The Art of the Helicopter John Watkinson - Karatunov.net

Other types of rotorcraft 361
Fig. 9.11 Focke-Achgelis Fa-223 was powerful and capable. The weights below the rotor head are a vibration
absorber for the cyclic control. (Steve Coates)
war the Fa 223 became the first helicopter to fly the English channel when the RAF
recovered a captured machine (Figure 9.11).
The largest helicopter in the world was also a side-by-side. The Mil V-12 (Figure 9.12)
used the drive trains and rotors of the Mil 6, itself a huge machine, with the rotation
of one system reversed. Side-by-side helicopters have the disadvantage that the pylon
structure needed to carry the rotors invariably causes drag. Considerable masses are
cantilevered at the end of these pylons and it is also difficult to obtain enough structural
rigidity.
9.7Coaxial helicopters
The coaxial helicopter configuration was frequently seen in the experimental period as
the contra-rotation offered torque cancellation. However, the coaxial machine also has
some idiosyncrasies in autorotation and once the single rotor machine was perfected
the coaxial was simply too complicated except for special applications. For use on
naval vessels, where hangar space is limited, the absence of the tail rotor allows a more
compact hull for a given load capacity. The Kamov machines demonstrate that amply.
The coaxial configuration has also been used with success on unmanned helicopters.
Provided that the two rotors are not too far apart, the coaxial rotor system in the
hover behaves very much like a single rotor with the same total solidity. This is not
true if the vertical separation is significant, because if the wake of the upper rotor has
started to contract the lower rotor will encounter increased inflow velocity and will