Flying the Helicopter
Basic
Instead of fixed wings, a helicopter has rotating wings, the rotor blades, to
generate lift, just like the propeller to generate thrust. The lift increase
with engine speed or the pitch angle of the main rotor blades. For simplicity,
our mini helicopter only
controls the engine speed to increase or decrease its lift. However, a motor
driven system simultaneously generates torque that acts on the helicopter
fuselage, twisting the fuselage in the opposite direction to the main rotor.
This torque has to be countered by the thrust of the tail rotor blades installed
on the end of a tail boom. It is the mixer that co-ordinates the speed of the
main rotor and the tail rotor so as to alter the thrust of the tail rotor and
exactly balance the main rotor torque. By increasing or decreasing the speed of
the tail rotor and hence varying its thrust, the helicopter yaws either left or
right. Besides, a helicopter must also be controlled about two further axes:
roll and pitch. This task is performed by the cyclic control system.
The cyclic control system
If
the helicopter is in hover, both rings of the swash-plate and the rotor disc are
at right angle to the rotor shaft. When flying in a certain direction, i.e.
forwards, backwards or sideways, swash-plate should be slanted and tilt the
rotor disc in that direction in order to provide the thrust component required.
This is accomplished by the cyclic control system.
Fig. 3 Forces
acting on a helicopter when flying forwards
Let's see how the cyclic control system works when the helicopter is flying
forward. Referring to Fig.(2), when you
push
the elevator stick
on
your transmitter
forward,
the push-rod linked to the elevator servo moves upwards, this push-rod tilts the
outer ring as well as the inner plate of the swash-plate. And, the push-rod
linked with the inner plate also moves upward and turns the
flybar paddles
such
that one of the paddles increases its angle of attack and lift while the other
decreases its lift. Therefore, one paddle rises up and the other drops down,
which
in
turn, via linkage, connected to the rotor head as shown in Fig.(2),
make the main rotor blades turn around its axis
such
that the advancing blade decreases its angle of attack and lift while the
retreating blade increases its angle of attack and lift. Hence, the lift at the
rear of the rotor disc is increased while at the front it is decreased.
Consequently, the rotor disc, and the whole helicopter with it,
tilts forwards
and
provides the forward thrust component
required
for
the helicopter to fly forwards.
On
the contrary, when you pull
the
elevator stick backward,
the
helicopter
will
fly rearward.
Similarly,
when
you push the aileron stick
left
or right, the helicopter
will
roll
left
or right.
If you are a
beginner, you should consult other web pages, and preferably an experienced
flyer in your area who can help you. You should be aware that the main rotor
blades spin at a very high RPM and are capable of injuring someone if hit by
them. You must take care when you are flying to make sure there are no children
or animals in the room. In addition, make sure the room is large enough with no
obstacles such as furniture which could be hit while you are learning to come to
terms with the flight characteristics of your dragonfly.
Our
recommendation is to practice on the simulator first. Learn to control the heli
flying tail-in first (with the tail towards you). Then practice head-in, and
then side-in. A flying helicopter has sharp blades rotating at high speed, you
want to be able to control it when you fly the real thing. You'll be glad you
practiced on the simulator when your heli comes at you with its whirling blades
of death and you're able to send it away. Stand at a safe distance when flying,
at least six feet away.
Suitable flying space
should be indoors in a large room or if possible, a small hall or office without
obstacles is ideal. In this room you should have all doors closed as any wind
can affect the movement of the Dragonfly. If there is air-conditioning or
heating in the room, this should be turned off until you get used to the
characteristics and feel of the helicopter.
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