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Ok this may sound real dumb but anyway. I race RC boats. My buddy has a wood tunnel hull with epoxy paint. I was surprised they didn't glass the boat for saving weight. So my question is do you have to glass a airframe if your using epoxy paint such as Klass Kote ?

sensei

It is not a dumb question at all, if your buddies hull was balsa wood like an airframe then if for no other reason it would need glass on the surface to keep the swell back down under the top coat, but in the case of most hulls I have seen they are predominantly birch plywood with a tight grain and you can get by with epoxy resin, primer paint only.

Bob

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I am sure it's birch plywood. But you would advise on glassing a balsa airframe. I have to try the mini wax on some scrap and see what I am in for. I have a old G-Shark in the box from Pacific Aeromodel. All balsa sheeted over foam. I hate plastic wrap because it will wrinkle when the plane is baking in the sun, at one of those hot summer flyins

[email protected]

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Duh yea because balsa doesn't have a tight grain lol

sensei

You will love the ease of using the Minwax.

Bob

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Thanks much will defiantly try it

Viper1GJ

My Feedback: (20)

Bob,

Is Klass Kote epoxy paint compatible as a top coat over the Minwax urethane. Will it stick and not react with it over time?

Gary

sensei

Yes, it will work great over top of Minwax and glass as long as you apply K/K epoxy primer surfacer down first and sand as directed after cure by K/K. This would be the same process with most any automotive or aviation type finishing system and over a multitude of underlying substrates. I hope this answers your question.

Bob

raptureboy

Well one more opine. Use the waterbase Minwax instead. Dries quickly and can be recoated all in the same day and no it does not cause any issues with the grain swelling up. I would disagree with the comment you obtain no strength in using epoxy because when it is thinned it will be absorbed into the balsa and provide more "ding resistance" than shrink wrap, but it really is just a base for the finish. 3/4 oz cloth will go around any shape without any issues. I prefer to lay it on dry and then brush it with a stiff paint brush and allow it to adjust itself to the shape then apply the epoxy.

oliveDrab

ahHA!! I was waiting for somebody to say this....water-based instead of oil-based. But I do not understand your statement: "...no it does not cause any issues with the grain swelling up". Never mind - no need to explain - I'll just try it on a test panel.

How does the weight of a water-based Minwax finish compare to the weight of an oil-based Minwax finish?

sensei

Keep in mind fellows that I come from an entire life of owing and operating aerospace composites companies, I have around 130 employees that work for me today, so when I say that 1/2 or 3/4 oz cloth gives no strength, I say it very loosely because the strength it adds in this application is so far down the chain in hangar rash protection that it really is not worth even mentioning.

Bob

MTK

Many years ago I actually ran some tensile tests (with an Instron) of 1/16" balsa covered in various materials. There were soooo many opinions about which combo produced the best, strongest, lightest, yada yada.....

Bottom line was that the balsa picks up a bit of strength, both in the grain direction and cross grain direction, with any of the coverings, including wrinkle kotes that were well adhered. But most of the strength (at least 3/4) comes from the balsa itself (grain direction); the difference came in the cross grain direction with balsa nearly doubling its strength in cross grain. Somewhat obvious after doing the test, strength pick up was proportional to covering thickness....DUH!!!

Epoxy by itself or Klass Kote epoxy paint (actually K&B superpoxy back then) added little strength unless epoxy was applied very thick; I had a hell of a time applying paint as thick as laminating epoxy so I stopped after a few layers. Balsa as an engineered material was impressive and still is.....

One big surprise was that well adhered wrinkle kotes added considerable strength, more than stuff like super light glass or paper. Mylar polyester is a terrifically strong engineering material, particularly when tensilized. Our wrinkle kotes are only partially tensilized (stretched) so the benefit is partial. The disadvantage is that it becomes very difficult to adhere every square millimeter. That's where the wet installations shine

I wished I had normalized the data for weight and thickness.....

Nowadays I try to cover for lightness and smoothness first. Strength is always built into the structure and the covering is more of a stressed skin, like the skin on a grape, except as thin as I can muster. The main reason I prefer Esaki and dope. Min Wax polyurethane and Esaki should work great. Esaki is often colored already and there is practically no grain to fill, just pores.

