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Suppose the CG is located behind the rotor force line in
forward flight. If a gust of wind increases the angle of
attack, rotor force increases. There is also an increase
in the difference between the lift produced on the
advancing and retreating blades. This increases the
flapping angle and causes the rotor to pitch up. This
pitching action increases the moment around the center
of gravity, which leads to a greater increase in the angle
of attack. The result is an unstable condition.
If the CG is in front of the rotor force line, a gust of
wind, which increases the angle of attack, causes the
rotor disc to react the same way, but now the increase
in rotor force and blade flapping decreases the
moment. This tends to decrease the angle of attack, and
creates a stable condition.
TRIMMED CONDITION
As was stated earlier, manufacturers use a combination
of the various stability factors to achieve a trimmed
gyroplane. For example, if you have a gyroplane where
the CG is below the propeller thrust line, the propeller
thrust gives your aircraft a nose down pitching moment
when power is applied. To compensate for this pitching
moment, the CG, on this type of gyroplane, is usually
located behind the rotor force line. This location produces
a nose up pitching moment.
Conversely, if the CG is above the propeller thrust line,
the CG is usually located ahead of the rotor force line.
Of course, the location of fuselage drag, the pitch inertia,
and the addition of a horizontal stabilizer can alter
where the center of gravity is placed.
Propeller Thrust
Propeller Thrust
Center of Gravity Center of Gravity
Low Profile High Profile
Rotor Force
Rotor Force
Figure 16-9. A gyroplane which has the propeller thrust line above the center of gravity is often referred to as a low profile gyroplane.
One that has the propeller thrust line below or at the CG is considered a high profile gyroplane.
Figure 16-10. If the CG is located in front of the rotor force line, the gyroplane is more stable than if the CG is located behind the
rotor force line.
Blade Flapping—The upward or downward movement of the rotorblades
during rotation.
17-1
Due to rudimentary flight control systems, early gyroplanes
suffered from limited maneuverability. As technology
improved, greater control of the rotor system and more
effective control surfaces were developed. The modern
gyroplane, while continuing to maintain an element of
simplicity, now enjoys a high degree of maneuverability
as a result of these improvements.
CYCLIC CONTROL
The cyclic control provides the means whereby you are
able to tilt the rotor system to provide the desired
results. Tilting the rotor system provides all control for
climbing, descending, and banking the gyroplane. The
most common method to transfer stick movement to
the rotor head is through push-pull tubes or flex cables.
[Figure 17-1] Some gyroplanes use a direct overhead
stick attachment rather than a cyclic, where a rigid control
is attached to the rotor hub and descends over and
in front of the pilot. [Figure 17-2] Because of the
nature of the direct attachment, control inputs with this
system are reversed from those used with a cyclic.
Pushing forward on the control causes the rotor disc to
tilt back and the gyroplane to climb, pulling back on
the control initiates a descent. Bank commands are
reversed in the same way.
THROTTLE
The throttle is conventional to most powerplants, and
provides the means for you to increase or decrease
engine power and thus, thrust. Depending on how
the control is designed, control movement may or
may not be proportional to engine power. With many
gyroplane throttles, 50 percent of the control travel
may equate to 80 or 90 percent of available power.
This varying degree of sensitivity makes it necessary
Figure 17-1. A common method of transferring cyclic control inputs to the rotor head is through the use of push-pull tubes,
located outboard of the rotor mast pictured on the right.
Figure 17-2. The direct overhead stick attachment has been
used for control of the rotor disc on some gyroplanes.
17-2
for you to become familiar with the unique throttle
characteristics and engine responses for a particular
gyroplane.
RUDDER
The rudder is operated by foot pedals in the cockpit
and provides a means to control yaw movement of the
aircraft. [Figure 17-3] On a gyroplane, this control is
achieved in a manner more similar to the rudder of an
airplane than to the antitorque pedals of a helicopter.
The rudder is used to maintain coordinated flight, and
　
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