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Surface defects in fiberglass wheel pants

R

roee

Well Known Member
Just received my finishing kit (woohoo!) and am going through inventorying and inspecting everything. Well, I've found just a couple of minor defects so far, but there's one I'm not sure about and could use some advice from the group.

The fiberglass wheel pants all have these surface defects all over them, sort of an irregular spider web pattern of very thin grooves. I'm not sure if they're scratches or cracks (the pattern would suggest stress cracks), or how deep they are. I couldn't really get them to show up in a photo, but if you've seen them on yours then you'll know what I'm talking about. Interestingly, all six wheel pant pieces (3 wheel pants, 2 pieces each) had these defects, and none of the other fiberglass parts did. Anyway, so if anyone out there has seen this before, I'd like to learn what these defects are, and whether or not they'll weaken the material. I know I can fill to get rid of them cosmetically, but I want to make sure they aren't going to develop cracks in the future.

Thanks!
 
Solvent clean to get any mold release off
Sand to roughen surface
Fill with body putty "Bondo"
Sand smooth
Prime
Paint
Beautiful!
 
Yeah... but what ARE these defects?

Guys, thanks for the replies, but what I'm looking for is not advice on how to fill and finish fiberglass (I agree, use micro and stay away from Bondo). That's not the point. What I really want to know is:

What ARE these defects? Are they scratches? Defects in the mold? Stress fractures in the part? Crazing due to chemical reaction? What caused these defects? And are they just superficial defects, or are these parts substantially damaged and weakened?

I don't want to just slap a band-aid on it (i.e. fill it to make it pretty) if it's going to just cover up a real problem that's going to bite me down the road.

Thanks,
 
Remove gel coat...

Sand an area down a little and see if it is crazing in the gel coat.

If it's truly a crazing effect, it will most likely be limited to the gel coat. The only fix is to completely sand off the gel coat and fill - or spray with a thick, catalyzed primer/filler - such as Feather Fill.

http://www.aircraftspruce.com/catalog/cmpages/featherfill.php

gil A - had to do this to an entire sailplane...
 
The wheel pants are just like that. Sand, fill, prime, and paint as normal. When you're all said and done, your wheel pants will look good.
 
Ooops...

szicree said:
I don't think the wheel pants have a gelcoat.
Click to expand...

My white ones do....:)

Perhaps it's just a too thick layer of resin in the mold before the glass was added... they are still polyester resin aren't they?

gil A
 
Wheel Pants

Who made them? Sam James seems to be a huge supplier of composite parts for RVs and his stuff is very good. Just finish them like any other composite part and move on. Don't go too thick on filler or micro - it will crack. If you have a bunch to build up use flox or anothe layer of bid and after sanding that out see what's left to finish. You should get some other and more experienced composite advice soon when my canard brethren that frequent your forum notice this issue. Composites are easy to work with and VERY easy to fix. Relax and have fun with it after all those RIVETS! :eek:
 
Vans Gear fairings

As is the case with the rest of Vans fiberglass work, the fairings are made by the lowest bidder who can turn them the fastest:mad::mad:. The fairings are vacuum bag molded and it is impossible to get all the air out of the process. The lines are wrinkles in the bag where the excess resin was not worked out. The fairings appear to have enough glass but show lots of air and voids from the molding process. As with the other fiberglass, we have had to sand, some re-glass on edges and cracks (emp fairing), then fill prime with two part fill primer, then paint. Whatever you use for filler should be squeegee on and then sand (and repeat again probably) till you get the surface you want. Thank goodness my airplane partner Mike Brown is really good with glass.:):)

TylerB
N174MT (Empty Pockets)
RV7A Almost there
 
male/female molds

TylerB said:
...... The fairings are vacuum bag molded and it is impossible to get all the air out of the process. The lines are wrinkles in the bag where the excess resin was not worked out. ....

TylerB
Click to expand...

Since we are talking about wheel pants (see first posting) that would imply that a male mold is used.

