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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 (posi- tion 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 pro- gresses. 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 encoun- tered. 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 refer- ence 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 cir- cles 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, immedi- ately 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 

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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 head- ing directly upwind. Immediately enter a bank in the opposite direction 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 refer- ence 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 com- plete, 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 ground- speed. 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 heli- copter 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 heli- copter 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 

