Those silly designers that still rely on a tail rotor - don't they know that coaxes are BETTER?
Igor Sikorsky once said, "There will be times when the theory and the facts do not agree, young gentlemen. In that case, it is my ernest belief that you should respect the facts."
The facts are:
TR's "lose" about 3% of the power that the helo has.
Coaxes have about 10% higher cruise drag due to the very high mast and the two rotor heads.
The bottom rotor of a coax has significantly less efficiency than the top because the scewed flow and disturbed air it operates in.
Self-midair is a big problem with coaxes (thus the high mast to separate the disks)
The ABC/X2 is a very very high offset (very stiff) rotor so that it makes it possible to have a lower mast and less disk separation. This helps solve 2 and 4 above.
TANSTAAFL for sure. 95% of all helos have a single main rotor and a tail rotor/fan. Why? because it works well, probably better than anything else.
Then why the X2/ABC? Speed, which will cost some hover efficiency, but will allow a helo to challenge tiltrotors while still hovering and maneuvering very well at low speed, something tiltrotors will never do well.