BTW folks, Polyurethane finishing material, same as dope, are very simple to work with. There isn't any mixing (except thinner) required and pot life is indefinite. Of course epoxy paint like Klass Kote has a pot life of two days so it's not a big deal. Another BTW- As we did with old K&B Superpoxy paints, KK paint I use for bedding the coverings is clear, unfilled. I mix it and leave it alone for an hour to incubate and settle its chemistry. Then I mix thinner and use it. The gestation period allows the cross linking of the plastic to occur more completely, forming a superior plastic barrier against the elements. If you decide to use epoxy paint as the bedding resin, do not omit this step

vertical grimmace

My Feedback: (1)

I have seen some guys moving up to 1oz. cloth on some aircraft. Mainly because it is easier to work with. I avoid 1/2 oz. as it runs way too easy when trying to apply it. I have mainly worked with the 3/4oz stuff and it has gone quite well.

I wonder about the oil based poly U. This is the first thread I have seen that mentioned. I have used the Water based Polycrylic quite a bit, and it is my favorite so far. One thing to keep in mind here. It is recommended to put on a seal coat of laquer or dope over the bare wood before the WPU to avoid the water from warping, swelling the balsa. Also, with the WPU, most of it evaporates away, creating a very light covering in the end. I can fiberglass and paint an airplane lighter than one I cover with wrinkle coat. The finish will look good for a long time as well. So long as I do not meet Terra Firma.
WPU, 3/4 oz cloth, latex house paint, airbrush, Pica FW 190

jmpups

My Feedback: (1)

I haven't used the west system, if it is a two part finishing resin, they all work the same as well as the process of applying the cloth. I personally use Zap finishing resin. On aircraft up to 25lbs, I use 3/4oz cloth. Lay it on one half of the wing bottom side first with about 2" overhang all around. The cloth will go around curved wingtips without any problem. Mix your epoxy, it goes a long way. Have a small throw away paint brush, old credit cards work well as squgees, and paper towels and denatured alcohol. Starting from the middle of the surface pour a good amount of epoxy the length of the surface. get the credit card and just start squgeing the epoxy away from the center to the ends of the surface. Use a large enough mixing cup to catch the excess epoxy as you get to the edges. When dry, a med grit sandpaper run along the edge of the finished surface will remove the excess cloth. You are going to remove most of the epoxy using this process. The more epoxy you remove, the less sanding you will have as well as a smoother surface. There are to thoughts , first is to put a second coat of resin and sand . I use 3/4 oz cloth because it is lighter and the fills with just one coat and a heavy coat of primer does the rest. Using the paint brush around irregular shapes works fine. Don't be afraid to overlap the cloth over trailing edges, or even using pieces over parts of the fuse or tail section. The cloth is light enough to not leave any seems.

vertical grimmace

My Feedback: (1)

Oh, one more point. I think the Peel ply technique is only viable with a resin. Being that it is chemical cure, it will dry regardless of the exposure to air. Peel ply would Not work, with polycrylic.

MTK

VG,

When I get heavy handed with the thinner materials (paints, dopes, etc) I use ***** wipes to pick up excess. It works for laminating/finishing epoxy also but one can't leave it on there until epoxy cures. Peel ply might have an advantage there but I have not done that for finishing. Molded and vacuum packed parts, yes but not on finished surfaces

sensei

I have also used peel ply for many years, but only on areas that we require a secondary structural bond line, I have never used it for cosmetics.

Bob

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Where do you get the Peel Ply paper stuff. My dad always used plastic wrap. It sucked because it would fold a crease and have a deformity in the glass work. More sanding. That looks perfect for a job. Would wax paper work as well ?

vertical grimmace

My Feedback: (1)

Aircraft spruce sells it. It is actually a lightweight dacron covering material. It can be used as covering or peel ply.

Peel ply is just anything used that does not stick to cured epoxy resin. I have heard of dress lining material from a fabric store being used. From my research, and I will admit, I have not used peel ply yet, the purpose is to create a very smooth surface that gets you closer to finish without having to fill the weave. This eliminates the "flow coat step". , or second coat of resin to fill the weave.
The peel ply captures the excess resin and allows it to be spread out evenly under the ply. It was my understanding, the peel ply is removed after the resin has fully cured.

