Classic Fundamentals...a tutorial...post your building techniques HERE!

Creating Classic Pattern models can be even more fun and rewarding if one has a few little tricks of the trade. The RCU Classic Pattern Forum may benefit from a specific thread for the "drive by" RCU reader/poster to consume or share information...like..."Ask Jeeves" or the "Shell Answer Man"...hence this thread.

Post your build, rig, prep, finish, engine, mechanical, R/C system ideas or questions HERE! Maybe the smart folks at RCU will make this a "Sticky" and keep it up front?

Tools, tools and more hand tools. The photos show tools I use to measure, shape, copy, bore and drill.

Have an idea and are too lazy or shy, lack the technology to post...give me a call and I will give you some assistance.

Rusty Dose
Team Futaba
Team YS Parts and Service
Editor "Classic Pattern-Trader"
(312) 580-6838 office Chicago
[email protected]

Bonding glass cloth on wing skins - Historically I, maybe all of us, used polyester and the toilet paper technique to bond glass cloth to center sections and wing skins. My "new" technique is to use west systems with fine dacron cloth as a peel ply. I use a bondo squeegie over the dacron. The dacron cloth peels off very easily after the epoxy is set. This cuts the prep work and time by about half over the classic tp method. I've used this on both classic pattern and pylon wings with great success.

OK... what's "west systems"? What's a "peel ply"? What's a "bondo squeegie"? How is the dacron cloth used? What is the "fine" kind of dacron cloth? As you may have guessed, I still use TP and polyester. The last tip I tried was to use acrylic lacquer to bond 3/4 oz. fiberglass cloth to the balsa surfaces. Did it once, never again. When direct sunshine warms up the surface, the acrylic starts to bubble. This does get ugly.

ChiefK

I don't want to steal Rusty's thread but this works great and provides a very robust finish. I'll be more specific. West Systems is a commercial epoxy resin. I use 105 resin and 205 or 206 hardener. When mixed the consistency is like syrup. It will become very viscid when heated. If left in the mixing cup it will flash very fast so it needs to be spread out immediately after mixing. I use a short nap roller (1/8") to apply to the wood. Lay on the 3/4 oz cloth, pull tight - same as the tp method. The squeegies I use are intended for auto body filler but there are many sources for hard plastic squeegies that are used for laminating etc. I squeegie the glass into the surface of the wood and squeegee out any excessive resin - there is very little if the epoxy is spread evenly with the roller. The dacron cloth I buy from a sewing place. It is fine mesh shiny white stuff intended for dress liners - very inexpensive. I was leery when I started doing this so I recommend doing a test sample on a scrap wing core to perfect the technique. Spread the dacron over the wetted glass and squeegie the whole thing smooth. It will bend around wing tips and edges but not as well as the glass does. Some resin may bleed up throught the cloth which is ok. Ideally the dacron will be slightly wetted out the same as you would want with glass alone. Let the whole lot harden then peel the dacron off. The dacron soaks up the excess resin and leaves few if any pin holes. A light sanding and it's ready for primer. If you get the layup too dry, there will be pin holes and/or dry spots. In this case. Sand lightly and squeegee a coat of epoxy over it. Very little epoxy will be used but the pinholes and dry spots will be filled.

peel ply is as simple as a yard of white dress liner (pure polyester cloth if i remember right). i wet the center section with epoxy, lay the cloth, wet it again and then lay the dress liner. take a credit card or a roller and squeeze out the resin. you can over do it i found out. anyway, when the epoxy dries just peel the dress liner away. there's a super smooth epoxy finish in front of you. i've heard vacuum bagging is even smoother.

instead of epoxy i used polyester resin for my center section on my last 2 builds. the peel ply works equally as well there.

On glassing:

While the peel-ply approach is a definite and required technique, I've learned about the magic of epoxy and alcohol. I like to think of alcohol as an epoxy tamer so to speak. When using epoxy (typically laminating epoxy but long dry epoxy can be used too with almost similar results) for a wing center section, I typically paint thinned out epoxy over the cloth in several layers after wetting out the center section. Depending on the thinness of the adhesive, the layup comes out to be very smooth and glass like.

In doing the center sections, I typically start with heavy glass cloth and proceed on to light glass. In most cases I'll go with 6 oz cloth followed by 3/4 oz cloth but in some cases I'll use 2 oz cloth in a third intermediate layer or sometimes will avoid using 6 oz cloth when weight is critical. The size of the cloth of course changes depending on the layer and cloth weight involved. Regardless, I like to finish with 1-2 layers of 3/4 oz cloth which produces the top glass like finish.

I've found that when using this liquid paint on technique, peel-ply is not required as it produces very good results. The trick is in making sure that the solution is thoroughly mixed and blended as epoxy and alcohol tend to want to separate. Of course, the alcohol evaporates quickly as the epoxy cures and all that's left is the smooth glassed surface. I also often use a Bondo scraper to remove any excess adhesive and to thoroughly wet the cloth.

David.

David, can you clarify one point? What type of alcohol do you use, denatured or isopropyl? Or does it really matter which you use? I've never been clear on which should be use for thinning epoxy.

