Coaxial vs Single rotor configuration....Performance and Flying Qualities

[Contra]

Always wondered.......despite an established and well researched "single main rotor + tail rotor" config ...what was N I Kamov's inspration behind the seemingly complex and untreaded "Coaxial " territory.

Starting this thread to discuss concrete results on
1.==> Performance advantages
2.==> Handling qualities (Stability and manoeuverability)
3.==>Other factors

Performance
A 10 to 16% advantage in terms of useful load has been cited by the Coaxial helicopters in various books/research papers/ claims.
Q. Whats the explanation for this ?

Handling Qualities
How do the longitudinat / lateral / directional stability compare with a conventional configuration helicopter?
Coments on the manoeuverability and comparison.

Please pitch in and lets all get enlightened.
For starters I found a sort of compendium of all research on Coaxial helicopters....
http://www.humanpoweredhelicopters.org/articles/nasa-tp-3675.pdf

Quiet a few point of views and gets confusing on the results.

[aerobat77]

hey ! i,m not a helicopter specialist, but i think the advantages are the same like in contra rotaing propellers in aircraft.

the advantage is that on one hand you can transmit more power/thrust/lift for a given rotor diameter and on the other hand there are no power losses from a tangential airflow which is "wasted" on a single prop installation.

on the other hand its a good question why only kamov went for it - when it would be a real advantage for helicopters many others would design it the same way.

and i cannot say anything about stability differences .