Spinning

What are we trying to achieve: raise awareness of the seriousness of both Stalling and Spinning to investigate the effect of different modes of flight in relation to stalling and spinning to make you aware of the situations of increased risk so you are better armed to recognise and respond to them before the situation becomes critical What aren t we trying to achieve teaching you detailed technical theory as this that can be researched from the many books available on the subject.

History Early aviators didn’t understand what a spin was or how to recover. They knew that flying fast avoided a ‘sudden dive’ Early flying techniques included skidding the aircraft round the turn with the rudder. The standard spin recovery was developed in the mid 1920’s

Definition of a stall The glider can stall at any attitude and at any speed if the Angle of Attack reaches the critical angle which is approximately 15 degrees. Stalling speed depends on the following factors: Wing Loading: If the wing loading increases so does the stalling speed. Wing loading can be effected by: All Up weight Cable tension during winch launching Contamination: Contamination of the wing by water, bugs or anything similar.

Symptoms of the stall Inability of the elevator to raise the nose or stop it going down (this is the only symptom that is always present) Other symptoms are: The nose attitude is higher than normal The speed is slow or reducing Changes in airflow noise Flickering of airspeed indicator Buffet Change of effectiveness of the primary controls Unusual control positions for the phase of flight e.g. lots of out turn aileron High rate of descent

Stall recovery Moving the stick forward decreases the angle of attack and allows the wing to start flying again

Why a stall turns into a spin Asymmetric Stall: This is where each wing has a different angle of attack resulting in a rolling motion of the aircraft towards the wing with the higher angle of attack. Yawing swings the glider sideways and creates the asymmetric stall of the wings. This results is the relative airflow now striking the aircraft at an angle thus reducing the lift capacity of the down going wing and increasing the angle of attack and further enhancing the stall and roll. If we do not effect a recovery from the initial stall symptoms then the stall will develop into a spin. This involves all 3 axis, Yawing, Rolling and Pitching.

The Full Spin Autorotation is sustained by allowing the down going wing to have a larger angle of attack than the up going wing by holding the stick back and the rudder applied in the direction of rotation.

Symptoms of a Spin Rapid Entry Rapid Rotation ASI Flickers No Significant G forces Controls Ineffective

Spiral dive Symptoms: Slow entry Slow rate of rotation Increasing Airspeed Increasing G forces Controls remain effective

Conservation of Momentum The glider will rotate faster when the nose pitches down due to the reduced angle of attack The tail plane mass is pulled further away from the centre of rotation due to centrifugal force and is creating more drag and slows the rotation The reduced rotation caused by the increased drag causes the nose to pitch down reducing the angle of attack and increasing the rotational speed Increased rotational speed throws the tail out due to centrifugal forces and the effect is repeated.

Recovery procedure Recovery from the spin. This is achieved by: Full opposite rudder Centralisation the ailerons Stick progressively forward until the rotation stops Centralise rudder Recover from the ensuing dive

Wing Loading Unaccelerated Stall: Level trimmed flight where the stick is eased back to increase the angle of attack slowly until the aircraft is stalled e.g. 1G = (1000lbs) Accelerated Stall: A more positive movement of the controls to change the gliders direction generating positive G loading e.g. 2 G (twice as heavy 2000lbs) Decelerated Stall. A negative movement of the control to reduce the weight of the aircraft in flight e.g..75G ( 3 quarters of the 1G weight 750lbs) Cable Loading. The cable pull produced by the winch is trying to pull the glider against the generated lift. This affect is at its greatest at the top of the winch launch. In addition during a winch launch the glider can be supporting in excess of 200lbs of cable.

Winch Launch A Stall (created by aggressive rotation causing acceleration vertically(0 to 30Knots or 3000 per min), plus the additional cable weight and cable pull, produces a High G loading e.g. 2G resulting in the stalling speed increasing from 36knots to 50 knots) + Little rudder OR Little crosswind causing Yaw and Roll, turning the stall into a Asymmetrical stall + Correction with course aileron input to effect a recovery. This only increases the angle of attack and stalls the wing further. The cable pull provides a source forward motion and a Flick Roll or Horizontal Spin is the likely outcome.

Final Turn Low & Slow with a large angle of attack (Stretching the glide to get to the airfield) + Over Ruddered turn causing yaw and roll + Wind Gradient, Gust or Curl over + Correction with coarse aileron input to effect a recovery. This only increases the angle of attack potentially creating an asymmetrical stall and the initiation of a spin. No height to recover and a rapid meeting with the ground is highly likely

Launch Failure Reduced G during pushover reduces stalling speed. With reduced G the glider can turn below stall speed at 1 G Once the wingloading increases the glider will spin

Questions?