FB

Much clearer... but one more question. When you resin the dacron down on top of the glass cloth and allow it to set up, why is it not bonded to the glass surface? What allows it to be simply "peeled" off?

ChiefK

ChiefK,

That's the same question I had, but you beat me to it..

David

ALWAYS use denatured alcohol. Isopropyl that is availible to the public contains up to 30% water! Use of isopopyl alcohol will make the epoxy rubbery.

Rick,

as Jeff points out, it is preferable to use 100% alcohol. However, a little clarification of what that means might be in order.

My understanding of the term denatured alcohol is that it is given to solutions that contain other dissolved chemicals. It is essentially comprised of ethyl alcohol or ethanol (level 2 carbon) which is what provides the smooth feeling after a couple of drams of Scotch. Because pure ethanol is fit for drinking (well, not to me...), US and Canadian law prohibits the sale of it in drug stores in it's pure natural form. It is therefore denatured. The denaturing process often consists of adding up to 30% by volume of other solutes including in some cases 10% methyl alcohol or methanol (level 1 carbon). Although the other solutes (~20% by volume) make the whole solution undesirable for drinking (single malt is considerably better), the methanol is key since it not only is used as fuel in Indy 500 race cars but it is also used as the main fuel in our glow engines. Further, methanol, when ingested, can cause blindness and if the eyes are exposed to sufficient methanol externally, they can also be affected either temporarily or permanently. I am living proof of the latter case but we won't go into that topic. In short, the denaturing process of ethanol and subsequent sale in drug stores is in principle a legal one as I can't really see how it would be a safety one assuming the solution contains methanol.

In Canada drug stores actually carry rubbing alcohol which is essentially denatured alcohol but contains no methanol - hence, safety and legalese are taken care of. But..., the issue with many of these denatured alcohols is that they also contain a certain amount of water (usually to provide a solvent for substances such as camphor) which, as Jeff also points out, is undesirable when mixing with epoxy. In short, ideally one would purchase 100% ethanol for our application assuming it can be obtained. For years I've used a bottle of pure ethanol that I purchased abroad a long time ago. When it's finished, I'll have to consider my options.

To briefly mention isopropyl alcohol or isopropanol, it is an isomer (molecular re-arrangement) of propanol (level 3 carbon) which is used as an antiseptic, rubbing compound and solvent. While in principle, if it were easily obtainable, 100% propanol might be as suitable an epoxy solvent as ethanol (I haven't tried this so I can't be certain), the problem is that isopropanol is sold in even more weak solutions. The bottle I have here is actually 50% by volume with the remaining 50% being water only. Typically, isopropanol is sold with no added methanol so it is considered widely safe.

In summary, I think the trick really is, in the absence of 100% ethanol or propanol, to find a solution that contains the least amount of water and other dissolved chemicals. Many bottles indicate the percentage by volume of the active ingredient prominently so one can try a couple of different formulations based on that figure. Personally though, I make an effort to stay away from methanol containing solutions for reasons mentioned above. Unfortunately, glow engines prevent me from abstaining entirely...

And with that brief dissertation, please follow Jeff's advice and use low water content denatured alcohol. I think that I actually enlightened myself on most of this as I wrote it.

David.

P.S. This note has provided some inspiration. I might have to go and pick up a bottle of Lagavulin this evening.

http://www.scotchwhisky.com/focus/lagavulin.htm

Isopropyl alcohol is primarily for medical use. Denatured alcohol is a solvant.

ChiefK

Wow! Sure opened a can of worms with that question!

David, thanks for your thoughts and experienes. I normally use isopropyl for exopy clean up and such. I buy it @ 90% concentration. I used to be able to buy denatured at the drug store, but no more, only isopropyl. I don't do a lot of expoy thinning, but I have used isopropyl in the past for thinning with no ill effects. Time to go buy some denatured!

FB

I have succesfully used plain methanol for epoxi thinning both for laminating and as a paint to fuelproof tank and engine area.It works well by taming the epoxi pot life ( I do it even with 30 min epoxi glue ) and allowing it to flow better and to fill the glass cloth accurately with a simple pincel.
I usually mix my own glow fuel so....

I just bought 99% isopropyl at Meiers (sp?) grocery store the other day. They had in 30%, 70%, 90%, and 99% alcohol forms.

You can also get denatured at most hardware stores in quarts and sometimes gallons.

Acetone is another great thinner, also found in hardware stores.

Andy

Andy,

Nice to have that bit of info. Since isopropanol seems to be readily available in varying strengths in the US, the question remains how, if any, does the fact it is an isomer affect its properties when mixed with epoxy? I'm sure that at 90 and 99% it works well but it be interesting to learn further what the reason is for using an isomer of the pure form for medical applications. Something to look into...

Acetone is a great solvent for many things (particularly paint). I just dislike the way it smells.

David.

P.S. LatinRClover, be careful with that methanol. As mentioned, it is a dangerous substance especially if accidentally mixed with hot water. Don't ask...

David,

I don't use solvents of any sort with epoxy, except to clean up. I prefer heat to thin it out.

