stability to the aircraft. At the same time, the rapid movement of the motors
through the air keeps them comparatively cool during operation.
Cyclic control is provided by varying the speeds of the motors as they
move around their circular path. For example, to provide a left-hand roll
force, the motors slow down as they enter the left-hand semicircle, and
speed up as they enter the right hand semicircle. This patented control
method requires no actuation servos and few moving parts, resulting in an
extremely small, lightweight and mechanically simple aircraft.
Uniquely, both the aircraft's rotors turn in the same direction. This is
possible because the rotors are driven by their on-board motors, rather
than by an engine mounted within the fuselage. There are therefore no
torque reactions produced. Furthermore the rotors have no mechanism for
tilting independently of each another; their gyroscopic behaviours are
therefore combined. If the rotors turned in opposite directions these
behaviours would cancel each other out, making the aircraft very unstable.
Owing to the large combined gyroscopic reaction from the two rotors, the
helicopter's attitude control inputs get shifted a full 90 degrees clockwise
during actuation. To make the aircraft pitch (forwards or backwards), a roll
force must be applied. This is done by operating the two rotors' roll cyclics
in unison. To make the aircraft roll, a pitch force must be applied. This is
done by changing the front and rear collective controls in opposition, i.e.
the overall lift of one rotor is increased while that of the other is reduced.
To make the aircraft yaw, the two rotors' roll cyclics are operated in
opposition. The two gyroscopic reactions try to pitch the aircraft in both
directions at once and as a result, the aircraft as a whole doesn't tilt.
Instead, the front rolls one way and the back rolls the other way! This
causes the fuselage to twist along its length; the airframe is designed to
allow this. In the twisted state, the two ends of the aircraft are pulled
sideways in opposite directions, resulting in a yaw motion.
Although there are no torque reactions from driving the rotors, bearing
friction does tend to turn the fuselage in a clockwise direction. To prevent
this, a continuous anticlockwise yaw input is required. This is provided by
the cyclic controls as described above, and is the reason why the aircraft's
propellers start at different instants as the throttle is raised from minimum.
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