Warped fiberglass wingtips

lostpilot28 · #1 03-10-2008, 05:14 PM

I hope I'm not the only builder to experience this problem...maybe someone out there has an easy fix. I've attached my wingtips to my wings using #6screws and nutplates, but while I was looking at the finished work I noticed that one wingtip has a flat spot on the bottom (about 6" diameter) and the other wingtip has a flat spot on both the top and bottom (about 4" diameter top and bottom) in roughly the same location, a few inches aft of center.

All of the flat spots are very close to the flange that mounts to the wing. I've tried using a heat gun to smooth it out, but in my attempts to not burn the tips I probably was overly conservative with the heat...hence, it didn't work.

What's the best way to fix this? I made a rib out of 1" thick blue foam and stuck it in there, but I ended up with a "low spot with a ridge in it". Not a good solution. Any help here is greatly appreciated.

Oh, and I did a search for this, but couldn't find a good enough answer.

fstringham7a · #2 03-10-2008, 05:42 PM

Sonny

I checked mine out as I just did them about three weeks ago.....still in the wing stand.....

No flat spots but they are far from perfect.....It is the nature of fiber glass!!!!Some builders, http://www.theairplanegarage.com/Wings/wing_tips.htm have gone to great lengths to perfect the shape but at what cost in time, money, and flight time............

Fiberglass can be worked with to get that show quality look if one has the desire.....

Frank @ SGU RV7A last 1001 details

Transporter · #3 03-10-2008, 07:49 PM

FWIW, since I haven't tackled my wingtips yet...

You might try glassing in a fiberglass stiffener. A fiberglass sail batten would work well and shouldn't add much weight. Battens are very springy and would help pop out the dent from the inside without a lot of effort or expense (batten stock runs $2-7 per foot, depending on width)

Try West Marine: www.westmarine.com (or other boatbuilding supply source) and search for an untapered batten.

I'd try bonding a batten to the inside of the tip using epoxy thickened to make a 'putty.' Once this is set up you can cover the batten with a strip of fiberglass tape. Shouldn't need much in the way of finishing since it's on the inside...

Regards,
Mike

lostpilot28 · #4 03-10-2008, 07:56 PM

Hi Frank,
Thanks for the link...I'm amazed that the builder on that site went as far as he did to get them straight.

The flat spots in mine are not nearly as bad as his. I doubt you'd be able to see them unless the airplane were painted a dark, glossy color. Unforuntately, that will be my choice...they will be painted a medium to dark blue and I'm afraid the flat spots will be visible at that point.

So, I'm still looking for (simple) suggestions to fix this problem. I was thinking of temporarily installing a rib to apply outward pressure, then mount the tips on the wing. I could then heat it up and let it cool while it's in it's "normal" shape. Just a thought, but I don't know if it'll work.

Any ideas?

mike109g6 · #5 03-11-2008, 12:53 AM

Quote:

Originally Posted by lostpilot28

Hi Frank,
Thanks for the link...I'm amazed that the builder on that site went as far as he did to get them straight.

The flat spots in mine are not nearly as bad as his. I doubt you'd be able to see them unless the airplane were painted a dark, glossy color. Unforuntately, that will be my choice...they will be painted a medium to dark blue and I'm afraid the flat spots will be visible at that point.

So, I'm still looking for (simple) suggestions to fix this problem. I was thinking of temporarily installing a rib to apply outward pressure, then mount the tips on the wing. I could then heat it up and let it cool while it's in it's "normal" shape. Just a thought, but I don't know if it'll work.

Any ideas?

Try some foam blocks-High density-sanded to the conture that you are looking for with about a 2" overlap of the diameter of the flat spot. Heat the wingtip up with your heat gun on the side to be worked only. Again heat up about 2" diameter larger than the flat spot. Insert the foam block, position it, and just let the fiberglass cool naturally. You could also put some halogen work lights over it and let them sit for a while, Check often to make sure that they are not blistering the gelcoat. The block should work out most of the flat spot-it probably won't do all.
Mike H 9A/8A

RudiGreyling · #6 03-11-2008, 01:01 AM

Wow that guy went through a lot of trouble, He should just consider buying a new better tip though.

Mine wasn't bad, but I did hear about it collapsing sometimes and that it needed re-inforcing, so you might use this method to fix it up.

I took some ordinary styro foam cut in long in 1" x 1" square for the lenght of the wingtip, then fiber glassed the long foam pieces midway inside the wing tip with the fiber mat going over the top and sides of the foam, one lenght on top and on the bottom. The foam and fiber glass mat creates a box channel around the foam stiffening up the tip the lenght of the tip with little weight added. This is not my idea so I can't take credit for it!

If you can get your tip in the right shape then box it in the way I describe I think it might do the job, you might have to make 2 or 3 parralel channel boxes though.

I don't have an exact picture, but below you can see a sample of what I am talking about, this picture was taken during a mock line up of some wingtip lights, ignore the lights, look at the re-inforcing.

lostpilot28 · #7 03-11-2008, 05:08 PM

Thanks guys...I'm going to try the thick foam blocks, as per Mike's suggestion. I would think it would work...if it oil-cans, then I'll add stiffeners. I'm trying to minimize unecessary work and weight.

Tom Martin · #8 03-11-2008, 05:14 PM

I guess I am a metal guy at heart so when I see something like this I use a piece of .025 or .032 angle and bond it in place. The nice thing about the angle is that you can flute it to get exactly the curve you need. I usually drill the thing in place and hold it there with clecoes while the resin/flox cures. After that the holes are just filled in and sanded smooth.

Martin Sutter · #9 03-11-2008, 07:05 PM

As a builder of multiple RV's and Tech Counselor I have seen wing tips run from nice all the way to garbage. Small imperfections can be fixed as described by the previous posts but mayor distortions are not worth the effort. On my last project I had a particularly bad tip that had a 2" twist in it as well as a large wrinkle across the top surface and curled up edges along the top and bottom. The tip looked like it was taken out of the mold before it was cured and set open side down on the floor. Not wanting to wait for a new one and the hassle of sending the old one back I proceeded to slice and re-glass it, heating it to take out waves and internally stiffen it. The results were less than perfect and I spent about 30hrs with it.

My advice is to scrap the bad one and ask for a new one.

Martin Sutter
building and flying RV's since 1988

mike109g6 · #10 03-11-2008, 11:48 PM

Quote:

Originally Posted by lostpilot28

Thanks guys...I'm going to try the thick foam blocks, as per Mike's suggestion. I would think it would work...if it oil-cans, then I'll add stiffeners. I'm trying to minimize unecessary work and weight.

Sonny,
If the foam block works to your liking, and you're afraid of it 'oil-canning', just glass or hot glue the block in. It would only take a 2oz strip of cloth to secure it top and bottom. Don't glass it in until after you paint and you are sure that the shape is satifactory since you're using dark colors. It would be no real weight addition, a couple of ounces at most, just wet the cloth strips, don't soak it with resin. A 2" wide 'L' shaped piece top and bottom, fore and aft will hold the foam block in place.
Mike H 9A/8A