tandem rotor helicopters
with thanks to the helicopterpage

Tandem rotor helicopters operate a little differently than do the single rotor variety. In a tandem rotor helicopter, you have no tail rotor, so there is no translating tendency to deal with, but you still have pedals for directional control at a hover. Your cyclic control, which is used as it always has been in single rotor helicopters, has not changed either. The only thing different in terminology for tandem rotor aircraft is the term "Thrust control", which is used to describe the collective pitch control lever. It is used in the same way as any other collective, but the tandem guys use the term thrust control.

Rotor Position for Level Hovering

Tandem rotor helicopters operate in forward flight by using "Differential Collective Pitch" or "DCP". DCP is basically just increasing more pitch in one rotor system then the other to make the aircrafts attitude change. By increasing the pitch in the aft system more than the forward system, the aircraft will tilt nose low, and accelerate forward. To climb without changing airspeed, more pitch is placed in both systems simultaneously. It is really a matter of aircraft attitude more than anything else. If the aircraft is in a nose high attitude, it will climb and bleed off airspeed. If it is too nose low, it will dive and increase airspeed. The amount of pitch put in each rotor system will dictate airspeed and altitude. The pilot will fly the aircraft just like any other, but the rotor systems will act in a way peculiar to tandem helicopter flight. The picture here is of a tandem helicopter in level hovering flight. Notice both rotor systems are depicted as level. The actual blades will "Cone" a bit. What this means is they will bend upwards to the tip. The more the weight on the aircraft, the more the blades will cone. For our descriptive purposes, the pictures will not depict coning.

Here's a Chinook doing slope operations.

Rotor Position for Manoeuvring

You will notice in the first of these two pictures both of the rotor systems are tilted to one side. This is what allows the aircraft to fly sideways. This is accomplished by using lateral cyclic, and a corresponding pedal input to maintain directional control. What the cyclic and pedals do is actually put inputs to the rotor systems to make them both tilt the same direction, as if there were two cyclics both putting in duplicate inputs to the two rotor systems. In the second picture, you see the front rotor system level, and the aft system tilted, allowing the helicopter to pivot around the forward mast. This can be a handy manoeuvre when there is little room to move the nose, but plenty of room to swing the tail of the aircraft. This is accomplished by using large pedal inputs and small cyclic inputs to make the aircraft pivot around its nose. The manoeuvres just happen mainly by feeling your way through it while you judge your distances, make sure your engine, or engines are working properly, and that you are not going beyond the aircrafts limitations. You are so busy doing other things, you do not actually think about the actual control inputs to induce the manoeuvre.


More Rotor Position for Manoeuvring

In the first of these two pictures, you see both rotor systems are tilted in opposite directions. This is accomplished by pedal only inputs. By depressing one pedal over the other, cyclic inputs are put in both systems in opposite directions to pivot about the centre of the aircraft. Both rotor systems receive equal cyclic inputs, and the helicopter just spins nicely at its centre without the pilot having to move his cyclic control at all. In the second picture, a pivot around the tail is depicted. This is accomplished by heavy cyclic inputs by the pilot, and little or no pedal inputs. This will make the tail stay in one place, and the nose of the aircraft moves laterally until it spins about the aft mast. (Also known as the aft vertical shaft, due to its height). This is accomplished by a complicated system that requires a lot of linkages, a lot of control tubes, and a pilot who trusts his maintenance crew to make sure it all was put together properly.