Sunday, October 11, 2009

Straight-and-Level Flight

It is impossible to emphasize too strongly the necessity for forming correct habits in flying straight and level. All other flight maneuvers are in essence a deviation from this fundamental flight maneuver. Many flight instructors and students are prone to believe that perfection in straight-and-level flight will come of itself, but such is not the case.
It is not uncommon to find a pilot whose basic flying ability consistently falls just short of minimum expected standards, and upon analyzing the reasons for the shortcomings to discover that the cause is the inability to fly straight and level properly.

Straight-and-level flight is flight in which a constant heading and altitude are maintained. It is accomplished by making immediate and measured corrections for deviations in direction and altitude from unintentional slight turns, descents, and climbs. Level flight, at first, is a matter of consciously fixing the relationship of the position of some portion of the airplane, used as a reference point, with the horizon. In establishing the reference points, the instructor should place the airplane in the desired position and aid the student in selecting reference points. The instructor should be aware that no two pilots see this relationship exactly the same. The references will depend on where the pilot is sitting, the pilot’s height (whether short or tall), and the pilot’s manner of sitting. It is, therefore, important that during the fixing of this relationship, the pilot sit in a normal manner; otherwise the points will not be the same when the normal position is resumed.

In learning to control the airplane in level flight, it is important that the student be taught to maintain a light grip on the flight controls, and that the control forces desired be exerted lightly and just enough to produce the desired result. The student should learn to associate the apparent movement of the references with the forces which produce it. In this way, the student can develop the ability to regulate the change desired in the airplane’s attitude by the amount and direction of forces applied to the controls without the necessity of referring to instrument or outside references for each minor correction.

The pitch attitude for level flight (constant altitude) is usually obtained by selecting some portion of the airplane’s nose as a reference point, and then keeping that point in a fixed position relative to the horizon. [Figure 3-3] Using the principles of attitude flying, that position should be cross-checked occasionally against the altimeter to determine whether or not the pitch attitude is correct. If altitude is being gained or lost, the pitch attitude should be readjusted in relation to the horizon and then the altimeter rechecked to determine if altitude is now being maintained. The application of forward or back-elevator pressure is used to control this attitude.

The pitch information obtained from the attitude indicator also will show the position of the nose relative to the horizon and will indicate whether elevator pressure is necessary to change the pitch attitude to return to level flight. However, the primary reference source is the natural horizon.

In all normal maneuvers, the term “increase the pitch attitude” implies raising the nose in relation to the horizon; the term “decreasing the pitch attitude” means lowering the nose.

Straight flight (laterally level flight) is accomplished by visually checking the relationship of the airplane’s wingtips with the horizon. Both wingtips should be equidistant above or below the horizon (depending on whether the airplane is a high-wing or low-wing type), and any necessary adjustments should be made with the ailerons, noting the relationship of control pressure and the airplane’s attitude. [Figure 3-4] The student should understand that anytime the wings are banked, even though very slightly, the airplane will turn. The objective of straight-and-level flight is to detect small deviations from laterally level flight as soon as they occur, necessitating only small corrections. Reference to the heading indicator should be made to note any change in direction.

Continually observing the wingtips has advantages other than being the only positive check for leveling the wings. It also helps divert the pilot’s attention from the airplane’s nose, prevents a fixed stare, and automatically expands the pilot’s area of vision by increasing the range necessary for the pilot’s vision to cover. In practicing straight-and-level-flight, the wingtips can be used not only for establishing the airplane’s laterally level attitude or bank, but to a lesser degree, its pitch attitude. This is noted only for assistance in learning straight-andlevel flight, and is not a recommended practice in normal operations.

The scope of a student’s vision is also very important, for if it is obscured the student will tend to look out to one side continually (usually the left) and consequently lean that way. This not only gives the student a biased angle from which to judge, but also causes the student to exert unconscious pressure on the controls in that direction, which results in dragging a wing.

With the wings approximately level, it is possible to maintain straight flight by simply exerting the necessary forces on the rudder in the desired direction. However, the instructor should point out that the practice of using rudder alone is not correct and may make precise control of the airplane difficult. Straight–and-level flight requires almost no application of control pressures if the airplane is properly trimmed and the air is smooth. For that reason, the student must not form the habit of constantly moving the controls unnecessarily. The student must learn to recognize when corrections are necessary, and then to make a measured response easily and naturally.

To obtain the proper conception of the forces required on the rudder during straight-and-levelflight, the airplane must be held level. One of the most common faults of beginning students is the tendency to concentrate on the nose of the airplane and attempting to hold the wings level by observing the curvature of the nose cowling. With this method, the reference line is very short and the deviation, particularly if very slight, can go unnoticed. Also, a very small deviation from level, by this short reference line, becomes considerable at the wingtips and results in an appreciable dragging of one wing. This attitude requires the use of additional rudder to maintain straight flight, giving a false conception of neutral control forces. The habit of dragging one wing, and compensating with rudder pressure, if allowed to develop is particularly hard to break, and if not corrected will result in considerable difficulty in mastering other flight maneuvers.

For all practical purposes, the airspeed will remain constant in straight-and-level flight with a constant power setting. Practice of intentional airspeed changes, by increasing or decreasing the power, will provide an excellent means of developing proficiency in maintaining straight-and-level flight at various speeds. Significant changes in airspeed will, of course, require considerable changes in pitch attitude and pitch trim to maintain altitude. Pronounced changes in pitch attitude and trim will also be necessary as the flaps and landing gear are operated.

Common errors in the performance of straight-andlevel flight are:
  • Attempting to use improper reference points on the airplane to establish attitude.
  • Forgetting the location of preselected reference points on subsequent flights.
  • Attempting to establish or correct airplane attitude using flight instruments rather than outside visual reference.
  • Attempting to maintain direction using only rudder control.
  • Habitually flying with one wing low.
  • “Chasing” the flight instruments rather than adhering to the principles of attitude flying.
  • Too tight a grip on the flight controls resulting in overcontrol and lack of feel.
  • Pushing or pulling on the flight controls rather than exerting pressure against the airstream.
  • Improper scanning and/or devoting insufficient time to outside visual reference. (Head in the cockpit.)
  • Fixation on the nose (pitch attitude) reference point.
  • Unnecessary or inappropriate control inputs.
  • Failure to make timely and measured control inputs when deviations from straight-and-level flight are detected.
  • Inadequate attention to sensory inputs in developing feel for the airplane.

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