A stall must occur before a spin can take place. The principle difference that transforms a straight-ahead stall into a spin entry is that one wing stalls more than the other. This usually happens when there is an element of yaw as the stall breaks, and occurs most often when the airplane is in uncoordinated flight. Stalling with crossed controls is a major cause of spins, and usually happens when either too much or not enough rudder is used for existing yawing forces. If an airplane is near the stalling angle of attack, and if more lift is lost from one wing than from the other, that wing will drop more quickly than the other, creating a roll toward the wig with less lift. As this wing drops, its local relative wind will come more from below, further increasing the angle of attack for that wing. Likewise, as the airplane rolls around its center of gravity, the upper wing has a lower local angle of attack, and continues to develop some lift. This situation of unbalanced lift tends to increase as the airplane yaws toward the low wing, accelerating the higher outside wing while slowing the inner, lower wing still more. As with other stalls, the nose drops, and and as inertial forces come into play, the spin usually stabilizes at a steady rate of rotation and descent.
Watch your airspeed! (Or not)
Most of today’s pilots have been taught that stalls occur when the angle of attack of the wing reaches a critical point. In the majority of GA single-engine aircraft, that critical AOA is around 16-18 degrees above the flight path. If the flight path is 18 degrees nose down, a steep dive, the aircraft will stall as the attitude approaches level flight.
Less well understood is the importance of the relative wind acting on the wing. Relative wind is always opposite the direction of travel of the aircraft, so if an aircraft is descending in a level attitude, the AOA is greater than if the aircraft was in level flight.
The diagram illustrates the position of the wing in various flight attitudes. Attitude is only indirectly related to angle of attack. The wing can be stalled when it is a near level position, above the horizon or below.
Many pilots believe that an airplane won’t stall until it reaches the stall speed (Vs) published in the POH. Stalls and spins both result from a disruption of airflow over the wing. It is important for all pilots to know that a stall or spin can occur at ANY airspeed and at any attitude. If the wing reaches its critical angle of attack, it will stall. A spin will result when one wing has a lower coefficient of lift than the other.
Incipient Spin: This is the first phase and exists from the time the airplane stalls and rotation starts until the spin is fully developed.
Fully Developed Spin: Exists from the time the angular rotation rates, airspeed, and vertical descent rate are stabilized from one turn to the next.
Spin Recovery: It is crucial that you initiate recovery from an inadvertent spin as soon as possible, since many airplanes will not recover from a fully developed spin, and others continue for several turns before recovery control inputs become effective. The recovery from an incipient spin normally requires less altitude, and time, than the recovery from a fully developed spin. Keep in mind that although some characteristics of a spin are predictable, every airplane spins differently, and an individual airplane’s spin characteristics vary depending on configuration, loading, and other factors.
Where the primary goal in recovery from a straight-ahead stall is to reduce the angle of attack to restore airflow over the wings, spin recoveries have the additional goal of stopping the rotation. The complex aerodynamics of spins may dictate vastly different recovery procedures for different airplanes, so no universal spin recovery procedure can exist for all airplanes. The recommended recovery procedure for some airplanes is simply to reduce power to idle and let go of the controls, and others are so resistant to spins that they can be considered spin-proof. You should be intimately familiar with the procedures in the POH for the aircraft you will be flying. Here is a general recovery procedure, but it should not be applied arbitrarily without regard for the manufacturer’s recommendations:
Although the POH is the primary reference for recovery from a spin, the following can be used as a general procedure:
P – Retard the throttle to idle. In most aircraft, power hampers the recovery.
A – Ailerons neutral. Many pilots will attempt to recover from the spin using the ailerons. This may actually make the problem worse.
R – Apply full opposite rudder. Apply rudder opposite the rotation of the spin. If you have trouble determining which way the airplane is spinning, look at your turn coordinator or turn needle. It will indicate the direction of rotation.
E – Apply forward elevator. Immediately after applying opposite rudder, apply a quick forward motion on the control yoke and hold anti-spin controls until the aircraft starts to recover.
D – Recover from the dive. Once you have completed the four previous steps, and the rotation stops, recover from the dive. The descent rate may be over 5000 feet per minute and the airspeed will rapidly exceed redline. Remember to neutralize the rudder after the rotation stops.