[Jamie]

I am trying to finish up my cowl. I have all of the camlocks installed around the sides and top of the firewall and I have hinges running along the sides. Somehow when I made the cut for the very bottom of the cowl I managed to cut off about 1/4 inch too much. So now I need to add some back. Can someone give me some good advice on how to do this? Yes, I know I need to somehow lay up an extension on the inside and then fill it...but how do I do the extension? Do I need to lay up some flat glass strips on the bench then bond those back to the cowl?

Thanks,
Jamie

 

[sf3543]

I have done this before and it has held up over time.
First, bevel the edge you want to extend, as that will provide more grip for the new piece.
Then rough it up, for mechanical grip.
I lay a piece of aluminum, or something flat and smooth on the back side and tape it on with packing tape, extending beyond the edge. This will hold the new material while it sets up.
Then lay up the epoxy with glass material.
Once that sets up, peel off the piece of aluminum, or what ever, from the back and sand everything to shape.
You can fill any voids with epoxy and flox and even lay on an additional layer on the back for added strength, if you wish.

 

[Ironflight]

Steve's basic technique is what I have done, but instead of a piece of aluminum, I have used a piece of wide tape (duct tape works) stuck to the outside of the cowl, extending past the edge. For the part extending past (that is going to get epoxy laid on it, add a piece of vinyl tape onto the sticky side of the duct tape (sticky to sticky) so that the new glass is laid onto the vinyl - that way it will separate cleanly.

Just had a thought - I suppose you could cut a thin strip of peel-ply instead of the vinyl tape....I wonder how that would work?

Anyway - I had to do this trick a number of times - no problems, edges are all still intact!

Paul

 

[Jamie]

Thanks, Gentlemen.

I'll give that a try. Sounds simple enough.

VAF comes through again...

 

[Hawkeye7A]

'Nother technique

Hi Jamie,
I pulled a similar boo-boo. What I did was to clamp the affected trailing edge of the cowling down on the bench with a straight piece of 2 X 4 and some 3-mil plastic sheeting under it. I then laid up some epoxy/flox mix onto the edge (after first roughing it well) and laid it out further than the missing area. After it cured I had a bit of rough stuff to sand on the inside but the outside was smoother than the cowling exterior itself. And, I just used tin snips to bring the edge back to where it needed to be. Neat thing about glass is that it's a bit easier to fix the mistakes than metal. (Oh HECK no, I will never build a plastic airplane!)

 

[aadamson]

Did I read that right? You extended a thin surface by just using a build up of flox and epoxy? If you didn't use any cloth, you'll be fixing that again if a couple of years or less. Flox and epoxy alone will have *no* structural strength as an edge extension material.

The other suggestions of doing it with a layup on the inside beveled edge are the correct one and if you want to save some weight and increase the strength, use some carbon fiber instead of eglass. The other option, depending on how thick it is that you need, is to use a foam sandwich with glass or carbon layers on the inside and outside. Then the edge can be "hollowed" out and filled with epoxy/flox, or epoxy/micro depending on how strong you are looking to retain. Also, if the edge is suppose to bear weight, then don't do this last method.

Don't worry, we've all be there. I did it on my elevator inside edges. I miss cut them by about 1/4" and had to bevel and apply carbon layups to extend it back out and recut it. Good thing that isn't a structural component on my Lancair

 

[Jamie]

Ok guys...I followed your advice.

I took about four pieces of duct tape and put them together, then taped it to the inside of the cowl. Then I put some vinyl tape on on the overlapping duct tape. Then I butted up glass into the beveled edge as best as possible. I used BID for all of this.

Many hours later I had this (nevermind the jagged edge...I only need 1/4 inch so it's getting trimmed off):

Then I laid up another layer on the inside. Just trying to make sure this is strong since the camlock holes will be lay very close to the joint. I'm going to intentionally try to get the camlock rivet holes (since they carry the load) on the 'old' part of the cowl. [edit: nevermind this...the cowl just gets big holes and the grommets and studs]

Thanks again, guys. I think this is going to work well.

 

[Ironflight]

Twelve hours from "Hey, how do I fix this?!" to "All done - that wasn't too bad!"

It's why I have a love-hate relationship with fiberglass. I hate the mess....but I love it because it forgives all sins....

Good going Jamie!

Paul

 

[Finley Atherton]

Did I read that right? You extended a thin surface by just using a build up of flox and epoxy? If you didn't use any cloth, you'll be fixing that again if a couple of years or less. Flox and epoxy alone will have *no* structural strength as an edge extension material.

Basically I agree, however I think there is some application for the epoxy/flox technique provided the extension will be no more that about 1/16”. I added up to 1/16” and an very confident it will hold up in the long term. If you do this you need the best possible bond. Sand a generous bevel on the edge of the cowl with very coarse paper. Apply a thin layer of epoxy to the beveled surface before applying the flox and do not mix the flox too dry.

Fin
9A
Vari-Eze

 

[aadamson]

Basically I agree, however I think there is some application for the epoxy/flox technique provided the extension will be more that about 1/16?. I added up to 1/16? and an very confident it will hold up in the long term. If you do this you need the best possible bond. Sand a generous bevel on the edge of the cowl with very coarse paper. Apply a thin layer of epoxy to the beveled surface before applying the flox and do not mix the flox too dry.

Fin
9A
Vari-Eze

Actually, I'd beg to differ with you in good form... I'd mix that flox *really* dry. It's the epoxy that's brittle, not the flox.

The problem with your approach is the *only* thing that is creating a bond is the thin epoxy edge between the old surface and the extended one. Even a simple wrap of my .75 oz cloth would probable solve the problem and it would hardly be noticable.

But as they say, to each their own... I just know I wouldn't do it. It's *gonna* break, right at the seam between old and new...

 

[Finley Atherton]

Actually, I'd beg to differ with you in good form... I'd mix that flox *really* dry. It's the epoxy that's brittle, not the flox.

The problem with your approach is the *only* thing that is creating a bond is the thin epoxy edge between the old surface and the extended one. Even a simple wrap of my .75 oz cloth would probable solve the problem and it would hardly be noticable.

But as they say, to each their own... I just know I wouldn't do it. It's *gonna* break, right at the seam between old and new...

Fair enough. We will obviously not agree about this. Certainly your wrap of cloth would provide extra strength. Let me just clarify a few points. The edge of the cowl needs to be bevelled. This will provide a larger bonding surface. By "thin layer of epoxy" I mean just enough to make sure the bevelled edge is damp with epoxy (done by smearing a layer on with a gloved finger). By ?not too dry? I mean, mix in just enough flox to make the mixture stand up. This is the instruction for mixing flox in the Vari-Eze Manufacturing Manual.

Fin
9A
Vari-Eze