Van's and Fiberglass

I'd like to preface the following rant with the fact that I actually enjoy fiberglass work and am not a fiberglass hater like many. I have considerable experience working with a variety of materials including vacuum bagging with glass and carbon. My plane is an RV7 so your kitglass may vary slightly. I molded all of my tail glass into the various parts. These can be seen at Brad Olivers site at www.rv7factory.com under the tips section. Also understand, for me, all fiberglass work must be perfect and I didn't stop until it was.

Facts- Van's uses to OEM's for their glass. The cowl and wheelpants are made from an Epoxy glass lay up. The wingtips and tail glass are polyester resin with significant gel coating.

The gel coated polyester parts are relatively easy to work with although you must understand that there are many voids in the glass that are covered by the gel coat. These need to be discovered and filled or they will manifest themselves later.

My real frustration came with the cowl. As I began my prep by liberally washing the cowl with acetone and sanding with 150 grit paper, I noticed that much of the cowl had voids in the areas of the honeycomb structure. Voids are simply a lack epoxy to fill the weave or structure.

I sprayed a coat of Feather fill primer on the cowl to see how extensive the problem was. The primer really brings out the problems and it was much worse than I suspected. My first thought based on my experience, was that this was a very simple fix by adding more epoxy to the layup during manufacturing.

There are many techniques to fill the inadequate layup. Some use epoxy and microfiller squeegeed in. Others use Rage or other types of fillers. I used a few different techniques to see what worked best.

When I thought I was really close to being done with the filling, I sprayed on 3 relatively heavy coats of Feather Fill primer on the cowl. I was still shocked at how much was still unfilled!!! I now filled the remainder of voids by "fingerpainting" Feather Fill into the voids.

This is when I realized, "okay, I like working with this stuff and I'm totally frustrated. I can imagine what the average builder is going through." I wrote and email to Van's asking why the cowl quality was so inconsistent with the quality of the rest of the kit and why to different types of glass stuff was being used. Regarding the cowl I mentioned that the fix was rather simple.

I received an email back from Van's that said if they had to add more epoxy the price would go up. Regarding the polyester glass stuff, he said that polyester was cheaper and easier for the end user to work with. So where is the logic? The cowl pieces are the biggest glass pieces in the kit and the most visible, so why are they the toughest to work with?

I replied and said that Van's was probably the major income source for these OEM's. (may or may not be accurate) If Van himself called and said, "the glass quality is not to my standards, please fix," I'll bet the cowl would be improved.

I also noted in my reply that the fix,(in my estimation) would only require 6-8 oz of additional epoxy to fix the problem. Our retail price of epoxy would put this at roughly $1 per ounce. At wholesale, (manufacturers price) it would only be about 1/2 to 2/3's of that. So, $6-8 retail for higher quality cowl, I'm in!!!

Finally, I said that if the kit prices were raised a nominal amount for improved glass work, sales would not suffer. I don't believe anyone would make the decision to not buy based on an increase of a few dollars. This is especially true when you realize it is going to cost you more than that to fill the cowl when you get to that point.

Now where everyone can step in and affect change for future builders, the reply from Van's also included the statement, "we don't get that many complaints on the fiberglass."

For those who have completed their planes or are in the process of working on the glass, simply send an email to Van's to provide a few thoughts on the quality.

Please understand that I'm not complaining about the overall kit quality. The past couple of years have been some of the most rewarding of my life and I love my 7. I will be traveling the Country proudly flying the Van's flag and preaching the benefits of the RV line to who ever will listen.

My only purpose to make Van's aware that the glass work is probably the lowest quality point of the kit. I believe they don't receive more complaints is that the glass is usually at the end of the project. We get caught up in the process and when done we forget the undesireable things.

Lets help out those behind us in the process.

re: why epoxy and not polyester on the cowl

I believe it comes down to the epoxy is a better choice for large structures because it's structural properties are far superior to polyester. I believe you'd probably end up with a lighter layup with epoxy than polyester since you can have a thinner part.

Pinholes are a PITA. I've had some success in the past using this technique, but I've always been hesitant to mention it here because someone's gonna warp their cowl, or otherwise make a huge mess.

The whole problem is getting something thin enough to flow into the holes, right? Okay, well there's a way to make epoxy practically water thin....heat it up. I use a hair dryer, sometimes a heat gun, to heat up the epoxy after I've squeeged it on. The little bits that's are just floating over the pinholes will flow right in. Problem solved....works for me, anyhow. It doesn't need a lot of heat!!! Just a little bit will do it. Certainly cool enough to touch. Think nice warm bath water.

disclaimer: If you use this technique and melt/warp your cowl, cause the epoxy to flash cure, cause a fire, etc it's you're own darn fault. I'm not recomending this...it's just how I've always done it.

edit: an added benifit of this is that it will cause the epoxy to cure faster AND will tend to make the epoxy more brittle. Normally, this isn't something you want, but in this case it will sand better. Wear a mask because if you overheat it, it can smoke and give off nasty fumes.

