Vertical Stab - Leading Edge Warp

[mswain]

While bending the tube for my vertical stab i managed to get a little out of plane. If I lay it on my table, the ends are flat but it's about 1/8" proud in the middle.

Just wondering if I should start over or someone have a good idea how to take the bow out? I.e. Heat?

I could prob clamp it in place and weld it up, but I'm not sure if it would stay straight when taken out of the clamps.

Just fishing for ideas.




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[Chris In Milwaukee]

If I remember, Eric made small adjustments to his wing square and alignment with heat. I *think* that if you heat the underside of the tube, when it cools it will shrink. That may pull it down. Do you have Eric's manuals? I think it's in the third one.

[BTAZ]

Personally, if I had the extra material on hand and was still set up to do the bending, I could probably make a second one in less time then messing around straightening the first one.......

As a rule, my second piece always seems to take half the time and comes out better/more refined then the first.

The third piece is ripe to be ruined by overconfidence.....

If I didn't have the material on hand, I would probably start applying pressure cold(strategically block/screw the piece to be up off of the build table) to persuade it into shape, taking care to not kink the tube. It would likely take a couple attempts to find the right place to hold solid and the right place to lift/twist but should be achievable.

Heat works as Chris described; the heated metal shrinks a bit when it cools so identify the "long side" of the bend and heat it. But you will need to be careful not to end up with a localized correction and a wavy looking final product.

[Chris In Milwaukee]

I was thinking about the localized heating and wavy effect after I wrote this. That would be no fun.

[sbmurphey]

When I formed my horizontals, I had about the same (1/6" - 1/8") correction needed on mine. Ended up cold forming the bends back into shape by scaling up a technique I learned shooting archery. To avoid creating the wave as mentioned above, I determine where the bend starts and stops, placed a block with rounded corners under the diverging area and apples some opposite pressure at the center of the bend. Considering the natural bending of this part, I had a slight compound bend to work out and had to make several small adjustments as opposed to one large bend.

I also confirmed BTAZ's comment above. My second one looked much better and my final part for the vertical stab only required a minor adjustment after bending.

[Ed Welfred]

I usually find it difficult to correct an unwanted bend in a curved piece of tubing. If you make a second piece put a reference line down the length of the new tube. This helps to keep the bend on a single plain. A small piece of angle iron works well for drawing a reference line. I found the smaller tubing on the trailing edge of the elevators to be much harder to bend on a single plain so getting it figured out now will help latter.

[whee]

I know we are want to build the best plane we can; since perfect isn't possible we do our best to make it close to perfect while still making progress toward completion. With that in mind I have to say, I don't think an 1/8" bow is all that bad. Sure, it's not perfect but even if you did remake a new one that was perfect is it still going to be perfect after you finish welding the ribs to it? If the welding warps it are you going to again start over? I have parts on my plane that are nearly perfect, parts that were perfect till I welded them then they bowed and I couldn't straighten them and was unwilling to remake them, and I have parts that I sourced elsewhere that are so not straight I wondered if the fedex guy ran them over before he dropped them off (ok, that's an exaggeration but they are way more warped than an 1/8").

So, I say try to straighten it using the methods mentioned and if that doesn't work then remake it; whatever it takes to make you satisfied. If you decide to remake it please keep all your "seconds" and I'll use them to build another off road flying machine😉