Use of Rudder On A300-600 & A310
Use of Rudder On A300-600 & A310
Use of Rudder On A300-600 & A310
December 2010
Yaw control
General
In flight, yaw control is provided by the rudder, and directional stability is provided by the vertical
stabilizer. The rudder and vertical stabilizer are sized to meet the two following objectives:
Provide sufficient lateral control of the aircraft during crosswind takeoffs and landings, within the published crosswind limits
(refer to FCOM Operating Limitations chapter).
Provide positive aircraft control under conditions of engine failure and maximum asymmetric thrust, at any speed above Vmcg
(minimum control speed - on ground).
The vertical stabilizer and the rudder must be capable of generating sufficient yawing moments to maintain directional control of
the aircraft. The rudder deflection, necessary to achieve these yawing moments, and the resulting sideslip angles place significant
aerodynamic loads on the rudder and on the vertical stabilizer. Both are designed to sustain loads as prescribed in the JAR/FAR 25
certification requirements which define several lateral loading conditions (maneuver, gust loads and asymmetric loads due to engine
failure) leading to the required level of structural strength.
Certification requirements
For certification in accordance with CS-25/FAR 25.351, loads on the stabilizer and the rudder are defined, considering yawing
maneuvers as shown below, for a range of speeds from Vmc (minimum control speed) to VD/MD (maximum design speed), from
sea level up to maximum altitude, and over the full range of aircraft weights and Center of Gravity limits:
1 With the aircraft in unaccelerated and stabilized straight flight, the rudder is suddenly displaced to the maximum available
deflection at the current aircraft speed (fig 1).
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vides the design basis for the vertical stabilizer and rudder. The
above loads define the limit loads according to JAR/FAR 25
requirements. These loads correspond to the maximum loads to be
expected once in service.
According to CS-25/FAR 25 requirements, the ultimate loads are
defined as the limit loads multiplied by a prescribed safety factor
of 1.5 unless otherwise specified. The aircraft structure must be
able to support limit loads without detrimental permanent deformation and ultimate loads without failure for at least three
seconds. Higher loads could lead to structural failure.
Rudder control
The rudder surface is controlled by three actuators, commanded
by a cable run from the rudder pedals, to which input yaw damping and turn coordination functions are added by the rudder control system.
The rudder travel limiter system, controlled by the Feel and
Limitation Computers (FLC), is designed to progressively reduce
Fig 2
Caution
Sudden commanded full, or nearly full, opposite rudder movement against a
sideslip can generate loads that exceed the limit loads and possibly the ultimate loads and can result in structural failure.
This is true even at speeds below the maximum design maneuvering speed,
VA. Certification regulations do not consider the loads imposed on the structure when there is sudden full, or nearly full, rudder movement that is opposite the sideslip.
Fig 3
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the available total rudder travel depending on aircraft speed. This provides sufficient yaw control within the entire flight envelope,
including engine failure and maximum asymmetric thrust. This also limits the lateral loads on the stabilizer and rudder so that they
remain within the certification limits.
Rudder travel is limited as a function of the aircraft
speed (IAS), as shown below:
At low speeds, the rudder
deflection required to maneuver
the aircraft in yaw is large, and
so are the resulting pedal displacement and forces.
At higher speeds , pedal displacements and forces are
smaller.
Therefore, as speed increases,
the rudder deflection required
by any lateral maneuver (eg,
engine failure and maximum
asymmetric thrust) decreases,
and consequently, so do rudder
pedal displacement and associated forces. Rudder pedals displacement is almost linearly
proportional to rudder deflection.
Fig 5
Fig 6
At higher speeds, for example at 250 kt, see ref B, the maximum available rudder deflection is
reduced to approximately 10 degrees. It is consequently obtained with less rudder pedals displacement which represents a 18 daN
force applied on the pedals (60% of the maximum force to reach full pedal travel).
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Operational recommendations
In order to avoid exceeding structural loads on the rudder and vertical stabilizer, the following recommendations must be observed.