Ground reference maneuvers may be used as training exercises to help develop a division of attention between the flightpath and ground references, and while controlling the helicopter and watching for other aircraft in the vicinity.
Other examples of ground reference maneuvers are flights for photographic or observation purposes, such as pipe line or power line checks. Prior to each maneuver, a clearing turn should be accomplished to ensure the area is free of conflicting traffic.
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 develop 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 during the various legs of the airport traffic pattern, and is also useful in observation and photographic flights.
Maintaining ground track while trying to fly a straight line can be very difficult for new pilots to do. It is important to understand the effects of the wind and how to compensate for this. For this maneuver, pick a square or rectangular field, or an area bounded on four sides by section lines or roads, with sides approximately a mile in length. The area selected should be well away from other air traffic. Fly the maneuver approximately 500 to 800 feet above the ground, which is the altitude usually required for an airport traffic pattern. If the student finds it difficult to maintain a proper ground track at that higher altitude, lower the altitude for better ground reference until they feel more comfortable and are able to grasp the concept better. Altitude can be varied up to 800 feet as proficiency improves.
Fly the helicopter parallel to and at a uniform distance, about one-fourth to one-half mile, from the field boundaries, and not directly above the boundaries. For best results, position flightpath outside the field boundaries 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, there will be no usable reference points to start and complete the turns. In addition, the closer the track of the helicopter is to the field boundaries, the steeper the bank necessary at the turning points. The edges of the selected field should be seen 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 field should be the same regardless of whether the course is flown to the left or right. All turns should be started when the helicopter is abeam the corners of the field boundaries. The bank normally should not exceed 30°–45° in light winds. Strong winds may require more bank.
The pilot should understand that when trying to fly a straight line and maintain a specific heading, aircraft heading must be adjusted in order to compensate for the winds and stay on the proper ground track. Also, keep in mind that a constant scan of flight instruments and outside references aid in maintaining proper ground track.
Although the rectangular course may be entered from any direction, this discussion assumes entry on a downwind heading. [Figure 9-15] while approaching the field boundary on the downwind leg, begin planning for an upcoming turn. Since there is a tailwind on the downwind leg, the helicopter’s groundspeed is increased (position 1). During the turn, 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). This is normally the steepest turn of the maneuver.
As the turn progresses, the tailwind component decreases, which decreases the groundspeed. 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 crabbed into the wind in order to maintain the proper ground track. Keep in mind that in order to maintain proper ground track the helicopter may have to be flown almost sideways depending on the amount of wind. The forward cyclic that is applied for airspeed will be in the direction of the intended flight path. For this example, it will be in the direction of the downwind corner of the field. However, since the wind is now pushing the helicopter away from the field, establish the proper drift correction by heading slightly into the wind. Therefore, the turn 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 for the next turn. Since a wind correction angle is being held into the wind and toward the field, this next turn requires a turn of less than 90°. Since there is now a headwind, the groundspeed decreases during the turn, the bank initially must be medium and progressively decrease 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.
Continue to evaluate each turn and determine the steepness or shallowness based on the winds. It is also important to remember that as the bank angles are adjusted in the turn, the pilot is subsequently forced to make changes with the flight controls.
- Faulty entry technique.
- Poor planning, orientation, and/or division of attention.
- Uncoordinated flight control application.
- Improper correction for wind drift.
- Failure to maintain selected altitude and airspeed.
- Selection of a ground reference with no suitable emergency landing area within gliding distance.
- Not flying a course parallel to the intended area (e.g., traffic pattern or square field).