I feel that this is a more advanced finishing technique, and may not be something to try the first time out. And Like I said, the peel ply would be used with resin and not the poly-u technique.

[email protected]

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Thanks much.

cublover

My Feedback: (47)

Bob,,,am I wrong??... its called " Tensile strength". meaning how much pressure it will take to break... I know you know this...i was reply'n to the guy who said it adds "NO strength what so ever"... That statement is wrong!! agree?

Tensile strength= maximum stress before breakage. I simply made the statement that it DOES add strength. As far as my plane...its 136 plane with a dle111,,,,49 lbs is heavy??...I had a 90 inch plane that was 37lbs, and it flew great....so does the Spacewalker... I think to many people put to much on the weight....Your right,,its nice to get a plane as light as possible, but when a plane is loaded with 4 battery's, smoke, and fuel tanks...QT each... fuse is solid ply all the way back, and built to take a beating...its gonna weigh just a tad more!!..hahaha...49 was light I thought.... and the spacewalker is covered in light weight ultra light fabric from Superfabric primed and panted, then cleared. There is a lot to this plane, but it is a huge plane....i seen a 1/3 scale cub on floats that was pushing 40......I thought I did pretty good!!..hahaha
[h=1][/h]

cublover

My Feedback: (47)

But I will say Bob,,,you got some cool ass stuff in the hanger......I have a new project for this winter,,,,just wait bud....just wait....hAHAHAHA

2walla

My Feedback: (10)

There is another option vice using the cloth altogether. The "liquid sheeeting" subject had a long thread on here a couple of years ago. It is two part and is brushed directly on the surface. I think it is a two part polyurethane - might bea repackaged product called styrospray? It looks like it does a good job. I know the principle is sound as back in the day I would finish my quickie 500 racers by using "mod podge" to seal the balsa then rattle can epoxy paint. No cloth.. It looked as good as anything else and was just as durable as a glass based finish.

vertical grimmace

My Feedback: (1)

One thing is for sure, a fiberglassed finish, well done, is as good as it gets. For WW2 heavy metal, it is just the way to go. Beyond the durability (no wrinkles), It creates the perfect surface for more detail like panel lines and rivets.

sensei

Again the strength is miniscule in an application for top coating, it is just a means to an end. The truth is you will get more strength from MonoKote then you ever get will with a single ply of 1/2 or 3/4 oz. glass and epoxy or glass and Minwax and the repairs from a hangar rash dent is much easier to repair as well. for instance... Dent your wing going out of the house from door frame with plastic covering, in most cases inject a little water in dented area with syringe, allow moisture to swell balsa, allow one or two days for moisture to dry out, re-iron area. and your done. Now take the same scenario going out of the house with a painted airframe or a CARF airframe and get a dent..... Now I do agree with Vertical Grimmace, there is nothing in terms of a fine looking airplane then glassed and painted, I mean it doesn't get any better then that.

Weight... You have to understand, in my world of design and fabrication of an airplane with a 136" span and in the case of something like a Spacewalker, there is just not allot of fuselage area per say and then powered with only a lightweight 111cc power plant, I see the all up weight being a good match at around 30-32 lbs. max. not 49 lbs.

On F/G there is a thread started by a buddy of mine around three years ago, he asked me to help him perform a documented lightening operation on a brand new out of the boxes 40% SD Models Yak 54, now these airplanes are huge if you have ever been next to one with a 139" span and a great deal of fuse on them. Just about all of them out of the box and assembled ready to fly came in at the mid to high 50s. Long story short, when we finished that airplane it weighed RTF 36 lbs. with a DA 170cc on the nose. We then took the airplane to the Heat Wave 3D fly in held in Oklahoma each year for its first real showing. They actually had calibrated 3 point scales waiting for us and everyone that was there to see what the truth really was. My own 52% Extra 300 design came in at 48 LBS. with a 150" span running a DA 200cc 4Cyl. So as you can see, 49 lbs. is heavy in my book. Now, I would love to see another one of your build threads because I just enjoy seeing very talented craftsmen like yourself build and finish your master pieces.

PS here are a couple of pics of my buddy's Yak. at the lake and the Heat Wave...

Bob