SPIN AWARENESS AND AVOIDANCE
Objective
To teach the student the avoidance and proper recovery from spins.
Elements
• Uncoordinated stalls
• Aerodynamics of a spin
• Recovery procedure

Schedule
Discussion 0:30
Equipment
Model airplane
Instructor Actions
Discuss what is a spin (an aggravated stall that results in autorotation). Autorotation results from unequal angles of attack on the wings. The key is aggravated (i.e. uncoordinated). Draw or show the corkscrew/helical flight path of a spin. The difference between a spin and a steep spiral: spin—airspeed low, wings stalled; spiral—airspeed increasing, not stalled.
Discuss the aerodynamics of a spin. Draw a wing in straight-and-level flight and in slow flight. Use actual angles of attack. Typical light aircraft wings stall at 18-22º. How can you enter a spin? Wing exceeds critical angle of attack with yaw acting on aircraft (uncoordinated). That is, a stall when in a slipping or skidding turn. Danger of base to final turn—cross controlled stall leading to spin.
The high wing has the greatest lift due to the greater airspeed, and overall less drag and lower angle of attack. The low wing has the least lift (due to lower airspeed) and greatest parasitic drag due to its higher angle of attack.
Center of gravity affects the spin characteristics. An aft CG makes spin recovery more difficult. The worst case is the aircraft may enter into a flat spin if CG is too far back, making recovery impossible.
Center of gravity affects the spin characteristics. An aft CG makes spin recovery more difficult. The worst case is the aircraft may enter into a flat spin if CG is too far back, making recovery impossible.
Phases of a spin:
• Entry—pilot provides input for the spin
• Incipient—aircraft stalls, rotation starts to develop; may take 2 turns in most aircraft, usually 5-6 seconds
• Developed—rotation rate, airspeed, vertical speed are constant, typically 500 fpm altitude loss, just above 1G load factor; airspeed at or below stall speed; rotation is around all 3 axes, as high as 7000 fpm descent
• Recovery—lower angle of attack below the critical value, may take from a quarter to several turns to recover

The recovery process is as follows (“PARE”):
• Power – reduce to idle
• Ailerons – position to neutral
• Rudder – full opposite against the rotation
• Elevator – brisk elevator control full forward to brake stall
• After spin rotation stops, neutralize the rudder
• Smoothly apply back-elevator pressure to raise the nose to level flight Common Errors

· Failure to establish proper configuration prior to spin entry

· Failure to achieve and maintain a full stall during spin entry

· Failure to close throttle when a spin entry is achieved

· Failure to recognize the indications of an imminent, unintentional spin

· Improper use of flight controls during spin entry, rotation, or recovery

· Disorientation during a spin

· Failure to distinguish between a high-speed spiral and a spin

· Excessive speed or accelerated stall during recovery

· Failure to recover with minimum loss of altitude

· Attempting to spin an airplane not approved for spins

References

FAA-H-8083-3A Airplane Flying Handbook p. 4-12

FAA-S-8081-6CS Flight Instructor for Airplane Single-Engine Land and Sea PTS p. 1-56

http://flight.derekbeck.com/

AdvisoryCircular-faa

DEFINITIONS.
A stall is a loss of lift and increase in drag that occurs when an aircraft is flown at an angle of attack greater than the angle for maximum lift. If recovery from a stall is not effected in a timely and appropriate manner by reducing the angle of attack, a secondary stall and/or spin may result. All spins are preceded by a stall on at least part of the wing. The angle of the relative wind is determined primarily by the aircraft's airspeed. Other factors are considered, such as aircraft weight, center of gravity, configuration, and the amount of acceleration used in a turn. The speed at which the critical angle of the relative wind is exceeded is the stall speed. Stall speeds are listed in the Airplane Flight Manual
(AFM) or the Pilot Operating handbook (POH) and pertain to certain conditions or aircraft configurations, e.g., landing configuration. Other specific operational speeds are calculated based upon the aircraft's stall speed in the landing configuration. Airspeed values specified in the AFM or POH may vary under different circumstances. Factors such as weight, center of gravity, altitude, temperature, turbulence e.t.c

Angle of Attack.
Angle of attack is the angle at which the wing meets the relative wind. The angle of attack must be small enough to allow attached airflow over and under the airfoil to produce lift. A change in angle of attack will affect the amount of lift that is produced. An excessive angle of attack will eventually disrupt the flow of air over the airfoil. If the angle of attack is not reduced, a section of the airfoil willreach its critical angle of attack, lose lift, and stall.
Exceeding the critical angle of attack for a particular airfoilsection will always result in a stall.

Airspeed.
Airspeed is controlled primarily by the elevator or longitudinal control position for a given configuration and power. If an airplane's speed is too slow, the angle of attack required for level flight will be so large that the air can no longer follow the upper curvature of the wing.
The result is a separation of airflow from the wing, loss of lift, a large increase in drag, and eventually a stall if the angle of attack is not reduced. The stall is the result of excessive angle of attack - not airspeed. A stall can occur at any airspeed, in any attitude, and at any power setting.

