How The Coaxial Counter-Rotating System Works - GRAUPNER micro light indoor Montage- Und Betriebsanleitung

How the coaxial counter-rotating system works

Instead of using a tail rotor to balance the main rotor torque, the coaxial counter-rotating system
has two main rotors, one above the other, turning in opposite directions. This makes it possible
that the torque of the two rotors can exactly balance each other so that the fuselage won't be
twisted during hovering or in straight flight.
Fig. (1) is a schematic layout of the coaxial counter-rotating system, which includes: two motors,
two coaxial main shafts and rotors driven separately by two motors through gears.
Fig. (1): Schematic layout of the coaxial counter-rotating system
1. Upper rotor blade 2. Inner main shaft 3. Upper rotor drive gear 4. Upper rotor drive motor
5. Lower rotor blade 6. Outer main shaft 7. Lower rotor drive gear 8. Lower rotor drive motor
Since the two rotors are driven by two motors separately, you can cause different torques of the
two rotors ( maintaining constant overall thrust) by increasing the speed of one motor and de-
creasing the speed of the other to turn the helicopter left or right around the vertical (yaw) axis.
This is used instead of the tail rotor control in conventional helicopters to turn around in hovering
or change direction in flight.
The speed of the motors are controlled by the throttle stick as well as the yaw stick on the
transmitter. When you push forward the throttle stick towards full power position, the speed of
both upper and lower motor increases. Hence the speed of both upper and lower rotor blades
increase. However, when you push the rudder stick to the left or to the right, the speed of one
motor increases and the speed of the other motor decreases. Hence the speed as well as the
torque of one rotor increases and the torque of the other rotor decreases. Therefore the heli-
copter will be turned to the left or to the right.
Just like helicopters with a single main rotor and a tail rotor, the pitch stick controls the helicopter
to fly forwards or backwards, and the roll stick is used to roll the helicopter to the left or to the
right.
This is carried out by the servos linked to the swashplate which in turn tilts the lower rotor disc
so as to make the helicopter fly forwards or backwards, to the left or to the right.
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