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made [Figure 7-7] or the WSC could drift to the side if the
wind correction angle is not maintained. The remainder of
7-7
25
TAKEOFF ROLL ROTATION—LIFT-OFF CLIMB
Wind
Figure 7-8. Crosswind takeoff.
Figure 7-7. Wing correction angle (or crab angle as is is commonly
called).
Ground Track • Flightpath
Heading
Wind
Correction
Angle
(Crab
Angle)
Wind
the climb technique is the same used for normal takeoffs and
climbs maintaining the proper ground track with the proper
wing correction angle/crab angle. [Figure 7-8]
In addition to normal takeoffs, additional common errors in
the performance of crosswind takeoffs are:
• Letting the windward side of the wing get too high.
• Allowing the wing to weathervane into the wind
during the takeoff roll.
• Not obtaining additional speed before rotation.
• Too slow of a rotation during lift-off.
• Inadequate drift correction after lift-off.
Ground Effect on Takeoff
Ground effect is a condition of improved performance
encountered when the aircraft is operating very close to
the ground. Ground effect can be detected and measured
up to an altitude of about one wingspan above the surface.
[Figure 7-9] However, ground effect is most signifi cant when
the WSC aircraft is maintaining a constant attitude at low
airspeed and low altitude. Examples are during takeoff when
the aircraft lifts off and accelerates to climb speed, and also
during the landing fl are before touchdown. When the wing
is under the infl uence of ground effect, there is a reduction
in upwash, downwash, and wingtip vortices.
Since the WSC wing is a high wing aircraft, the effects
are not as pronounced as a low wing airplane, but during
rotation, the reduction in induced drag is about 25 percent
and decreases as the WSC aircraft climbs. At high speeds
where parasite drag dominates, induced drag is a small part
of the total drag. Consequently, the effects of ground effect
are of greater concern during takeoff and landing.
7-8
Figure 7-9. Ground effect area.
Significant ground effect
with wheels just off the ground Noticeable ground effect
up to half wingspan
No Noticeable ground effect with wing
at full wingspan above the ground
Wingspan
On takeoff, the takeoff roll, lift-off, and the beginning of the
initial climb are accomplished in the ground effect area. As
the aircraft lifts off and climbs out of the ground effect area
the following occurs.
• The WSC aircraft requires an increase in angle of
attack to maintain the same lift coeffi cient.
• The WSC aircraft experiences an increase in induced
drag and thrust required.
Due to the reduced drag in ground effect, the aircraft may
seem capable of taking off below the recommended airspeed
with less thrust. However, as the aircraft rises out of ground
effect with an insuffi cient airspeed, initial climb performance
may prove to be marginal due to increased drag. Under
conditions of high density altitude, high temperature, and/or
maximum gross weight, the aircraft may become airborne
at an insuffi cient airspeed but unable to climb out of ground
effect. Consequently, the aircraft may not be able to clear
obstructions or may settle back on the runway. The point to
remember is that additional power is required to compensate
for increases in drag that occur as an aircraft leaves ground
effect. But during an initial climb, the engine is already
developing maximum power. The only alternative is to lower
pitch attitude to gain additional airspeed, which results in
inevitable altitude loss. Therefore, under marginal conditions,
it is important that the aircraft take off at the recommended
speed that provides adequate initial climb performance.
Ground effect is important to normal fl ight operations. If
the runway is long enough, or if no obstacles exist, ground
effect can be used to advantage by utilizing the reduced drag
to improve initial acceleration. Additionally, the procedure
for takeoff from unsatisfactory surfaces is to take as much
weight on the wings as possible during the ground run, and to
lift off with the aid of ground effect before true fl ying speed
is attained. It is then necessary to reduce the angle of attack
to attain normal airspeed before attempting to fl y away from
the ground effect area.
Short Field Takeoff and Steepest Angle
Climb
Takeoffs and climbs from fi elds in which the takeoff area is
short or the available takeoff area is restricted by obstructions
require the pilot to operate the WSC aircraft at the limit of its
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Weight-Shift Control Aircraft Flying Handbook(90)
