# AIRCRAFT SPIN:
Table of Contents:
- What Is Aircraft Spin?
- Four Phases Of Aircraft Spin
- Aircraft Spin – Entry Phase
- Aircraft Spin – Incipient Phase
- Aircraft Spin – Developed Phase
- Aircraft Spin – Recovery Phase
What Is Aircraft Spin?
In aviation, an aircraft spin is an aggravated stall resulting in autorotation about the spin axis wherein the aircraft follows a corkscrew downward path. As the airplane rotates around a vertical axis, the outboard wing is less stalled than the inboard wing, which creates a rolling, yawing, and pitching motion. The airplane is basically descending due to gravity, rolling, yawing, and pitching in a spiral path.
The rotation results from an unequal AOA on the airplane’s wings. The less-stalled rising wing has a decreasing AOA, where the relative lift increases and the drag decreases. Meanwhile, the descending wing has an increasing AOA, which results in decreasing relative lift and increasing drag. A spin occurs when the airplane’s wings exceed their critical AOA (stall) with a sideslip or yaw acting on the airplane at, or beyond, the actual stall.
An airplane will yaw not only because of incorrect rudder application but because of adverse yaw created by aileron deflection; engine/prop effects, including p-factor, torque, spiraling slipstream, and gyroscopic precession; and wind shear, including wake turbulence. If the yaw had been created by the pilot because of incorrect rudder use, the pilot may not be aware that a critical AOA has been exceeded until the airplane yaws out of control toward the lowering wing.
A stall that occurs while the airplane is in a slipping or skidding turn can result in a spin entry and rotation in the direction of rudder application, regardless of which wingtip is raised. If the pilot does not immediately initiate stall recovery, the airplane may enter a spin. Maintaining directional control and not allowing the nose to yaw before stall recovery is initiated is key to averting a spin. The pilot must apply the correct amount of rudder to keep the nose from yawing and the wings from banking.
Spins can be entered intentionally or unintentionally, from any flight attitude and airspeed—all that is required is sufficient yaw rate while an aircraft is stalled. Upon recognition of a spin or approaching spin, the pilot should immediately execute spin recovery procedures.
Four Phases Of Aircraft Spin:
There are four phases of an aircraft spin and as follows,
- Entry phase
- Incipient phase
- Developed phase
- Recovery phase
1. Entry Phase (Aircraft Spin):
In the entry phase, the pilot intentionally or accidentally provides the necessary elements for the spin. The entry procedure for demonstrating a spin is similar to a power-off stall. During the entry, the pilot should slowly reduce power to idle, while simultaneously raising the nose to a pitch attitude that ensures a stall. As the airplane 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 AFM/POH specifies otherwise.
2. Incipient Phase (Aircraft Spin):
The incipient phase occurs from the time the airplane stalls and starts rotating until the spin has fully developed. This phase may take two to four turns for most airplanes. In this phase, the aerodynamic and inertial forces have not achieved a balance. As the incipient phase develops, the indicated airspeed will generally stabilize at a low and constant airspeed and the symbolic airplane of the turn indicator should indicate the direction of the spin. The slip/skid ball is unreliable when spinning.
The pilot should initiate incipient spin recovery procedures prior to completing 360° of rotation. The pilot should apply full rudder opposite the direction of rotation. The turn indicator shows a deflection in the direction of rotation if disoriented. Incipient spins that are not allowed to develop into a steady state spin are the most commonly used maneuver in initial spin training and recovery techniques.
3. Developed Phase (Aircraft Spin):
The developed phase occurs when the airplane’s angular rotation rate, airspeed, and vertical speed are stabilized in a flightpath that is nearly vertical. In the developed phase, aerodynamic forces and inertial forces are in balance, and the airplane’s attitude, angles, and self-sustaining motions about the vertical axis are constant or repetitive, or nearly so. The spin is in equilibrium. It is important to note that some training airplanes will not enter into the developed phase but could transition unexpectedly from the incipient phase into a spiral dive. In a spiral dive the airplane will not be in equilibrium but instead will be accelerating and G load can rapidly increase as a result.
4. Recovery Phase (Aircraft Spin):
The recovery phase occurs when rotation ceases and the AOA of the wings is decreased below the critical AOA. This phase may last for as little as a quarter turn or up to several turns depending upon the airplane and the type of spin. To recover, the pilot applies control inputs to disrupt the spin equilibrium by stopping the rotation and unstalling the wing. To accomplish spin recovery, always follow the manufacturer’s recommended procedures. In the absence of the manufacturer’s recommended spin recovery procedures and techniques, use the spin recovery procedures. If the flaps and/or retractable landing gear are extended prior to the spin, they should be retracted as soon as practicable after spin entry.
- Reduce the Power (Throttle) to Idle.
- Position the Ailerons to Neutral
- Apply Full Opposite Rudder against the Rotation
- Apply Positive, Brisk, and Straight Forward Elevator (Forward of Neutral)
- Neutralize the Rudder After Spin Rotation Stops
- Apply Back Elevator Pressure to Return to Level Flight
The following discussion explains each of the six steps:
1. Reduce the Power (Throttle) to Idle – Power aggravates spin characteristics. It can result in a flatter spin attitude and usually increases the rate of rotation.
2. Position the Ailerons to Neutral – Ailerons may have an adverse effect on spin recovery. Aileron control in the direction of the spin may accelerate the rate of rotation, steepen the spin attitude and delay the recovery. Aileron control opposite the direction of the spin may cause flattening of the spin attitude and delayed recovery; or may even be responsible for causing an unrecoverable spin. The best procedure is to ensure that the ailerons are neutral.
3. Apply Full Opposite Rudder against the Rotation – Apply and hold full opposite rudder until rotation stops. Rudder tends to be the most important control for recovery in typical, single-engine airplanes, and its application should be brisk and full opposite to the direction of rotation. Avoid slow and overly cautious opposite rudder movement during spin recovery, which can allow the airplane to spin indefinitely, even with anti-spin inputs. A brisk and positive technique results in a more positive spin recovery.
4. Apply Positive, Brisk, and Straight Forward Elevator (Forward of Neutral) – This step should be taken immediately after full rudder application. Do not wait for the rotation to stop before performing this step. The forceful movement of the elevator decreases the AOA and drives the airplane toward unstalled flight. In some cases, full forward elevator may be required for recovery. Hold the controls firmly in these positions until the spinning stops. (Note: If the airspeed is increasing, the airplane is no longer in a spin. In a spin, the airplane is stalled, and the indicated airspeed should therefore be relatively low and constant and not be accelerating.)
5. Neutralize the Rudder After Spin Rotation Stops – Failure to neutralize the rudder at this time, when airspeed is increasing, causes a yawing or sideslipping effect.
6. Apply Back Elevator Pressure to Return to Level Flight – Be careful not to apply excessive back elevator pressure after the rotation stops and the rudder has been neutralized. Excessive back elevator pressure can cause a secondary stall and may result in another spin. The pilot must also avoid exceeding the G-load limits and airspeed limitations during the pull out.