The Electric Ducted Fan
The electric ducted fan (EDF) is used to power jet-style model airplanes. The ducted fan is a much more affordable alternative to model jet engines. Ducted fans can be powered by either two-stroke glow fuel engines, or by electric motors.
Since electric motors and battery systems have advanced greatly in the last few years, powerful EDF models have become more and more common.
The ducted fan is a very simple concept. It consists of a fast spinning fan in a duct, or shroud. Air is taken in at the front of the EDF, and is accelerated by the action of the fan.
The exhaust air has enough thrust to propel the airplane forwards. Note that unlike true jet engines, no fuel is burned inside the fan housing. This means that temperatures are much lower, and the demands on materials and systems are lower as well.
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The duct must be designed for maximum efficiency. The air intake and the inside surface of the duct need to be smooth, to prevent turbulent airflow. The size of the exhaust nozzle is important too. In general, a smaller nozzle will mean faster exit air speed. However, too small a nozzle will result in significant backpressure, sometimes enough to stall the fan blades.
When considering conversion of electrical energy into thrust, the electric ducted fan will be less efficient than a large two-bladed propeller. However on some models, the EDF just looks better, so the designer compromises. And with modern brushless motors and LiPoly batteries, high-performance scale ducted fan models are possible. Scale jets with over 1 Kilowatt of power and retractable landing gear can be achieved with these modern components.
There are now many good options on the market for the beginning electric ducted fan flier. The T33 model made by Kyosho was one of the first viable ones. It flew well and could be upgraded easily. Unfortunately it is no longer in production, but sometimes appears for sale on Ebay.
The Wattage Turbo Hawk and Turbo Vector are two good entry level EDF models, available from Hobby People. They are affordable foam planes, easy to put together, and fly well.
Other reputable models include the Flash E-74 from eam.net, the Alpha Jet from Hobby Lobby, Bob-E-Cat from ejf.com, Parkjet from Mountain Models, and the FV-1000 from Kyosho.