A lot of the engineering of helicopter flight seems to be devoted to cancelling torque; hence the tail rotor or other structures to add a counteracting force.
Why not have contra-rotating coaxial rotors in all choppers? From everything I’ve read, this design is easier to fly and more maneuverable.
Good grief, I got bumped by flight answering my very quesito. Creepy… 
Hmmm. Now I gotta wonder. The Russian
KA-50 appears to have superior airspeed and maneuverability to the Apache.
The Kaman HOK-1 Huskie turned out to be a very stable aircraft with its intermeshing rotor system. I’ve heard, but do not have a cite, that it was deemed “too stable” for flight training.
Remember, I am not dismissing coaxial, or at least tandem rotor systems, just those that do not use any cyclic pitch. All of the problems I descibed above disappear when you introduce cyclic pitch (though some new ones arise). Remember, no flying aircraft I am aware of (besides the airscooter) uses CG motion for control, they all use some form of cyclic (even if it doesn’t go through a swahplate).
Thanks for your excellent expositions! Just wondering, do the controls for, say, a Chinook, differ significantly from a more conventional rotor+tail rotor design?
They are designed to have the same basic controls from a pilot’s perspective. They certainly handle different, but much of this is just due to the size, not necessarily the fact that there are two rotors.