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Pilot's Handbook of Aeronautical Knowledge
Flight Controls

Flight Control Systems

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Pilot's Handbook of Aeronautical Knowledge



Table of Contents

Chapter 1, Introduction To Flying
Chapter 2, Aircraft Structure
Chapter 3, Principles of Flight
Chapter 4, Aerodynamics of Flight
Chapter 5, Flight Controls
Chapter 6, Aircraft Systems
Chapter 7, Flight Instruments
Chapter 8, Flight Manuals and Other Documents
Chapter 9, Weight and Balance
Chapter 10, Aircraft Performance
Chapter 11, Weather Theory
Chapter 12, Aviation Weather Services
Chapter 13, Airport Operation
Chapter 14, Airspace
Chapter 15, Navigation
Chapter 16, Aeromedical Factors
Chapter 17, Aeronautical Decision Making




Application of rudder is used to counteract adverse yaw. The
amount of rudder control required is greatest at low airspeeds,
high angles of attack, and with large aileron deflection Like
all control surfaces at lower airspeeds, the vertical stabilizer/
rudder becomes less effective, and magnifies the control
problems associated with adverse yaw.

All turns are coordinated by use of ailerons, rudder, and
elevator. Applying aileron pressure is necessary to place
the aircraft in the desired angle of bank, while simultaneous
application of rudder pressure is necessary to counteract the
resultant adverse yaw. Additionally, because more lift is
required during a turn than when in straight-and-level flight,
the angle of attack (AOA) must be increased by applying
elevator back pressure. The steeper the turn, the more elevator
back pressure is needed.

As the desired angle of bank is established, aileron and rudder
pressures should be relaxed. This stops the angle of bank from
increasing, because the aileron and rudder control surfaces are
in a neutral and streamlined position. Elevator back pressure
should be held constant to maintain altitude. The roll-out
from a turn is similar to the roll-in, except the flight controls
are applied in the opposite direction. Aileron and rudder are
applied in the direction of the roll-out or toward the high wing.
As the angle of bank decreases, the elevator back pressure
should be relaxed as necessary to maintain altitude.

In an attempt to reduce the effects of adverse yaw,
manufacturers have engineered four systems: differential
ailerons, frise-type ailerons, coupled ailerons and rudder,
and flaperons.

Differential Ailerons
With differential ailerons, one aileron is raised a greater
distance than the other aileron is lowered for a given
movement of the control wheel or control stick. This produces
an increase in drag on the descending wing. The greater drag
results from deflecting the up aileron on the descending wing
to a greater angle than the down aileron on the rising wing.
While adverse yaw is reduced, it is not eliminated completely.
[Figure 5-6]

Differential ailerons.
Figure 5-6. Differential ailerons.

Frise-type ailerons.
Figure 5-7. Frise-type ailerons.

Frise-Type Ailerons
With a frise-type aileron, when pressure is applied to the
control wheel or control stick, the aileron that is being raised
pivots on an offset hinge. This projects the leading edge of
the aileron into the airflow and creates drag. It helps equalize
the drag created by the lowered aileron on the opposite wing
and reduces adverse yaw. [Figure 5-7]

The frise-type aileron also forms a slot so air flows smoothly
over the lowered aileron, making it more effective at high
angles of attack. Frise-type ailerons may also be designed
to function differentially. Like the differential aileron, the
frise-type aileron does not eliminate adverse yaw entirely.
Coordinated rudder application is still needed wherever
ailerons are applied.

Coupled Ailerons and Rudder
Coupled ailerons and rudder are linked controls. This is
accomplished with rudder-aileron interconnect springs, which
help correct for aileron drag by automatically deflecting
the rudder at the same time the ailerons are deflected For
example, when the control wheel or control stick is moved
to produce a left roll, the interconnect cable and spring pulls
forward on the left rudder pedal just enough to prevent the
nose of the aircraft from yawing to the right. The force applied
to the rudder by the springs can be overridden if it becomes
necessary to slip the aircraft. [Figure 5-8]