Priming the Fuselage

I've decided to Alodine and prime the fuselage before doing more installation work.  For primer I'll use Poly Fiber White Epoxy Primer.  I plan to shoot it with Poly Fiber's Poly-Tone for the top coats.

Repairs to Skin Panel P/N 0412116 (fig. 23-31)

 The center skin on the top of the rear fuselage (fig. 23-31) had 2 wrinkles, one on each side, which hammered out nicely.  Rather than replace the skin it seemed better to patch them while the other skin was removed.  I am trying to make a good flying plane not a show plane.  This is a slow process as is.

Along with these 2 patches I reinforced the stiffener on this skin and the stiffeners on the bottom skin below the one removed.  The repair manual has a repair using 0.050" x 1/2" x 1/2" aluminum angle for a stiffener.  This was done for the flanges which were slightly bent by the tent collapse.

 The first task was to drill out the rivets along one of the stiffeners.  I didn't want to unrivet too much at one time. The rivets on the formers were 1/8" and the rivets along the flanges were 3/32".

 The first step was to draw a visible center line on the flange for locating through the rivet holes.  A rivet hole was drilled at one end and the angle clecoed in place to locate the hole at the other end. Next 2 intermediate holes were marked and drilled.  The effort was to make the center line follow the rivet holes as close as possible.

 With Clecos about every 6 inches the rest of the holes were center punched and drilled.

Because the skin was still off it was easy to rivet the stiffener in place and then do the next one.

 With the stiffeners all done patches were made for the skin.  The damage area was drawn on the skin with a felt marker and then drawn on a piece of paper to lay out each patch. The damaged area was smaller on the left side.  The red lines are about where the curve start to help me form the bend in the correct place.

 The patch was cut out and all the holes punched.

To form the bend I used a piece of a heavy 3" card board tube.  A short piece of 3" schedule 40 PVC pipe would work well also.  The patch was formed around the tube by hand until it fit snug to the fuselage skin.

The patches are on the inside of the skin so holes were drilled from inside the fuselage through the skin.  As each hole was drilled a Cleco was installed to help keep the patch from moving slightly.

 Once each patch was ready to install it was primed with zinc chromate primer.

The patches were riveted in place before the aft shin was reinstalled.

 The seams on the old skin were lightly cleaned and all the joint areas primed with zinc chromate.

Ah, the fun part, my 6'-5" frame squeezed into the tail, ear plugs in place and bucking bar in hand.

Make sure your rivet gun operator is well trained before you crawl in there.  You can't see what they are doing until it's all done.

One shiny new skin in a sea of old aluminum.  Fortunately there was very little corrosion in the joints so once painted this should be good for many years more.

Forming the New Skin Panel (fig. 23-32)

For the stiffener flanges on the sides I thought I would make my own break.  It was a good idea but I could not make the bend well on a sample more than about 2 feet long.  Instead I went over to my friends shop, John Gaertner at Blue Swallow Aircraft, and used his break.  A 40 mile drive and ten work minutes to do what I wasted hours trying to do at home.  I did bend a shoe on John's break to assure the the radius would not be too small.

 I had no easy solution for the large curves rolled in the corners.  I decided I needed to form them around as large a pipe as I could to prevent leaving bend marks in the aluminum.  I tried 8" PVC pipe but it was too large.
I worked out where the bend basically started and the center of each bend on the end templates.  Then I transferred the marks to the blank panel.  This gave me references to make the bends since the radius tapers smaller from front to back.

 I like to find non-traditional uses for tools.  This may be one of my best yet.  I'm using the ShopSmith to form sheet aluminum.  I don't suppose they planned for that, but here are these nice stiff steel tubes which support the mechanism.  I was looking at the tubes thinking those are about the size of the 3 tubes used in a roller, why not use them.
My dad made a box below the tubes which catches saw dust, and tools I'm to lazy to put away.  The mechanism is opened, like when you use it as a drill press.  I slipped the piece of particle board, used while duplicating the rivet holes, under the tubes and put blocks of wood in the box to hold it snug to the tubes.

 I wedged the strip of wood under the end of the metal to help lift it.  I found it worked better with another strip of wood inside and the 2 clamped together.  I just forgot to take pictures with it clamped on.
You lift the strip of wood and control where the tubes are making the bend using the corner marks

 I found I had to wedge pieces of wood under the bent aluminum to get the radus tight enough.

Make a small bend, move slightly, and repeat.  With a little care to not over bend at any one spot, and regularly taking it out to check it against the end templates you can slowly work it to create a good fit without any evidence it was bent around the tubes.

Form one side then reverse it and form the other side.  You end up with a very nice piece ready to rivet in place.

Making the New Shin Panel (fig.23-32 P/N 0412117)

My computer died and one thing after another it's a year and a half later and I'm finally getting caught up on postings.

 The flattened panel was used to cut a new blank from 0.032" 2024-T3 aluminum.  I cut it with the grain aligned like on the original panel from a 4 foot wide sheet.

 The flattened panel was clamped to the new blank with 2x4s to hold it flat to the sheet of particle board under the new skin.  I wanted the 2 pieces a  flat as possible to prevent misalignment of the holes.

Using the Whitney punch with the nib ground off a 1/8" punch I started duplicating the holes.  Even though everything is clamped and can't move I like installing Cleco clamps as I go to assure nothing moves.

 The nut-plate holes were then duplicated at the aft end.

 The stiffener flange on each side is 1/2" tall and the bend for it starts 3/8" from the centerline of the rivet holes.

 To punch the holes along the side the flange was cut off on the band saw.  With the ends held in place with Cleco clamps each side was again clamped to the particle board and the rivet holes duplicated.  The Cleco's helped take out any wrinkling from the straightened damage.

 The next thing was to layout the cut lines.  Graphite lead should not be used to draw on aluminum so I used masking tape to draw the cut lines.
Even if you use long smooth edge snips to trim the curved cuts it's hard not to get small wrinkles form the snips.
One way to prevent this is to make the cuts with a band saw, or table saw for straight cuts and then file them smooth.

Just make sure you mask the back side to prevent scratching it on aluminum chips

 The finished blank ready to form.

 I accidentally damaged my blank and had to make another one.  This time I cut the long straight side cuts with a Plexiglas cutter and a straight edge clamped to the aluminum and the piece of particle board.  This is a trick the aluminum siding guys use.  The cutter has a hooked blade which scratches the aluminum and then you bend and break it along the scratch.  The 0.032" aluminum is as thick as this will work with and even then it takes several passes to get the scratch deep enough to fold and break.  If the scratch is deep enough to make a bump on the back side it will bend and break.  With 0.016" aluminum 2 passes is usually enough.  It works even easier with dead soft aluminum.