I have been looking at building an airplane then down the road a UAV and have a question. Looking at a RQ-11 Raven Platform but I am wondering would a ducted fan work better than a propeller? If the fan is the way to go, what about placing two ducted fans on the main fuselage under the main wing? The plan is no ailerons to start with. Any comments would be great.
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You could use a ducted fan to replace a rear tail surface. Properly design, a ducted fan, can either produce high speed thrust or low speed thrust but not both. The main problem with installing ducted fans to aircraft designed for props is that the characteristics of the airframe (never exceed speed for instance) are suited for a particular prop or DF. DF will produce thrust at higher Ve (speed of the thrust). If the aircraft is quite low in drag, the ducted fan can produce thrust efficiently at a higher speed. The problem with 2 ducted fans under the wing, drag and yaw of the airframe are affected. also single engine out will produce a yaw, possibly leading to a spin/stall. Try and keep everything along the centreline, try to reduce drag. 1 big advantage of the DF in RC/smal UAV apps is that the prop is protected from damage. Having said all that the ducts are extremely complex and difficult to make accurately. Hope this helps Ed
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For the same diameter, a ducted fan is more efficient than a propeller. This is because the duct eliminates tip losses.
Ducted fans are made for higher speeds. They get more efficient the higher RPM is. Thrust is not so good at the lower RPMs.
You could use a ducted fan to replace a rear tail surface. Properly design, a ducted fan, can either produce high speed thrust or low speed thrust but not both. The main problem with installing ducted fans to aircraft designed for props is that the characteristics of the airframe (never exceed speed for instance) are suited for a particular prop or DF. DF will produce thrust at higher Ve (speed of the thrust). If the aircraft is quite low in drag, the ducted fan can produce thrust efficiently at a higher speed. The problem with 2 ducted fans under the wing, drag and yaw of the airframe are affected. also single engine out will produce a yaw, possibly leading to a spin/stall. Try and keep everything along the centreline, try to reduce drag. 1 big advantage of the DF in RC/smal UAV apps is that the prop is protected from damage. Having said all that the ducts are extremely complex and difficult to make accurately. Hope this helps Ed
thanks for the input.