Joined Mar 2010
EDF Helicopter Help
Hey I'm new to this forum and into R/C ing in general actually but, I was wondering if I could get some help. I want to make a ducted fan helicopter sort of like those you see in avatar (scorpion) or on the Starcraft 2 previews. I have one of those walkera 3 4 and its fun to play with so, Id want to make it small, like a living room flier like the walkera.
The problem is I dont know anything about R/C in general, including where to buy parts to build (Everything Ive found so far doesn't list complete infromation about the part). Second i figured id ask more experianced people as to if it is even possible to make.
I have a little background in Engineering and physics so i can probally keep up with a mathmatical approach.
San Carlos, California, United States
Joined May 2002
Since nobody has posted, I'll comment.
There is a fundamental problem with using ducted fans for helicopter lift.
If you look at propeller propulsion systems, there are basically two characteristics: exhaust velocity and thrust.
Exhaust velocity is the speed of the airstream produced by the rotor. Thrust (sometimes called static thrust) is the amount of "push" generated.
Large rotors spinning at low speeds are efficient for moving a large amount of air at low velocity. Stated otherwise, it provides high thrust at low exhaust velocity.
Small rotors spinning at high speeds are efficient at moving a small amount of air at high velocity. Stated otherwise, it's low thrust, but high exhaust velocity.
When a helicopter is flying, you mainly want thrust. The exhaust velocity is much less important, because it is generally not importan for a helicopter to rise quickly. Therefore, large rotors are more efficient for this application. If you use an EDF for this application, it is very inefficient because an EDF converts most of the power into a high velocity exhaust rather than a high thrust exhaust.
This is why most helicopters use large rotors at low speed rather than small rotors at high speed.
There are some tricks around this, however. Much like a transmission can convert high RPM/low torque to low rpm/high torque, there are some (inefficient) methods to convert high velocity/low thrust to low velocity/high thrust. The Hiller Flying Platform used an EDF-like fan and used a specially-designed shroud around the fan to increase static thrust.
The basic gist of this is tha EDF-style fans are the wrong lift source for hovering aircraft, IMHO.
If you are absolutely determined to do this, I would recommend investigating the V-22 Osprey, since it is the closest real-world equivalent to your ideal design. There are also some threads in the VTOL forum about the Osprey, which I would recommend reading.
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