Rotor Configurations Tandem Rotor  Intermeshing Rotors Coaxial Rotors  Figure 1-6.  Tandem rotor helicopters.  Figure 1-5.  Igor Sikorsky designed the VS-300 helicopter  incorporating the tail rotor into the design.  Figure 1-7.  Coaxial rotors.  Most helicopters have a single, main rotor but require a  separate rotor to overcome torque which is a turning or  twisting force. This is accomplished through a variable  pitch, antitorque rotor or tail rotor. This is the design that  Igor Sikorsky settled on for his VS-300 helicopter shown  in  Figure 1-5.  It has become the recognized convention for  helicopter design, although designs do vary. Helicopter main  rotor designs from different manufacturers rotate in one of  two different directions (clockwise or counter-clockwise  when viewed from above). This can make it confusing when  discussing aerodynamic effects on the main rotor between  different designs, since the effects may manifest on opposite  sides of each aircraft. For clarity, throughout this handbook,  all examples use a counter-clockwise rotating main rotor  system when viewed from above. For clarity, throughout this handbook, all examples use a  counter-clockwise rotating main rotor system when viewed  from above. Tandem rotor (sometimes referred to as dual rotor) helicopters  have two large horizontal rotor assemblies, instead of one  main assembly and a smaller tail rotor.  [Figure 1-6]  Single  rotor helicopters need a tail rotor to neutralize the twisting  momentum produced by the single large rotor. Tandem  rotor helicopters, however, use counter-rotating rotors, each  canceling out the other’s torque. Counter-rotating rotor  blades will not collide with and destroy each other if they  flex into the other rotor’s pathway. This configuration has  the advantage of being able to hold more weight with shorter  blades, since there are two blade sets. Also, all the power  from the engines can be used for lift, whereas a single rotor  helicopter must use some power to counter main rotor torque.  Because of this, tandem helicopters make up some of the  most powerful and fastest rotor system aircraft. 1-4 Coaxial rotors are a pair of rotors turning in opposite  directions, but mounted on a mast, with the same axis of  rotation, one above the other. This configuration is a noted  feature of helicopters produced by the Russian Kamov  helicopter design bureau.  [Figure 1-7] Intermeshing rotors on a helicopter are a set of two rotors  turning in opposite directions, with each rotor mast mounted  on the helicopter with a slight angle to the other so that  the blades intermesh without colliding.  [Figure 1-8]  This  arrangement allows the helicopter to function without the  need for a tail rotor. It has high stability and powerful lifting  capability. This configuration is sometimes referred to as a  synchropter. The arrangement was developed in Germany 