Ground Reference Maneuvers

RECTANGULAR COURSE

The rectangular course is a training maneuver in which the ground track of the helicopter is equidistant from all sides of a selected rectangular area on the ground. While performing the maneuver, the altitude and airspeed should be held constant. The rectangular course helps you to develop a recognition of a drift toward or away from a line parallel to the intended ground track. This is helpful in recognizing drift toward or from an airport runway or helipad during the various legs of the airport traffic pattern or prescribed route.

For this maneuver, pick a square or rectangular field, or an area bounded on four sides by section lines or roads, where the sides are approximately a mile in length. The area selected should be well away from other air traffic. Fly the maneuver approximately 600 to 1,000 feet AGL, which is the altitude typically required for an airport traffic pattern. You should fly the helicopter parallel to and at a uniform distance, about one-fourth to one-half mile, from the field boundries, not above the boundries. For the best results, position your flight path outside the field boundries just far enough away that they may be easily observed from either pilot seat by looking out the side of the helicopter. If an attempt is made to fly directly above the edges of the field, you will have no usable reference points to start and complete the turns. In addition, the closer the track of the helicopter is to the field boundries, a steeper bank will be necessary at the turning points. You should be able to see the edges of the selected field while seated in a normal position and looking out the side of the helicopter during either a left-hand or right-hand course. The distance of the ground track from the edges of the the field should be the same reguardless of whether the course is flown to the left or right. All turns should be started then the helicopter is abeam the corners of the field boundries. The bank normally used should not exceed 30 degrees.

Although the rectangular course may be entered from any direction, this discussion assumes entry on a downwind heading. Please refer to the Figure above. As you approach the field boundary on the downwind leg, you should begin planning for your turn to the crosswind leg. Since you have a tailwind on the downwind leg, the helicopter's groundspeed in increased (Position 1). During the turn onto the crosswind leg, which is the equivelent of the base leg in a traffic pattern, the wind causes the helicopter to drift away from the field. To counteract this effect, the roll-in should be made at a fairly fast rate with a relatively steep bank (Position 2).

As the turn progresses, the tailwind component decreases, which decreases the groundspeed. Consequently, the bank angle adnn 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 degree 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 to the upwind leg. since a wind correction angle is being held into the wind and towards the field while on the crosswind leg, this nect turn requires a turn of less than 90 degrees. 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 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 increasing groundspeed. During and after the turn onto this leg, the wind tends to drift the helicopter towards the field boundary. To comphensate for the drift, the amount of turn must be less than 90 degrees (Position 9).

Again, the rollout from this turn must be such that as the helicopter becomes level, then ose of the helicopter is turned slightly away from 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 the 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 degrees 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 for all the legs. It is important to anticipate the turns to comphensate for groundspees, drift, and turning radius. When 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 may 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.

The maneuver should be perfrormed 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 immeadiate selection of the steepest bank that is desired throughout the maneuver.

The discussion that follows is based upon 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, immeadiately 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 perpendicular to it and heading directly upwind. Immeadiately 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 the 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 dependant upon 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 on course, when it is on direct upwind or downwind headings or there is no wind. One would think of the fore and aft (longitudinal) 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 the crosswind position. The stronger the wind, the greater the crab angle for any given position for a turn of even radius. The more nearly the helicopter is to the 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 a radius depends on the airspeed of the helicopter, the velocity of the wind, and the initial bank chosen for the entry.

TURNS AROUND A POINT

This training maneuver requires you to fly constant radius turns around a preselected point on the ground using a bank of approximately 30 degrees, while maintaining a constant altitude. Your objective, as in other ground reference maneuvers, is to develop the ability to subconciously control the helicopter while dividing attention between the flight path and ground references, while still watching for other traffic in the vicinity.

The factors and principles of drift correction that are involved in S-turns are also applicable in this maneuver.

As in other ground track maneuvers, a constant radius around a point will, if any wind exists, require a constantly changing angle of bank and angles of wind correction.

The closer the helicopter is to a direct downwind heading where the groundspeed is greatist, the steeper the bank, and faster the rate of turn required to establish the proper wind correction angle.

The more nearly it is to a direct upwind heading where the groundspeed is least, the shallower the bank, and slower the rate of turn required to establish the proper wind correction angle.

It follows, then, that throughout the maneuver, the bank and rate of turn must be gradually varied in proportion to the groundspeed.

The point selected for Turns Around a Point should be prominant and easily distinguishable, yet small enough to present a precise reference. Isolated trees, crossroads, or other similar small landmarks ar usually suitable. The point should be in an area away from communities, livestock, or groups of people on the ground to prevent possible annoyance or hazard to others. since the maneuver is performed between 600 and 1,000 feet AGL, the area selected should also afford an opportunity for a safe emergency autorotation in the event it becomes necessary.

To enter turns around a point, fly the helicopter on a downwind heading to one side of the selected point at a distance equal to the desired radius of turn. When any significant wind exists, it is necessary to roll into the initial bank at a rapid rate so that the steepest bankis attained abeam the point when the helicopter is headed directly downwind. By entering the maneuver while heading directly downwind, the steepest bank can be attained immeadiately. Thus, if a bank of 30 degrees is desired, the initial bank is 30 degrees if the helicopter is at a correct distance from the point. Thereafter, the bank is gradually shallowed until the point is reached where the helicopter is headed directly upwind. At this point, the bank is gradually steepened until the steepest bank is again attained when heading downwind at the initial point of entry.

Just as S-turns require that the helicopter be turned into the wind in addition to varying the bank, so do turns around a point. During the downwind half of the circle, the helicopter's nose must be progressively turned toward the inside of the circle; during the upwind half, the nose must be progressively turned toward the outside. The downwind half of the turn around the point may be compared to the downwind side of the S-turn, while the upwind half of the turn around the point may be compared to the upwind side of the S-turn.

As you become experienced in performing turns around a point and have a good understanding of the effects of wind drift and varying of the bank angle and wind correction angle as required, entry into the maneuver may be made from any point. When entering this maneuver from any point, the radius of the turn must be carefully selected, taking into account the wind velocity and groundspeed so that an excessive bank is not required later on to maintain the proper ground track.

Common Errors

Faulty entry technique.

Poor planning, orientation, or division of attention.

Uncoordinated flight control application.

Improper correction for wind drift.

An unsymmetrical ground track during S-Turns across the reference line.

Failure to maintain selected altitude or airspeed.

Selection of a ground reference where there is no suitable emergency landing area within gliding distance.

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