Free flight (model aircraft)

The essence of free flight model aircraft is that their flight path is pre-programmed, and once released, they are not directly controlled by the operator. When flown competitively, the usual aim is to launch the model into rising air, and to fly for the maximum time.

Free flight models may be broadly divided into four categories:

• gliders
• rubber-powered
• power
• indoor

Within each category, there are different classes. Typically, there is an FAI world-championship class, a so-called mini class, an open class, and possibly any number of unofficial classes, for which regional or national competitions may be held.

Gliders have no onboard motive power. The only energy inputs are the launch, and any rising air encountered during the flight. The FAI glider class is F1A, also known as A/2 or Nordic glider. The model must have a maximum area (wing plus tail) of less than 34 dm², and a minimum weight of 410 g. Launch is by hand tow, using a cable of less than 50 m length. The mini glider class is A/1 (F1H). A/1 gliders must have less than 18 dm² total area, and weigh at least 220 g. Open glider contests are rarely flown, and most competitors in such contests use F1A gliders. Other glider classes include magnet-steered gliders - essentially a free flight slope soaring class, and hand-launched glider (usually abbreviated HLG). HLGs are small models which are launched from level ground simply by being thrown hard. This is one of the more athletic of the free flight disciplines.

Rubber-powered models are powered by the stored energy of a twisted elastomeric material. These range from the simple rubber-band powered toys available in many toy stores, up to the open rubber class, examples of which often use 200 g of rubber in their "motor". The FAI rubber class is F1B, also known as Wakefield. Charles Dennis Rushing has written on the history of the Wakefield Cup (http://www.btinternet.com/~kaynes/Wakebook/wkbkhome.htm). F1B models may have a maximum of 30 g of rubber motor, and the empty weight of the airframe must be at least 200 g. The maximum total area of the model must be less than 19 dm². The mini rubber class is Coupe d'Hiver (also known as F1G). "Coupe" models have no area restrictions. The maximum weight of rubber allowed is 10 g, and the minimum empty weight of the airframe is 70g. (need Coupe history here - 100g vs 80g, min cross-section etc). Open rubber is a popular event, featuring large models with enormous amounts of rubber crammed into them. Open models often have 50% of their flying weight composed of rubber. P-30 is a common beginner's event. A P-30 must use an unmodified commercially available plastic propellor. P-30 has a maximum wingspan of 30 inches, and uses 10 g of rubber. The empty airframe must weigh at least 40 g.

Power models are those with an onboard power source which is not a rubber motor. Frequently this is an internal combustion engine. However, the category also includes compressed gas motors and electric power. The FAI power class is F1C.

Indoor models are (as the name suggests) models designed to fly indoors. These models usually require a large space, such as a sports hall, aircraft hanger, salt mine or similar. Most indoor models are rubber-powered, very light weight, and flown to achieve the maximum duration. The absolute record with a rubber-powered indoor model is a little over an hour on a single flight, with an average propeller speed of about 45 turns per minute. The most-widely flown FAI indoor class is F1D.

Although most indoor aircraft are rubber-powered, both gliders and power aircraft (usually compressed gas or electric) are also flown indoors. Some events concentrate on scale replicas of man-carrying aircraft. Others feature unusual flight configurations, such as ornithopters, helicopters, or autogiros.