A

Airhead

Active Member
Not to start a new thread on canopy bending, because I have read through a lot of the posts regarding canopy frame persuation, but I have a more detailed question I have not found mentioned.

I just finished the roll bar install (some bending required). After mounting the canopy frame, my front and rear bows appear shaped OK (so far), but the side (square) tubes need additional curvature added (especially in the aft 1/3 of each) to match the fuselage.

My question is; what methods have others used successfully to make slight bends in this tube? I have this sneaking suspicion that because it is square it will have more of a tendency to buckle or crack than round tubes. Also, unlike reshaping the bows, where they can be pushed or pulled from the ends, it seems that the sides need to be bent individually.
 
Conduit Bender

I used a 3/4" conduit bender paddded with a lot of duct tape. I followed the directions and bent the side rails to the contour of the sides only to find out that the frame would no longer slide past the aft skin. I ended up having to remove some bend.
 
I used blocks of wood cut from a 2X4 which I screwed to the benchtop - one on each side of where I wanted the side tube bent, then a third block where I wanted to exert the bending force, screwed to the bench on the other side of the tube from the first two blocks (so that this third block wss between and on the opposite side of the tube to the other two). The take a large screw clamp, one side agaisnt the centre block, the other against the tube, tighten it until you have the bend that you desire.
Bill Brooks
Ottawa Canada
RV-6A finishing
 
Thanks guys for the quick responses. You have no idea the relief at getting some good advice when facing a tough challenges like the canopy (then again, you probably do since you've been through this). It looks like the three block method with pressure on the center block is the way to do this. How much over-bending and springback did you experience? Say as compared to the roll bar ,where I had to pull the bottom together almost 5 inches to achieve a 1/4inch permanent set.

Also I'm wondering if something like the conduit bender suggestion may be necessary for the last 4 to 6 inches or so, because it seems you run out of room for the aft bock, or looked at another way, the blocks will get so close together, the force required will increase tremendously.
 
You don't need that much....

pressure to achieve some movement, but the square tubing will take more than you might think. If you go thru my photos: http://picasaweb.google.com/bakerfamilyenator/SlidingCanopyFrameBending# and look at the captions, you'll see that I did the bending of the last few inches with 2x4's screwed to the bench.

The thing that I had to keep in my head was that, for every movement, large or small, there was another movement at the other side, IF the frame was not made (completely) immoveable. Read thru Van's article from some years ago: http://www.vansaircraft.com/pdf/canopy.pdf

HTH!
 
Don't bend anything until you are SURE you have to bend it. I thought my square tubes were in need of a bend, but what was actually happening was that the whole frame needed a twist. Twisting it caused the aft end of the square tube to rotate out and down.. and it all fit.

And whatever you do, don't jump on it like the instructions say.... if you do, find a friend with a welding torch. Don't ask how I know. :eek:
 
I would counsel not messing with the square bars. They are very stiff and jury-rigged bending affairs will likely land you in more trouble. After four canopies I know that you can fairly easily accommodate bows and bars that are more proud of the adjacent sealing surface than Van's 1/16" than if at or beneath the surface. Keep in mind that moving the rear spread of the bars will reposition the pins so they may not meet the blocks in the right place.

I believe you're better off adjusting the rear bow so the canopy surface will be for sure be above (proud) of the top fuse skin; the skirts can accommodate a tremendous over-proud mis-match, the sides to a lesser degree. Recontouring the bows will move the bars AND you'll be hard pressed to keep it all symmetrical with the center bow. As you're bending the bows, watch for parallelism between the bars and deck - that's important for side skin overlap and appearance of the rivet lines. Don't be squeamish about using washers on the bows as at the roll bar. It's a lot easier than screwing around with the last fraction of contour adjustment.

John Siebold
 
John,

My unbent side tubes lines up as follows;

Having achieved the front of the square tubes at 1/16" in on each side (with a very small initial bend of the front bow inwards), the rear is at 3/16" out and 1/4" out (proud) on the left and right sides respectively. The 1/16" in (per plan) holds true until about half way back, and then it is obvious the tube radii just flatten out. Both sides are within 1/16" (vertically) of parallel with the side decks and the same on both sides, so I don't yet suspect any twist.

It's hard for my to see how I would get the side skirts to fit snug with that kind discrepancy on the aft portion. Plus I have read (and also mentioned in plans) that the canopy will pull the frame even further outboard.
 
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