Van's and fiberglass

RV7Guy said:

Now where everyone can step in and affect change for future builders, the reply from Van's also included the statement, "we don't get that many complaints on the fiberglass."

Click to expand...

You've gotta be kidding!

First, I'm really surprised that Van's is not aware that just about everyone moans about filling the zillions of pinholes in the cowl. How many hours of work is that for the typical builder? A lot!

Second, I'm even more surprised that this is something that can be made better at the factory. I was always under the impression that it was not possible to do it better. Of course, I just assumed this - I don't know anything about the manufacturing process for these cowls. A buddy of mine who has built two RV4s saw my cowl and was shocked at how much better it was than the ones he received from Van's for his RV4, so they are making progress.

I personally would pay extra money to have all the fiberglass done better. In fact, I bought upper and lower fairings, premade. That was at least a couple of hundred dollars.

I appreciate Van's quest to keep things as inexpensive as possible, but I think they are leaving a lot of money on the table. They could have a "rough" cowl and a "finished" cowl, and charge more. One phone call to the supplier, and an extra part number. More profit. Once they realize that everyone buys the better cowl, they can drop the other one. I think they should hook up with Sam James - his cowl is very cool.

Anyway, thanks for the "rant"!

The pinhole epidemic on my 6A glass added another 60 hours to my overall painting bill not to mention the previous 80 that I already did on the parts before I gave up and handed them over to the professional. We found the best solution was to warm up the parts carefully with a heat gun and ROLL thick primer over the whole thing. As the part cools, the air inside the pockets contracts, pulling the primer into the void. A couple coats and you are ready to spray over top.

Not fun or cheap.

I absolutely agree, I'd pay another $1000 to have glass actually ready to paint from Van's and this was a lame excuse. The rest of the kits are so nice!

I haven't started any of my fiberglass yet, but I've been to Wally's class, and I read all I can. I'm still leary of starting, but I know I'm going to start soon. I doubt it will be as bad as I suspect once I focus on it, just like many other parts of this kit that I have tackled so far.

That said, I'd say most builders don't complain because we don't know anything about fiberglass until we delve into it for this project. At least that's my experience, and I doubt I'm alone on that thought. We don't know that it can (and maybe should?) be better! We don't have the experience to talk to Van's intelligently about it. We must leave that to others that are "in the business." From what I have heard, I'd be happy to pay some addition money for 'better' components, if it saves me a headache or two and some time.

Greg

Prepreg Glass parts require a lot of finish work

RV7Guy said:

I have considerable experience working with a variety of materials including vacuum bagging with glass and carbon.

Click to expand...

I guess this is your first exposure to a "prepreg" glass part. It was not made with a wet layup.
The cowls are made with glass cloth that is woven from glass fibers that are precoated with a small amount of heat activated epoxy resin. All of the layup layers are fitted into the mold, vacume bagged, and then put into an oven with a vacume applied. The amount of resin is not adjustable. Infact to have a strong but still very light part, the resin needs to be kept to a minimum. This is why prepreg parts are desirable.

If you where building a composite aircraft kit from one of the companies that use prepreg layups for the entire airframe (the now out of production Giles kits are one that comes to mind) you would be dealing with this on the entire exterior surface of the airplane.

I use Polyfiber "Smooth Prime" on all prepreg parts. I thin it slightly with water and roll on four or five coats with a foam roller. The documation says you can spray it but I never do. It sands so easily that it doesn't matter if the surface finish is realy smooth. After sanding with 150 then 220, spray finish primer and paint. Done.

How about we e mail this link of posts to Van's, maybe get some more comments in here before we do. I personally am a fiberglass dummie and am not looking forward to this work, especially being friends with Darwin (OK, I admit it) and knowing what he and others have gone through.......

rvbuilder2002 said:

I use Polyfiber "Smooth Prime" on all prepreg parts. I thin it slightly with water and roll on four or five coats with a foam roller. The documation says you can spray it but I never do. It sands so easily that it doesn't matter if the surface finish is realy smooth. After sanding with 150 then 220, spray finish primer and paint. Done.

Click to expand...

Maybe I'm missing something but I can't seem to find the "smooth prime", it looks like their products are mostly for fabric coating, could you help with a part # or something?


http://www.aircraftspruce.com/menus/cs/polyfiber.html

Pre preg

rvbuilder2002 said:

I guess this is your first exposure to a "prepreg" glass part. It was not made with a wet layup.
The cowls are made with glass cloth that is woven from glass fibers that are precoated with a small amount of heat activated epoxy resin. Done.

Click to expand...

No, I worked with it before. This is the worst example of it though. My friend just finished a Lancair Legacy and it wasn't nearly this bad.

Since the part is bagged the mold could have epoxy brushed in before the vacuum is applied.

There are ways to make the cowl better without adding much time or materials. This appears to be a cost savings measure.

If the effort is to make it light, the effort is somewhat being wasted on all the filler necessary to make it right.

