Spin (aerodynamics)
[1] Spins can be entered intentionally or unintentionally, from any flight attitude if the aircraft has sufficient yaw while at the stall point.
[3] Either situation causes the aircraft to autorotate toward the stalled wing due to its higher drag and loss of lift.
A spin differs from a spiral dive, in which neither wing is stalled and which is characterized by a low angle of attack and high airspeed.
[7] One common scenario that can lead to an unintentional spin is a skidding uncoordinated turn toward the runway during the landing sequence.
The result is twofold: the nose of the airplane drops below the horizon, and the bank angle increases due to rudder roll.
They may simply choose to make the final turn earlier and shallower to prevent an overshoot of the runway center line and provide a larger margin of safety.
Proper recovery procedures were unknown, and a pilot's instinct to pull back on the stick served only to make a spin worse.
In early aviation, individual pilots explored spins by performing ad-hoc experiments (often accidentally), and aerodynamicists examined the phenomenon.
In an effort to neutralize the forces pinning him against the right side of the cockpit, he applied full right rudder, and the aircraft leveled out 50 feet (15 m)[17] above the ground.
In spite of the discovery of "Parke's technique", spin-recovery procedures were not a routine part of pilot training until well into World War I.
Russian aviator Konstantin Artseulov, having independently discovered a recovery technique, somewhat different from Parke's and Hawker's, on the frontlines, demonstrated it in a dramatic display over the Kacha flight school's airfield on September 24, 1916, intentionally flying his Nieuport 21 into a spin and recovering from it twice.
[20] Later, Artseulov, at the time an instructor at the school, went on to teach this technique to all of his students, quickly disseminating it among the Russian aviators and beyond.
[21] In 1917, the English physicist Frederick Lindemann conducted a series of experiments in a B.E.2E[22] that led to the first understanding of the aerodynamics of the spin.
In Britain, starting in 1917, spin recovery procedures were routinely taught by flight instructors at the Gosport School of Special Flying, while in France, at the School of Acrobacy and Combat, Americans who had volunteered to serve in the famous Lafayette Escadrille were by July 1917 learning how to do what the French called a vrille.
[23] During the 1920s and 1930s, before night-flying instruments were commonly available on small aircraft, pilots were often instructed to enter a spin deliberately to avoid the much more dangerous graveyard spiral when they suddenly found themselves enveloped in clouds, hence losing visual reference to the ground.
In almost every circumstance, the cloud deck ends above ground level, giving the pilot a reasonable chance to recover from the spin before crashing.
The mnemonic "PARE" simply reinforces the tried-and-true NASA standard spin recovery actions—the very same actions first prescribed by NACA in 1936, verified by NASA during an intensive, decade-long spin test program overlapping the 1970s and '80s, and repeatedly recommended by the FAA and implemented by the majority of test pilots during certification spin-testing of light airplanes.
In some aircraft that spin readily upright and inverted, such as Pitts- and Christen Eagle-type high-performance aerobatic aircraft, an alternative spin-recovery technique may effect recovery as well, namely: Power off, Hands off the stick/yoke, Rudder full opposite to the spin (or more simply "push the rudder pedal that is hardest to push") and held (aka the Mueller/Beggs technique).
Even though this method does work in a specific subset of spin-approved airplanes, the NASA Standard/PARE procedure can also be effective provided that care must be taken to ensure the spin does not simply cross from positive to negative (or vice versa) and that a too-rapid application of elevator control is avoided as it may cause aerodynamic blanketing of the rudder rendering the control ineffective and simply accelerate the spin.
The aileron application creates a differential induced drag that raises the nose toward a level pitch attitude.
Differential drag now lowers the nose returning the plane to a normal spin from which the PARE technique is used to exit the maneuver.
of such aircraft is often more effective in arresting the spin rotation than the rudder(s), which usually become blanked by the wing and fuselage due to the geometric arrangement of fighters.
Some World War II airplanes were notoriously prone to spins when loaded erroneously; for example, the Bell P-39 Airacobra.
On the other hand, the Cornfield Bomber was a case where the ejection of the pilot shifted the center of gravity enough to let the now-empty aircraft self-recover from a spin and land itself.
Such maneuvers must be performed with the center of gravity in the normal range and with appropriate training, and consideration should be given to the extreme gyroscopic forces generated by the propeller and exerted on the crankshaft.
Guinness World Records lists the highest number of consecutive inverted flat spins at 98, set by Spencer Suderman on March 20, 2016, flying an experimental variant of the Pitts S-1 designated the Sunbird S-1x.
Where the slots are located ahead of the ailerons, they provide strong resistance to stalling and may even leave the airplane incapable of spinning.
Even large, passenger-carrying single-engine airplanes like the Cessna Caravan must be subjected to one-turn spins by a test pilot and repeatedly demonstrated to recover within no more than one additional turn.
With a small number of airplane types the FAA has made a finding of equivalent level of safety (ELOS) so that demonstration of a one-turn spin is not necessary.
The rapid rotation, combined with the nose-down attitude, results in a visual effect called ground flow that can be disorienting.
