Chapter 9 — Ground Reference Maneuvers
S-Turns Across a Road
An S-turn across a road is a practice maneuver in
which the powered parachute’s ground track describes
semicircles of equal radii on each side of a
selected straight line on the ground. [Figure 9-5] The
straight line may be a road, fence, railroad, or section
line that lies perpendicular to the wind, and should
be of sufficient length for making a series of turns. A
constant altitude should be maintained throughout the
maneuver; do not go lower than 200 feet.
S-turns across a road present one of the most elementary
problems in the practical application of the turn
and in the correction for wind drift in turns. The application
of this maneuver is considerably less advanced
in some respects than the rectangular course. However
it is taught after the student has been introduced
to the rectangular course in order that he or she may
have a knowledge of the correction for wind drift in
straight flight along a reference line, before attempting
to correct for drift by applying a turn.
The objectives of S-turns across a road are to develop
the ability to compensate for drift during turns, orient
the flightpath with ground references, follow an assigned
ground track, arrive at specified points on assigned
headings, and divide the pilot’s attention. The
maneuver consists of crossing the road at a 90° angle
and immediately beginning a series of 180° turns of
uniform radius in opposite directions, re-crossing the
road at a 90° angle just as each 180° turn is completed.
To accomplish a constant radius ground track requires
a changing rate of turn and angle of bank to establish
the wind correction angle. Both will increase or decrease
as groundspeed increases or decreases.
The bank must be steepest when beginning the turn on
the downwind side of the road and must be shallowed
gradually as the turn progresses from a downwind
heading to an upwind heading. On the upwind side,
the turn should be started with a relatively shallow
bank and then gradually steepened as the powered
parachute turns from an upwind heading to a downwind
heading. In this maneuver, the powered parachute
should be rolled from one bank directly into the
opposite just as the reference line on the ground is
crossed.
Before starting the maneuver, a straight ground reference
line or road that lies 90° to the direction of
the wind should be selected, then the area should be
checked to ensure that no obstructions or other aircraft
are in the immediate vicinity. The road should be
approached from the upwind side, at the selected altitude
on a downwind heading. When directly over the
road, start the first turn immediately. With the powered parachute headed downwind, the groundspeed is
greatest and the rate of departure from the road will
be rapid; so the roll into the bank must be fairly rapid
to attain the proper wind correction angle. This prevents
the powered parachute from flying too far from
the road and from establishing a ground track of excessive
radius. During the latter portion of the first
90° of turn when the powered parachute’s heading is
changing from a downwind heading to a crosswind
heading, the groundspeed becomes less and the rate of
departure from the road decreases. The wind correction
angle will be at the maximum when the powered
parachute is headed directly crosswind.
After turning 90°, the powered parachute’s heading
becomes more and more an upwind heading,
the groundspeed will decrease, and the rate of closure
with the road will become slower. If a constant
steeper bank were maintained, the powered parachute
would turn too quickly for the slower rate of closure,
and would be headed perpendicular to the road prematurely.
Because of the decreasing groundspeed and
rate of closure while approaching the upwind heading,
it will be necessary to gradually shallow the bank
during the remaining 90° of the semicircle, so that the wind correction angle is removed completely and the
wing becomes level as the 180° turn is completed at
the moment the road is reached.
At the instant the road is being crossed again, a turn
in the opposite direction should be started. Since the
powered parachute is still flying into the headwind,
the groundspeed is relatively slow. Therefore, the turn
will have to be started with a shallow bank so as to
avoid an excessive rate of turn that would establish
the maximum wind correction angle too soon. The
degree of bank should be that which is necessary to
attain the proper wind correction angle so the ground
track describes an arc the same size as the one established
on the downwind side.
Since the powered parachute is turning from an upwind
to a downwind heading, the groundspeed will
increase and after turning 90°, the rate of closure
with the road will increase rapidly. Consequently, the
angle of bank and rate of turn must be progressively
increased so that the powered parachute will have
turned 180° at the time it reaches the road. Again, the
rollout must be timed so the powered parachute is in
straight-and-level flight directly over and perpendicular
to the road.
Throughout the maneuver a constant altitude should
be maintained, and the bank should be changing constantly
to affect a true semicircular ground track.
Often there is a tendency to increase the bank too
rapidly during the initial part of the turn on the upwind
side, which will prevent the completion of the
180° turn before re-crossing the road. This is apparent
when the turn is not completed in time for the powered
parachute to cross the road at a perpendicular
angle. To avoid this error, the pilot must visualize the
desired half circle ground track, and increase the bank
during the early part of this turn. During the latter part
of the turn, when approaching the road, the pilot must
judge the closure rate properly and increase the bank
accordingly, so as to cross the road perpendicular to it
just as the rollout is completed.
Common errors in the performance of S-turns across
a road are:
• Failure to adequately clear the area.
• Gaining or losing altitude.
• Inability to visualize the half circle ground
track.
• Poor timing in beginning and recovering from
turns.
• Faulty correction for drift.
• Inadequate visual lookout for other aircraft.
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