation Engineer. Flying nut. Gadget geek.

Discussion

One thought on “Inverted flight fuel tank mods

  1. Now, remove the fuel tank and transfer the marks on to the #2 rib, including the depth. The holes were cut in the #2 rib using a unibit. I made 1″ holes for the main fuel lines and 3/4″ holes for the fuel sight gauge lines.

    Posted by Caroline Hardin | January 24, 2013, 1:27 pm

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