Radio Control: Scale
Bob & Dolly Wischer
SCALE Speed Again: Bradford Powers ("About the Size of It," MA, Jan. '78) has some additional thoughts on that controversial subject, scale speed. He writes:
"Since, from time to time, the subject of scale speed keeps popping up, it has occurred to me that in view of the growing interest in scale models, the formulation of rules for realistic speeds might be in order.
"As I pointed out in my article, 'About the Size of It,' most models approximate dynamic models and behave in more or less the same way, so that so-called 'visual' speeds (1/4 the full size speed for a 1/4-scale model, for example) are unattainable short of something in the nature of a kite, or the Gossamer Condor. For example, the Sig Ryan at around 10 pounds behaves pretty much as a dynamic model and will have a landing speed of around 25 mph, since it is a 1/3-scale model. In order to reduce the speed at landing to 1/8 that of the real airplane, or 12 mph, the weight would have to be reduced to around two pounds, which I'm sure you will agree is unattainable for all practical purposes.
"In the same January issue of Model Aviation, John Preston, in his article 'You and Your Scale Model,' pointed out his preference for light models which tend to fly more realistically. With this approach I wholeheartedly agree, and accordingly it has occurred to me that 'realistic' speed rules might go as follows:
1) 'Unattainable' visual speed would be the ultimate goal, and would rate 100 points, where indeed the speed of the model would be that of the prototype divided by the scale factor. (For 1/4 scale, the speed would be 1/4 that of the prototype.)
2) A 'fast' model, essentially with the characteristics of a dynamic model, having a speed equal to that of the prototype divided by the square root of the scale factor, would receive zero points, since it would represent no innovative effort on the part of the builder to reduce the speed. (For 1/4 scale the speed would be 1/2 the speed of the prototype, as the square root of 1/4 is 1/2.)
3) Points for realism would, then be awarded to the contestant who has come closest to 'visual' speed by virtue of clever innovation and miserly weight saving. Thus, if I can land my Ryan at 18 mph, I would get 50 points, since my speed is about half way between the easy 25 mph and the unattainable 12 mph.
"This should probably apply only to landing speeds for several reasons. I realize it would involve developing a method of measuring speeds fairly accurately, from two people with stopwatches and walkie-talkies to Lord knows what. This would apply to scale models; pattern jobs are probably at their best at 'high mach numbers.' What do you think?
"Kit builders, who represent the largest portion of scale modelers, have little choice in the outcome of flying weight. The kit manufacturer and original designer have decided what the plane will weigh. Innovative ideas to reduce speed, if they are not incorporated in the prototype, will not appear on the model. Only the scratch builder can exercise some control over the weight and therefore the scale speed. He is already surrounded with difficulties in design, construction and learning to fly his" or both. For example, if you normally roll the airplane to the right, try using a touch of right rudder when performing the half roll from inverted to upright flight. Remove all controls smoothly when the airplane is upright. Good Luck.
Recently I received a letter from George Feiger who states, "I am a regular reader of your column in Model Aviation and I have a query which I hope you will be able to answer. I have built a pusher design for a .15 engine, and find the Fox does not in fact make the crankshaft for clockwise rotation advertised in the parts list for my Fox .15 Schneurle. Thus I have to locate an 8 x 3 or 8 x 4 pusher prop. I have the Tornado 8 x 6's but Duke Fox advised me against using them. (Editor: Probably for reasons of size.) Do you know of any other source of pusher props in my size range? It would be a shame to abandon a completed model."
If any of you can help, please write to George Feiger, 876 LaPara Ave., Palo Alto, CA 94306.
It is easy for me to empathize with his problem. In 1966, I built a six-foot-span canard (tail-first) RC model featuring an all-movable stabilizer and a pusher engine configuration. The Supertigre 56 I wanted to use couldn't be modified for reverse rotation, so the engine had to be fitted with a pusher propeller. Unfortunately, the largest pusher prop available at that time was a 10-6 nylon one. If you have ever tried to put a 10-6 prop on that large an engine, you know how little thrust was available to fly the airplane.
Ron Van Putte, 12 Connie Drive, Shalimar, FL 32579.
creation. The rule book determines, to a large extent, his choice of plane and his methods, provided he is contest oriented, and he is the individual who spends a substantial portion of his life in an effort to produce a winning plane with international competition potential.
Our most important concern is to convince scratch builders that they should make an attempt to compete. A very small percentage of scale models, whether scratch or kit-built, ever appear on the contest scene. In our opinion this is a result of scale modelers' unwillingness to be controlled by rules, and their independent attitudes. As an example, the new Quarter Scale Association is strongly against any form of competition or judging of their efforts and do not wish to detract from their enjoyment by making rules.
