I really dont know where to post this question, so if its in the wrong forum, I apologize in advance and Ill move it.

If one has a full balsa sheeted airplane (NOT fiberglass/composite), what is the advantage of "monokoting" vs. priming and painting the airplane?

Some say a weight savings, but is there really a noticable weight difference once the painting and sanding have been completed? What are the advantages of the traditional heat shrink?

Im not talking about a scale airplane, but something like a sport flyer, along those lines.

Thanks!

The advantages of covering the plane in a film covering are:

1. Relative ease of application.
2. The covering is already fuel proof.
3. Less time involved than painting.
4. Weight savings (more on this further down )

Disadvantages:

1. Depending on the size of the plane, is cost. The bigger the plane, the more covering (and $$$) you go through.
2. Unless you are careful when applying the covering, you will have a lot of bubbles.
3. The color(s) you want may not be available.
4. I have found that the quality of the adhesive AND the shrinkability of MonoKote has deteriated in the last several years. Ultracote still has excellent adhesive and shrinkability, as does SolarTex (fabric covering ).

Advantages of painting:

1. Depending on the size of plane, the costs may be noticeably lower (larger planes is where you really see the $$$ difference ).

2. An infinite selection of colors.

3. Depending on the type of paint you use, you can litterally have a mirror finish.

Disadvantages of painting:

1. Specialized equipment is needed (This is normally a one time thing and you may already have some of the equipment - compressor, spray gun, airbrush)

2. The sheeted surface MUST be perfect as the least little defect will show.

3. The balsa MUST be sealed. If it is not sealed properly the grain of the wood WILL show. The "old time" method for sealing balsa was a mix of clear dope and talcum powder, then sanding when dry. I imagine commercial wood sealers would do the same job with less work at about the same (or less ) weight. The dope/talc mix can add weight to a plane in a hurry.

4. After a couple of years, the paint/finish will show cracks due to the wood flexing and drying out.

5. Paint CAN BE heavy (most paints usually are ) when compared to a film covering. Latex is the only exception I am aware of, and it needs to be clear coated to make it fuel proof.

If you really want to paint the plane with a minimum of weight gain and problems, I would suggest glassing the plane using the polyurethane method, painting with latex paint and then clear coating the latex. The above mentioned method will add about 8 oz - 10 oz to a 60 size plane over monokoting.

In addition to what Campy said, if your plane has a film covering its better if you have to make repairs. Just get your left over covering and iron it on; its a perfect color match. On the other hand, if your plane is painted and you have to make a repair it will be time to get out the paint sprayer which is usually more of a hassle. I have a painted plane that is 15 years old. The left over paint went bad years ago. If I have to ever make a repair I will have to get some new paint, automotive most likely, computer color matched, which will require me to shell out some real $$, even for a small repair, so there are other potential problems with painting as well.

Thanks for the responses.

Can you guess a ballpark figure percentage-wise on weight gain over the traditional film method? Obviously this will change depending on size, but is there a general rule of thumb, say 2% heavier? 15% heavier?

Thanks again!

It's probably hard to pin down even that far, given how many variables there are in different finishes and between builders. Here are a link or two with interesting info on paint finishes:

http://www.egpworld.com/ultrahobby/t...INGARTICLE.htm

There is also a wonderful article in the Feb 2005 MA from Phil Granderson about his finish method on his Diva CL stunter. He covers the entire plane with carbon fiber mat, even the cap strips.. Then he covers the open areas with silkspan and finishes the whole thing with dope, top coated with clear auto paint.

If you fill and paint balsa without tissue, silkspan, .5 oz glass cloth, or CF, you will likely get the grain showing up soooner or later.

Any paint finish can get heavy if you put too much filler and paint on. The keys to a good paint finish include getting the wood absolutely ready to paint before you ever start, and then using sandpaper-lots of it. The materials matter less than the prep work and sanding.

Well, I think that all wood needs some type of covering, even if you intend to paint. You need silk or slikspan at the very least. If you just use sanding filler and primer, you will get stress cracks everywhere. Paint on wood just doesn't offer any strength. The wood will split along the grain eventually just form the loads and deformation in flight. Yuck !

Thanks again for the responses. I didnt consider the strength the shinked covering can contribute to the structure as another benefit, but it is.

Ill check out the link on my lunch break.

Thanks!

It is obvious from the responses that the answer isn’t clear-cut and there are advantages and disadvantages either way. However the decision is really quite simple. If you normally use film and are comfortable with it then it is the obvious choice. If you usually paint and feel more comfortable with it then do it. I have used fabric and dope for more than forty years and for me the results are good, and repairs are easy. I have never seen the “stress” cracks some have mentioned and never had trouble matching colors when repairing, since most dope colors are standard, and being a solvent type paint, it’s easy to blend the new with the old.

As far as weight, the paint film resulting from painting with aircraft dope is quite thin and light when dry. It is at least comparable to a plastic film finish and eliminates the problem of peel off and bubbles that are often seen with the plastic.

Both methods give good results. It is mostly a matter of personal preference.

One method of covering balsa with plastic is to seal it at the edges and then shrink it with a heat gun. If you try to iron it down you will get wrinkles and bubbles. Most directions for covering sheeted surfaces advise ironing from the center out. Be sure you have plenty sealer on the wood or the grain will surely show through the plastic no matter the brand. Wood should be sealed just as well for covering with plastic as it is for painting. After going to all that trouble it's almost as simple to paint it after it's prepared.

From my limited experience I would have to say that film covering takes a lot of practice and frustration to obtain good results. You have too practice and experiment to see if you like it. I don't, but painting takes more time. It has taken me twice as much covering as it should but I am determined to get it right. I have tried both methods, ironing it down and stretching and shrinking from the edges and I'm still wondering why I got involved. This is supposed to be fun. Very exasperating. Good luck. Dave