Better quality cowls

I for one would welcome better quality with less finishing required. I hate fibreglass and it hates me; anything I can do to ease the pain I will, even if it means buying non-Vans, and even if at higher cost (such as Holy Cowl; though I haven't compared pricing on that yet). I'm several years away from needing to worry about it, but enough builders tell Vans they'd like better quality then maybe when it comes my turn it'll be sorted. Please, if not for yourself, do it for me!!

Here is some advice and opinion.

RV7Guy said:

My real frustration came with the cowl. As I began my prep by liberally washing the cowl with acetone.

Click to expand...

Most Fiberglass "experts" tell me don't use acetone as it will just contaminate it in facts lowers bond strength of additional plies. Sanding is good enough. Blow it off with "clean" oil water free air or clean dry lint free cloth. I take this on good advice of a Pro Lancair builder. It makes sense. I was into the solvents myself but he convinced me to stop that practice. If you want to apply some more epoxy or additional plies the KEY or secret is to sand with 80 grit. Solvent is not goodness. Go figure.

RV7Guy said:

I sprayed a coat of Feather fill primer on the cowl to see how extensive

Click to expand...

Most experts recommend applying the primer filler with a roller to force the primer into the holes. Spraying just "gaps" the hole which is exposed when sanded. You are NOT trying to fill a big surface low spot, you are filling pin holes. So force the filler into the holes. When you spray you just cover holes, you don't fill. After sanding, guess what, they reappear!

RV7Guy said:

Now where everyone can step in and affect change for future builders, the reply from Van's also included the statement, "we don't get that many complaints on the fiberglass."

Click to expand...

Vans NEW cowl is soooooooooooooo much better than the old poly and gel coat. I would rather deal with pin holes to get a lighter cowl that fits better and is dimensionally stable (heat) and does not have big waves to fill. I spent soooo much time on my RV-4 cowl to get flat surfaces. Fill big waves and low spots or a bunch of pin holes? Old cowls "shrink" over time from heating & cooling. Trim lines that fit perfect at the firewall are not so tight when the old cowls shrunk after 900 hours. Epoxy will not do this.

RV7Guy said:

For those who have completed their planes or are in the process of working on the glass, simply send an email to Van's to provide a few thoughts on the quality.

Click to expand...

I will not be writing because they have made great improvements on their fiberglass. An epoxy rich cowl would be heavier, and since its NOT structural, its OK IF it has some dry spot. Simply seal with epoxy. My RV-7 cowl had no dry area and love the sandwich core construction, which is way flatter, stiffer and lighter than the old solid laminate cowls. The new cowls just fit better. No complaints.

I guess you can't make all the people happy all the time. I feel your pain but hope you can work with what you have, since that is likely all you will get. Follow the suggestions above and I think you will have better luck filling PH's. George

Unfortunately the surface finish of my new RV10 epoxy parts are no better than those on my 6 year old RV6A glass parts. They just look nice from a distance and are a bit lighter. The old gel coated polyester parts were way easier to finish than the new epoxy stuff is.

The aftermarket replacement fairings I bought for my 6 a couple years back were perfect- no pin holes. A joy to sand, prime and paint.

Link to smooth prime

briand said:

Maybe I'm missing something but I can't seem to find the "smooth prime", it looks like their products are mostly for fabric coating, could you help with a part # or something?


http://www.aircraftspruce.com/menus/cs/polyfiber.html

Click to expand...

I typed in smooth prime under "search".
Try this link http://www.aircraftspruce.com/catalog/cspages/smoothprime.php

Scott

George's Experts

.

1.) Acetone (or similar solvent) is the only way to effectively remove embedded contaminates in the the epoxy. It could be release agent if a mold was used or the film that comes to the surface as the epoxy cures.If you have noticed in any advice I've given in the past it is to always clean with some sort of tough cleaner.

Sanding immediately will only grind the contaminates into the glass. Now you run the risk of never getting your paint to adhere properly.

2) Using a roller is okay but can "pull" the primer back out of the holes you were just trying to fill. Spray and then pushing the primer in with your fingers is one of the most effective ways.

I didn't start this to getting into a contest on techniques. Anything I post is based on first hand experience or knowledge and not from a multileveled source.

George, don't write if you don't want to. You clearly have the expertise in every area of aviation, building, painting, and flying at your disposal. For those that don't, a quick note to Van's MAY cause some positive change. Just because the cowls are better than they were, doesn't mean they still can't be improved upon. It is clear they can.

In the scheme of things, the glass quality does not match the quality of the kit. From the feedback, it is obvious that others agree and share the frustration.

rv6ejguy said:

I'd pay another $1000 to have glass actually ready to paint from Van's...

Click to expand...

Sounds like an aftermarket business in the making!!!

dan said:

Sounds like an aftermarket business in the making!!!

Click to expand...

Lol...yeah. I'll be happy to finish anyone's cowl who's willing to pay me $1000.

