Helicopter flying is not easy, everyone knows that. However, hovering is particularly difficult.
Most students really struggle to master the hover, often feeling like the helicopter is some kind of uncontrollable beast.
So what makes it so hard to hover in a helicopter?
Helicopters and Stability
An aircraft – or any other system – is said to be stable if it can recover from small changes to its position. For instance, a cone resting on its base is stable, while one resting on its tip is unstable, since it can be very easily tipped over.
Most fixed-wing aircraft are inherently stable, so that if you take your hands off the controls, they will continue flying, at least for a short time.
However, this is not the case for helicopters, which are unstable. This means that constant pilot input is required on the controls, and if the pilot stops ‘flying’ the aircraft, it will oscillate wildly or get out of control in some other way. The situation is a little more complicated than this, but basically it is this inherent instability which makes helicopter hovering so difficult.
Hovering – You Have to be Close to the Ground
Many students who can manage to control the helicopter to some extent at altitude still struggle with hovering. Part of the reason for this is that hovering is always done close to the ground, and in fact, those students were probably altering their altitude by tens or even hundreds of feet when in the air. OK, you might think, so why not learn to hover at altitude first? The main reason is that it is quite dangerous to come to a hover at a height unless you are very, very careful; it is easy to get into a condition known as vortex ring, in which the helicopter falls into its own downwash. So, students need to learn to hover close to the ground, where there is very little room for error.