Since scale speeds are largely unattainable, a rule to award points for slow flight would be, in our opinion, unfair and unwise considering the effect it may have on the quantity of contest entries. To remain competitive we would need planes to which weight would be added or removed, at the center of gravity, to compensate for the wind velocity, and without exceeding the maximum allowable total weight.
We attended the Mint Julep Scale Meet recently and our entry was the lightly loaded Pober Pixie. While it missed the high static score by a couple of points, its final placing was fifth. The winners in both Expert and Sport classes were large, fast twin-engined planes, Bob Underwood's new DeHavilland 88 in Expert, and Corky Heitman's Douglas A-26 in Sport class. Corky's Douglas is powered with a pair of Kraft 61s and weighs 20 pounds, has speed to match its power. Is a lightly loaded plane on equal footing with the heavier, fast-flying ships? We will be hard to convince.
Substitute Materials: On all of our recent planes we have made extensive use of birch plywood and spruce strips to replace balsa. There are numerous advantages, especially in strength. In places where 1/8" balsa would be used, such as planking a simple (not compound) curved fuselage deck or side, 1/32" plywood can be formed in one piece which leaves no glue seams to sand and assembly time is substantially decreased.
A heavy paper pattern is cut first to avoid waste and to be certain of a proper fit. The plywood is then cut to the pattern shape, moistened on its outer surface to promote flexibility and white glued to the fuselage framework. Rubberbands hold it securely, with scrap wood blocks under the bands along the ply edges to add pressure at those points where it tends to resist forming. We have found that the easiest way to moisten the plywood is under a stream of warm water. Wipe off excess drops on the inside surface where the glue comes in contact, since we do not wish to dilute the glue. A moist surface actually seems to promote penetration of glue and is an advantage.
With 1/32" plywood covering the structure beneath can be kept to a minimum. Bulkheads or formers at 4-in. intervals with a single stringer near the center is sufficient, providing only enough strength to avoid collapsing the framework under the rubberband load. Sanding the first ply along edges afterwards seems to have no effect on strength and the slight undulations and gaps where panels join can be easily disguised with Epoxolite.
Weight of plywood as compared with balsa is variable, depending on the species used. Under average conditions we find that the plywood should be about 1/8 the thickness that would be used if the part were balsa. At that thickness ply weighs less than hard balsa but more than soft or contest balsa. In every case the plywood is superior in strength and needs only the minimum of framework underneath, preferably spruce. In addition, it is resistant to the indentations that plague a balsa-covered plane, which seem to appear no matter how carefully it is handled. The balsa plane requires some sort of finish to harden its surface. Without this protection it is forever vulnerable to nicks and dents. The ply covering needs only a few coats of clear dope, sanded lightly, to prepare for the color finish. The dense surface fills quickly, showing no grain.
For internal structures a 1/16" plywood bulkhead is equivalent in weight to 1/4" balsa and is far superior in durability. Where bulkheads meet the adjacent fuselage sides gusset strips should be used for greater glueing area. For extreme rigidity we make laminations of plywood using white glue and C clamps for pressure. Four laminations of 3- or 5-ply 1/16" thick produces the most rigid 1/4" plywood for a firewall-mounted engine or landing gear. A 20-ply 1/4" thickness has greater strength than 5-ply commercial grades. Parts such as canopy frames, jigsawed from these multi-laminations, are strong, even in thin sections. Laminating removes all warps in plywood.
Super Documentation:
The Mint Julep Scale Meet is held in the ideal spot for a contest, at Falls of Rough State Park in Kentucky. Contestants are housed in a modern lodge or in cottages on the shores of a lake a short distance from the airstrip that is used for the contest, a perfect setup for anyone owning a plane. Hank Pohlmann flew in from his home at Montezuma, Iowa. He had modified the baggage compartment of his Cessna 172 to carry two models, a Beechcraft Bonanza which was his entry, and a model of his Cessna. During a lull in the static judging the officials offered to score the Cessna, just for practice. Imagine Hank's surprise when he found the Cessna received a higher score than his Bonanza entry. He had the perfect documentation, the prototype was parked right there where all judges could compare directly, but he had entered the wrong plane.
Weather conditions for cross country flying are quite unpredictable in April and Hank's trip proved to be an adventure, departing Montezuma in darkness at 4 a.m. just ahead of a weather front. Low ceilings on Sunday raised some doubts about the return flight. Our Pixie had entered the clouds during a spin entry that morning. When Hank departed at noon conditions had improved considerably.
The Mint Julep Scale Meet is conducted in a very businesslike manner, under ideal conditions at the park, and we would not hesitate to attend in the future.
Bob and Dolly Wischer, R. 1, S-221 Lapham Peak Road, Delafield, WI 53018.
Transcribed from original scans by AI. Minor OCR errors may remain.
