COVERING WITH FILM
COVERING WITH OS AND OTHER FILMS
OS film is straightforward to use providing that you remember to handle it properly. It shouldn’t be beyond the ability of anyone who has built a couple of indoor models of any kind. I have set out the procedure in great detail, so it seems complicated. But as always, describing is much more long winded than doing, so don’t be put off!
You will need: A large cutting mat, Film, some ¼ sq balsa, some old fashioned new double edged razor blades, a can of photomount spray, couple of brushes (see below) and a tin of lighter fuel,
The most important thing to remember is that it snags and tears easily, so you need to work slowly, use an absolutely snag free cutting mat and take note of my comments re sharp blades for cutting.
The procedure I use personally is as follows:
1.I keep the underside of a large cutting mat (or even better, a sheet textured matting card from Hobbycraft or similar, as this makes lifting the film easier) purely for cutting film and nothing else. I make sure that there is nothing to snag the film on it before starting.
2.I cover my flying surfaces flat and crack in the dihedral later. I make a frame from ¼” sq balsa which is at least 1” larger all round that the wing/tail. You collect a set of frames after a while. Remember that the film is only 12” wide, so you may have to get wing, tail & fin out of the same length of film that you cut off. So plan it before cutting it off the roll, or you will waste a lot of film.
3.CAREFULLY roll out the length of film you need onto the mat. BEFORE CUTTING IT OFF TO LENGTH INSERT SOME TISSUE BETWEEN THE REST OF THE FILM AND THE END OF THE FILM ON THE ROLL. This prevents the ‘sellotape stuck down and impossible to find the start’ effect. If film sticks to itself, it is nearly impossible to find the start again without tearing it.
4.To cut film, some people use a soldering iron (allowing for some heat shrinkage on the edges). I always muck this up, so I use the old fashioned double-edged razor blades (Wilkinson are much the best, as they stay sharper). I number the corners of the blade with a CD marker pen and ONLY DO TWO CUTS WITH EACH CORNER. More than this risks tearing the film. Pulling the film VERY slightly taut while cutting helps.
5.Smooth out the film on the mat by gently blowing (take great care not to blow any spit, which wrinkles the film) and brushing with a large soft brush (I use a 2” wide proper watercolour brush, but a woman’s makeup brush would be ok too). NB: Some people crumple the film very tightly and then tease it out before laying it on the mat. This has the advantage that the film is less likely to pull away from the wing outline when the model is under load and makes propellors easier to cover. It is not clear whether there is any aerodynamic gain with either 'crumpled' or 'smooth' film. It is easier to start with smooth film until you gain experience.
Once you have got it as smooth as you can, place the frame on newspaper and spray it LIGHTLY from about 15” away with photomount. I use 3M Super 77, which is expensive , but comes out in a really fine spray, sticks well, and is lighter because it doesn't soak into the wood. It can be removed with Ronseal lighter fuel. It is hard to find. I get mine from http://www.lawson-his.co.uk/scripts/products.php?cat=Spray%20Adhesives .
*** I have changed my method here recently. I smear the balsa frame with Vaseline instead of spraying it. This allows some gentle smoothing out of the film and the residue film can be peeled off easily after covering is complete.
Place the frame (sticky side down obviously) carefully on the film, taking care not to move it sideways, which would create wrinkles. Hold the frame down and cut it away from the rest of the film. Try to disturb the rest of the film as little as possible, as you might need it for the tail later.