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while keeping the upwind wing from rising by the use
of aileron.
When an airplane is airborne, it moves with the air
mass in which it is flying regardless of the airplane’s
heading and speed. When an airplane is on the ground,
it is unable to move with the air mass (crosswind)
because of the resistance created by ground friction on
the wheels.
Characteristically, an airplane has a greater profile or
side area, behind the main landing gear than forward
of it does. With the main wheels acting as a pivot point
and the greater surface area exposed to the crosswind
behind that pivot point, the airplane will tend to turn or
weathervane into the wind.
Wind acting on an airplane during crosswind landings
is the result of two factors. One is the natural wind,
which acts in the direction the air mass is traveling, while
the other is induced by the movement of the airplane and
acts parallel to the direction of movement. Consequently,
a crosswind has a headwind component acting along
the airplane’s ground track and a crosswind component
acting 90° to its track. The resultant or relative wind is
somewhere between the two components. As the
airplane’s forward speed decreases during the afterlanding
roll, the headwind component decreases and the
relative wind has more of a crosswind component. The
greater the crosswind component, the more difficult it is
to prevent weathervaning.
Retaining control on the ground is a critical part of the
after-landing roll, because of the weathervaning effect
of the wind on the airplane. Additionally, tire side load
from runway contact while drifting frequently generates
roll-overs in tricycle geared airplanes. The basic
factors involved are cornering angle and side load.
Cornering angle is the angular difference between the
heading of a tire and its path. Whenever a load bearing
tire’s path and heading diverge, a side load is created.
It is accompanied by tire distortion. Although side load
differs in varying tires and air pressures, it is completely
independent of speed, and through a considerable
range, is directional proportional to the cornering angle
and the weight supported by the tire. As little as 10° of
cornering angle will create a side load equal to half the
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supported weight; after 20° the side load does not
increase with increasing cornering angle. For each
high-wing, tricycle geared airplane, there is a cornering
angle at which roll-over is inevitable. The roll-over
axis being the line linking the nose and main wheels.
At lesser angles, the roll-over may be avoided by use
of ailerons, rudder, or steerable nosewheel but not
brakes.
While the airplane is decelerating during the afterlanding
roll, more and more aileron is applied to keep
the upwind wing from rising. Since the airplane is
slowing down, there is less airflow around the ailerons
and they become less effective. At the same time, the
relative wind is becoming more of a crosswind and
exerting a greater lifting force on the upwind wing.
When the airplane is coming to a stop, the aileron control
must be held fully toward the wind.
MAXIMUM SAFE CROSSWIND VELOCITIES
Takeoffs and landings in certain crosswind conditions
are inadvisable or even dangerous. [Figure 8-18] If the
crosswind is great enough to warrant an extreme drift
correction, a hazardous landing condition may result.
Therefore, the takeoff and landing capabilities with
respect to the reported surface wind conditions and the
available landing directions must be considered.
Figure 8-18. Crosswind chart.
Before an airplane is type certificated by the Federal
Aviation Administration (FAA), it must be flight tested
to meet certain requirements. Among these is the
demonstration of being satisfactorily controllable with
no exceptional degree of skill or alertness on the part
of the pilot in 90° crosswinds up to a velocity equal to
0.2 VSO. This means a windspeed of two-tenths of the
airplane’s stalling speed with power off and landing
gear/flaps down. Regulations require that the demonstrated
crosswind velocity be included on a placard in
airplanes certificated after May 3, 1962.
The headwind component and the crosswind component
for a given situation can be determined by reference
to a crosswind component chart. [Figure 8-19] It is
imperative that pilots determine the maximum
crosswind component of each airplane they fly, and
avoid operations in wind conditions that exceed the
　
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