Spin (flight) Spin (flight) T-tail Category="Aviation risks"In flying, a spin is a special case of a stall, with the aircraft descending rapidly and rotating about a vertical axis. It is characterized by low airspeed, a high rate of descent, and high yaw and roll rates. In most aircraft, a spin is a stable condition that will continue until the aircraft descends into the ground unless the pilot takes action to recover from it.

Types of spin

A spining aircraft usually has a large positive Angle of attack (resulting in the stall) and usually a large nose-down pitch angle. A spin can be entered in any attitude, however; a negative angle of attack in a spin is called an "inverted spin". A spin in which the nose is more-or-less level with the horizon is a "flat spin." Flat spins can be very difficult to recover from because there is little or no smooth airflow over the control surfaces. In many aircraft a flat spin is unrecoverable.

One needs to be very careful to distinguish spins from spiral dives. In both cases the aircraft is pointing down, rotating, and descending rapidly, but in a spiral dive the wings are not stalled, and the speed builds up very rapidly. Also, the rate of rotation is usually slower. A spin is usually a stable state, and can be maintained indefinitely provided there is sufficient height. In a spiral dive the aircraft can quickly exceed the aircraft's maximum speed, resulting in flutter, and major Structural failure.

A special kind of spin is called the "snap roll". This is a spin entered from horizontal flight, usually with rudder and opposite aileron (adverse yaw). The resulting maneuver looks like a very fast (snap) roll.

How a spin occurs

A spin will occur if an aircraft stalls while yawing. The yawing can be aerodynamic (Sideslip angle, Rudder, Adverse yaw from the ailerons) or Thrust related (one engine inoperative on a multi-engine aircraft where the engines are mounted away from the centreline).

If the aircraft is yawing while it stalls, the outer wing will be moving faster than the inner wing, and so the inner wing will be more stalled and will drop. As it drops its angle of attack increases still further, aggrevating the stall. This continues to yaw the aircraft as the inner wing produces more drag than the outer.

This may happen during an uncoordinated turn or other maneuver. The commonest moment for a spin to occur is while the pilot is making his final turn before landing - he may use too much rudder while flying too slowly, thus stalling while yawing.

An aircraft may be deliberately spun for purposes of training, test flying, or Aerobatics. A spin is usually entered by flying the aircraft into a stall condition. As the stall point is reached, the Rudder (and sometimes opposite aileron) is used to yaw the aircraft. It is a common misconception that the outboard wing is still flying while the inner wing is stalled; in reality both wings are stalled.

Recovery

In a normal (upright) spin the nose is down and rotating quickly. It is tempting to attempt to recover by pulling the nose up and using opposite aileron to lift the lower wing, but this will only make the spin tighter: up elevator will only deepen the stall, and aileron inputs at high angle of attack result in more yawing (due to adverse yaw).

The correct technique (on most aircraft) is to:

Use the rudder to stop the rotation
Ease the stick forward to break the stall. A
As the rotation stops, center the rudder and gently pull out of the resulting dive.

Pulling out too quickly can cause a secondary stall. In many general-aviation aircraft an alternative recovery method is simply to release the controls and let the airplane's natural stability break the spin. CAUTION: Consult your Pilot's Operating Handbook (Approved Flight Manual) for correct spin recovery techniques for your aircraft, as they may differ significantly from the description above.

Several thousand feet may be lost in this maneuver. Spins should only be practised with an experienced instructor, with plenty of Altitude, and only in clear airspace. Prior to performing a spinning exercise, proper checks should be carried out, such as the standard HASELL check.

Aircraft design

A spin should only be performed deliberately on an aircraft that is certified for it, otherwise the stress could damage the airframe. It is also possible that the aircraft may not be capable of recovering from the spin at all, especially if the centre of gravity is too far aft. In the United States, spinning requires the use of approved parachutes unless training is being conducted by a flight instructor toward a rating.

Some powered aircraft and gliders are designed to be difficult or impossible to spin, even in an uncoordinated stall. These designs have a greater Angle of attack towards the center of the wing than the tips, so that the centre stalls first and the ailerons remain effective.

Many training aircraft are highly resistant to entering a spin. However, some other aeroplanes spin very easily and require correct recovery procedure to exit the spin. Of those aeroplanes that do spin, many are not rated for this maneuver and may be very difficult to recover or may sustain structural damage if it is attempted. A well known example of this is the Piper Tomahawk, a plane initially certified for spins, then conspicuously de-rated for spins following a number of fatal accidents.

Spinning is often feared by pilots, especially novices, yet spin recovery is no longer a compulsory part of the Private Pilot License syllabus. However, it makes good sense for every pilot to know how to get out of a spin should it occur. Practice makes this much easier, because the sensation of spinning is generally unpleasant and disorienting at first.