Problems Caused by the Tail Rotor
As you will now understand, the tail rotor is very useful. But it does cause some problems.
New helicopter pilots soon find that most helicopters hover with one skid lower than the other.
Why is this?
Well, the use of the tail rotor results in an extra force being applied, which tends to move the helicopter to one side, usually the right. We call this ‘tail rotor drift’, and of course it needs to be stopped.
This can be done in one of three ways: pilot input on the cyclic, adjusting the control rigging so that when the cyclic is centralised the rotor disc (the disc the rotors make when they are turning) is actually tilted, or mounting the gearbox at an angle so that the drive shaft to the rotor is offset.
However, in solving the tail rotor drift issue we create another problem. If the tail rotor is mounted below the level of the main rotor – and most are – a force is produced between the horizontal component of lift which is being used to offset the tail rotor drift, and tail rotor thrust itself. This force tends to roll the helicopter to the left, and the effect is known as ‘tail rotor roll’. It means that the helicopter hovers left-skid-low. It is not really a problem, but is something that pilots need to know about.
Confused? Don’t worry; helicopter aerodynamics is quite complicated, and becomes more so the more you look into it. Hopefully some of these things will become clearer as time goes on. However, if you are planning on learning to fly helicopters, remember that you can fly perfectly well without understanding the details of this stuff, or turning over and crashing… though knowing about some of it definitely helps.
Decoding Science. One article at a time.