Seriously, if it's worth that much to you, I would suggest going down to your local autobody or boat repair/builders shop and asking them what they'd charge to fill your pinholes. I'm guessing they'll do it for a pretty reasonable price.

A question of quality control

I would suggest that Vans has grown from a backyard business to become a serious aerospace business...but that their quality control procedures may not have kept pace with their development.

A year or so ago when I was concerned about the quality of some Vans powdercoated component I emailed and asked them for a copy of their powdercoating specification as supplied to subcontractors (as with their composite suppliers they have a couple of them). To my amazement they said that they did not have a written specification.

When a company buys on price and without a written specification they are almost certain to obtain inferior goods and services. Subcontractors sensing that price is paramount to the purchaser will cut corners to keep their quote low if they are given a free reign on procedures. In the case of powdercoaters the first thing to suffer will be the pretreatment (cleaning/degreasing and passivation) of the product. I am sure composite manufacturers will also have their own way of cutting corners when there is no written specification.

It would be interesting to know if in fact Vans adheres to any QA standards at all. The most common one in manufacturing is ISO9000. AS 9000 is the Aerospace standard and the current version is AS9100.

Some people might argue that implemented QA programs could add significantly to the cost of the components. I personally did not find that to be true. In fact it forced me to be more organised and run a better business with less problems resulting from rejected products.

60 hours to fix all the pin holes in all my -6A glass parts X $45 hr. Of course the first 10 were spent trying different techniques until he found one that worked. He said this was the worst glass he'd ever seen. He's faster now. I'm glad I could fund his education! It will come in handy on the RV10!

dealing with the pinholes

I don't have an RV, but I have sanded many of them starting with the 4s. The epoxy pre-preg cowls are a big improvement over the heavier poyester parts. Pinholes are part of the deal. The cost of fixing the pinholes is not adding a little epoxy. Another layer of material, specifically designed to minimize pinholes would have to be added to the layup process.
But the answer today is to deal with the pinholes most efficiently. My technique is a bit different tha those mentioned. Heating resin is certainly a good idea. I totally endorse the hair dryer as opposed to a heat gun. It is almost impossible to overheat the structure with a hair dryer. I use that technique to seal the inside with a few table spoons of epoxy. (Thinning the epoxy with ANY solvent changes the mechanical and chemical properties of the epoxy!)
The pinholes on the outside are best dealt with by getting any good two part epoxy and using a roller to apply. Get the white foam 4 or 6 inch rollers from the big blue or orange stores and apply in at least two directons. The pressure from the foam will push the primer into the little holes. Spraying the material forms a sheet that bridges over the holes. This forms thousands of little air springs. The foam will deal with all but the largest of these. A small amount of epoxy and micro or West 410 and a spreader will solve the rest.
Hope this helps.
Charles Wilhite

First of all, anyone who would like to contact me off list can get my address where to send their cowls and I will fill all pinholes and get them in primer, ready to paint, for a measly sum of $550.00 + shipping back to you.
(Really; serious... this could be a great way to finance the RV )

On another serious note; if you guys keep conspiring to force Van's to deliver a "perfect" kit to you, you might find that you could soon be paying $50,000 for a SB kit. Be careful about what you ask for.

Vans fiberglass work !!!

my experience with builing an RV6A and an RV10
Vans metal work is excellent on a scale of 10 it rates a 10...fiberglass is under average it rates a 4

Holy Cowl

Trust me I have a Holy Cowl and I called it alot of bad names trying to fill the thousands of holes just like you had with Van's. When I called Sam on this problem that I thought I was buying a better product than Van's his answer was "everyone else's product has pin holes why should mine be any better"!!!! So when you get a reply like that your confort facter goes way down. This may be an opportunity for the OEM that makes Van's to offer a better part for more money??
Frank Thorman
N821BF 9A
160+ hrs flying

Experts do count - acetone bad?

RV7Guy said:

Please people do not listen to the latest comments by George regarding his "Experts."

Click to expand...

First the guy who told me NOT to use acetone to clean before bond is a PRO
builder that makes several million dollar Lancairs every year. If you go to the
Lancair discussion groups, you will find DON'T WIPE WITH Acetone!!!! Sand
with 80 grit (ed: for bonding only, 120-150 for surfice finish prep) .

I did not believe it at first but test have been done, and the BOND strength is
lowered with samples that where wiped with Acetone. By test I mean Peal Ply
test and Tension Coupon test.

I trust people who know better than I and don't need to re-invent the wheel.
With fairings, strength is not an issue, so do as you like. If anyone is not
convinced do the research and people who work with fiberglass. You should
get a the same story, may be not.

It makes you feel better to wipe the acetone on, but the additional plies
would stick better if you leave the acetone off. Blow it off (with clean air),
vacuum, but don't wipe it. It contaminates the surface. # 80 Grit is key
(ed, for additional plies only not prep for surface finish) .

