Recovering from a poor repair

[rdeis]

Hi, all. I read the threads about weblets and repair with weblets, but this one has a new -er -- wrinkle on the problem.

I inherited a Laser with a failed wing. The top skin buckled outward about halfway between the root and tip. A previous repair attempt injected too much epoxy under the skin so there is now a bulge under the location of the original failure. Furthermore, the weak spot simply moved further outboard to the edge of the bulge.

Originally I thought that cutting slits in the skin, rebonding the skin to the foam with the proper epoxy and adding weblets would do the job, but that would leave a huge error in the airfoil at that spot.

Current plan is to sand the wing smooth and straight around the area of the repair, and then add a patch new cloth. I have .014 and .018 carbon, and several weights of glass available.

Sound like a reasonable plan?

Also- my dad and I are debating whether weblets are still wise or necessary. With the thicker cloth I'd guess they aren't necessary to prevent buckling of the skin patch, but they could help distribute the load more evenly from the original skin on either side through the new cloth of the repair.

Any suggestions/opinions?

[rdwoebke]

How bad is the bulge? Can you post a picture?

This is a guess, but I wonder if the foam is somehow also damaged below the buckle and the weblets might not be a bad idea to help support that area because of some problems with the foam.

Ryan

[rdeis]

I knew you'd ask for that, just didn't have a camera available at the time..

Here:

[rdwoebke]

I knew you'd ask for that, just didn't have a camera available at the time..


Me in particular or us in general? :)

OK, first I'm not the expert on this stuff, but I have fixed up 2 Psykos...

I'd first try to find out if the foam is somehow broken or messed up. To do that, I'd deflect the flap all the way down and then kind of "bend the wing" just a bit gently to have the delam raise up. Is the foam all messed up, if so, then I'd suggest the weblets are in order. If not, then perhaps you can get by without the weblets (and your red lines to me seem like a bit overkill, but then I'm not the end all expert).

Is that glass over your carbon in your proposed fix shot? If so, I think that is a great idea, the glass will sand better if you need to do any sanding and finish easier. But, I'd go with glass about 1 to 1.5 inches beyond the carbon to kind of feather the fix.

If you get a bunch of epoxy under the skin, and then of course saturate the epoxy in the cloth, then the weblets might not be neccesary.

You asked if the bagging process will fix dents/indentations in the LE. It will to some degree fix that on the top surface. Anything that is still not fixed you can fill with filler. The LE you will probably have to sand some and possibly do some filler/finish up work after the bagging. But that is no huge deal.

Hopefully Phil B. or another bagged wing expert will chime in here as well.

Oh, and this is absolutely fixable, and I'm sure you'll be happy with your Laser.

Ryan

[rdeis]

Me in particular or us in general? :)

Whoever answered first! (And you in particular are quick :) )

Is the foam all messed up, if so, then I'd suggest the weblets are in order. If not, then perhaps you can get by without the weblets (and your red lines to me seem like a bit overkill, but then I'm not the end all expert).

Agree on the overkill- 4 of the 5 is plenty, I think, and the length is probably excessive as well. IIRC they ought to taper at a 3:1 slope and don't need to go more than a couple of inches either side of the failure- though in this case they'll need to extend beyond the patch as well.

I'll look more closely at the foam.


Is that glass over your carbon in your proposed fix shot? If so, I think that is a great idea,

The patch shown is unidirctional 0.014 carbon, but I was plannning to feather it in with light glass as you suggest.

Anything that is still not fixed you can fill with filler. The LE you will probably have to sand some and possibly do some filler/finish up work after the bagging.

OK.

Oh, and this is absolutely fixable, and I'm sure you'll be happy with your Laser.


Excellent. I'm not sure where it will fit in my hangar just now, between the Falcon I'm still learning and the big Gabby I plan to get going on shortly, I'm fairly well stocked. I may just fix it up and sell it- if so the buyer will know exactly what was done! (Though I've had several offers on the Falcon that I'd intended to keep... Maybe sell that and keep this? Decisions, decisions...)

[lincoln]

If the foam is messed up, I wonder if you could cut or sand it back, put in a patch of new foam, and sand that down to match the rest.

[rdwoebke]

IIRC they ought to taper at a 3:1 slope and don't need to go more than a couple of inches either side of the failure- though in this case they'll need to extend beyond the patch as well.

One other thing you could use for the webs, is carbon rods. That was suggested on Ed Anderson's repair thread (I think part of the "now I have a Thermal Dancer" thread. You might want to read that one.





The patch shown is unidirctional 0.014 carbon, but I was plannning to feather it in with light glass as you suggest..
It was hard to tell since the glass was on top. If that is .014 carbon that is pre-epoxy cured, then that is something I have not tried. I have only fixed the Psyko wings with fiberglass and 1K (3 ounce I think it is also called) uni carbon. I can't say how a pre-cured piece of carbon would work.





Excellent. I'm not sure where it will fit in my hangar just now, between the Falcon I'm still learning and the big Gabby I plan to get going on shortly, I'm fairly well stocked.

I'd suggest it might make a good "daily driver" type plane, aka something you fly when the practice day is turbulent or if you fly at a place with a less than green grass LZ, to keep that Gabby all pretty.

Most folks would not say 3 TD planes is excessive. I only have 2, but have considered building a 3rd set of wings...

Ryan

[rdeis]

It was hard to tell since the glass was on top. If that is .014 carbon that is pre-epoxy cured, then that is something I have not tried.

Not pre-cured-- it's cloth with carbon fibers span-wise loosely woven with glass fibers chord-wise.

[rdwoebke]

Normally, when folks talk about composites, they talk about thickness of composites in pre-cured. So 014 would be those 014 thick pre-cured carbon strips.

When talking about fabrics, folks normally talk about the K of the carbon tows (I still don't understand that) or the weight of the cloth as in 3 oz/sq yard.

So that had me a bit confused, and I thought better to confirm before you do something that might not work. :)

Ryan

[rdeis]

You're right- my apologies for the confusion. I measured the cloth thickness with a caliper.

*UPDATE*

Here's the thread on the 2nd (and correct) repair job: http://www.rcgroups.com/forums/showthread.php?t=944028

[Wazmo]

When talking about fabrics, folks normally talk about the K of the carbon tows (I still don't understand that) or the weight of the cloth as in 3 oz/sq yard.

The "K" size of carbon tows is the number of carbon filaments (in thousands) contained in the tow. So, a 3K tow contains 3,000 carbon filaments.

http://www.aircraftspruce.com/catalog/cmpages/yarntow.php
http://www.rcgroups.com/forums/showthread.php?t=851347