Ultrafilm Covering Tips
An article by Roger Schroder,
as published in Indoor News and Views (INAV)
I have recently completed a Pieces Easy B according to the 1992 design update by Earl Van Gorder and it provided an opportunity to improve my covering technique. In general, I try not to touch the micro-lite, but either handle it between sheets of newspaper or on a frame. It this respect, micro-lite is treated like micro-film.
To start a covering job, I lay down a flat sheet of newspaper that has been cut to a width about 1/16 to I/8 in. wider than the roll of micro-lite film. The length is about 12 in. I unroll micro-lite on the paper trying to keep it straight and flat. Wrinkles can be smoothed by lightly blowing on the film, or as last resort, working the film with fingers.
As soon as the micro-lite is smoothed out, lay another similar sized sheet of newspaper on top of the film. Now the film is captive between the two sheets of newspaper. The film, and paper, can be cut to the length desired with a straight edge and razor blade. It can be picked up and carried around without worry.
I use a simple frame for covering which is illustrated in the drawing. It is made from a sheet of hard 1/4 x 3 x 36 balsa. Cut the balsa sheet in half, square the ends and sand the long edges smooth. You end up with two similar sheets about 14 to 18 in. long. Drill two undersize 1/8 in. holes in a lower corner of each sheet (about where shown on the drawing). Cut two 1/8 dia. steel wires to a length of about 10 in. Slip the wires through the sheets as shown. I found that reinforcing around the holes helps. The wires need to be a snug fit so that the position of the sheets along the wires can be adjusted, but the sheets stay put when the frame is handled.
The film needs to be transferred to the frame. Adjust the wires of the frame so the frame width is about 1/2 in. less than the length of the cut film/newspaper laminate. 3M contact spray is the best for sticking film to the frame. Lightly spray the top edges of the frame, remove the top sheet of newspaper an invert the frame onto the exposed film. Press down to be sure the film, is attached to the frame. Lift the frame. Some newspaper will stick, but can usually be peeled away easily. Set the frame down with the film up. Adjust the frame along the wires so the film is straight and slightly slack. The slack will be greater if you are covering a wing with a curved airfoil.
At this point I formerly misted some 3M spray onto the wing, or whatever I was covering, and then laid the wing onto the slack film. Four things invariably happened. They are:
1.The film jumped toward the wing as I laid the wing on the film.
2. The film never ended up flat on the wing.
3.The slack varied when the film jumped and messed up the airfoil shape.
4. l got into a foul mood.
For the 92 Pieces, I changed my technique. The wing was laid on the film dry without any adhesive. The frame could then be adjusted to straighten out any wrinkles and have the slack match the airfoil shape. After adjusting, I sprayed some 3M into a cup and added thinner to it until it was mostly thinner and a little adhesive. I used a very small brush to paint the thin adhesive on all the outlines and ribs where the film was supposed to stick to the wood. I had to let it dry for some minutes. Acetone may be a quicker drying solvent, but I didn't know if it would cloud the film. Once the adhesive was dry, the film was cut along the wood outlines with a hot wire cutter (Dr. Bates wonder cutter). I was very pleased with the resulting covering job.
Note that there are no ends to my frame. The end of the film is not supported by the frame. This is an advantage because 1 can build the dihedral into a wing and then cover it, one panel at a time, by using film lengths just a little longer than the panel to be covered. The lack of ends on the frame allows me to (carefully) lay a tip panel on the film, attach it with liquid adhesive, and then cut it away from the frame. When doing this, the rest of the wing must be supported correctly to get the tip panel to lay flat onto the film.