My composite experience is in real aerospace structure when I was an
engineer for Boeing. What we do is HOT TUB technology, so there is no need
to get all wrapped up around the axial about it. Skip the ACETONE and you
will be better off.

In my humble opinon. George

PS Roll the initial filler on and PUSH it into the holes. Use your fingers or
squeegee. Don't wipe everything off with acetone use air or a vacuum. You
want filler in the holes NOT acetone. That is the advice Van's Aircraft has
given me, but what do they know. There are 100 variations on what steps to
do.

Yes the pinholes are definitely more work. The lack of Van's fixing the problem may be an indication of difficulty in doing so. I only say this because I'm sure they have heard of it many times. An easy fix wouldn't hurt.

It's always nice to keep the base the same. Epoxy on Epoxy and polyester on polyester. I decided to get away from that reasoning and used Evercoat "Slick Sand" on the cowling. It's about the consistency of honey and can easily be squeegied on...and into the holes. (Always go in both directions.) It is polyester base but it goes off hot enough to not care what it's sitting on. It's 2-part and gray in color. I just kept mixing a little and applying as I discovered more holes. I did the same with the gear leg fairings and rudder fairing. It sands nice too.

When we built pre-preg honeycomb structures while working in the composites shop, we'd use frozen sheets. You simply lay them on the mold and bag them. They begin to cure as they thaw. Heat shortens the cure. We'd vacuum bag the piece and throw it in the walk-in oven. The holes are dependant on the manufacturer of the pre-preg. They could use a little more resin. Adding just enough to help the cowlings wouldn't be a big deal. On the other hand, the stuff might be a standard used on numerous other non-RV parts.

I wouldn't be overly concerned about the filler getting to the bottom of the holes. As long as you cover them, your paint will shield them. You wont stick your finger through them when the paint cures anyway. The paint will be the equivalent of a 3" table top over a cereal bowl.

There are plenty of examples of good lay up work on finished parts. Van's chose a cheaper method. I'd say it was a tradeoff between price and what they thought the builder could deal with. It sucks that there are as many holes as there are. On the other hand, doing the baffling and making the canopy fit right sucks more.

You can always start early. Get some filler now. When you're bored...or between areas, take it and fill a little. By the time you're ready for paint, you won't have any to worry about.

The only thing Acetone is good for is cleaning tools. There's nothing better than a freshly sanded surface for adhesion beteen resin impregnated parts. Sure, you can thin some resins but having it on the surface changes the molecular structure of the bond at the surface. Any solvent that's strong enough to break down....and then spread the contaminants across the surface is undesireable. Guys do this sometimes while prepping aluminum for paint. Instead of soap and water they use laquer thinner or something else. They end up with a micro thin layer of contaminants because the stuff cleaned too much...and took everything with it.


John
Air Force, Lockheed, Agusta, Raytheon, Boeing - Composites and Depot structures- 22 years
http://experimentalrv7.com

Part of the 51% ???

I figure Van's uses this cowl thing as part of the 51% rule...
With all the pre-punched holes, perfect CNC cut parts, etc, etc...I figure they've got to get the builder's hours up "somewhere".

The scoop with acetone:

It's not a problem wiping down a cured fiberglass part with acetone as long as the acetone is fully evaporated before sanding (edit: ALWAYS sand it/rough it after cleaning it if you choose to clean it like this) it in preperation for a layer of cloth/filler whatever. When I do it I use a hair dryer to be absolutely sure that the acetone is gone gone gone. Given this, there is no problem with acetone.

Here's the problem: Epoxy does not fully harden for a long time. Well after the epoxy seems like it's set it is still in the "green" phase. This is an important time if you're doing layups because additional layups will chemically link with the still curing epoxy. If you do a layup and then come back the next day, wipe down with acetone what you think is cured epoxy from the night before and try to do a layup on top of that the bond may not be nearly as strong as it should or could be.

Feel like guessing when it's ok to wipe? Me neither. The basic rule of thumb I use is I clean with acetone when I first start working on a premanufactured part and dry it with a hair dryer....I mean REALLY dry until I'm absolutely sure it's done. This gets off any manufacturing crud than might be on it. From that point on the only thing it sees is sandpaper, clean air and love. If I'm laying it up myself there's no reason to be wiping anything with acetone because presumably the fiberglass doesn't come precontaminated with anything.

What everyone's said about this so far is pretty much on the money in various situations, and certainly if I were builing a glass airplane I would VERY careful about introducing any foreign chemicals to my layups, bordering on compulsive.

disclaimer: I've gleamed this over years of working with the stuff and this is just what works for me...don't take my word for anything. Call manufacturers and do your own research. Post what you find...if I'm wrong, I want to know about it

Stuff in the Rag

jcoloccia said:

The scoop with acetone:

It's not a problem wiping down a cured fiberglass part with acetone as long as the acetone is fully evaporated before sanding (edit: ALWAYS sand it/rough it after cleaning it if you choose to clean it like this) it in preparation for a layer of cloth/filler whatever. When I do it I use a hair dryer to be absolutely sure that the acetone is gone gone gone. Given this, there is no problem with acetone.

