Need help fixing this
 

This is for you fiberglass repair experts out there. I need ideas on how to reinforce the crack on the spar which the builder caused by making a hole on it just to run the servo leads. The crack traveled all the way to the leading edge. this is how I bought it here on RCU it was never disclosed to me prior to the sale. Anyway, being that I don't know a thing about glassing I would need advise from the first initial cut on the wing to ideas on how to reinforce that spar (thankfully it's not the main spar) and finally how to do the finish repair and what kind of materials I would need. Any help woud be appreciated...

thanks,

Hornet 1

RE: Need help fixing this
 

Dont you just guys who dont disclose problems such as this ? How deep does the crack go ? If its just a surface crack or not very deep I would use a piece of BVM poly ply ( proably the .015 thick), this item is also known as G-10 epoxy glass I think. You will have to sand the paint off the wing where you want to glue this or atleast scuff it up good. I'd sand it down to where there is little or no paint. You can pre paint the poly ply so after its glued on with 5 min epoxy there is no finsihing required and it will just look like a lot of full sized aircraft that have areas patched. I've used this method many times, sometimes just an easy way to repair the finish ( I use .010 thicknes for this) and other times to actually repair damage like you have.

RE: Need help fixing this
 

Thin foam safe CA would be a start it bonds well to the glass. as far as paints go check with your local automotive paint store for a match. We work with composites a lot and I have seen many repairs like this.

P. Richards aka Swat Team

RE: Need help fixing this
 

Its a foam core wing. I think its a surface crack . but my main concern is how to get in there to fix the spar. if you look closely at the picture you will see that the builder sanded almost all the way through the spar just to get the wires through. I can't do it though the servo opening because then the servo would not fit back in its place. I highlighted the crack with a red marker.

thanks,

Hornet 1

RE: Need help fixing this
 

I see the cracked spar now. Its hard to say with out seeing it in person. Id use thin ca inot the cracked spar and then glue a peice of carbon or poly ply or ply wood to the face of the spar, front and rear if possible. Make sure you rough up the surfuces good to get good glue adhesion. After you have glued to the face of the spar can you wrap that area with carbon cord or sewing thread and then saturate the wrap with CA ?

RE: Need help fixing this
 

it looks to me as though the box for the servo is just that. not a spar just a ply box. if it is a spar its really thin one that i wouldn't trust in my jet...as for the glass crack, im no expert so i will leave that one alone

RE: Need help fixing this
 

Hornet,

What model is this, might help in establishig what has been sanded through and what structural integrity has or has not been impeached. I would tend to think like donniercjet that this is actually part of the servo box, but would not trust this without finding out a bit more!!!

Gazzer

RE: Need help fixing this
 

I also agree that it looks just like a servo box and not a spar. Go to my web page and see the reapir I did on a BVM F-86 that was similiar to this. It is located in the FAQ section

http://www.crcja.org/

Or better yet, the short version,

http://www.crcja.org/faq/repairs.htm

In this cace the wing had stress cracks that also originated at the sevo box location, since back in the days this had a RAM 750, I decided to make sure it would be more than strong enough.

Turbulence

RE: Need help fixing this
 

Its a YA F-18 single. I also have the newer ARF 18 plug in wings and it has 2 spars so this is where I'm geting the idea of two spars on this wing. I think the front spar was just a convenient place for a servo box. correct me if I'm wrong.

Hornet 1

RE: Need help fixing this
 

I would get a piece of plywood, 3/32 and cut a spar doubler with the same taper as the spar, but trimmed off so it is 1/16 under the skin line on top. Then take an .06 carbon rod and use that as a spar cap reinforcement.

You get it into the wing by slicing thru the skin right next to the existing spar with a dremel wheel. The slice needs to be as long and thick as the ply reinforcement. You can remove foam down to the other wing skin with a soldering gun or hot wire used with just enough heat to melt the foam away.

You can put the ply in with epoxy or polyurethane glue and you can put the carbon rod over the top by sliding one end in under the skin, then the other. Make sure it all has a good coat of glue. Fill the skin gap with balsa. Sand smooth and cover the whole crack with 1 oz glass. Feather-sand into the rest of the skin, prime & paint. You always want to cover cracks in skin glass from the outside with more glass, even with light glass. If you just glue/paint over a crack, it will reappear.

RE: Need help fixing this
 

Hey guys,

Thank You all very much for all your advise. It is definitely easier when we have acces to a broad range of knowledge.

thanks again,

Hornet 1