Indoors
As the name suggests, indoor models are designed to fly indoors. These models are typically very light in weight because they do not have to withstand external weather conditions.
There are a number of classes of indoor free flight models. Some are scale reproductions but others are designed purely to fly for as long as possible. These models are timed with a stopwatch.
The FAI is the international organising body for all air sports worldwide, including aeromodelling. The FAI sanctions World and European Championships for the ultimate indoor duration class designated F1D. F1D models must have a minimum weight of 1.2 grams and a maximum wing span of 55 cm. These models are constructed from very light balsawood sheet and strip, boron filament, carbon fibre, and a transparent covering of plastic film less than 0.5 micrometres thick. The models are powered by 0.6 grams of rubber in a single loop about 9.0 inches long that can be wound to take around 1500 turns. The average propeller RPM during a flight is less than 50 and these models fly at less than walking pace. F1D models require a large space, such as a sports hall, aircraft or dirigible hangar, with the famous atrium of the West Baden Springs Hotel having been previously used for indoor free flight competitions in the United States, and there is even a salt mine in Romania 400 feet (120 m) underground that has hosted the FAI world F1D championships several times. Single flight times approach forty minutes.
Although most other indoor model aircraft are also rubber-powered, gliders and aircraft powered by compressed gas or electric batteries are also flown indoors. Some classes concentrate on scale or semi-scale replicas of man-carrying aircraft. Others feature unusual flight configurations, such as ornithopters, helicopters or autogiros.
Indoor modelling is now about a century old. A history of indoor models may be found here.
Read more about this topic: Free Flight (model Aircraft)