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I've run into a problem that I know I've seen discussed on here before, but I can't find any of the more helpful suggestions:

I am near completing the left wing, the leading edge has been attached on the lower side. I used cargo straps to gently pull it around and align the spar holes with the top skin. These are now clecoed along the spar. Then working from the middle out one row at a time I have drilled and clecoed to the ribs.

I now have TWO rows of holes left to the leading edge, but the skin, particularly in the center, will not bend down to touch the ribs. The radius of the leading edge will not conform to the nose of the rib. It is worst towards the middle of the wing, by the time I move out to either end it seems ok. It feels like if I try any harder I will kink the skin.

I am sure I have read of some people "annealing" the radius. Is this what is necessary? If so, I understand I heat the metal with a propane torch until the sharpie marks disappear. Anybody have more specifics? Do I need a specific nozzle on my torch (the one I have makes an extremely sharp flame). Do I try to heat a larger area then quickly drill and cleco while it's still hot?

Help.

Thanks, Gordon

GordonTurner wrote:I've run into a problem that I know I've seen discussed on here before, but I can't find any of the more helpful suggestions:

I am near completing the left wing, the leading edge has been attached on the lower side. I used cargo straps to gently pull it around and align the spar holes with the top skin. These are now clecoed along the spar. Then working from the middle out one row at a time I have drilled and clecoed to the ribs.

I now have TWO rows of holes left to the leading edge, but the skin, particularly in the center, will not bend down to touch the ribs. The radius of the leading edge will not conform to the nose of the rib. It is worst towards the middle of the wing, by the time I move out to either end it seems ok. It feels like if I try any harder I will kink the skin.

I am sure I have read of some people "annealing" the radius. Is this what is necessary? If so, I understand I heat the metal with a propane torch until the sharpie marks disappear. Anybody have more specifics? Do I need a specific nozzle on my torch (the one I have makes an extremely sharp flame). Do I try to heat a larger area then quickly drill and cleco while it's still hot?

Help.

Thanks, Gordon

Hi Gordon,
As a scratch builder I bent my own skins so I cannot speak from experience, however, I share a hangar with a group that are building 2 kits and they mentioned they have had to straighten and re-bend their leading edge wing skins as the bend from the factory "crooked" they say.
(Re)bending the wing skins is very easy using the vacuum method, sounds like yours just might need a little extra bend in the center and that would be easily done this way, more info on the vacuum bending method can be found on my kitlog pages here:
http://mykitlog.com/users/display_log.p ... 84&row=130
http://mykitlog.com/users/display_log.p ... 85&row=129
http://mykitlog.com/users/display_log.p ... 19&row=128

There is also a video of this procedure someone else made floating around:
https://www.youtube.com/watch?v=2_QWPoFEhWc

PS. don't use the PVC pipe if you decide to do this, I had issues keeping it tight against the aluminium in the center, a steel pipe as they used in the video is preferable.

GordonTurner wrote:I am sure I have read of some people "annealing" the radius. Is this what is necessary? If so, I understand I heat the metal with a propane torch until the sharpie marks disappear. Anybody have more specifics? Do I need a specific nozzle on my torch (the one I have makes an extremely sharp flame). Do I try to heat a larger area then quickly drill and cleco while it's still hot?

Hi Gordon
I would not heat up and soften a structural part like the leading edge. The sharpie method will virtually take the temper out of it permantly.

I used the vacuum method to tighten the leading edge radius. A problem I had was a couple of minor kinks appeared in the middle. I think the problem was my bench wasn't dead flat. It took a bit of work to spoon out these kinks to salvage the skin. If doing it again I would definitely use the vacuum method.

Steve
Sonex 892

Hi Steve. Do you mean the kinks appeared during install, but the vacuum process then corrected the radius and fixed the problem? Or the vacuum process caused the kinks?

Thanks, Gordon

GordonTurner wrote:Hi Steve. Do you mean the kinks appeared during install, but the vacuum process then corrected the radius and fixed the problem? Or the vacuum process caused the kinks?

Thanks, Gordon

Hi Gordon

I probably made it sound worse than it was. The radius was too big so I vacuumed it to make it tighter. I only noticed the kinks after vacuuming, so assumed it was caused from the vacuuming. The same type of damage can be caused from mishandling.
Fortunately it was repairable and I didnt have to make new skins. My plane is also polished and its not noticeable.
Here is the only photo I could find of a kink, taken after the repair, circled with sharpie. I repaired them before dimpling / rivetting.

Steve
Sonex 892

GordonTurner wrote:I am near completing the left wing, the leading edge has been attached on the lower side. I used cargo straps to gently pull it around and align the spar holes with the top skin. These are now clecoed along the spar. Then working from the middle out one row at a time I have drilled and clecoed to the ribs.

I now have TWO rows of holes left to the leading edge, but the skin, particularly in the center, will not bend down to touch the ribs. The radius of the leading edge will not conform to the nose of the rib. It is worst towards the middle of the wing, by the time I move out to either end it seems ok. It feels like if I try any harder I will kink the skin.

I am experiencing this exact same thing. Is vacuum bagging the best method to safely increase the bend of the LE? I have read of the occasional person creating a kink in the skin during the process. Is there a surefire way to avoid that during vacuuming? Or, is there another way to increase the LE bend?

This problem was a bitch for me on both leading edges. My first, after using the vacuum bagging technique shown in the video, was ok. The second ended up with two kinks i could not remove. The worst, thanks be to the gods, fell exactly where i intended to put a landing light...far outboard. The second was less distinct, but is at about 1/3 out from the root. I couldn’t get it out, so plan to live with it. Not happy with that answer.

I used the ratchet straps and the padded 2x4 after drilling/clecoing the upper side. After I got the lower side pulled down enough to cleco the under surface side to the spar, I discovered the issue with the LE bend. Removed the LE skin, and now there are little tiny 'pops'/dings on the upper surface right where the forward edge of each of the ribs would touch the skin. I guess I didn't make a big enough relief in the forward part of the nose ribs. Those pops are not terrible, but they are noticeable. So I am going to make the relief cut a bit further back on the nose ribs, and do my best to spoon out the pops. Then, I'll give the vacuum bagging a try if there is no other way to tighten up that leading edge bend.

I used form-boards cut from particle board as well as ratchet straps to hold the skins in place (see photo).

Even that might not be enough if you haven't corrected the bend in the skins. I used a Tony Spicer bend brake to bend the skins because I scratch built. It worked well and was easy to control.

Peter

From my experience, it's not the bagging that causes the large puckers. It's caused by unevenly bringing the edges together. Went through two skins learning that little tid-bit.

If you do decide to bag, make sure to use a spacer to even-up the distance at the aft edge. I thing Billy Rofomoto made one.