Rough and Ready Aerospace: Step 6.2 Fuel tank assembly

To begin the assembly of the fuel tanks the first thing to do is get the ribs in place. The area under each rib is thoroughly cleaned with a Scotch Brite pad and then with MEK. The edges of the ribs get the same treatment. The is where the Rick Galati fay sealing method begins. Fay sealing just means that the two surfaces to be joined are both 'buttered' up before assembly such that the sealant is trapped in place by the fasteners (rivets). What makes the Galati method different than that described in the build manual is that he does not immediately rivet the wet sealant. Instead, using the Galati method, one clecos the parts together and allows the sealant to cure for some time before riveting. The cure time is what makes this method more attractive as the final result is less messy. Trying to rivet the nose ribs is tough enough without having to do the rivet wrestle with wet sealant oozing everywhere.

Here Carol is putting the final touches on the stiffeners by covering the rivet tails with a blob of Pro Seal.

Each riveted hole in the tank is sealed in three ways. The rivet head to the wing skin outside surface is sealed before the rivet is driven by placing a blob of sealant in the dimple. The mating surfaces between the inside skin and the rib or stiffener is sealed when the pieces are brought together. And finally, the edges of each piece (again, rib or stiffener) are sealed by applying a fillet of sealer around the perimeter of the piece.

The ribs are first attached with cleco through the nose so the the rib can be placed without rubbing off the sealant by trying to slide the rib in place.

In the two photos that follow the process begins. The top and bottom of each rib has sealant as does the inside of the skin where they meet.

When the inside ribs have been fastened through the leading edge, the skin can be closed around the ribs using the wing fixture to hold the skin closed.

The rear most clecos are put in first in order to pull in the skin tight around the rib. This takes a bit a force as the skin's lifelong preference has been to do otherwise.

Once the rear most cleco is in place, all of the other holes along the rib will be aligned. The rest of each rib continues without much drama. Occasionally a hole may not line up enough to get the cleco in. A dental pick our other sharp tool will usually to the trick. At this point the dimpled holes really want to just snap into place.

In the photos below, the rib under this line of rivets has already been glued with Pro Seal using the Galati method. The the dimple is then lightly counter sunk to clean the dimple of semi-dried Pro Seal. This allows the rivet to be set at the correct height with the addition of Pro Seal under the head.

Next a dab of Pro Seal is applied to the dimple.

Then the rivet is set in place. The excess Pro Seal is pushed out at both the top and bottom, insuring a good seal. Then the rivet is driven normally.

After riveting the skin to the internal ribs there were a still few details I had to complete before putting on the end ribs.

In the photo above the "anti-hangup" bracket is installed across the access plate in the tank that has a flop tube fuel pickup. The idea here is that the flexible nature of the flop tube could somehow allow it to get hung up on the access plate, so this bracket is attached across its diameter. I curved the center of the bracket to give some additional rigidity to the structure.

Here is another anti hangup detail. The diagonal brace keeps the flop tube out of trouble on the other side of its bay. In the right wing, the standard fuel pickup tube is fabricated and attached to the access plate.

This is the bulkhead end of the flop tube just before installation. Note that the safety wire prevents the flop tube from unscrewing itself from the right angle bulkhead fitting. If this were to happen, it might be the pilot and passenger that were screwed.

Don't panic, the tail end of the safety wire was neatly trimmed and curled over before the flop tube was installed.

Fuel tank vent line.

This is inside showing the vent line connection to the inboard rib and the doubler plate at the leading edge. In this photo the tank is upside down. When this photo was taken, the inside edge fillet had not yet been completed. Note the difference in the fillet between the inboard rib at right and the other rib at left.

Capacitive fuel level sending plate is installed.

Finally the fuel tank attach flange is riveted in place.

By this point the dogs have had enough and, no doubt, so has my gentle reader. The little dog takes the big bed.

And Carol was heading out as well. But not before we had attached the rear baffle.

The next day we riveted the skin to the rear baffle. All that remained for the left tank was to Pro Seal in the shop heads on the rivets we just drove and pray that it doesn't leak.