First step in the process is getting jigs built - the plans include a template cut-out that worked well. I made it a little larger than the template and lined it with foam weatherstripping to help avoid scratches. Since the tanks will obviously hold fuel, all ribs and skins were completely cleaned of any ink or markings that might subsequently dissolve and contaminate the fuel. Skins and rib edges were roughened to form a better surface for the sealant to adhere to.
Both fuel cells were initially clecoed to ensure the parts fit well and to help strategize the order of final riveting.
|Test fitting the fit of the fuel cells - I placed the skins in the jigs first, |
and then placed the ribs in, followed by the backplate.
|Rivnuts installed on end rib. Note holes for fuel pick-up and return lines (both of \|
which need to be enlarged before inserting the fittings).
I used a fay-sealing approach. A thin layer of fuel sealant was placed on the rib edges and on the skin surface. Popsicle sticks were my primary tool for applying and spreading the sealant. I tried to keep the layers thin to maintain the overall tertiary structure. The ribs were carefully set and clecoed on top of one side of the skin in their final intended location. After one side of each rib was clecoed, the skin was folded over and the opposing side of the ribs was clecoed in place. The skins were then placed in the jigs and allowed to sit overnight to allow the sealant to partially set, after which the ribs and skin were riveted using the provided sealed rivets.
|Fay-sealing a rib - the rear of the rib (in the clamp) is not sealed until the backplate|
is attached. Note that I just used an excess square of aluminum as a disposable mixing
pad for the sealant.
|Clecoed skin, ribs and stringer were placed in the jigs overnight to partially|
set prior to riveting.
|A bent rivet stem worked great to spread a layer of selant around each rivet tail|
for additional protection against leaks
|Skin, stringers, and ribs of both tanks riveted. Note that the backplates are not |
attached at this point.
After riveting (and cleaning up the excess sealant) I test fit the tanks on the wings to ensure everything still lined up correctly. The fuel cap, fuel drain, and the fuel fittings were then installed (note that it might have been easier to install the fittings on the ribs before attaching to the skin). Holes in the fuel drain and skin needed to be enlarged to allow use of the longer (and larger diameter) rivets. Care was used when attaching the drain to ensure that any excess sealant would not prevent a clear path for contaminants to be drained. The fuel pick-up bracket was also installed at this time.
|Fuel cap outer ring is installed with rivets. The fuel cell insert is then sealed in place using |
|Fuel cap insert is attached using only fuel sealant. A weight (titanium bucking bar) |
was used to keep the insert in place while the sealant set.
|After the sealant is allowed to set for a couple days, set, the backplate is riveted on while the |
cell is clecoed in position on the wing spar.
|Excess sealant was squeezed out of the backplate and resulted in the fuel cell sticking to the |
wing spar. It took a lot of work to pry the fuel cell off the spar.
|A thin layer of plastic (strips of a garbage bag) were used on the other wing |
to keep the cells from sticking to the spar while the backplate set in position.
The fuel sender was then attached to its support plate and the plate was bolted to the cells. Final step was to check for leaks (and fix any that did appear). I initially just tried to attach a balloon to one of the fuel fittings, but this did not work well. I therefore used some left-over components for the pitot/static tubing to attach a balloon to the overflow tubing. AN caps were used on the other fuel fittings to seal them. This method ended up working very well. The balloon is used to provide slight positive pressure in the tank so that leaks can be identified using soapy water - I found that even though I had a couple small leaks, the balloon still stayed inflated - so a balloon alone is not enough to verify a lack of leaks. After completion, the tanks were set aside until final installation on the wing.
|Verifying the fuel sender works prior to final installation.|
|One of two leaks I found - this one is from the fuel drain valve itself. |
The other leak was around a fuel fitting that was rectified using another
layer of sealant. I did not find any rivets that leaked.