AJ DeMarzos bottom skin repair
This weekend, I started to replace a torn sheet metal panel on the JT Coupe. The reason I bring this up is because it's the panel that extends from the back of the step to the cone of the fuse and appears to have a factory bend in it. A while back, I learned about this piece of metal and have seen the question asked elsewhere, probably the Swap Page. When I originally called Univair about it, no data existed which I thought strange and scary. I decided to drill it off since it needed drillin' off anyways. When it was finally removed, I found the curved piece of sheet metal, that I was positive was made in a die, was actually flat.
Either I didn't have enough foresight to take a before pic or I thought I did but didn't. This pic is after the panel was removed. Removal was quite straightforward. With a #40 drill bit the head of the rivet is pierced just below the base and the head is popped off with a chisel, or if you're a good sheet metal man, a swing of the bit. When all the heads are removed the part comes loose. The remainder of the rivet is supposed to be knocked out gently with the punch but I usually drill them out. Downside is that you could enlarge the hole, or worse.
In the next pic you'll see the removed part sitting directly on top of a piece of sheet metal on the table. Notice the weights to keep it flat as it did have some bow in there from 1946 and it was torn. First step is to copy all the holes with a #40 drill bit, the one used for 3/32 rivets and "cleco" (the silver sticks that are holding the sheets together) as I went along. You'll see them along the perimeter. I did some sequence when drilling so that the metal spread evenly as I worked, as it does move as you drill. These are preliminary holes and will be matched, sized correctly, then cleaned up.
This next picture shows the two pieces next to each other on the floor. The new piece while still raw looks pretty much the same, huh? After it's fitted, I'll finish it with files and sandpaper.
This one shows the part cleco'd up to the airframe for the initial fit, and by no means am I ready to put it on permanently. Must have the holes matched, be removed, holes cleaned, metal edge finished, alodyned, primed, refitted then riveted. For the observant folks, you'll note that the right gear is off and there's an orange jack under the spar. The coupe is on the trailer. Believe it or not, the jack, along with the fact that the big belly panel is missing, disallows full attachment of the part due to the airframe flex. Holes don't fully line up all the way around. Pretty cool, huh? As J said in his own post, I'll bet I'll need to use a few Cherry Max Structural Rivets in the process.
The belly panel was made in the same way, only there were about 180 holes to drill, match, cleco, clean and rivet. Obviously I'll need to finish the gear, take it off the trainer and go from there before I want to attach any of the metal. By no means did I post this to show my talents, I'm not that good. I thought that it may be interesting to a number of folks who didn't know what it's all about and show there's really nothing to it except time and patience. If you would like to see more, voice your thoughts as I'm sure there are a few others who would love to share this same type of experience. And yes, I'm working under the supervision of my A&P who has certified that I meet the requirements to take the three written tests to become a licensed mechanic.