Flying for Fun
The following fundamental material might lead the reader to say "I already know that," and skip this column. Yet, a brief refresher is in order considering a "failure to remember" in several instances. It's a Gas: The Earth's atmosphere is composed of molecules of several gases, ranging from oxygen to the rare ones such as helium. The atmosphere is held around the Earth's surface by gravity, and thins to nothing about 100 miles up. The closer to the earth's surface that atmosphere lies, the more dense it is. One law of physics states that heating a gas causes its molecules to disperse in proportion to the temperature; conversely, cooling the gas causes its molecules to move closer to each other, and it becomes more dense.
Flying for Fun
The Piper Skycycle Saga: In 25+ years, no column subject of mine has generated more mail responses than the Skycycle. I'm not talking several dozen letters, but more than 100! For months following the two columns, modelers wrote indicating strong interest in building models of the prototype. I had mentioned the possibility of a well-known and respected person dusting off his prototype molds and marketing his 1/3-scale Skycycle kit. He had asked for anonymity while he was making up his mind, so I forwarded the letters to him. I can now relate that the potential kitter was Bert Baker of Everett, Washington who was responsible for the design of those incredibly beautiful and good-flying Yellow Aircraft warbirds. Bert severed his association with the company a year ago or so, and was considering running some limited-production kits on his own.
Flying for Fun
Last month I tossed out a rule-of-thumb method that I use to loosely predict power requirements for models; in particular, I was attempting to assess the likelihood of Jim Hall's Super Kloud King flying with a Zenoah 445 twin. Jim's 18-foot model, with a chord of 36.75 inches, gives an area of 54 square feet (sq. ft.), or 7,900 square inches (sq. in.). At 90 pounds, the Super Kloud King would therefore have a wing loading of 26+ ounces/sq. ft.-not at all heavy for a model of such large size. By comparison, a full-scale Taylor E2 Cub has a wing loading of 70 ounces per sq. ft., and that is very light for a full-scale aircraft.
Flying for Fun
Really Big: Last month I mentioned 250 sq. in. (square inches) per .10 cu. in. (cubic inches) as a benchmark for light, low-speed model aircraft, such as Old-Timers and primary trainers. On the other hand, performance requirements lower that ratio as weight, required velocity, and aerobatic performance increase. A .60-size sport Pattern model will have, on average, about 800 sq. in., or 130 sq. in. per .10 cu. in. of power, and a wild unlimited-vertical-performance model will have as little as 60 sq. in. per .10 cu. in. Just for fun, I'll put those ranges into John Light's 1/2-size Laser. The model weighs 54 pounds, spans 144 inches (12 feet), and has about 3,900 sq. in. of wing area. Hence, a wing loading in the neighborhood of 32 ounces per sq. ft. is actually light for a model this size. The power plant is a 3W 200 twin (12 cu. in.) swinging a 30 × 10 propeller.
Flying for Fun
Let's discuss a part of construction that is a common source of trouble for newcomers, and sometimes for more-experienced builders. Hinging the movable surfaces of Radio Control (RC) models is not too difficult anymore, but many models are seen with huge spaces between the halves (gap), surfaces that bind when moved, surfaces that are not level, and worst of all, surfaces that are inadequately adhered to the model. These hinging problems are not limited to homebuilt models, but are frequently found on the acronym (ARF [Almost-Ready-to-Fly], RTF [Ready-to-Fly], RTC [Ready-to-Cover], ARTC [Almost-Ready-to-Cover], etc.) group of factory-built models. Occasionally the hinge installations are so poor that it's necessary to cut off the hinges and redo them.
