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same distance from the field boundary and at the same
altitude, as on other legs. Continue the crosswind leg
until the downwind leg boundary is approached (position
10). Once more you should anticipate drift and
turning radius. Since drift correction was held on the
crosswind leg, it is necessary to turn greater than 90° to
align the helicopter parallel to the downwind leg
boundary. Start this turn with a medium bank angle,
gradually increasing it to a steeper bank as the turn progresses.
Time the rollout to assure paralleling the
boundary of the field as the helicopter becomes level
(position 11).
If you have a direct headwind or tailwind on the
upwind and downwind leg, drift should not be encountered.
However, it may be difficult to find a situation
where the wind is blowing exactly parallel to the field
boundaries. This makes it necessary to use a slight
wind correction angle on all the legs. It is important to
anticipate the turns to compensate for groundspeed,
drift, and turning radius. When the wind is behind the
helicopter, the turn is faster and steeper; when it is
ahead of the helicopter, the turn is slower and
shallower. These same techniques apply while flying in
an airport traffic pattern.
S-TURNS
Another training maneuver you might use is the S-turn,
which helps you correct for wind drift in turns. This
maneuver requires turns to the left and right. The reference
line used, whether a road, railroad, or fence, should
be straight for a considerable distance and should
extend as nearly perpendicular to the wind as possible.
The object of S-turns is to fly a pattern of two half circles
of equal size on opposite sides of the reference line.
[Figure 9-16] The maneuver should be performed at a
constant altitude between 600 and 1,000 feet above the
terrain. S-turns may be started at any point; however,
during early training it may be beneficial to start on a
downwind heading. Entering downwind permits the
immediate selection of the steepest bank that is desired
throughout the maneuver. The discussion that follows is
based on choosing a reference line that is perpendicular
to the wind and starting the maneuver on a downwind
heading.
As the helicopter crosses the reference line, immediately
establish a bank. This initial bank is the steepest
used throughout the maneuver since the helicopter is
headed directly downwind and the groundspeed is at its
highest. Gradually reduce the bank, as necessary, to
describe a ground track of a half circle. Time the turn
so that as the rollout is completed, the helicopter is
crossing the reference line perpendicular to it and heading
directly upwind. Immediately enter a bank in the
opposite direction to begin the second half of the “S.”
Since the helicopter is now on an upwind heading, this
bank (and the one just completed before crossing the
reference line) is the shallowest in the maneuver.
Gradually increase the bank, as necessary, to describe a
ground track that is a half circle identical in size to the
one previously completed on the other side of the reference
line. The steepest bank in this turn should be
attained just prior to rollout when the helicopter is
approaching the reference line nearest the downwind
heading. Time the turn so that as the rollout is complete,
the helicopter is perpendicular to the reference
line and is again heading directly downwind.
In summary, the angle of bank required at any given
point in the maneuver is dependent on the groundspeed.
The faster the groundspeed, the steeper the
bank; the slower the groundspeed, the shallower
the bank. To express it another way, the more nearly
the helicopter is to a downwind heading, the steeper the
bank; the more nearly it is to an upwind heading,
the shallower the bank. In addition to varying the angle
of bank to correct for drift in order to maintain the
proper radius of turn, the helicopter must also be flown
with a drift correction angle (crab) in relation to its
ground track; except of course, when it is on direct
upwind or downwind headings or there is no wind. One
would normally think of the fore and aft axis of the helicopter
as being tangent to the ground track pattern at
each point. However, this is not the case. During the turn
on the upwind side of the reference line (side from
which the wind is blowing), crab the nose of the helicopter
toward the outside of the circle. During the turn
on the downwind side of the reference line (side of the
reference line opposite to the direction from which the
wind is blowing), crab the nose of the helicopter toward
　
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