Free Flight: Duration
HOW LONG? Aspect ratio (A/R)-the relationship of a wing's span to its average chord-is one of the many factors you must consider when designing a new model. A look at sailplanes, either RC models or fullscale, might convince you that a long, narrow wing is the best way to maximize glide performance. But is a high-aspect-ratio wing always the best choice? And how high is high? For some events, such as P-30 and Pee Wee-30, the rules limit the wingspan. In these cases, you should use as low an aspect ratio as possible, to maximize wing area.
Free Flight: Duration
BACK IN THE OLDEN DAYS (before carbon fiber and circle tow) towlines, like the gliders themselves, used to be simple. I remember one of our local experts who would show up at every contest with his red silk-covered Jasco Nordic 72 and a new 10-cent ball of kite string. When the contest was over, the string stayed behind. Now technology and the rules won't allow that. For one thing, the circle towhooks used now need a pull of 15 to 20 pounds to unlatch. The cotton kite string would break long before that. (So would the wings, but that's another story.) And the rules require that the line be wound up immediately after each flight. Common practice is to use a simple winch to reel up the line between flights. After the line is stretched out, it is unhooked from the winch. (Most fliers store the winch during tow by sticking into the back waistband of their pants.) The rules permit a small button to be attached to the end of the line to keep it from slipping through the flier's hand.
Free Flight: Duration
WHICH GLUE TO use? Growing up, the choice was easy . . . Ambroid was the stuff my father used, so I used it too. Later I began using cyanoacrylates (CyAs) for field repairs and aliphatic resin (Titebond) for general construction. If I was in a hurry, I'd opt for CyA for construction. But I really liked Titebond. It was cheap, easy to use, and safe. About 15 years ago, I built two A-1 glider wings-one using CyA, and the other, Titebond. The unfinished panels were stored away in a cardboard box, which, it turned out, happened to be under a leak in my workshop roof. When I discovered the leak, the box was full of water. The Titebond wing had rekitted itself, with all the parts floating around loose. The CyA wing was soggy but still intact. I weighted it down on a flat surface and let it air dry; it was fine.
Free Flight: Duration
COUPE PLANS: A few months back this column featured some photos and a description of Eric Johnson's potent new Dream Catcher Coupe. Now Eric is offering full-sized plans of the model. The plans for the 54-inch-span model are quite detailed and even include an isometric sketch of the modifications Eric makes to the Morrill Teeny Torque front end to accommodate a spinner. Construction is a cross between traditional balsa-and-tissue and current F1B practice. For example, both the wing and stab use balsa D-boxes combined with carbon-fiber trailing edges. The motor tube and boom are rolled balsa, but the tailboom steps down in size, much like the rolled aluminum-and-carbon Wakefield booms.
Free Flight: Duration
LAST MONTH WE DISCUSSED some of the basics of building two-piece wings. This time we'll look at some of the variations: Straight wing wires are a lot simpler to make and install than bent ones, but what if you don't want a wing with flat center panels? Well, if the wing is thick enough, you can angle the tubes slightly to give some dihedral in the mains. Usually the tubes are located tight against the top of the lower spar at the wing center, and against the bottom of the upper spar a few inches out. The easiest way to do this is to make the main spar as a separate, full-depth subassembly, with hardwood or carbon-fiber top and bottoms spars and a balsa filler in between. Make both main spars and trim to length. Bevel the ends for the desired dihedral.
