曝光台 注意防骗
网曝天猫店富美金盛家居专营店坑蒙拐骗欺诈消费者
to square the true airspeed and divide by 15 for miles
per hour (m.p.h.) or 11.3 for knots.
Distance from the pylon affects the angle of bank.
At any altitude above that pivotal altitude, the projected
reference line will appear to move rearward
in a circular path in relation to the pylon.
Conversely, when the airplane is below the pivotal
altitude, the projected reference line will appear to
move forward in a circular path. [Figure 6-13]
To demonstrate this, the airplane is flown at normal
cruising speed, and at an altitude estimated to be below
the proper pivotal altitude, and then placed in a
medium-banked turn. It will be seen that the projected
reference line of sight appears to move forward along
the ground (pylon moves back) as the airplane turns.
A climb is then made to an altitude well above the pivotal
altitude, and when the airplane is again at normal
cruising speed, it is placed in a medium-banked turn.
At this higher altitude, the projected reference line of
sight now appears to move backward across the
ground (pylon moves forward) in a direction opposite
that of flight.
After the high altitude extreme has been demonstrated,
the power is reduced, and a descent at cruising speed
begun in a continuing medium bank around the pylon.
The apparent backward travel of the projected reference
line with respect to the pylon will slow down as
altitude is lost, stop for an instant, then start to reverse
itself, and would move forward if the descent were
allowed to continue below the pivotal altitude.
The altitude at which the line of sight apparently
ceased to move across the ground was the pivotal
altitude. If the airplane descended below the pivotal
altitude, power should be added to maintain airspeed
while altitude is regained to the point at which the
projected reference line moves neither backward nor
forward but actually pivots on the pylon. In this way
the pilot can determine the pivotal altitude of the airplane.
The pivotal altitude is critical and will change with
variations in groundspeed. Since the headings
throughout the turns continually vary from directly
downwind to directly upwind, the groundspeed will
constantly change. This will result in the proper pivotal
altitude varying slightly throughout the eight.
Therefore, adjustment is made for this by climbing or
descending, as necessary, to hold the reference line or
point on the pylons. This change in altitude will be
dependent on how much the wind affects the groundspeed.
The instructor should emphasize that the elevators are
the primary control for holding the pylons. Even a very
slight variation in altitude effects a double correction,
since in losing altitude, speed is gained, and even a
slight climb reduces the airspeed. This variation in altitude,
although important in holding the pylon, in most
cases will be so slight as to be barely perceptible on a
sensitive altimeter.
Before beginning the maneuver, the pilot should select
two points on the ground along a line which lies 90° to
the direction of the wind. The area in which the
maneuver is to be performed should be checked for
obstructions and any other air traffic, and it should be
located where a disturbance to groups of people, livestock,
or communities will not result.
The selection of proper pylons is of importance to
good eights-on-pylons. They should be sufficiently
prominent to be readily seen by the pilot when completing
the turn around one pylon and heading for the
next, and should be adequately spaced to provide time
AIRSPEED
KNOTS MPH
APPROXIMATE
PIVOTAL
ALTITUDE
87
91
96
100
104
109
113
100
105
110
115
120
125
130
670
735
810
885
960
1050
1130
Figure 6-12. Speed vs. pivotal altitude.
Ch 06.qxd 5/7/04 7:35 AM Page 6-14
6-15
for planning the turns and yet not cause unnecessary
straight-and-level flight between the pylons. The
selected pylons should also be at the same elevation,
since differences of over a very few feet will necessitate
climbing or descending between each turn.
For uniformity, the eight is usually begun by flying
diagonally crosswind between the pylons to a point
downwind from the first pylon so that the first turn
can be made into the wind. As the airplane
approaches a position where the pylon appears to be
just ahead of the wingtip, the turn should be started
by lowering the upwind wing to place the pilot’s line
of sight reference on the pylon. As the turn is continued,
中国航空网 www.aero.cn
航空翻译 www.aviation.cn
本文链接地址：
AIRPLANE FLYING HANDBOOK 飞机飞行手册上(73)
