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of equal radii on each side of a straight road or other
reference line on the ground. The ground track resembles
a figure 8. [Figure 6-7 on next page]
Like the other ground reference maneuvers, its
objective is to develop division of attention while
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compensating for drift, maintaining orientation with
ground references, and maintaining a constant
altitude.
Although eights along a road may be performed with
the wind blowing parallel to the road or directly across
the road, for simplification purposes, only the latter situation
is explained since the principles involved in
either case are common.
A reference line or road which is perpendicular to the
wind should be selected and the airplane flown parallel
to and directly above the road. Since the wind is blowing
across the flightpath, the airplane will require some
wind correction angle to stay directly above the road
during the initial straight and level portion. Before
starting the maneuver, the area should be checked to
ensure clearance of obstructions and avoidance of
other aircraft.
Usually, the first turn should be made toward a downwind
heading starting with a medium bank. Since the
airplane will be turning more and more directly downwind,
the groundspeed will be gradually increasing and
the rate of departing the road will tend to become
faster. Thus, the bank and rate of turn is increased to
establish a wind correction angle to keep the airplane
from exceeding the desired distance from the road
when 180° of change in direction is completed. The
steepest bank is attained when the airplane is headed
directly downwind.
As the airplane completes 180° of change in direction,
it will be flying parallel to and using a wind correction
angle toward the road with the wind acting directly
perpendicular to the ground track. At this point, the
pilot should visualize the remaining 180° of ground
track required to return to the same place over the road
from which the maneuver started.
While the turn is continued toward an upwind heading,
the wind will tend to keep the airplane from reaching
the road, with a decrease in groundspeed and rate of
closure. The rate of turn and wind correction angle are
decreased proportionately so that the road will be
reached just as the 360° turn is completed. To accomplish
this, the bank is decreased so that when headed
directly upwind, it will be at the shallowest angle. In
the last 90° of the turn, the bank may be varied to correct
any previous errors in judging the returning rate
and closure rate. The rollout should be timed so that
the airplane will be straight and level over the starting
point, with enough drift correction to hold it over the
road.
After momentarily flying straight and level along the
road, the airplane is then rolled into a medium bank
turn in the opposite direction to begin the circle on the
upwind side of the road. The wind will still be decreasing
the groundspeed and trying to drift the airplane
back toward the road; therefore, the bank must be
decreased slowly during the first 90° change in direction
in order to reach the desired distance from the
road and attain the proper wind correction angle when
180° change in direction has been completed.
As the remaining 180° of turn continues, the wind
becomes more of a tailwind and increases the airplane’s
groundspeed. This causes the rate of closure
to become faster; consequently, the angle of bank
and rate of turn must be increased further to attain
sufficient wind correction angle to keep the airplane
from approaching the road too rapidly. The bank will
be at its steepest angle when the airplane is headed
directly downwind.
In the last 90° of the turn, the rate of turn should be
reduced to bring the airplane over the starting point on
the road. The rollout must be timed so the airplane will
be straight and level, turned into the wind, and flying
parallel to and over the road.
The measure of a student’s progress in the performance
of eights along a road is the smoothness and accuracy of
the change in bank used to counteract drift. The sooner
the drift is detected and correction applied, the smaller
will be the required changes. The more quickly the
student can anticipate the corrections needed, the
less obvious the changes will be and the more attention
can be diverted to the maintenance of altitude and operation
of the airplane.
Errors in coordination must be eliminated and a constant
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AIRPLANE FLYING HANDBOOK 飞机飞行手册上(70)
