Free flight (model aircraft)

Free Flight is the segment of model aviation involving aircraft with no active external control after launch. Free Flight is the original form of hobby aeromodeling, with the competitive objective being to build and launch a self controlling aircraft that will achieve the longest flight duration, within various class parameters.

The essence of free-flight is that the aircraft have no need for external control, for instance by radio. Aircraft of this type have been flown for over two centuries. They are designed to be inherently stable in flight; if disturbed by a gust of wind or a thermal current they will return automatically to stable flight. Their stability is achieved by a combination of design and trim, - the relationship between centre of gravity, wing and tailplane incidence and rudder setting.

With their much lower wing loading, free-flight aircraft fly much slower than the engine-powered radio-controlled aircraft that many people first think of when ‘model aircraft’ is mentioned. Most of them glide at little more than walking pace and few weigh more than 500 grams.

Usually the sole objective of free-flight competition is flight duration, and one of the sport’s fascinations and challenges is to design the most efficient aircraft within the various competition limits on parameters such as minimum weight, maximum wing area, and motive power.

Free flight models may be broadly divided into four categories:

When flown competitively, the usual aim is maximum flight duration. In the case of models flown outdoors, the modeler attempts to launch the model into rising column of air, a thermal. These outdoor free flight models tend to be designed for two very different flying modes: climbing rapidly under power or tow, and gliding slowly while circling with minimum fall rate. Much of the challenge in designing and flying these models is to maintain aerodynamic stability in both modes and to make a smooth transition between them. Modern models use mechanical or electronic timers to move control surfaces at preset times. Detecting the thermal into which to launch is vital and can involve several methods, ranging from radio telemetered temperature and windspeed measurements plotted on a chart recorder to Mylar streamers or soap bubbles to visualize the rising air.

Because competitions normally involve up to seven rounds during the day, each flown to a maximum flight time hard to achieve without thermal assistance; an automatic on-board timeswitch upsets the trim of the aircraft when the "max" is achieved, to bring the aircraft down safely and quickly. Locating and recovering the aircraft for further flights is an important part of free-flight. Many aircraft carry radio location beacons, and flyers will use GPS, binoculars, a compass and a directionally sensitive radio tracking receiver to assist them. A day's flying and retrieval may well involve 20 miles (32 km) or so on foot or on bike, depending on wind strength.

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Wikipedia