Global Aviator South Africa - May 2018

Global Aviator May 2018 / Vol. 10 / No. 5 53

By Helen Krasner

Helicopter

Transitions

Pic: Shutterstock

Helicopters are different from other aircraft, and that difference

extends to the terminology we use. For example, when an aircraft

taxies out to the runway, accelerates along it, and then leaves the

ground and starts to fly, what do you call the manoeuvre? That’s simple,

you might say. It’s a ‘take-off’, isn’t it? Similarly, when it returns to

the airfield, flies lower and lower, and then eventually touches the

ground, this is called a ‘landing’. Everyone knows that, don’t they?

factors which need to be borne in mind
when changing from one to the other.
To start the transition from the
hover to forward flight, the pilot
simply moves the cyclic forward,
which causes the helicopter to move
forward and accelerate. However,
these are not the only things which
happen. When a helicopter is hovering,
air is being drawn down through the

rotor system, and it collects beneath

the hovering helicopter. This so-

called ‘ground cushion’ of air means

that slightly less power is needed to

hover close to the ground than would

otherwise be the case. However, when

the helicopter is moved forward

from the hover, it literally falls off the

cushion of air. Therefore it starts to

sink, and it is necessary to raise the

collective a little to maintain height.

At any rate, this is what I and

many other helicopter students

learned as the explanation for this

loss of height, and it does make sense.

However, not everyone agrees with

this way of looking at the situation.

For while it is indeed true that as you

move the cyclic forward the helicopter

starts to sink, many authorities say the