It was a nice sunny morning, when my instructor demonstrated a two turn spin and its recovery on HPT-32 aircraft. We had taken off almost half an hour before that, checked controllability of aircraft by practicing hard tuns to wither side and then a stall to check for any negative characteristics like sudden wing drop or yaw before climbing to 9000 ft for spin. Before spin we cleared the area, identified a reference feature to help count the number of turns, tightened our straps once more. My instructor pulled the throttle to idle, kept the wings level and kept raising the nose as in going for a stall. Short of stall he applied full left rudder and kept the control stick fully back into the stomach. The aircraft yawed to the left with increasing yawing and rolling. For the deomnstration, I kept my hands on knees and feet flat on the cockpit floor.
“One turn, two turn!” he called out each time our nose crossed the reference point. “And recover” he said, “full opposite rudder, pause, stick moving centrally and progressively forward, spin stops, stick stops, rudders neutral and recover the aircraft” his actions matching the words he was speaking. It looked fairly simple and mechanical. But in my heart, I knew, it was a scary test which I had to pass to be a military pilot in Indian Air Force. It was one of the most violent manoeuvre, in which airspeeds were either too low or was not registered on the dial, the aircraft was spinning (pitching, yawing and rolling) with varying rates and with rapid loss of height. I was aware of instances when in which trainee pilot froze on controls or did not initiate recovery after stipulated number of turns or used a wrong technique leading to non-recovery of aircraft from spin. It was a real challenge, and I was determined to master it.
What is Spin?
A spin is a yaw aggravated stall which results in rotation about the spin axis. The aircraft follows a steep, “corkscrew” like, downward path. Spins can be entered, either intentionally or unintentionally, from any flight attitude and at practically any airspeed. If a stalled aircraft is subjected to a sufficient yaw rate, it will enter a spin. The yaw can be induced by improper use of the rudder or can be a result of the wing drop characteristics of the aircraft in question. In a spin, both wings are in a stalled condition but one wing will be in a deeper stall than the other. The drag is greater on the more deeply stalled wing causing the aircraft to autorotate (yaw) toward that wing. Spins are characterised by high angle of attack, low airspeed and high rate of descent.
How to Recover from Spin?
A specific and often counter-intuitive set of actions may be required to achieve a successful recovery from the spin. If the pilot uses incorrect technique or if the aircraft exceeds spin certification limitations or if the aircraft is improperly loaded (beyond aft centre of gravity limitations), the spin is likely to result in a crash.
In the event a spin is entered unintentionally, recovery actions should be taken immediately as considerable loss of altitude can result. If the aircraft is not certified for intentional spins or if the centre of gravity is beyond the aft limit, recovery may not be achievable.
If a specific spin recovery procedure has been identified by the aircraft manufacturer, that procedure must be used. Otherwise, recovery from an upright spin may be achieved by following the “PARE” mnemonic procedure first developed in the 1930’s by NACA:
- P – Power Idle – Reduce power on all engines to idle.
- A – Ailerons Neutral – Remove any aileron input.
- R – Rudder Opposite – Apply rudder opposite to the yaw (direction of the spin) until the spin stops. Then centralise the rudder.
- E – Elevator Through Neutral – Apply forward elevator (up to full control deflection if required) to reduce the angle of attack and unstall the wing.
Once the listed items have been successfully accomplished, adjust the power and the elevator inputs to return the aircraft to level, controlled flight.
What is Purpose of Spin?
In the early days of aviation, the 1920s and 1930s, spins were a manoeuvre required of military as well as commercial pilots. In the late 1940s, aircraft manufacturers riding on boom post WWII, started designing aircraft which were more spin resistant. in the year 1949, stall and spins were removed from the commercial pilot requirements. However, intentional spin and recovery manoeuvre has remained in military flying so as to eliminate fear of stall and spin from the military aviators mind, as well as train him to use counterintuitive techniques to recover and enhance ability to utilise the complete envelope of the aircraft including the boundary and corners of the envelope. Spin and Stall training further emphasises, the importance of planning future manoeuvre and energy management, which is very important in military aviation tobe successful.
In modern fighter aircraft, spin problem is primarily addressed by designing the aircraft to be as spin resistant as possible. However, it is very difficult to design a completely spin resistant aircraft due to lack of complete grasp of complex aerodynamics at high angles-of-attack. In addition, to increase manoeuvrability, fighter aircraft are designed to operate in post-stall regime. Any flight control problem, may lead to stall and spin. In view of the above, the training requirement of Spin and Recovery will continue to remain in military aviation for foreseeable future.
Your opinion?
Safe flight and Happy landings.
