Steep Turns and Steep Spiral - Performance Maneuvers (Part 1)

Steep Turns

Steep turns consist of single to multiple 360° to 720° turns, in either or both directions, using a bank angle between 45° to 60°. The objective of the steep turn is to develop a pilot’s skill in flight control smoothness and coordination, an awareness of the airplane’s orientation to outside references, division of attention between flight control application, and the constant need to scan for hazards. [Figure 1]

Figure 1. Steep turns

When steep turns are first demonstrated, the pilot will be in an unfamiliar environment when compared to what was previously experienced in shallow bank angled turns; however, the fundamental concepts of turns remain the same in the execution of steep turns. When performing steep turns, pilots will be exposed to higher load factors, the airplane’s inherent overbanking tendency, the loss of vertical component of lift when the wings are steeply banked, the need for substantial pitch control pressures, and the need for additional power to maintain altitude and airspeed during the turn.

As discussed in previous articles, when an airplane is banked, the total lift is comprised of a vertical component of lift and a horizontal component of lift. In order to not lose altitude, the pilot must increase the wing’s angle of attack (AOA) to ensure that the vertical component of lift is sufficient to maintain altitude. In a steep turn, the pilot will need to increase pitch with elevator back pressures that are greater than what has been previously utilized. Total lift must increase substantially to balance the load factor or G-force (G). The load factor is the vector resultant of gravity and centrifugal force. For example, in a level altitude, 45° banked turn, the resulting load factor is 1.4; in a level altitude, 60° banked turn, the resulting load factor is 2.0. To put this in perspective, with a load factor of 2.0, the effective weight of the aircraft will double. Pilots should realize load factors increase dramatically beyond 60°. Most general aviation airplanes are designed for a load limit of 3.8Gs. Regardless of the airspeed or what airplane is involved, for a given bank angle in a level altitude turn, the same load factor will always be produced. A light, general aviation airplane in a level altitude, 45° angle of bank turn will experience a load factor of 1.4 just as a large commercial airliner will in the same level altitude, 45° angle of bank turn.

Because of the higher load factors, steep turns should be performed at an airspeed that does not exceed the airplane’s design maneuvering speed (VA) or the manufacturer’s recommended speed. Maximum turning performance is accomplished when an airplane has both a fast rate of turn and minimum radius of turn, which is effected by both airspeed and angle of bank. Each airplane’s turning performance is limited by structural and aerodynamic design, as well as available power. The airplane’s limiting load factor determines the maximum bank angle that can be maintained in level flight without exceeding the airplane’s structural limitations or stalling. As the load factor increases, so does the stalling speed. For example, if an airplane stalls in level flight at 50 knots, it will stall at 60 knots in a level altitude, 45° banked turn and at 70 knots in a level altitude, 60° banked turn. Stalling speed increases at the square root of the load factor. As the bank angle increases in level flight, the margin between stalling speed and maneuvering speed decreases—an important concept for a pilot to remain cognizant.

In addition to the increased load factors, the airplane will exhibit what is called “overbanking tendency.” Recall from a previous article on the discussion of overbanking tendency. In most flight maneuvers, bank angles are shallow enough that the airplane exhibits positive or neutral stability about the longitudinal axis; however, as bank angles steepen, the airplane will exhibit the behavior to continue rolling in the direction of the bank unless deliberate and opposite aileron pressure is held against the bank. Also, pilots should be mindful of the various left turning tendencies, such as P-factor, which requires effective rudder aileron coordination.

Before starting any practice maneuver, the pilot must ensure that the area is clear of air traffic and other hazards. Further, distant references such as a mountain peak or road should be chosen to allow the pilot to assess when to begin rollout from the turn. After establishing the manufacturer’s recommended entry speed or the design maneuvering speed, the airplane should be smoothly rolled into the desired bank angle somewhere between 45° to 60°. As the bank angle is being established, generally prior to 30° of bank, elevator back pressure should be smoothly applied to increase the AOA. After the selected bank angle has been reached, the pilot will find that considerable force is required on the elevator control to hold the airplane in level flight—to maintain altitude. Pilots should keep in mind that as the AOA increases, so does drag. Consequently, power must be added to maintain altitude and airspeed.

Steep turns can be conducted more easily by the use of elevator trim and power as the maneuver is entered. In many light general aviation airplanes, as the bank angle transitions from medium to steep, increasing elevator up trim and adding a small increase in engine power minimizes control pressure requirements. Pilots must not forget to remove both the trim and power inputs as the maneuver is completed.

