Figure 4
Wheels/tires-braking forces and tires-cornering forces depend on the tire and runway conditions but also on each other, the higher the braking force, the lower the cornering force, as illustrated by Figure 5.
Tire Braking and Cornering Forces
100 90 80
70 60 50 40 30 20 10
0
Free rolling wheel
Figure 5
Force ( % )
Crosswind Landings
Page 6
AIRBUS INDUSTRIE Getting to Grips with
Flight Operations Support Approach-and-Landing Accidents Reduction
Transient effects such as the distortion of the tire thread ( caused by any yawing movement of the wheel ) or the activation of the anti-skid system affect the tire-cornering and wheel-braking forces ( in both magnitude and direction ) and, thus, affect the overall balance of friction forces.
As a consequence, the ideal balance of forces illustrated by Figure 3 rarely is steadily maintained during the initial landing roll.
Effect of Touchdown on Alignment
When touching down with some crab angle on a dry runway, the aircraft automatically realigns with the direction of travel down the runway.
On a contaminated runway, the aircraft tends to travel along the runway centerline with the existing crab angle.
Effect of Fuselage and Fin Side Force
As the aircraft touches down, the side force created by the crosswind component on the fuselage and fin tends to make the aircraft skid sideways (downwind) off the centerline, as illustrated by Figure 6.
Effect of Thrust Reversers
When selecting reverse thrust with some crab angle, the reverse thrust results into two force components, as illustrated by Figure 6:
.
A stopping force aligned along the aircraft direction of travel (runway centerline); and,
.
A side force, perpendicular to the runway centerline, which further increases the tendency to skid sideways.
Crosswind component
Touchdown Aircraft Reverse Reverse
with partial skidding cancelled thrust and
decrab sideways due to and brakes released pedal braking
fuselage/fin side force Directional reapplied
and reverse control and
thrust side centerline
force regained
Figure 6
Directional Control during Crosswind Landing
Crosswind Landings
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AIRBUS INDUSTRIE
Flight Operations Support
The thrust reverser effect decreases with decreasing airspeed.
As airspeed decreases, the rudder efficiency decreases and is further affected by the airflow disruption created in the wake of the engine reverse flow, possibly resulting in difficulties to maintain directional control.
Effect of Braking
In a high crosswind, cross-controls may have to be maintained after touchdown to prevent the into-wind wing from lifting and to counteract the weather-vane effect (some flight crew training manuals adequately state that the pilot should continue to fly the aircraft during the landing roll ).
However, into-wind aileron decreases the lift on the into-wind wing, thus resulting in an increased load on the into-wind landing gear.
Because the friction force increases as higher loads are applied on the wheels and tires, the braking force increases on the into-wind landing gear, creating an additional tendency to turn into-wind, as illustrated by Figure 7.
When the runway contaminant is not evenly distributed, the antiskid system may release the brakes on one side only.
Figure 7 Effect of Uneven MLG Loads on Braking
Getting to Grips withApproach-and-Landing Accidents Reduction
Maintaining / Regaining Directional Control
The higher the wheel/tire braking force, the lower the tire-cornering force; therefore, if the aircraft tends to skid sideways, releasing the brakes (i.e., by taking over from the autobrake) increases the tire-cornering and contributes to maintaining or regaining directional control.
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