That is certainly not the case for my early wheel pants... do you think that is the case for the later ones?
Female molds would be much more typical... and that would put the vacuum bag marks on the inside of the wheel pant.

gil A
 
My RV6 wheel pants are a glass fabric epoxy wet layup in a female mold. There is no sign that a vacuum bag was used. I believe that earlier ones were wet layup polyester with a gel coat. Mine are covered with fine surface lines that are a straight mirror of the mold surface - probably due to years of mold scraping, scuffing, cleaning and release application. Being a wet layup there are also areas of resin richness that show up when you hold it to the light. None of these is a problem.

Also I'd have no problem skim filling these minor cosmetic surface defects with "bondo" - assuming that they don't just sand out. It's done all the time in the aerospace composites business - there is even a mil spec for it. It's quick and easy to work and gives a great surface finish. The finishing companies have spent years making it so. I'll admit that bigger defects need a tougher reinforced filler like epoxy and micro balloons or even flox. Pin hole filling is another whole science!!!!
 
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TylerB said:
As is the case with the rest of Vans fiberglass work, the fairings are made by the lowest bidder who can turn them the fastest:mad::mad:. The fairings are vacuum bag molded and it is impossible to get all the air out of the process. The lines are wrinkles in the bag where the excess resin was not worked out.
Click to expand...

Vans has been using the same vendor(s) for glass parts for many years. Low ball bidders are not used.
The only parts vacume bagged are the epoxy prepreg parts (greenish or pink in color). Primarily cowlings, RV-8 canopy skirts, and RV-10 cabin top.
Parts with a white gel coat are wet layup polyester done in female molds (primarilly wing tips and empenage tips).
Wheel pants and gear leg fairings are wet layup epoxy in female molds with no gel coat (greenish translucent parts).

jsharkey said:
My RV6 wheel pants are a glass fabric epoxy wet layup in a female mold. There is no sign that a vacuum bag was used. I believe that earlier ones were wet layup polyester with a gel coat. Mine are covered with fine surface lines that are a straight mirror of the mold surface - probably due to years of mold scraping, scuffing, cleaning and release application. Being a wet layup there are also areas of resin richness that show up when you hold it to the light. None of these is a problem.

Also I'd have no problem skim filling these minor cosmetic surface defects with "bondo" - assuming that they don't just sand out. It's done all the time in the aerospace composites business - there is even a mil spec for it. It's quick and easy to work and gives a great surface finish. The finishing companies have spent years making it so. I'll admit that bigger defects need a tougher reinforced filler like epoxy and micro balloons or even flox. Pin hole filling is another whole science!!!!
Click to expand...

jsharkey is exactly right. Bodo is perfect for epoxy parts as long as you are filling voids such as pinholes, deep scratches, etc. It also works great for limited surface filling in areas that will not be subject to flexing, etc. It should be avoided near edges where a hard durable edge is desired. In these locations even micro is no good and a flox mixture should be used.
 
Thanks everybody for all the info. Sounds like it's probably fine, but I'm sending one wheel pant back to Van's so they can have a look it. I'll report back here when I get some answers from Van's.

BTW, I spoke with Van's today about this and a few other issues/questions on some of the composite parts that came in the finishing kit. They told me that they outsource the composite parts to a number of different vendors, and they aren't actually very familiar with the processes and materials themselves. No problem with outsourcing, but as for it going to the lowest bidder... here's a quick story, you decide. The cowling halves I just received are two different colors. The upper cowl is green, like I've always seen on RV's, and the lower cowling is pink, which I've never seen before. I asked Van's about it, and they said that their vendor for the cowlings recently switched to a different epoxy "because they could get it cheaper" (their words). Now, expensive doesn't necessarily mean good, and cheaper doesn't necessarily mean not-as-good. And saving money is a good thing, for Van's and for us. But there are a variety of epoxies out there in a wide range of quality, so I think it deserves some scrutiny. Van's simply didn't know what type of epoxy was used in the past, nor what type is used now. Both types might be up to snuff, but I'd sure like to know. To me it does seem like Van's might be a bit loosey goosey on the quality control.
 
The vacuum bagged, oven cured, prepreg epoxy cowls replaced wet layup versions. Any commercially available epoxy prepreg will be many times better than that.
Jim Sharkey
RV6 Tip-up O360-A1A FP
Nearly there!!!!
 
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