Global Aviator South Africa - May 2018

(lily) #1

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
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