What kind of Electric Motor would you choose for a RC rotorcraft?

[BradleyCHorton]

what kind of Electric Motor would you choose for a RC rotorcraft?

if you wanted to build a RC helicopter with weight of around 5 kjg/11 pounds?

what type of motor with with what power rating like

*RPM
*Voltage
*Ac or Dc motor
*Current rating

and dont you think to lift around 11 pounds / 5 kgs ,the motor would at least need around 10,000RPM..
i know it depends on the disc area,the Lift co-efficient ,the pitch of the blades,etc

but a standard RC helicopter which weighs 5kg/11 pounds needs atleast 10,000 RPM rating ,do you think i'm over estimating or under estimating?
Update : i am more concerned about the RPM required by the motor to lift 11 pounds of weight.

 

[Cyberdactyl]

One critical variable you didn't supply. . . what are you willing to pay?

You can go with perfectly capable cheap Asian brushless motors in the $8-13 range. Or mid-range motors that have a bit better balance and efficiency in the $15-25 range. Or the High-end, very well made motors in the $30-50 range.

 

[Craftydan]

11# is completly doable . . . but BIG.

this is a pro-sized rig, and usually needs the expertise to build/tune/fly it, and won't be cheap. Not trying to hold you back but you're looking at a heauge cash layout and the question hints to lack of experience . . . but assuming you've got the experience but not the technical background . . .

Shoot for a 2:1 thrust to weight ratio -- that means the TOTAL thrust at WOT for all your motors needs to be above 22#. (you'll need to bump that up quite a bit if 11# is only your payload). Next, choose a configuration -- unless you've got reasons against it, in that bracket I'd stear you toward an Octo, so each motor will need to produce *at least* 1/4 of your AUW.

Then start looking at motors for prop/thrust combos -- RPM and power means nothing to thust w/o knowing what prop you plan to swing, but swing the prop too slowly/weakly, and you'll never get the thrust you need. 11# => 1.25 kg/motor. That's fairly easy to attain with mid grade motors.

more weight? well depend how much more. Can you get away with fewer, stronger motors? yes, but you'll need to size them to the weight to keep at least 2:1.

beyond that, we'll need a better idea of your assumptions/plans to help.