Does a twin rotor not use any anti torque power?
Nope, a tandem rotor helicopter does not expend any power producing anti-torque effect. The two rotors rotate in opposite directions, thereby cancelling each other's torque without net expenditure of power on torque cancellation.
A single main rotor helicopter with tail rotor has to allocate 12 to 15 of per cent available shaft power to the tail rotor in vertical flight. Fast cruising flight unloads the tail rotor because the vertical stabilizer offsets the main rotor's torque, but this anti-rotor torque trim soaks up about the same per cent of available power by converting rotor torque to vertical stabilizer drag.
The opposed direction of rotor movements of a tandem helicopter also has a swirl-straightening effect on the air flow through the combined momentum disk, thereby slightly increasing vertical lift/thrust.
You are aware that the most efficient helo configuration for vertical thrust is a counter rotating, coaxial design because the coax. config. minimizes vorticity -- a fancier word for swirl -- of the momentum flux through the rotor disk? A coax helo theoretically should reduce power required by a factor of 1/(sqrt(2)) compared to a single main rotor design to hover with the same weight.
On the other hand, a tandem rotor helicopter is slightly less efficient than a single main rotor helo in forward flight because the rear rotor on a tandem has to fly in the somewhat turbulent wake of the forward rotor. Also, a tail rotor makes a single main rotor helicopter arguably and perhaps more maneuverable than a tandem or coax. layout.
Conclusion: coaxial or tandem rotor designs are better configurations for large transport hubschraubers, assuming that a large transport helo ought to optimize vertical flight rather than forward flight efficiency, and one can't have both in the same aircraft. Therefore, neither the CH-53 nor the MiL-26 are the optimum designs for their roles.
Sikorsky has circulated art work showing a big big coaxial helo or flying crane as their proposal for a new, very heavy lift helicopter for the Army. I suspect that the H-53 and the big MiL are single main rotor designs because that's all their parent firms knew how to build way back when.
A Chinook or Sea Knight in forward flight can obtain maximum lift and thrust, albeit at a slower cruising speed, by flying at a bit of a yawed angle. It gets the rear rotor somewhat out of the forward rotor's wake. Also, one can think of this as increasing the effective wingspan of a Chinook's rotary wings.
We have some Chinook pilots here at Peeprune who might tell us about flying the Chinook yawed versus not yawed.