Basically, like the propellers setup in this image without the tail end bit: enter image description here Where the propellers will be spinning in opposite directions. This would, in theory, counteract the angular momentum to a degree right? So would this be able to fly vertically upwards without spinning?

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    $\begingroup$ Welcome! The answer is yes. Seems to be a duplicate of Why does the Ka-50 (Hokum) have two main rotors, one on top of another? or How can a helicopter be designed without a tail rotor? $\endgroup$
    – mins
    Commented Jun 26, 2017 at 2:07
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    $\begingroup$ That rear propeller does not keep the helicopter from spinning, it helps tilt the vertical lift component into a horizontal one, meaning forward and backward motion. $\endgroup$
    – Ron Beyer
    Commented Jun 26, 2017 at 3:22
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    $\begingroup$ The rear propeller on that model is needed only because it is cheap one without cyclic controls. Better coaxial R/C helicopters have cyclic control and so don't need anything on the tail to fly in any direction (though they are usually designed for extreme self-righting stability, so can't pitch to fly very fast, unlike full-scale coaxials which are not, and which can fly at useful speeds. $\endgroup$ Commented Jun 26, 2017 at 6:17

2 Answers 2


Yes, because spinning in the opposite direction produces counterbalancing torque. Those rotor over rotor models adjust yaw by small variations in the speed of the rotors, so that one produces a bit more torque than another.

There are a number of large helicopters that use two main rotors to the same effect, such as the CH47 Chinook (front and rear) and the Kamov KA31 which uses the same rotor over rotor configuration as the model you picture.

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    $\begingroup$ I don't know about drones and toys, but co-axial rotor helicopters such as the Kamov Ka-31 and Ka-115 do not adjust yaw by varying the relative speeds of the rotors. The rotors are geared together and remain synchronized. It is the relative drag of the rotors that must be adjusted, which is easily managed via a separate swash plate for each rotor. $\endgroup$ Commented Jun 26, 2017 at 7:07
  • $\begingroup$ Varying rotor speeds is indeed how it's usually done on simpler RC models because having two motors is cheap at that scale and mechanically more sound - those models have a tendency to hit stuff, which would quickly damage the meshing. But good comment for the Kamov! $\endgroup$
    – MrBrushy
    Commented Jun 26, 2017 at 16:28
  • $\begingroup$ @SylvainBoisse, model rotors also have small angular momentum, so quickly accelerating them is possible. Full-scale rotors don't—moment of inertia scales with fifth power of diameter. So full-scale rotors can't be varied in speed with any useful precision. $\endgroup$
    – Jan Hudec
    Commented Jun 26, 2017 at 17:27
  • $\begingroup$ The very inexpensive models have fixed pitch blades, so they can't adjust yaw by varying pitch - so they only adjust speed. True that the KA31 will do this by varying pitch instead, a more accurate method. I should have mentioned that... $\endgroup$
    – tj1000
    Commented Jun 26, 2017 at 20:10

The 'fly vertically upwards' is achieved simply by increasing the rate of both motors. They still counteract each-other's torque so no spinning but now, because each rotor is angled to provide upwards force despite counter-spinning, they both provide more lift and "up she goes...."


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