Click to expand...

I hear you and fought this for a while, but rags have contamination. Acetone
is not always pure. (A can of Home Depot acetone had oil all over the can.
What was in it?)

It's not a "problem" but there can be fibers from the rag or other
contaminates transferred to the surface. There can be trace oil or even
worse, silicone on rags. You are just spreading it all over the surface. Even
new rags can be contaminated during manufacture.

That's my story and I am sticking to it. I had some hate mail on this so
people feel strongly that acetone rag wipes are goodness. Peace. Works for
you works for me, I just have changed my "process" to avoid it.

When you sand you scarf the surface and expose bare virgin material. Also
the strength test show not wiping produced stronger bonds?

I guess you can do the air dryer, but you may have tiny fibers from the
rag or other object in there. Blow off with clean air (no mosture, oil) and
good to go.

Also let's not get bonding additional plies and pin hole filling mixed up.


RV7Guy had lots of problems and wanted to start a letter campaign to Van to
increase resin content; Probably a good idea but weight and cost go up. I did
not have that much problem. He sanded and wiped his cowl, than sprayed
filler on. Sanding and acetone wipe downs can fill or bridge the pin holes with
STUFF, i.e., wax, dust and acetone. The acetone goes away but the stuff it
flushed in there stays. Spraying (can) just covers the over the pin hole not
fill the pin
hole.

Why even sand at least in the first pass. Just clean with wax and grease
remover. Soap and water? (smooth prime is water based filler)

ROLL the filler on and force the filler into the hole (again fingers, squeegee
what ever). Filler can't get into the hole if filled or bridged. You are not trying
for a smooth surface yet when filling holes. You are not worried about
surface prep. You are just trying to fill holes, not finish the surface yet.

After the holes are filled, you can do surface filling, sand with 150
grit all day and if you MUST, wipe with acetone, although acetone is a
counter productive step even for surface filler, for the same reasons it's
for bonding additional plies on. But if it makes you happy.... do it. Like you
say its not a problem with non-structural fiberglass. This is a minor deal.

I also feel better wiping the acetone on, and did it for years but the Lancair
builders tell me don't do it?

To each his own, but I have changed my technique on their advice. Could be
wrong but it seems after exposing the virgin material why fill the surfaces
with anything other than resin or filler.

George

"All info is my opinion or opinion of others that work with fiberglass planes everyday. Ignore or Use at your own risk."

I've always wondered about the whole "wipe with acetone" thing. If we assume that the surface has a bunch of wax, muck, and what-have-you on its surface and we wipe it with a solvent soaked rag, doesn't that just dilute and spread the contamination all over the part? I mean, you can dry the surface all day long with Granny's 5000 watt old-school hairdryer and all that's going to evaporate is the acetone, leaving behind a nicely distributed layer of the original crud. Now I know that some of the stuff will get stuck to the rag, but all of it? Most of it? I think that repeated wipings will do the trick, but I think that one pass with some solvent will do next to nothing. JMHO.

George, I agree with you, believe it or not. I wouldn't sand or prep before filling pinholes. I just wanted to make the point that acetone in and of itself is not evil or anathema to good adhesion or strength and also maybe try to explain where the "rules" come from and why. They're good rules especially for structural layups. That said, I don't think there's any glass work on an RV that warrants anything but scuffing off the sheen before priming or roughing with 80 or 100 grit before bonding.

As an aside, back when I was heavily into R/C aircraft, I'd almost always leave the cowl off....way too much work

Clarification

For those of you who are concerned about acetone, I'm not talking about bathing the part in acetone but a good liberal wipe down. The purpose is to remove any of the parting agent used in the mold. If you don't do this and only sand you are going to sand the parting agent into the glass and you will never get a permanent bond.

George, if you think the acetone is going to remain in the pin holes you are even less experienced than I thought. Even in cool weather acetone evaporates rather quickly.

The sanding breaks the surface and OPENS the pin hole even more so that it can be properly filled.

Rolling the filler is the only approved method according to George, so I suggest everyone do it this way and contact him for future advise on this and all other RV related topics.

Clearly I'm ignorant and my 30 years of working with fiberglass are all wrong. I'm done with the Forums for a while. Don't need the aggravation and constant conflict with a couple people who seem contrary to all ideas that aren't theirs.

Darwin,

I hope you'll reconsider ditching the forums. I, for one, appreciate info from guys like yourself who have actually been there/done that. I find that an awful lot of info here and elsewhere is of a second or third-hand nature, and therefore not particularly reliable. I've done a fair amount of body and paint work over the years and suffered through a lot of crappy advice before finally getting it right. Seems like everybody I met had some third-hand bit of "wisdom" to share. Nonsense that they read in some hotrod magazine or off a can of Bondo.

On the other hand, there is a TON of good info on here and us builders really need you flyers to help us out.

