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temporary blindness from lightning.
28.3.2 Don't change power settings; maintain
settings for the recommended turbulence penetration
airspeed.
28.3.3 Don't attempt to maintain constant altitude;
let the aircraft “ride the waves.”
28.3.4 Don't turn back once you are in the
thunderstorm. A straight course through the storm
most likely will get you out of the hazards more
quickly. In addition, turning maneuvers increase
stress on the aircraft.
29. Wake Turbulence
29.1 General
29.1.1 Every aircraft generates a wake while in
flight. Initially, when pilots encountered this wake in
flight, the disturbance was attributed to “prop wash.”
It is known, however, that this disturbance is caused
by a pair of counterrotating vortices trailing from the
wing tips. The vortices from larger aircraft pose
problems to encountering aircraft. For instance, the
wake of these aircraft can impose rolling moments
exceeding the roll control authority of the encountering
aircraft. Further, turbulence generated within the
vortices can damage aircraft components and
equipment if encountered at close range. The pilot
must learn to envision the location of the vortex wake
generated by larger (transport category) aircraft and
adjust the flight path accordingly.
29.1.2 During ground operations and during takeoff,
jet engine blast (thrust stream turbulence) can cause
damage and upsets if encountered at close range.
Exhaust velocity versus distance studies at various
thrust levels have shown a need for light aircraft to
maintain an adequate separation behind large turbojet
aircraft. Pilots of larger aircraft should be particularly
careful to consider the effects of their “jet blast” on
other aircraft, vehicles, and maintenance equipment
during ground operations.
29.2 Vortex Generation
29.2.1 Lift is generated by the creation of a pressure
differential over the wing surface. The lowest
pressure occurs over the upper wing surface and the
highest pressure under the wing. This pressure
differential triggers the roll up of the airflow aft of the
wing resulting in swirling air masses trailing
downstream of the wing tips. After the roll up is
completed, the wake consists of two counter rotating
cylindrical vortices. Most of the energy is within a
few feet of the center of each vortex, but pilots should
avoid a region within about 100 feet of the vortex
core. (See FIG GEN 3.5-16.)
29.3 Vortex Strength
29.3.1 The strength of the vortex is governed by the
weight, speed, and shape of the wing of the generating
aircraft. The vortex characteristics of any given
aircraft can also be changed by extension of flaps or
other wing configuring devices as well as by change
in speed. However, as the basic factor is weight, the
vortex strength increases proportionately. Peak
vortex tangential speeds up to almost 300 feet per
second have been recorded. The greatest vortex
strength occurs when the generating aircraft is
HEAVY, CLEAN, and SLOW.
29.3.2 Induced Roll
29.3.2.1 In rare instances, a wake encounter could
cause inflight structural damage of catastrophic
proportions. However, the usual hazard is associated
with induced rolling moments which can exceed the
roll control authority of the encountering aircraft. In
flight experiments, aircraft have been intentionally
flown directly up trailing vortex cores of larger
aircraft. It was shown that the capability of an aircraft
to counteract the roll imposed by the wake vortex
primarily depends on the wing span and counter-control
responsiveness of the encountering aircraft.
29.3.2.2 Counter-control is usually effective and
induced roll minimal in cases where the wing span
and ailerons of the encountering aircraft extend
beyond the rotational flow field of the vortex. It is
more difficult for aircraft with short wing span
(relative to the generating aircraft) to counter the
imposed roll induced by vortex flow. Pilots of
short-span aircraft, even of the high-performance
type, must be especially alert to vortex encounters.
(See FIG GEN 3.5-17.)
29.3.2.3 The wake of larger aircraft requires the
respect of all pilots.
30 AUG 07
AIP
United States of America
GEN 3.5-54
15 MAR 07
Nineteenth Edition Federal Aviation Administration
29.4 Vortex Behavior
29.4.1 Trailing vortices have certain behavioral
characteristics which can help a pilot visualize the
wake location and thereby take avoidance precautions.
29.4.1.1 Vortices are generated from the moment
　
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