Skybolt Fuel System

Page Index
-Main Fuel Tank

This page was updated on 03/04/2010
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Fuel Tank Installation
7/5/06- I hung my fuel tank from some clothesline to get an idea of how it fits. It is a very tight fit between the tubing that goes from 0-0 to 30 so right now the rear of the tank is 1 degree higher than the front. I would raise the front a bit, but it might not clear the front cabanes so I'm going to install the cabanes before finishing the tank installation.
7/5/06- To install the tank mount bushings, drilled 1/4" holes spaced 2" apart in a 2x4 and bolted the bushings to it.
7/5/06- Then I clamped the 2x4 in the proper position on the longeron.
7/5/06- Finally, I tack welded the bushings in place.
8/1/06- The tank just doesn't fit properly because the interior tubes that mount from 0-0 to 0-24 are located a bit too far inboard. I'm going to have to cut the 2 tubes out and re-weld them once the fuel tank is installed.
9/1/08- Here are the parts for 1 of 2 of my fuel valves. The handles came off a Stearman.
9/20/08- The fuel valve linkages are done. The top valve is for the upper wing tank, the bottom valve for the main tank. The top tank drains into the main tank.
10/22/08- After practice building 3 smoke tanks (the last one was a keeper), it's time to build the fuel tank. The design I'm using has an upper and lower compartment with a flop tube in the lower compartment for inverted flight. The tank is built in 2 sections. In this picture, I've bent the lower corners of the upper compartment. Next, I have to bolt the 4 formers together using the threaded rod.
10/23/08- I evenly spaced and bolted together the 4 formers, then bent the aluminum around the formers using cinch straps. The 1x2's under the straps are needed to make the aluminum lie flat against the straight surfaces.
10/25/08- After letting the aluminum take a 'set' overnight, I unbolted 3 of the formers, placing them evenly inside the aluminum tank wrapper. If you don't take the bolts out of the formers, you will never get the formers out of the wrapper without damaging it. The loose formers can easily be tapped askew and removed.
10/25/08- Here is a top view of the top compartment wrapper. Notice that I left the protective film in place while clamping and welding.
10/26/08- After popping the formers out of the tank wrapper, I trimmed .050" all the way around one former and 3/8" around a second former. The larger former is used to form the end panel around while the smaller former is used as the clamping plate. In this picture bent the bottom flange on my break and just started bending the top and side flanges with my mallet. I then took the panel out of the formers and used my shrinker to shrink the top flange. Just don't shrink it too much or it will really deform the panel.
10/26/08- I had to cut pie shaped pieces from the upper corners to make the metal lie down around the sharp radius.
11/2/08- I bent the bottom sump wrapper on my brake and then formed the end panels over forming blocks.
11/2/08- Once the upper wrapper was tack welded and the inside formers removed, the wrapper lost some of its shape. I still needed to install the baffles and end panels so I cut 2 female formers to hold the wrapper's shape.
11/2/08- The outside formers are simply clamped together using 2 cinch straps. The baffles are not riveted in place yet, just checking for fit.
11/2/08- The outside formers also allowed me to insert shims to get a perfect seam along the end panels for welding. I leave the protective plastic on until I absolutely have to remove it.
11/20/08- Here I've cut the vent holes in the tank and bent the vent and inverted vent lines and welded them to their 1/8" NPT bungs.
11/20/08- You can see the vent tubes sticking out of the bottom of the upper compartment. I have 4 holes in the front panel. They are for the fuel transfer line from the wing tank (1/4"), vent line (1/8", inverted vent line (1/8"), fuel return line (1/8"). If I don't need the fuel return line, I'll just put a plug in it.
11/20/08- An inside view of the baffles and the vent lines from the rear of the tank. There is a #40 hole drilled at the top of the vent lines for an anti-siphon.
11/20/08- The inside of the upper compartment and the rear panel with the fuel sender hole cut out.
11/20/08- Instead of pop rivets, I used 3/16" x 5/16" structural rivets to make sure that the baffles never come loose. (AN 426AD-6-5)
11/20/08- I used the driven rivets on the top and bottom and 3/16" pop rivets on the front and rear panels. Here, you can see the bottom sump being fitted to the top.
11/20/08- The front panel of the bottom sump is notched so that the standpipe and the vent tubes clear the flange on the panel. Notice that unlike the Mackenzie plans, I placed my standpipe and flop tube mount at the front of the tank rather than the rear. I made the change because I could envision that at a very high angle of attack, like anything between 60 and 90 deg with 1/2 tank of fuel, would cause the fuel in the sump to run back out the standpipe and uncover the flop tube pickup at the front of the tank.
11/20/08- Here is the rear view of the 2 compartments not yet welded together.
11/22/08- This is the bottom of the upper tank compartment. You can see the standpipe, inverted vent, and upright vent. Notice that I used 3/16 x 5/32 rivets to fasten the baffles to the bottom. There is also a patch plate to the left to cover my first standpipe hole that would not allow the standpipe to clear the bottom side of the sump. If you look closely, you can see the #30 pilot holes drilled around the perimeter to rivet the bottom sump.
11/22/08- After back drilling down through the sump flanges, it is now clecoed in place. I used 1/8" pop rivets spaced every 2". If I had made the sump flange 1/2" wide instead of 1/4" as called out in the plans, I could have used 3/16" rivets for extra strength. But the 1/8" rivets pulled it all together nicely anyway.
11/22/08- The front of the tank is tack welded. I still used my cinch strap and shim blocks to bring the sides up tight.
11/22/08- The rear of the tank is tack welded. I used 3/16" pop rivets to fasten the baffles to the rear panel just like the front.
11/24/08- Finish welding the tank seams. The recycle bin was perfect for holding the tank in a perfect position.
1/2/09- The rear view of the tank shows the fuel level sender. The jigs on top are for setting the tank at the proper height.
1/2/09- I bent and welded up the strap brackets out of some scrap 4130 and riveted them to the stainless .035 x 1" straps. You need 4' for each strap.
1/2/09- Since the tank was now completed, I reinstalled the 0-24 tubes to give me about 3/8" clearance between the straps and the tubes.
1/2/09- The tank height can be adjusted about 3/8" both ways.
1/2/09- At the plans height, the top sheet metal will clear the tank by about 1/4" at the firewall. That is my firewall template clamped in place.