Porosity in thin skin elevated cure epoxy based honeycomb core parts is an industry wide problem (aerospace not homebuilding). The issue is that the epoxy cures at typically 250 or 350, and any trapped volatiles in the resin (left over from the prepreg process or moisture absorption because of the highly hygroscopic nature of epoxies and fiberglass) flash off causing porosity. The solution is to apply more pressure. Vacuum bag/oven cure processes can only apply one atmosphere of pressure to the laminate during cure. However the vapor pressure of water is higher than one atmosphere at 250F, causing porosity in the laminate. Oh, and the core itself is hygroscopic and releases water during elevated cures.

Autoclaves are used on aerospace structures to cure the composite at typically 45psi for sandwich structures and 90 psi for laminates. However, the pressure of the autoclave is reacted through the honeycomb core into the outer plies only thought the cell walls. There is very little effective pressure in the composite over the core cell, so porosity forms. The solution is to use thicker skins, more plies (what Vans supplies is only a few plies over the core), develop exotic cure cycles that typically involves autoclaves ($$$), or switch to foam cores. You can add more resin, but this does not eliminate the volatiles/moisture, nor does it fix the problem.

When you are filling your pinholes just be glad you are not an airliner flying around with thin skins over honeycomb core all over you airplane (fairings, nacells, control surfaces). The changes in altitude effectively pumps moisture into the cells through the porous skin, filling them up with water. Eventually enough is there that when it freezes (up high), the skins will pop off. A lot of $ are spent on this problem, and only recently have the major airframers been able to resolve these problems. But they use autoclaves, not ovens.

As one who would know (he's been there, done that, had to explain it the the Navy) often says, "The road to **** is paved with honeycomb core"

As for surface prep, I am sure George is not recommending sanding the cowling surface with 80 grit sand paper. Sure if you are getting ready to bond a spar to a wing skin, but 80 grit on 2 or 3 plies (each .005" thick) will cut through one maybe more plies and weaken the structure and make matters worse. In this case, solvent wipes are the best method of surface prep. But you have to wipe the solvent on, and immediately wipe it off with a clean rag to remove the solvent and the dissolved contaminates. And this should be done multiple times.

After cure at elevated temps (if done right i.e held for adequate time for the cure temp), the epoxy molecules are fully crosslinked and are not affected by the solvents.

FWIW the glasair I built was about 1000% better in the fibreglass aspect to Vans kit. Minimal prep to get it ready for paint. I love my RV7 but would gladly pay a bit more for the glass work to be improved. I can honestly say that not a single fibreglass part on my 7 fitted properly . Everything had to be trimmed ,adjusted ,built up etc. Then all the pin holes!

Also there is more than one way of doing things . I filled pinholes using Vans method, my method or someone elses way. They all lead to the same results eventually. Patience being the key.

Glasair insists/requires all parts be wiped with acetone before bonding. They did tests showing that it was giving a better bond. Perhaps Vinelester reacts different to epoxy. I dont know.
Bob Herendeen flew aerobatics in a Glasair III pulling up to 9g and the plane still flies today. The layups held , and all had been wiped with acetone.
Honestly I dont believe it makes a major difference either way.

Maybe we could have a Vote for who would want better fibreglass parts and what we would be prepared to pay extra. Arguing between us wont help. Lets show Vans either way what the builder wants.
Let the majority win!

With all the required cleaning in an RV-7 project youl'd need a truck load of clean rags to solve the problem if you used acetone for all the big stuff. Acetone and MEK are primarily used for cleaning metals. Prior to bonding it's common practice to use clean cheese cloth with a small amount of MEK or acetone applied to it.

Sure, this stuff will clean but you'll have to clean over and over again if your dealing with a large surface like a cowling. The first wipe down just spread crap around. The second thins it out a little. The third does a little better. The fourth...well it might be ready. Reality is, the strong cleaners are de-greasers and wax/silicone removers. After that stuff is gone, soap and water can be used....or an air dry if you're sure the part is clean. There's no use cleaning with acetone unless acetone is the only cleaner strong enough to remove something you're trying to get off the part. Small metal pieces are different because you have a limited surface and nothing soaks in. Cleaning takes a wipe down for the big stuff...and then another with clean cheese cloth.

If you ever tried cleaning bare aluminum with acetone or MEK you'll see what a mess it can be..and how many rags it takes before you don't see the black crap anymore.. Soap gets that off because it's just strong enough to remove..but not strip or thin whatever may be left.

I'd sand the cowl with 150-180. Blow it off. Then go over it with whatever filler you desire. Again, squeegie for and aft or side to side. Poke it in with a stif bristle brush...and then squeegie. The problem is that the filler rolls down into the hole and then gets pulled out on the same stroke. It never had a chance to grab on to anything. There's also air in the hole that prevents the filler from getting in. It's a hydraulic lock effect. Squeegying is better because it allows air to escape as you cross the hole. To assure it does, come back across it from the opposite direction. Poking it or jamming it in with a brush helps it stick to the inside of the hole...and assures that when you squeegy it..it sticks to the inside.

