Radio Control: Scale
Bud Atkinson
SPRING IS ABOUT here and in most of the country winter is behind us, and a hard one it was for most! This reporter sure didn't get in much flying. Oh, well, it made for more building time. Usually, the so-called non-flyable months are ideal for building that particular scale bird. With the short-comings of the previous contest season in mind, we try to improve the new project. The 1977 year will have the same set of rules we had in 1976, so there are no changes to incorporate in that '77 scale bird, as far as rules go.
As I have said before, interest in biplanes is growing and is being incorporated into many scale contests as an added event. By the provisional biplane rules a 10% flight score will be given to stand-off or look-alike biplanes that can be proved to be modeled after a full-size biplane. I think this is good. We don't end up with another pattern event flying just two-winged airplanes. By the way, you biplane scalers here in the mid-west, or any part of the country for that matter, the KCRC Assn. will have a biplane contest in Kansas City this coming fall. More information later!
Have you noticed more and more scale biplane kits hitting the market? Many are airplanes that can be used in biplane pattern as well as stand-off scale contests. The array of scale and stand-off scale kits are many and varied. You don't have an excuse for not building a stand-off scale this year. There is everything from WWI to WWII to present-day aircraft. There also are plan services in all the magazines, as well as mail-order dandies from Bob Holman and Sid Morgan, and many more.
We see in one magazine, growth of interest in 1/4A stand-off, which I have predicted will become very popular. The set of rules they came up with looks sensible. Also our old scale buddy Willie Northrop has proposed a very interesting old-timer, so to speak: a large, 1/4-scale stand-off fun event, or fun-fly stand-off scale. There's always something about a large scale model to stir the adrenalin. Scale has surely come of age! You could almost say we have covered the full spectrum from the smallest to the largest. If there isn't something in there for you now, you just aren't a scale nut!
I have received several letters concerning the replacement by foam wings of wood wings in some kits. I have yet to see a wood wing that could not be made of foam. And, of course, the foam wing has various advantages. I must qualify that statement somewhat. Bill Northrop's large 1/4-scale models in most cases are not too desirable when constructed of foam because of weight, but even these could be of foam if you were not concerned with his aim of making them very light. On the other end of the spectrum, 1/2A scale makes it desirable to go with a foam wing, using the glass tape or even a small imbedded hardwood spar for strength, and covered with Monokote or Solarfilm. Or, in some cases, just painting with several coats of foam paint. Solarfilm is more desirable because it requires less heat to shrink it. Of course, other than the 1/2A-size scale jobs, your foam wings should be covered with one of three materials.
Balsa sheet 3/32 to 1/16 thick for skinning is one. In most cases, a hard balsa leading edge is desirable because it is easier to keep the core true, and also will avoid unwanted dings. The majority of scale wings taper considerably at the tip and it's hard to keep the balsa from cracking on such a small radius, so the wood edge makes things easier. The next choice of covering for your wing is the strong, pliable 1/64" 3-in. wide plywood. With this you must use a balsa leading-edge for good results. The raw plywood is a little heavier than balsa, but, in the long run, weighs about the same when finished; you need not silk cover the plywood because it's very close-grained birch wood, and needs very little filling. It's used a lot on Formula I craft because of its exceptional strength. The third covering material is called posterboard and can be purchased at most art stores. This cardboard is somewhat heavier than balsa or the plywood but, of course, you don't need any filling and little paint need be used. It is a quick, cheap substitute for the ply and balsa, but I would not advise its use for one of your better competition scale models. Also, on damp days care should be taken, for, after all, it is cardboard! For a sport stand-off, stand-off or smaller 25- to 40-size bird it works fine.
I have built many scale birds using foam wings but have yet to use a spar in any because I don't deem it necessary, and many have weighed 8 to 12 lb., as well as some twins in the 14- to 16-lb. class. Be sure to add two plywood gussets (example, a 640- to 700-sq. in. wing), about 12 in. long, and the depth of the airfoil of the wing. Make sure when applying the contact cement on wing cores and skin that both are well covered. But do not over-load with glue be- cause the contact cement constitutes 50% of the weight. Make sure the skin is well attached to the core; 50% of the strength of a wing is in its skin.
After wing halves are epoxied together, always apply at least a 3-in.-wide glass tape to the center of wing and epoxy it well. Cut-outs for servos, etc., can weaken the center of the wing. The tape will join the skin of the right wing to the left. A foam wing, in many cases, especially on a tapered wing, is truer than an all-wood wing can be. Also, wash-in or wash-out can be achieved more satisfactorily.
One of the more complex to cut is an elliptical wing, such as on a Spitfire or a Typhoon. Since we cannot cut a curved core in most cases, this can be achieved by cutting back on the leading and trailing edge, then cutting the elliptical shape. Carefully shape with a sharp knife and sandpaper block to match the airfoil of the foam core. This is not as hard as it sounds. I built a Hawker Fury several years ago using this method, and the wing came out very well.
The Stuka and Corsair also have rather unique wings which may be cut in several sections, with plywood gussets attached to form the inverted gull-wing effect. If foam wings for scale models are new to you, get some foam and try different types of wings. You will be surprised what can be done with foam and a little ingenuity.
Bud Atkinson, 734 North 6th St. Terrace, Blue Springs, MO 64015.
Transcribed from original scans by AI. Minor OCR errors may remain.
