Allowing the nose of the glider to get excessively low during a steep turn may result in a significant increase in airspeed and loss in altitude, creating a spiral dive. If the pilot attempts to recover from this situation by applying only back elevator pressure, the limiting load factor may be exceeded, causing structural failure. To recover from a spiral dive properly, the pilot should first reduce the angle of bank with coordinated use of the rudder and aileron, then smoothly increase pitch to the proper attitude.
Common errors during spiral dives include:
- Failure to recognize when a spiral dive is developing.
- Rough, abrupt, and/or uncoordinated control application during recovery.
- Improper sequence of control applications.
All flight instructor applicants must be proficient in spins. A spin may be defined as an aggravated stall that results in autorotation wherein the glider follows a downward corkscrew path. As the glider rotates around a vertical axis, the rising wing is less stalled than the descending wing, creating a rolling, yawing, and pitching motion. The glider is basically being forced downward by rolling, yawing, and pitching in a spiral path. [Figure 8-17]
The autorotation results from an unequal angle of attack on the glider’s wings. The rising wing has a decreasing angle of attack in which the relative lift increases and the drag decreases. In effect, this wing is less stalled. Meanwhile, the descending wing has an increasing angle of attack, past the wing’s critical angle of attack (stall) where the relative lift decreases and drag increases.
A spin is caused when the glider’s wing exceeds its critical angle of attack (stall) with a sideslip or yaw acting on the glider at, or beyond, the actual stall. During this uncoordinated maneuver, a pilot may not be aware that a critical angle of attack has been exceeded until the glider yaws out of control toward the lowering wing. If stall recovery is not initiated immediately, the glider may enter a spin. If this stall occurs while the glider is in a slipping or skidding turn, this can result in a spin entry and rotation in the direction that the rudder is being applied, regardless of which wingtip is raised.
Many gliders must be forced to spin and require good judgment and technique to get the spin started. These same gliders may be put into a spin accidentally by mishandling the controls in turns, stalls, and flight at minimum controllable airspeeds. This fact is additional evidence of the necessity for the practice of stalls until the ability to recognize and recover from them is developed.
Often a wing drops at the beginning of a stall. When this happens, the nose attempts to move (yaw) in the direction of the low wing. This is when use of the rudder is important during a stall. The correct amount of opposite rudder must be applied to keep the nose from yawing toward the low wing. By maintaining directional control and not allowing the nose to yaw toward the low wing before stall recovery is initiated, a spin is averted. If the nose is allowed to yaw during the stall, the glider begins to skid in the direction of the lowered wing and enters a spin.
A glider must be stalled in order to enter a spin; therefore, continued practice of stall recognition helps the pilot develop a more instinctive and prompt reaction in recognizing an approaching spin. It is essential to learn to apply immediate corrective action any time it is apparent the glider is approaching spin conditions. If it is impossible to avoid a spin, the pilot should immediately execute spin recovery procedures.
The flight instructor should demonstrate spins and spin recovery techniques with emphasis on any special spin procedures or techniques required for a particular glider. Before beginning any spin operations, the following items should be reviewed:
- GFM/POH limitations section, placards, or type certification data sheet, to determine if the glider is approved for spins
- Weight and balance limitations
- Proper recommended entry and recovery procedures
- The requirements for parachutes. It would be appropriate to review current Title 14 of the Code of Federal Regulations (14 CFR) part 91 for the latest parachute requirements.
A thorough glider preflight should be accomplished with special emphasis on excess or loose items that may affect the weight, CG, and controllability of the glider. Slack or loose control cables (particularly rudder and elevator) could prevent full antispin control deflections and delay or preclude recovery in some gliders.
Prior to beginning spin training, the flight area above and below the glider must be clear of other air traffic. Clearing the area may be accomplished while slowing the glider for the spin entry. All spin training should be initiated at an altitude high enough for a completed recovery at or above 1,500 feet AGL within gliding distance of a landing area. There are four phases of a spin: entry, incipient, developed, and recovery.
