Radio Technique
I added a pushbutton to the side of my Ace RC Silver Seven transmitter which controlled the mode-XPO or LIN (normal, linear control)-of the control response. You couldn't tell by looking which control mode was in use. Then, I set up my Aquila sailplane with the maximum possible control throws and an aft CG. This resulted in a very sensitive-flying plane. We took this rig to four different flying fields on Long Island, NY and asked for volunteer pilots. Each "guest pilot" was handed the box, after I had the glider up and trimmed for level flight. He was then asked to stand the plane on a wingtip and pull through the tightest possible turn, then concentrate on how difficult it was to get back to slow, level flight. As soon as it was accomplished, he was asked to repeat the exercise in the opposite direction. Then, I pushed the mode-switch button and asked for two more steep turns and recoveries. While the plane was still in the air, I asked for a report on the differences, and for his preferences.
Radio Technique
FROM time to time, people ask me how I keep up the flow of ideas for this column. Well, this magazine is the only one that gives you, the reader, a target (address at the end of the column). Therefore, I get at least a dozen letters per month and try to answer them. That takes a bunch of time. In order to recoup the investment, some of the questions lead to columns, on the assumption that if one person takes the time to actually sit down and write, another hundred or so "would like to, but . . . ." If I sound enthusiastic about a product, it's because I have personally used it for a while, tested it against my expectations and against competing products, and come up with the idea that it's great. Since practically everything I write about is purchased with my own personal cash, the range of subjects is somewhat limited.
Radio Technique
HOW MANY TIMES have you had that feeling, during a split-S or pullout from a high-speed dive, that the elevator just wasn't doing its job? Kinda gets you in the throat, doesn't it? Let's take a look at what's happening in that situation. (See drawing below.) Airspeed is high, because engine power and gravity are working together. The airplane is flying nose-high through the air, because you've got the elevator full UP! Air is approaching the wing leading edge from below. It is turned by the wing so that it leaves the wing going down (which is why it's called downwash). Thus, you see why the air approaches the horizontal tail from above, giving the tail an angle of attack. This angle adds to the elevator deflection angle. You-the pilot-like that, because it helps the pullout. The elevator servo may not agree, however, because it has to work harder to reach the position you've commanded it to.
Radio Technique
LAST month, we gave you a parametric equation for picking the size servo you need. It was based on the usual aileron or elevator situation, in which a tapered wood strip is attached to the trailing edge of a wing or stabilizer by some kind of hinge in the gap. This month we will extend the discussion into mass- and aerodynamically-balanced surfaces, with some discussion of dynamics. First, let's look at various kinds of servo loads. Loads on Your Servos. Static overloads. The throttle is the control that should be least likely to damage a servo, yet (due to carelessness) it most frequently is the one that eats them! The cause is simply that the owner doesn't test his setup carefully enough, before committing it to service.
Radio Technique
EVERYONE wants to use the cheapest, lightest battery pack possible! So, how do you figure what size pack to choose? There is the classical method (which was invented by rubber-motor experts). You know the drill: wind it 'til it breaks-then back off a turn or two! The counterpart in RC is the guy who "uses what he has," until the crash. Then he buys the next larger size to replace it. It's an exciting way to separate the good stuff from the trash, but a little hard on the model. The mathematician knows that "All you have to do is multiply your average operating current by your desired operating time to find necessary battery capacity."
