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
progresses forward with its own power, it must also
move upstream at the same rate the river is moving
it downstream. This is accomplished by angling the
boat upstream sufficiently to counteract the downstream
flow. If this is done, the boat will follow the
desired track across the river from the departure point
directly to the intended destination point. Should the
boat not be headed sufficiently upstream, it would
drift with the current and run aground at some point
downstream on the opposite bank. [Figure 9-1]
As soon as a powered parachute becomes airborne,
it is free of ground friction. Its path is then affected
by the air mass in which it is flying; therefore, the
powered parachute (like the boat) will not always
track along the ground in the exact direction that it is
headed. When flying with the longitudinal axis of the
powered parachute aligned with a road, the powered
parachute may get closer to or farther from the road
without any turn having been made. This would indicate
the air mass is moving sideward in relation to the
powered parachute. Since the powered parachute is
flying within this moving body of air (wind), it moves
or drifts with the air in the same direction and speed,
just like the boat moved with the river current. [See
Figure 9-1]
Figure 9-1. Wind drift.
9-3
When flying straight and level and following a selected
ground track, the preferred method of correcting
for wind drift is to head the powered parachute sufficiently
into the wind to cause the powered parachute
to move forward into the wind at the same rate the
wind is moving it sideways. Depending on the wind
velocity, this may require a large wind correction angle
or one of only a few degrees. When the drift has
been neutralized, the powered parachute will follow
the desired ground track.
To understand the need for drift correction during
flight, consider a flight with a wind velocity of 30
knots from the left and 90° to the direction the powered
parachute is headed. After 1 hour, the body of air
in which the powered parachute is flying will have
moved 30 NM to the right. Since the powered parachute
is moving with this body of air, it too will have
drifted 30 NM to the right. In relation to the air, the
powered parachute moved forward, but in relation to
the ground, it moved forward as well as 30 NM to the
right.
There are times when the pilot needs to correct for
drift while in a turn. [Figure 9-2] Throughout the turn
the wind will be acting on the powered parachute from
constantly changing angles. The relative wind angle
and speed govern the time it takes for the powered
parachute to progress through any part of a turn. This
is due to the constantly changing groundspeed. When
the powered parachute is headed into the wind, the
groundspeed is decreased; when headed downwind,
the groundspeed is increased. Through the crosswind
portion of a turn, the powered parachute must be
turned sufficiently into the wind to counteract drift.
To follow a desired circular ground track, the wind
correction angle must be varied in a timely manner
because of the varying groundspeed as the turn progresses.
The faster the groundspeed, the faster the
wind correction angle must be established; the slower
the groundspeed, the slower the wind correction
angle must be established. You will see then that the
PPC should have the steepest bank and fastest rate of
turn on the downwind portion of the turn and have
the shallowest bank and slowest rate of turn on the
upwind portion.
The principles and techniques of varying the angle
of bank to change the rate of turn and wind correction
angle for controlling wind drift during a turn are
the same for all ground track maneuvers involving
changes in direction of flight.
When there is no wind, it should be simple to fly along
a ground track with an arc of exactly 180° and a constant
radius because the flightpath and ground track
would be identical. This can be demonstrated by approaching
a road at a 90° angle and, when directly
over the road, rolling into a medium-banked turn, then
maintaining the same angle of bank throughout the
180° of turn. [Figure 9-2]
To complete the turn, the rollout should be started at a
point where the canopy will become level as the powered
parachute again reaches the road at a 90° angle
and will be directly over the road just as the turn is
completed. This would be possible only if there were
absolutely no wind and if the angle of bank and the
rate of turn remained constant throughout the entire
中国航空网 www.aero.cn
航空翻译 www.aviation.cn
本文链接地址：
Powered Parachute Flying Handbook动力伞飞行手册(71)