In the entry phase, the pilot provides the necessary elements for the spin, either accidentally or intentionally. The entry procedure for demonstrating a spin is similar to a stall. As the glider approaches a stall, smoothly apply full rudder in the direction of the desired spin rotation while applying full back (up) elevator to the limit of travel. Always maintain the ailerons in the neutral position during the spin procedure unless the GFM/POH specifies otherwise.
The incipient phase takes place between the time the glider stalls and rotation starts until the spin has fully developed. This change may take up to two turns for most gliders. An incipient spin that is not allowed to develop into a steadystate spin is the most commonly used in the introduction to spin training and recovery techniques. In this phase, the aerodynamic and inertial forces have not achieved a balance. As the incipient spin develops, the indicated airspeed should be near or below stall airspeed. The incipient spin recovery procedure should be commenced prior to the completion of 360° of rotation. The pilot should apply full rudder opposite the direction of rotation.
The developed phase occurs when the glider’s angular rotation rate, airspeed, and vertical speed are stabilized while in a flightpath that is nearly vertical. This is, when glider aerodynamic forces and inertial forces are in balance and the attitude, angles, and self-sustaining motions about the vertical axis are constant or repetitive, the spin is in equilibrium.
The recovery phase occurs when the angle of attack of the wings drops below the critical angle of attack and autorotation slows. Then, the nose drops below the spin pitch attitude and rotation stops. This phase may last for a quarter turn to several turns. To recover, control inputs are initiated to disrupt the spin equilibrium by stopping the rotation and stall. To accomplish spin recovery, the manufacturer’s recommended procedures should be followed. In the absence of the manufacturer’s recommended spin recovery procedures, the following steps for general spin recovery are recommended:
- Position the ailerons to neutral. Ailerons may have an adverse effect on spin recovery. Aileron control in the direction of the spin may increase the rate of rotation and delay the recovery. Aileron control opposite the direction of the spin may cause the down aileron to move the wing deeper into the stall and aggravate the situation. The best procedure is to ensure that the ailerons are neutral. If the flaps are extended prior to the spin, they should be retracted as soon as possible after spin entry.
- Apply full opposite rudder against the rotation. Ensure that full (against the stop) opposite rudder has been applied.
- When rotation stops, apply a positive and brisk, straightforward movement of the elevator control past neutral to break the stall. The forceful movement of the elevator decreases the excessive angle of attack and breaks the stall. The controls should be held firmly in this position.
- After spin rotation stops, neutralize the rudder. If the rudder is not neutralized at this time, the ensuing increased airspeed acting upon a deflected rudder causes a yawing effect. Slow and overly cautious control movements during spin recovery must be avoided. In certain cases, it has been found that such movements result in the glider continuing to spin indefinitely, even with antispin inputs. A brisk and positive technique, on the other hand, results in a more positive spin recovery.
- Begin applying back-elevator pressure to raise the nose to level flight. Caution must be used not to apply excessive back-elevator pressure after the rotation stops. Excessive back-elevator pressure can cause a secondary stall and result in another spin. Care should be taken not to exceed the G-load limits and airspeed limitations during recovery.
It is important to remember that the above spin recovery procedures are recommended for use only in the absence of the manufacturer’s procedures. Before any pilot attempts to begin spin training, the pilot must be familiar with the procedures provided by the manufacturer for spin recovery.
The most common problems in spin recovery include pilot confusion in determining the direction of spin rotation and whether the maneuver is a spin or a spiral. If the airspeed is increasing, the glider is no longer in a spin but in a spiral. In a spin, the glider is stalled and the airspeed is at or below stalling speed.
Common errors when encountering/practicing spins include:
- Failure to clear area before a spin.
- Failure to establish proper configuration prior to spin entry.
- Failure to correct airspeed for spin entry.
- Failure to recognize conditions leading to a spin.
- Failure to achieve and maintain stall during spin entry.
- Improper use of controls during spin entry, rotation, and/or recovery.
- Disorientation during spin.
- Failure to distinguish a spiral dive from a spin.
- Excessive speed or secondary stall during spin recovery.
- Failure to recover with minimum loss of altitude.
- Failure to recover above minimum altitude with a landing area within gliding distance.