engineering question

[S-A-B-E-R->]

guys can some one tell me the exact science and machinsm behind coaxal rotors how opposit spin on same boom is achieved?

Kamov Ka-50 - Wikipedia, the free encyclopedia
a link for example

 

[gambit]

To simplify it...

Imagine a rod inside a tube. The rod has its own rotor attached to its top. The tube has its own rotor attached somewhere on its length. A common engine, with some creative differential gearing, will turn both rod and tube but in opposite direction. The complexity begins where we have to stabilize both spinning items to be in sync with each other, mainly so that they do not collide and result in a catastrophic event.

The main reason why coaxial designs are not popular with helo manufacturers is not because of the mechanical complexity, which is considerable but certainly DOES NOT prevent field operation and maintenance, but because of the unfortunate side effect of unwanted downwash from the top rotor onto the lower rotor, creating a potential for uncontrollable vortexes that can send the aircraft out of control. That potential increases in dynamic environmental and atmospheric conditions, fancy phrasing for a windy day.

 

[Safriz]

To simplify it...

Imagine a rod inside a tube. The rod has its own rotor attached to its top. The tube has its own rotor attached somewhere on its length. A common engine, with some creative differential gearing, will turn both rod and tube but in opposite direction. The complexity begins where we have to stabilize both spinning items to be in sync with each other, mainly so that they do not collide and result in a catastrophic event.

The main reason why coaxial designs are not popular with helo manufacturers is not because of the mechanical complexity, which is considerable but certainly DOES NOT prevent field operation and maintenance, but because of the unfortunate side effect of unwanted downwash from the top rotor onto the lower rotor, creating a potential for uncontrollable vortexes that can send the aircraft out of control. That potential increases in dynamic environmental and atmospheric conditions, fancy phrasing for a windy day.

hi,
what would be the benifit of such a setup? is it to get rid of the tail rotor?
can a flywheel rotating opposite to the rotor do the job? it wont have a downwash.

 

[gambit]

hi,
what would be the benifit of such a setup? is it to get rid of the tail rotor?

Yes.

can a flywheel rotating opposite to the rotor do the job? it wont have a downwash.

Not possible. On a single rotor helo, the tail rotor is used to change the helo's facing direction. On a coaxial design, controlling both rotors in terms of rotating speed and blade pitch is how the coaxial design change direction.

On a single rotor design, the rudder pedals changes the tail rotor's blade pitch, essentially 'blowing' air from side to side, allowing the helo to change its facing direction.

On a coaxial design, if both rotors are at the same speed and their blades' pitch are the same, the helo fixed its facing direction. There is something called 'reactive moment' or 'reactive torque' compensation and disparity that the rudder pedals affects when activated by the pilot...

Helicopter aerodynamics | free-books

In all dual-rotor helicopters, the main rotors rotate in opposite directions. In this way the mutual reactive moments are balanced, and the necessity of having a tail rotor is eliminated. Thus the power loss from the engine is reduced.

When torque from both are balanced, or compensated, the helo does not change direction. When there is a disparity between the two by reducing the speed of one, depending on which rudder pedal (left or right) is depressed, then the helo can change direction. Having blades instead of a solid flywheel to exploit aerodynamic forces make these directional changes faster.