You can also extend the pot life by cooling the pot. It makes it thicker to spread, but that's what the heat gun is for.

Andy

PS - I prefer the smell of acetone over isopropyl any day of the week!

Interesting about the methanol being so dangerous. I have been involved with a certain motor racing sport which we mix distilled water and methanol for anti-detonation injection and other than drinking it I always considered it relatively safe. We used to use the same mix in airliners too. Of course as we learn more about skin absorption the dangers prove a little more serious. The hot water mix danger seems near explosive or a fumes/vapors problem?

I can't wait to use the dress lining and epoxy technique on my latest project. I have never done it that way after 40 plus years of glassing center sections! Thanks guys...

Chris...

David,

dhal22 is apparently not available to answer my question about "peel-ply". Can you give me some understanding about how the dacron can be "peeled" after essentially bonding it to the underlying glass?

ChiefK

ChiefK, sorry, i didn't realize you were asking me. the dacron term threw me. i was calling it dress liner or peel ply. i have no idea why the peel ply doesn't stick to the epoxy. there is a king kobra thread in the kit building forum where the builder uses peel ply thoughout the finishing stage. i tried it and liked it. i wouldn't even say you need to practice the technique. it is pretty simple.

The dacron cloth has a shiny texture kind of like the finish on the nylon cloth in a windbreaker. It is also very strong and flexible. It will stick to the epoxy when the epoxy is not cured but does not readily bond very well to the cured epoxy. I have tried some tests by peeling off the dacron with the epoxy in different stages of curing. During hot weather in florida the epoxy will start to harden in about 45 minutes and be solid in less than two hours. At about two hours the peel ply will come off but requires some strategic tugging to not damage the underlying finish. With an overnite cure, the dacron cloth will readily pull off with a lot less effort. I found it hard to believe until I tried it!

If you're just doing a center section, a test is probably not necessary. I do three bids of 2 ounce in a center section and 3/4 oz on the entire top or bottom of a wing in one layup. This does require everything to be precut, and planned because the working time is limited. Once everything is ready, it probably only takes about 15 minutes to do the work! Using multiple bids (layers) of the 2 ounce cloth works best for me because it is thin enough that it can be faired smooth under the peel ply and no additional finishing is necessary. For example on a classic pattern wing I will lay a two inch width, then a four inch width, then a 5 inch width. I will post some pictures when I get home.

Chris,

that's right. Vaporization is the issue with substances containing methanol. Since pure methanol vaporizes at room temperature, adding it to boiling or very hot water causes the water vapor to become saturated with methanol and in turn, if it comes in contact with the eyes, can cause damage to the tissues and even to the optic nerve (this latter typically happens if ingested and is what can lead to blindness).

I wasn't going to get into it but since we are here... Due to an experiment in a lab during my academic years, a methanol containing substance was poured down the sink as required by the procedure and subsequently drained with water. Unfortunately the water faucet contained very hot water even if the cold tap was turned on and the reaction was immediate. My eyes were thoroughly immersed in this hot methanol saturated water vapor and my eye sight went foggy instantly. After that my vision was blurry for what seemed like a week or two. In the end it never did return fully and I went from having what used to be excellent vision to slight short sightedness. The immediacy and impact of the accident never quite left me and I remember the event and day vividly to date. Unfortunately, although it sounds like a superhero creating scenario the long term effect hasn't been quite as positively dramatic.

David.

Greg,

I'm not sure if this is directed at me but in a nutshell, Dacron is a polyester fabric. It is made from the same compounds used to make polyester resins for use with glass fibers (e.g., in the production of FG fuses). As we know, epoxy and polyester resins (or fibers) don't bond and as the epoxy cures over the glass, the Dacron is rejected from the bonding process making it easy to peel off once fully cured.

Think of it a bit like cooking eggs in good old Teflon pans - breakfast won't stick. Actually on that note, we should avoid use of Teflon pans as it can decompose under certain conditions and release toxic substances into our food. (If interested, read http://en.wikipedia.org/wiki/Teflon#Safety.) Ceramics are available today that do a pretty fair job for breakfast ease of washing.

I would expect Dacron to simply be absorbed into the bonding process if polyester resin was used for glassing a wing center section but I've never seen this as I don't use polyester resin (the fumes are too strong for my liking as you may appreciate from the tale in the post above...).

For further reading, this page may be of interest:

http://en.wikipedia.org/wiki/Polyethylene_terephthalate

Interesting that in the production of Dacron, methanol can be a byproduct.

David.

Thanks for bearing with me guys... I think I'm getting closer to understanding this. I do need a little more clarification though. Are you saying that if I bond multiple layers of fiberglass cloth to my wing centersection using epoxy resin, I can use more epoxy resin to layer a piece of dacron cloth over the whole thing, and the dacron will "peel off" after setting, leaving me with a smooth epoxy finish over the center section. Is that correct, or do I need to use polyester resin for the initial layup and epoxy resin for the dacron layer? (I'll look forward to the photos robm12)

you can use either resin for glassing you center section. no need to switch mid application to the other. i say give it a practice run. i squeezed so much resin out the 1st time i had to reapply it. it's just too easy to do.