By Jerry Smith
Building my House of Balsa Schoolyard Spacewalker was great fun. The laser-cut parts fit perfectly, and assembly was fast. Although it was designed for a small glow engine, I decided to modify and power it with electric using a Torque 930 motor, 35A ESC and a 1350mAh 3-cell LiPo battery. When it came time for covering, I ran into a problem covering the wingtip. Covering a wing panel with film covering is fairly simple and easy to do, even for those with little skill; that is, until you get to the wingtip. Of course, all wingtips are different shapes, and not all fall in the category of difficult to cover. Some have a gentle taper to a rounded tip with very few compound curves, making covering a simple process. Others can be more difficult. The wingtip I describe here is one of those that can’t be covered along with the wing. The better way is to cover it separately. Although you will end up with a seam on the final wing rib, you will find it a more reasonable approach to success.
I went through this covering process with UltraCote film covering several times and noticed that it makes a difference how the film covering is cut from the roll. I found it best to leave extra material when covering the length of the wing, and then use the piece trimmed off at the end to cover the tip. Using a piece of film cut parallel to the edge of the roll will cause it to sag severely in the shrinking process. The secret for success is to make sure the piece you cut is perpendicular to the roll edge. Oh, yes, this tip will also work with MonoKote.
So, heat up your covering iron and trim iron, grab a sharp knife and follow along in the photos my process for covering that pesky wingtip.
Tools required for covering and covering the wingtip. (DSC9749) Typical problem wingtip, with the covering problem occurring between the gusset and the leading edge. Cover the wing panel and trim off at the last rib, leaving a generous overlap ironed down against the rib. The rib thickness is not enough surface area to retain the film when shrinking. Note: Black marks indicate the amount of overlap covering fore and aft.
On the piece of covering to be applied, develop a contour to fit the rib for an even overlap seam, generally to the shape of the rib contour. The overlap should be approximately 1/4 inch.
Using the trim iron, tack the covering at one end to the rib just inside the black mark. Later, you can remove the black mark with alcohol. Grabbing the loose end, pull it across the top of the rib for an even-width seam, and iron in place. You are now ready to tack and iron down the opposite side.
Before you start to tack down the covering, place the wing on the workbench with the wingtip extending over the edge. Use a sandbag to hold it down, so you’ll have two hands to work with. Starting near the front, pull the covering straight down and tack it in place. Work along in small increments toward the trailing edge. Now, move to where you started, and do the same thing going forward. Try and get the covering as tight as you can. Lift and retack, if necessary, as you go along. The covering should lay flat and tight without gathering and bunching up.
Trim off the excess covering, and seal it in place with the covering iron. Using the trim iron, shrink the covering staying away from the seams on both sides. Gently glide the iron over the surface until the covering is wrinkle-free. You will have to do this four times, on each side of each tip, to complete the wing.
What a beautiful wingtip, and not a wrinkle to be seen. A covering job you can be proud of!