Facsimiles ranging in size from a few inches to many feet in length intended to represent actual or imagined airplanes in reduced scale, for display or flying purposes.
Flying models take many forms. They can be unguided after launch and known as free-flight, or FF, models; constrained and controlled by wires and known as control-line, or C/L, models; or controlled remotely by radio signals and known as radio-control, or R/C, models. From an aerodynamics standpoint, models will always suffer from what is known as scale effect, obtaining smaller maximum lift coefficients and greater drag coefficients. However, wing loadings, or weight divided by wing area, are much lower, so landing speeds are much lower than for full-scale aircraft. Modern model engines are sufficiently light and powerful that it is possible to build a model that has more thrust than its weight and can climb straight up or even hover. Structurally, models profit from a different scale effect and are less likely to suffer in-flight or landing damage.
Free-flight, or FF, models can be the least expensive flying models, the easiest to build from raw materials, and the easiest and safest to fly by oneself. However, they are the most demanding of trim and stability because of their “launch-and-pray” nature. The smallest and lightest models can be flown indoors or on very calm mornings or evenings.
Powered models are normally flown outside. They usually utilize a timer-controlled dethermalizer that tips up the leading edge of the horizontal stabilizer to prevent them from being lost if rising air and wind would otherwise take them out of sight. Contests with free-flight models usually involve trying to keep them aloft for the maximum amount of time for each of the different classes of models.
Control-line, or C/L, models are the next least expensive flying models and have the additional advantage that they cannot fly out of sight and be lost. They also provide tactile feedback to the flier, because they are flown on steel lines, mostly stranded stainless-steel cables, that range from about 30 feet to about 70 feet in length. The lines are attached to a control handle in the flier’s hand that operates the elevator through a bellcrank. Manipulation of this handle grants the flier the option of using a full hemisphere of space, inverted or upright. Control-line flying has a unique dependence on surface winds, because the planes are connected to the ground through the flier. Inverted flight requires extra learning, because response to control handle movements is reversed.
Control-line models include sport/trainers, scale, stunt, carrier, speed, and race types. Scale control-liners feature engine power, retractable gear, “bombs,” and other realistic details. Stunt models are optimized for aerobatics and use a symmetrical wing section that enables them to make inverted and upright maneuvers. They often use a flap on the trailing edge of the wing that is mechanically linked to the bellcrank, so that it deflects oppositely to the elevator and enhances the maximum lift available for abrupt maneuvering. Carrier models are judged on the difference between their maximum and minimum speeds and for their ability to grab a wire with their tail hook for landing. Speed models are used in contests, which are won by the fastest speeds, with either piston or jet power, for a specified number of laps. Racer-type models are flown with two or more fliers in the circle, to a specified number of laps and with mandatory pit stops. Combat contests require two fliers in the circle, each trying to cut the opponent’s trailing streamer, often flying at speeds of more than 100 miles per hour.
Radio-control, or R/C, models require a battery-powered miniature receiver with a separate channel for each servo. A servo is an electric motor that rotates a shaft one way or the other from the neutral position, based on the movement of a lever in the transmitter held by the flier. The number of channels utilized varies from two or three for trainers to six or more for sophisticated models that are determined to fully emulate their full-scale counterparts.
Radio-control models are the most popular form of model airplane flying, no doubt because of the challenge involved with flying them well and because of their good simulation of full-scale flight. They also require the most time to learn how to fly without crashing. They are the most expensive type of flying model and require the most sophisticated models. However, the best R/C models, both airplanes and helicopters, can perform all the same aerobatic maneuvers, and more, as can their full-scale counterparts.
The most difficult problem to overcome in first learning to fly R/C airplanes is that the airplane apparently responds differently whether it is going away or coming toward the flier. It is also difficult for the beginner to judge the landing approach and landing. In this, computer-based simulators can be of considerable assistance. Competitive R/C events include combat, precision aerobatics, and pylon races.
Gravity was the original power plant for both FF and R/C gliders. Twisted rubber strands were the next power plant, used until the 1930’s, when the first miniature spark-ignition engines were commercially produced. In the 1940’s, the much simpler and lighter glow-plug engine, which required a battery only for starting, appeared. Diesel and compressed-air engines are used in small models. Jet engines have been available since the 1940’s. Electric motor engines are the newest type of power plant, providing quiet and clean power.
Lennon, Andy. R/C Model Aircraft Design. Wilton, Conn.: Air Age, 1996. A comprehensive text with minimal mathematics that includes coverage of canard and tailless designs. Mackey, Charles. Pioneers of Control-Line Flying. Anniston, Ala.: Precision Aerobatic Model Pilots’ Association, 1995. An account of how C/L flying dominated powered model flying from the early 1940’s to 1960’s, when R/C models became more available and more reliable. Simons, Martin. Model Aircraft Aerodynamics. 4th ed. Herts, England: Model & Allied Publications, 1999. A good general reference for the aerodynamics and performance of model aircraft, including many suitable airfoils. Thornburg, Dave. Do You Speak “Model Airplane?”: The Story of Aeromodeling in America. Albuquerque, N.Mex.: Pony X Press, 1992. A history of the national championships, the people, the models, the FF beginnings, and the C/L and R/C revolutions, written in an engaging, easy-to-read, and amusing style. Winter, William J. The World of Model Airplanes: Building and Flying Free-Flight, Control-Line, and Radio-Controlled Models. New York: Charles Scribner’s Sons, 1983. An excellent overview of the building and flying aspects of all three types of model airplanes.
Forces of flight