Classical
The classical layout is also sometimes referred to as the ‘Sikorsky’ type. This configuration is currently the most common, and has a single horizontally rotating main rotor to provide both lift and thrust, and a vertically rotating tail rotor to counteract torque reaction, and provide directional control.
Examples of this configuration are Sikorsky S61, S76, AS332 & AS225 Supe Pume etc.
Notar
Designed to overcome the operating problems associated with tail rotors, the Notar (NO Tail Rotor) helicopter uses the classical design layout, but has a ducted air supply and vertical stabilizers to counteract torque reaction and provide directional control.
A typical example is the MD 600N Explorer.
Tandem
The tandem configuration provides two horizontally rotating main rotors, mounted at the front and rear of the fuselage, which in some helicopter types overlap or intermesh (the main rotor blades pass through the same arc, but in opposite directions). No separate tail rotor is required as torque reaction is cancelled by the rotors turning in opposite directions.
Examples of this configuration are the CH 46 Sea Knight and CH47 Chinook
Side-by-Side
This layout is also characterised by having two horizontally rotating main rotors, except that these are mounted at the sides of the fuselage.
An example of this configuration is the V22 Osprey aircraft, although this is a compound aircraft that offers advantages of both helicopter and aeroplane flight modes.
Side-by-Side Intermeshing
This configuration is similar to the Side-by-Side, but the rotors are generally connected to a common single main rotor gearbox, and rotate at an angle to the fuselage, overlapping or intermeshing into each other.
Co-Axial or Contra-Rotating
This design has two main rotors mounted on separate shafts, but with a common axis of rotation, and the rotors are mounted one above the other, turning in opposite directions.
