Mon Nov 02 2020

Canopy forward skin

So, I did some research last night and determined that basically nobody does anything to improve the bend around this canopy frame. They just flex it around and rivet it down. I'm not saying there is anything wrong with that approach...lot of RVs flying with the skin like that. I just think that it's likely...nay nearly guaranteed...that the tension from the skin will pull the canopy frame wider. I decided I'm going to try to make a partial bend at this location. First step was to check the bend in the triangular gusset arms to determine what bend radius to use. It looks like this gusset has a 1/8" radius on the outside surface, so the inside radius of the skin cannot be any larger (although slightly smaller would be OK).

In order to mark the bend location on the skin, I first placed a piece of tape on the flat side of the canopy frame where the top edge of the tape was conincident with the tangent line formed where the bend and the flat side meet. That is the bottom piece of tape here.

Then, I needed to transfer that edge location to the skin. So, I placed another piece of tape above it with the sticky side out so that when I clecoed the skin in place, this piece of tape would stick to the skin. I'm temporarily holding it in place with another narrow strip along it's top edge.

I also needed to determine the bend angle. Here at the forward end, the bend angle diminishes to essentially zero. At the aft bow, the bend angle is approximately 12.5 degrees.

My first attempt to transfer the bend location to the skin didn't work, but I tried a couple other approaches and was able to transfer that line to the underside of the skin.

That line I transferred is where the bend is completed and where the flat portion begins. so, I calculated the bend allowance for a 12.5 degree bend around a 1/8" radius (it's about .030) and marked the start of the bend. I also offset the start of the bend by 1/8" and marked a line which should be concident with the nose of the bending tool.

Speaking of the bending tool, since I can't use the finger brake for this bend, I routed a 1/8" radius onto the edge of a piece of scrap angle. I also quickly filed out any irregularities left by the router.

OK, Bend tool clamped in place.

It's hard to see here, but that bend is too far outboard. It definitely didn't come out correctly. Hrmpf. Good thing I have sufficient material to try again.