Consequently, the bank angle and rate of turn must be reduced gradually to ensure that upon completion of the turn, the crosswind ground track continues to be the same distance from the edge of the field. Upon completion of the turn, the helicopter should be level and aligned with the downwind corner of the field.

However, since the crosswind is now pushing you away from the field, you must establish the proper drift correction by flying slightly into the wind. Therefore, the turn to crosswind should be greater than a 90° change in heading (position 3). If the turn has been made properly, the field boundary again appears to be one-fourth to one-half mile away. While on the crosswind leg, the wind correction should be adjusted, as necessary, to maintain a uniform distance from the field boundary (position 4).

As the next field boundary is being approached (position 5), plan the turn onto the upwind leg. Since a wind correction angle is being held into the wind and toward the field while on the crosswind leg, this next turn requires a turn of less than 90°. Since the crosswind becomes a headwind, causing the groundspeed to decrease during this turn, the bank initially must be medium and progressively decreased as the turn proceeds. To complete the turn, time the rollout so that the helicopter becomes level at a point aligned with the corner of the field just as the longitudinal axis of the helicopter again becomes parallel to the field boundary (position 6). The distance from the field boundary should be the same as on the other sides of the field.

On the upwind leg, the wind is a headwind, which results in an decreased groundspeed (position 7).

Consequently, enter the turn onto the next leg with a fairly slow rate of roll-in, and a relatively shallow bank (position 8). As the turn progresses, gradually increase the bank angle because the headwind component is diminishing, resulting in an increasing groundspeed.

During and after the turn onto this leg, the wind tends to drift the helicopter toward the field boundary. To compensate for the drift, the amount of turn must be less than 90° (position 9).

Again, the rollout from this turn must be such that as the helicopter becomes level, the nose of the helicopter is turned slightly away the field and into the wind to correct for drift. The helicopter should again be the 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.

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 the inside of the circle. In either case, it is obvious that the helicopter is being crabbed into the wind just as it is when trying to maintain a straight ground track. The amount of crab depends upon the wind velocity and how nearly the helicopter is to a crosswind position.

The stronger the wind, the greater the crab angle at any given position for a turn of a given radius. The more nearly the helicopter is to a crosswind position, the greater the crab angle. The maximum crab angle should be at the point of each half circle farthest from the reference line.

A standard radius for S-turns cannot be specified, since the radius depends on the airspeed of the helicopter, the velocity of the wind, and the initial bank chosen for entry.