Smoke On Go

Stalling, Autorotation and Spinning – Part 4 – The Recovery from a Spin

We now have a reasonable understanding as to how an aircraft might behave in a spin. We know that if we are to achieve and maintain a steady state in a spin that we have to “default” to a situation in which the stick is being held fully backwards, the ailerons are being kept neutral, the rudder is fully applied, and the throttle has been pulled back so that the engine is at idle power.

It is vital to meet all of these conditions if a quick and uneventful recovery is going to be affected, this being, after all, exactly what we want!

The spin recovery process is about to begin. What we need to do first is stop the rotation of the aircraft and so opposite rudder to the direction of spin is applied. The rudder is always powerful enough to counteract the aerodynamic auto-rotative moments. If opposite rudder was to be held fully applied and the stick was to be held fully back, the rotation would stop and then the aircraft would start spinning to the other side.

However, at a very early stage in the recovery procedure, the stick must be moved well forward so as to unstall the aircraft. What we want to do is recover as expeditiously as possible and with a minimum loss in height. There is never any purpose associated with prolonging the recovery.

So, opposite rudder is applied and two beats later the stick is moved forward. The tempo is akin to the military timing when changing direction on the parade ground where troops move to the beat of WUN, two, three, WUN. In some aircraft, particularly the Harvard, the force required to move the stick forward can be fairly heavy, and many pilots are actually ready to use two hands to do so, if necessary.

The elevator is used to break the inertial pitching moment and to get the nose down so that the wings meet the air at an angle below the stalling angle of attack. Two things happen in sequence at this stage. Firstly, as opposite rudder is applied the rotation rate starts to slow down slightly. However, as we already know when the stick is moved forward the spin actually accelerates dramatically. Some aircraft might then even rotate for as many as three extra turns, all at a very fast rate. This could actually leave you in some doubt as to whether the aircraft was in fact actually recovering. The important thing here is not to panic or lose focus and to incorrectly pull the stick back towards where it had been, because then the aircraft would never, ever, recover from the spin.

These extra rotations, that are in fact very fast in nature, also occur because of an added gyroscopic event that has as yet not been covered. There are in fact two other gyroscopic effects. One comes from the entire fuselage and the other from the wings. Remember that a gyroscope is any rotating mass. This is true of all wheels or other masses that are in a state of rotational movement. So, as both the fuselage and wings rotate in the spin, they have also become gyroscopes. These are huge gyroscopes that are as big as the aircraft itself! The fuselage is commonly known as the “B” (for body) gyro and the wings as the “A” (for aerofoil) gyro.

Let’s look at the fuselage, which has now become a gyroscope because its mass is rotating clockwise in our right-hand spin. As the stick is moved forward, a force is created that is being applied in two different places.  Firstly, it is being applied to lift the tail and unstall the aircraft. This force precesses through 90 degrees and acts upwards on the left wingtip. Secondly, the very same force from the elevators is being simultaneously applied to the top side of the engine to push the nose downwards, thereby also unstalling the aircraft. This force also precesses through 90 degrees from where it was applied and transfers to the right wingtip, where it acts downwards.

The net result is that the very same auto-rotative forces that gave rise to the onset of the spin are increased dramatically, as the down going wing is pushed down. This results in a greater degree of stalling with even less lift and more drag being generated than there was, way back at the beginning of the maneuver. On the left side, the wing that moves upwards, experiences an increase in lift and a reduction in drag.

The lift/drag differential between the wings is increased and the auto-rotative force or “motor” is enhanced, thus causing a very high rotation rate.

The number of “accelerated” spins that the aircraft will do during the recovery will depend on how soon the stick is pushed forward after rudder is applied. If the forward stick application is rushed and occurs before the rudder has started slowing the rotational rate down, the effects of the conservation of momentum will be high. Additionally, the strength of the “B“or “Body” gyro will also be high and the enhanced precessional effects will give rise to aerodynamic auto-rotative effects that cause very high rotational rates and where up to three very fast spins could occur.

On the other hand, if the stick forward application is delayed somewhat, and only after the rudder had already started to reduce the spin rate, the effect of the stick forward application will result in fewer accelerated spins. This is in fact the result that is desired .

Please be aware that we are talking about fractions of seconds here and that there is an extremely fine line between whether the aircraft will spin through one turn of accelerated spin or up to three turns of accelerated spin.

As the spin stops and the aircraft unstalls, the rudder must be centralized, the wings leveled, and the aircraft pulled out of the dive. Avoid any negative “g” as it is uncomfortable. In a carbureted engine it will cause momentary engine failure.

As the aircraft recovers from the spin, centralize the rudder, roll the wings level and ease out of the dive. Continue pulling out of the dive until the aircraft is in the climbing attitude, and then restore the power gently as the aircraft’s nose cuts the horizon.

Unless you have vast spinning experience, please do not attempt spins on your own. The experience is like nothing you have ever experienced before. If you have minimal spinning experience, make sure there is a pilot with you that is indeed familiar with your aircraft’s spinning idiosyncrasies.

Part 5 of the series on spins will cover what the British call “Flick Rolls” and what the Americans call “Snap Rolls”. These manoeuvres are closely related to the basic spin. 




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