Configuration.
Flaps, landing gear, and other configuring devices can affect an airplane's stall speed.
Extension of flaps and/or landing gear in flight will usually increase drag. Flap extension will generally increase the lifting ability of the wings, thus reducing the airplane's stall speed. The effect of flaps on an airplane's stall speed can be seen by markings on the airplane's airspeed indicator, where the lower airspeed limit of the white arc (power-off stall speed with gear and flaps in the landing configuration) is less than the lower airspeed limit of the green arc (power-off stall speed in the clean configuration).

V sub so. V sub so means the stall speed or the minimum steady flight speed in the landing configuration.

V sub s1. V sub s1 means the stall speed or the minimum steady flight speed obtained in a specific configuration.

V sub A. V sub A is the design maneuvering speed which is the speed at which an airplane can be stalled without exceeding its structural limits.

Load Factor. Load factor is the ratio of the lifting force produced by the wings to the actual weight of the airplane and its contents. Load factors are usually expressed in terms of
"G." The aircraft's stall speed increases in proportion to the square root of the load factor. For example, an airplane that has a normal unaccelerated stall speed of 45 knots can be stalled at 90 knots when subjected to a load factor of 4 G's. The possibility of inadvertently stalling the airplane by increasing the load factor (by putting the airplane in a steep turn or spiral, for example) is therefore much greater than in normal cruise flight. A stall entered from straight and level flight or from an unaccelerated straight climb will not produce additional load factors. In a constant rate turn, increased load factors will cause an airplane's stall speed to increase as the angle of bank increases. Excessively steep banks should be avoided because the airplane will stall at a much higher speed or, if the aircraft exceeds maneuvering speed, structural damage to the aircraft may result before it stalls. If the nose falls during a steep turn, the pilot might attempt to raise it to the level flight attitude without shallowing the bank. This situation tightens the turn and can lead to a diving spiral. A feeling of weightlessness will result if a stall recovery is performed by abruptly pushing the elevator control forward, which will reduce the up load on the wings. Recoveries from stalls and spins involve a tradeoff between loss of altitude (and an increase in airspeed) and an increase in load factor in the pullup. However, recovery from the dive following spin recovery generally causes higher airspeeds and consequently higher load factors than stall recoveries due to the much lower position of the nose.
Significant load factor increases are sometimes induced during pullup after recovery from a stall or spin. It should be noted that structural damage can result from the high load factors imposed by intentional stalls practiced above the airplane's design maneuvering speed.

Weight. Although the distribution of weight has the most direct effect on stability, increased gross weight can also have an effect on an aircraft's flight characteristics, regardless of the CG position. As the weight of the airplane is increased, the stall speed increases. The increased weight requires a higher angle of attack to produce additional lift to support the weight

Altitude and Temperature. Altitude has little or no effect on an airplane's indicated stall speed. Thinner air at higher altitudes will result in decreased aircraft performance and a higher true airspeed for a given indicated airspeed.
Higher than standard temperatures will also contribute to increased true airspeed. However, the higher true airspeed has no effect on indicated approach or stall speeds. The manufacturer's recommended indicated airspeeds should therefore be maintained during the landing approach, regardless of the elevation or the density at the airport of landing.

Snow, Ice or Frost on the Wings. Even a small accumulation of snow, ice or frost on an aircraft's surface can cause an increase in that aircraft's stall speed. Such accumulation changes the shape of the wing, disrupting the smooth flow of air over the surface and, consequently, increasing drag and decreasing lift. Flight should not be attempted when snow, ice, or frost has accumulated on the aircraft surfaces.

Turbulence. Turbulence can cause an aircraft to stall at a significantly higher airspeed than in stable conditions. A vertical gust or windshear can cause a sudden change in the relative wind, and result in an abrupt increase in angle of attack. Although a gust may not be maintained long enough for a stall to develop, the aircraft may stall while the pilot is attempting to control the flightpath, particularly during an approach in gusty conditions. When flying in moderate to severe turbulence or strong crosswinds, a higher than normal approach speed should be maintained. In cruise flight in moderate or severe turbulence, an airspeed well above the indicated stall speed and below maneuvering speed should be used.

DISTRACTIONS. Improper airspeed management resulting in stalls are most likely to occur when the pilot is distracted by one or more other tasks, such as locating a checklist or attempting a restart after an engine failure; flying a traffic pattern on a windy day; reading a chart or making fuel and/or distance calculations; or attempting to retrieve items from the floor, back seat, or glove compartment. Pilots at all skill levels should be aware of the increased risk of entering into an inadvertent stall or spin while performing tasks that are secondary to controlling the aircraft.