Electric ducted fan
An electric ducted fan or EDF is a relatively compact power plant that consists of an electric motor and small, multi-bladed propeller located inside a shroud and which spins at very high RPMs. This is less efficient than a propeller, especially at low speeds and most ducted fan models need twice as much power as a similar model with a prop for the same performance. The main advantage of a ducted fan is that it can be hidden in a scale jet model, resembling a jet engine.
They are available for both electric and gas engines, although they have only become widely used with the recent improvements in electric flight technology for model aircraft. It is possible to equip a model jet aircraft with two or four electric ducted fans for much less than the cost of a single jet turbine or large gas engine, enabling affordable modeling of multi-engine planes, including military bombers and civilian airliners.
Compared to a standard propeller, a ducted-fan generates more thrust per cross-sectional area. The shaped duct often limits installation to recessed areas of the fuselage or wings. Ducted fans are popular with scale models of jet aircraft where they mimic the appearance and feel of jet engines, as well as increasing the model's maximum airspeed. Speeds of up to 200 MPH (320km/h) have been recorded on electric-powered ducted fan airplanes, largely due to the high amount of RPMs produced by ducted fan propellers. They are also found on non-scale and sport models and even lightweight 3D flyers. Like propellers, fan units are modular components and most fan-powered aircraft can accommodate a limited selection of different fan units.