I had to come back to the info about autoclaves...and the "been their..done that" thing. Autoclaves are great for a multimillion dollar manufacturing process. Fact is, all that stuff has to be repaired out in the field. Big and Small. It's all re-skinned, stripped, cleaned, beat on, sanded, heated and exposed to all kinds of potential problems. After going through advanced composites training and then working in composites for nearly 22 years, I've seen just about everything having to do with composites on transport and fighter aircraft. I definitely agree that a structure must be free of water. I had a bad experience with a wingtip repair on an F-15. It froze and blew up in flight. Not just a separation. We manufactured spoilers for KC-135's, C-5's and C-141's. Autoclaves were used for more exotic compound curved pieces that we couldn't duplicate. Still, everything we did had a process to eliminate possibilities of voids and moisture. It included heating, cleaning, vacuum and all kinds of other stuff you can do in your garage. We just did alot of it.

Voids were the worst because the air would expand. Condensation would eventually form and little by little the void would expand. We used ultrasound on the deep stuff like Boron Skins but much of it was located doing a coin tap. Sometimes we'd get away with an injection of 9309 or 934. Other times we'd replace the skin and core. AH-64 rotor blades were a problem. They're layed up with a combination of titanium spars and a honeycomb/Fiberglass skin/core. Still, we'd cut out the core, reskin and then repair the overlapping spars by bonding with Hysol 9309 and scrim cloth. I never did see one of them explode like the wingtip did. F-15 rudders were terrible for this. A combination of vibration and moisture nearly tore them apart. During 907 Mods on the entire fleet of C's and D's We rebuilt the upper 1/3rd of the vertical stabilizer and torque box assy's, inserting sections of core after routing it all out. Titanium blocks were used for reinforcement along the forward spars. Hysol 934 was used for bonding. It was mixed by hand and never vacuumed to pull the bubbles out. (By the way, you can suck the bubbles out of structural adhesive using a vacuum and a glass bowl with a lid) For all the scientists out there..I can say the work was crude and nasty..but it worked.

We'd glass the flaps on the 141's. It took 2-3 guys just to hold the sheets because they were so big. We'd lay it up just like a surfboard. By the way...Surfboard builders use parafin wax for a hot coat to prevent moisture from interfering with the cure at the surface. Kinda like gas in a TIG welder. You mix it with the resin. It floats to the top and dries like a shield over the uncured resin. Then the resin goes off. The result is a tack free polyester surface that's nearly polished. Polyester normally gets tacky and difficult to sand simply because of the moisture interaction at the surface.

Oh yeah...have you ever coin tapped a C-141? Thats real fun. Structural panels, cargo doors, spoilers, lightning strips, radomes and all the wheel well areas. It takes 5 guys 3 hours.

Anyway, I've been their too. It's all on how you understand whats going on with what you're working with. The talk about third hand information is correct. Since we are probably working within the confines of a garage or living room...or maybe even a hangar, we probably won't see much in the way of an autoclave.

I'd suggest keeping things simple and experimenting a little. There are some things you shouldn't do. Make sure you know what they are. You will remember the things you figured out much longer than you do the things someone told you. Always weigh the advice from others. Take it all and come up with a solution.

Oh...here's the surfboard..


What a mouth full
john - http://experimentalrv7.com

Try coin tapping this!

http://www.newairplane.com/en-US/Extras/TechnologySpotlight/composite.htm

Oh, by the way, no fillers or pinholes on this airplane! Fillers will crack and flake off after 40 years of hard service.
Here are some more photos.

http://www.boeing.com/companyoffices/gallery/images/commercial/787/k63374.html

http://www.boeing.com/companyoffices/gallery/images/commercial/787/k63211-1.html

John,

Dude, you blinded me with science!! That was a whole lot of very cool info. I also just checked out the paint section of your site -- very nice work. I do have one small bone to pick though. In my opinion you were a little unfair in your appraisal of HVLP guns. I have a Sata and I love it soooo much better than my other conventional guns. It sprays a perfect pattern and is so easy to control sometimes I feel like I'm painting with a brush. It also doesn't fill the entire shop with paint mist. I'm sure some of the HVLP's aren't great, but I can tell you that the Sata most definitely doesn't suck. Beautiful paint by the way.

Food for Thought

One thing only I know and that is that I know nothing.
Socrates (BC 469 ? BC 399) Greek Philosopher of Athens.

So much information, so much food for thought. Not necessarily all based on knowledge, but still, thought provoking and even enlightening at times. With all this food for thought, I have to be careful to avoid indigestion. Unfortunately, by then time I get to the pin holes, they will be long forgotten and I?ll have to learn about it all over again. This must be the education part. When do I get to the recreation? Oh, I know. When I get to fly my beautiful, pin-holed, possibly unpainted RV-7.
Darwin, please don?t bail on us. Your input is valuable and your kindness in the past is appreciated.