Science Fair Project Encyclopedia
In flying, a spin is a special case of a stall. In a spin one wing is flying but the other is deeply stalled. The aircraft is rotating rapidly about its vertical axis, losing altitude quickly, with low indicated airspeed. The spin condition is called autorotation (not to be confused with autorotation of rotary-wing aircraft). A spin is a stable condition that will continue until the aircraft descends into the ground unless the pilot takes action to break the spin.
A spin may occur when a stall occurs that affects one wing more than the other. This may happen during an uncoordinated turn or other manoeuver. An aircraft may be deliberately spun for purposes of training, test flying, and aerobatics. A spin is usually entered by flying the aircraft into a stall condition. As the stall point is reached, the rudder is used to yaw the aircraft. The outward wing will keep flying, the inner wing will stall, and the aircraft will enter the spin.
A spin in which the aircraft is still essentially the right way up (though falling in a nose-down attitude) is called a normal or upright spin; one in which it is upside-down is called an inverted spin.
A spin should only be performed deliberately on an aircraft that is rated 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 back.
Some aeroplanes and sailplanes are designed to be difficult or impossible to spin, even in a skiding stall. These designs have a greater angle of attack towards the center of the wing than the tips, so that the centre stalls first. 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 manoever and may be very difficult to recover or may sustain structual damage if it is attempted. There are still many stall/spin 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.
In a 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. This technique will almost certainly not work, and will make the spin tighter.
The correct technique (on most aircraft) is to use the rudder to stop the rotation and ease the stick forward to break the stall. 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.
Several thousand feet may be lost in this manoeuver. 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.
When practising spins one needs to be very careful to distinguish them from a spiral dive. 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 build up very rapidly. Also, the rate of rotation is usually slower. A spin is a stable state, and can be maintained indefinitely provided there is sufficient height. In a spiral dive the aircraft will quickly exceed the aircraft's maximum speed (VNE), resulting in flutter, and major structural failure.
The recovery technique was only discovered during the First World War at the Experimental Physics Station, Farnborough by Frederick Lindemann, prior to this, spins were much feared by pilots as they were almost always fatal. The Sopwith Camel is famous for killing more of its own pilots than the enemy did during World War One, mainly due to its truly horrible spinning characteristics.
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