To maintain bank angle, altitude, as well as orientation, requires an awareness of the relative position of the horizon to the nose and the wings. The pilot who references the aircraft’s attitude by observing only the nose will have difficulty maintaining altitude. A pilot who observes both the nose and the wings relative to the horizon is likely able to maintain altitude within performance standards. Altitude deviations are primary errors exhibited in the execution of steep turns. If the altitude does increase or decrease, changing elevator back pressure could be used to alter the altitude; however, a more effective method is a slight increase or decrease in bank angle to control small altitude deviations. If altitude is decreasing, reducing the bank angle a few degrees helps recover or stop the altitude loss trend; also, if altitude is increasing, increasing the bank angle a few degrees helps recover or stop the altitude increase trend—all bank angle changes should be accomplished with coordinated use of aileron and rudder.

The rollout from the steep turn should be timed so that the wings reach level flight when the airplane is on heading from which the maneuver was started. A good rule of thumb is to begin the rollout at ½ the number of degrees of bank prior to reaching the terminating heading. For example, if a right steep turn was begun on a heading of 270° and if the bank angle is 60°, the pilot should begin the rollout 30° prior or at a heading of 240°. While the rollout is being made, elevator back pressure, trim, and power should be gradually reduced, as necessary, to maintain the altitude and airspeed.

Common errors when performing steep turns are:
  • Not clearing the area
  • Inadequate pitch control on entry or rollout
  • Gaining altitude or losing altitude
  • Failure to maintain constant bank angle
  • Poor flight control coordination
  • Ineffective use of trim
  • Ineffective use of power
  • Inadequate airspeed control
  • Becoming disoriented
  • Performing by reference to the flight instrument rather than visual references
  • Failure to scan for other traffic during the maneuver
  • Attempts to start recovery prematurely
  • Failure to stop the turn on designated heading

Steep Spiral

The objective of the steep spiral is to provide a flight maneuver for rapidly dissipating substantial amounts of altitude while remaining over a selected spot. This maneuver is especially effective for emergency descents or landings. A steep spiral is a gliding turn where the pilot maintains a constant radius around a surface-based reference point while rapidly descending—similar to the turns around a point maneuver. Sufficient altitude must be gained prior to practicing the maneuver so that at least three 360° turns are completed. [Figure 2] The maneuver should not be allowed to continue below 1,500 feet above ground level (AGL) unless an actual emergency exists.

Figure 2. Steep spiral

The steep spiral is initiated by properly clearing the airspace for air traffic and hazards. In general, the throttle is closed to idle, carburetor heat is applied if equipped, and gliding speed is established. Once the proper airspeed is attained, the pitch should be lowered and the airplane rolled to the desired bank angle as the reference point is reached. The steepest bank should not exceed 60°. The gliding spiral should be a turn of constant radius while maintaining the airplane’s position to the reference. This can only be accomplished by proper correction for wind drift by steepening the bank on downwind headings and shallowing the bank on upwind headings, just as in the maneuver, turns around a point. During the steep spiral, the pilot must continually correct for any changes in wind direction and velocity to maintain a constant radius.

Operating the engine at idle speed for any prolonged period during the glide may result in excessive engine cooling, spark plug fouling, or carburetor ice. To assist in avoiding these issues, the throttle should be periodically advanced to normal cruise power and sustained for a few seconds. If equipped, monitoring cylinder head temperatures provides a pilot with additional information on engine cooling. When advancing the throttle, the pitch attitude must be adjusted to maintain a constant airspeed and, preferably, this should be done when headed into the wind.

Maintaining a constant airspeed throughout the maneuver is an important skill for a pilot to develop. This is necessary because the airspeed tends to fluctuate as the bank angle is changed throughout the maneuver. The pilot should anticipate pitch corrections as the bank angle is varied throughout the maneuver. During practice of the maneuver, the pilot should execute three turns and roll out toward a definite object or on a specific heading. During rollout, the smooth and accurate application of the flight controls allow the airplane to recover to a wing’s level glide with no change in airspeed. Recovering to normal cruise flight would proceed after the establishment of a wing’s level glide.

Common errors when performing steep spirals are:
  • Not clearing the area
  • Inadequate pitch control on entry or rollout
  • Gaining altitude
  • Not correcting the bank angle to compensate for wind
  • Poor flight control coordination
  • Ineffective use of trim
  • Inadequate airspeed control
  • Becoming disoriented
  • Performing by reference to the flight instrument rather than visual references
  • Not scanning for other traffic during the maneuver
  • Not completing the turn on designated heading or reference

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