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Cracks in Jell Coat RV-7 Wingtips

P

pburf

I'm New Here
At about 250 hrs air time, my 2008 RV7 developed cracks in the gel coat on the wing tips. I have been learning aerobatics and max G to date is +4/ 0-

The cracks run fore/aft parallel with direction of flight and the outboard edge of the tips, and inboard about 2 inches from the outboard edge of the wingtips.

On close inspection, the wingtips appear to have been laid up using a single piece of woven fiberglass cloth, except at the very outboard edge of the wingtips, where there are at least 2 additional layers of cloth. My cracks have developed beside the inboard edge of the 2 addtional layers of cloth where there is only 1 layer of cloth.

Are these cracks common?

How deep/wide should I excavate the cracks in preparation for filling with fiberglass resin and "bubbles"?

PBurf
Windsor ON
 
This is the first time I remember anyone having cracks as you describe.

The basic repair process is to sand away the gell coat around the crack - I would remove it for a couple of inches in each direction from the crack. Then, apply one or more layers of glass cloth as reinforcement. Finally, fill and blend in the repair with a microballoon/epoxy mix. Without the additional layers of cloth, any repair will eventually crack right where the original cracks were.
 
hmmm

I noticed them in mine also. Pretty much the same appearance and pattern. I'm at 220 hours.

I'll have to look closer now to see the extent.
 
I noticed them in mine and I haven't even flown yet. Off comes the gel coat, as soon as it warms up and I can finish the job (too cold overnight for epoxy to cure well). Those tips do not represent the pinnacle of fiberglass part construction.
 
gereed75 said:
I noticed them in mine also. Pretty much the same appearance and pattern. I'm at 220 hours.

I'll have to look closer now to see the extent.
Click to expand...

I personally wouldn't use gel coat on parts so thin and flexible. For boats and bath tubs, sure go for it. Stress cracks are going to happen. If you're repairing in cold environments you might want to use a polyester resin which you can mix hotter to aid in curing. Typically, gel coat parts will be made with polyester resin because they're compatible. If epoxy was the structural resin then they would need to use a tie coat so the different materials could bond together. I seriously doubt they went that route. If you need small amounts of polyester resin, most hardware stores and auto supply houses will stock it. That's because it works good for bath tubs and boat repairs.
 
gelcoat cracks

My -7 has no cracks in the wingtips. It is a 2004.

Also, some do fill the wingtips with foam to help prevent flexing and deformation over time.

Mine are holding up well, although others have complained of deformation.
 
Reinforcement

On the opening page of VAF, look under Articles and look for the information on wing tips. I wrote a couple of articles on the installation and reinforcement of the wing tips.

The tips flex considerably without reinforcement. The simple process greatly strengthens the tips with minimal weight gain.
 
RV7Guy said:
On the opening page of VAF, look under Articles and look for the information on wing tips. I wrote a couple of articles on the installation and reinforcement of the wing tips.

The tips flex considerably without reinforcement. The simple process greatly strengthens the tips with minimal weight gain.
Click to expand...

I saw them last year and printed them. I wound up doing something slightly different- I have a bunch of big sheets of 2" thick blue styrofoam so I made ribs from the stuff, glassed them in place and then carved the foam out. Added maybe a couple of ounces per tip and made a huge difference in stiffness. The whole job took a few hours over a weekend. Your articles inspired me to do the work, and it was well worth it- thanks!
 
Here's what NOT to do......

The large flat area in the last 1/4 chord or so to the rear was quite floppy and I didn't see how I could block sand there. Soooooo, I supported the exterior flat surfaces and poured two-part expanding urethane foam into the tail end of the tip cavity. Ahh, wonderful....the foam core provided nice firm surfaces to fill and sand as desired.

Fast forward about six months into flying. One day I looked across a wingtip and noticed the surface had developed a bunch of crazy lumps and waves in the area over the foam core. It appears the expanding urethane foam will undergo additional expansion, perhaps in response to reduced ambient pressure (altitude) and/or increased temperature. Wouldn't matter in a boat with thick hull and deck skins, but our tip skins are too thin to resist internal pressure. The expansion isn't homogenous, thus the lumps.

One of these days I'll pull the tips and remove the foam. Hopefully the glass will relax back toward flatness. We'll see.
 
Where did you get the 2" foam

Lars said:
I saw them last year and printed them. I wound up doing something slightly different- I have a bunch of big sheets of 2" thick blue styrofoam so I made ribs from the stuff, glassed them in place and then carved the foam out. Added maybe a couple of ounces per tip and made a huge difference in stiffness. The whole job took a few hours over a weekend. Your articles inspired me to do the work, and it was well worth it- thanks!
Click to expand...

Lars
I have the same cracks (170 hours) where did you find the 2" blue foam as I looked for this in HD and Lowes as I was going to use this to insulate my hangar some.
 
How to fix

:confused::confused::confused:Dan,
My tips look like ocean waves lots of dips and waves.I tried to use a heat gun and push them out and cracked the gel coat. What process should I use? And how should I go about fixing the crack? I have seen people cut them to get the dips out then glass them back but it's hard to know where to cut.I know you cannot use that much filler. One of them has already been drilled to the wing the other one has not.Any advise would be greatly appreciated from any body who has been there and I know everybody has I have yet to see any straight tips right out of the box.Well off to the shop I go to work on the skirts some more who would have thought it would take four months to fit a skirt? I like the Todds canopy but it has it disadvantage.
DanH said:
Here's what NOT to do......

The large flat area in the last 1/4 chord or so to the rear was quite floppy and I didn't see how I could block sand there. Soooooo, I supported the exterior flat surfaces and poured two-part expanding urethane foam into the tail end of the tip cavity. Ahh, wonderful....the foam core provided nice firm surfaces to fill and sand as desired.

Fast forward about six months into flying. One day I looked across a wingtip and noticed the surface had developed a bunch of crazy lumps and waves in the area over the foam core. It appears the expanding urethane foam will undergo additional expansion, perhaps in response to reduced ambient pressure (altitude) and/or increased temperature. Wouldn't matter in a boat with thick hull and deck skins, but our tip skins are too thin to resist internal pressure. The expansion isn't homogenous, thus the lumps.

One of these days I'll pull the tips and remove the foam. Hopefully the glass will relax back toward flatness. We'll see.
Click to expand...
 
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