SPINNING PART 1, OVERCOMING THE FEAR OF A SPIN.
During your flying training, you may have been lucky enough to experience a spin. Unfortunately it is no-longer a syllabus requirement for either the PPL or CPL course. So quite probably you will only have been taught how to avoid spin situations. Undoubtedly this absence of experience will have contributed to the mystique of the spin.
I remember very clearly a good friend talking to me one morning about his desire for some proper spin training. I had to take my student to the Little Gransden Beginners day, when I arrived, the airfield owner telephoned me to say that there had been an accident and this same person had an engine failure and spun at low level into the ground. If only we had done a single trip together he would be alive today! Spin training would undoubtedly have made him much more aware of pre spin conditions and certainly would have instilled the reactions necessary to avoid entering or at the very worst would have provided the tools necessary to smartly recover from a wing drop. I certainly believe that it was a bad decision to remove spinning from the PPL syllabus. Certainly there is a growing list of Commercial Airline accidents and “occurances” that have led many of the worlds aviation authorities, including EASA to reach the same conclusion and from 2018 onwards, all newly qualified commercial pilots will be required to have undergone upset prevention and recovery training. We recommend every pilot completes our Spinning and Upset Recovery Course At the end of this course you will be fully equipped to avoid spins and recover from them with out delay at every stage and will understand them fully. The course also covers many other flight upset situations and you will end up a much better pilot and will certainly thoroughly enjoy the learning experience.
Having started with a morbid account that reinforces the need for spin training, it is reassuring to remember that spinning does not kill people, but hitting the ground does! We make very sure this does not happen. We operate to a base height of 1,000 feet. This means that we aim to be fully recovered from any “botched up” manoeuvre by 1,000 feet. In actual fact, since recovery from botched up manoeuvres is key to the learning process, I would allow enough height for the student to be able to recover, get this wrong and still have sufficient height to recover myself before passing 1,000 ft. Of course part of the aim of spin training is to grow justifiable confidence, so we measure the height at spin entry and at spin exit and we count each half turn and recover on heading. After many repetitions we can be absolutely certain and confident of being able to precisely control every aspect of the spin.
It is perfectly normal to have a degree of anxiety prior to spinning, indeed it would be unhealthy not to have a strong self preservation instinct. Certainly in aerobatic circles almost everybody will admit to being anxious before their first solo spin. Indeed overcoming these hurdles is one of the joys of the sport but is reassuring to know that everybody who has made the journey has felt the same way. The moto of No 1 Parachute Training School is “Knowledge Dispels Fear”. This is certainly true and to overcome a fear of spinning requires proper training in a professional environment and lots of practice.
SPINNING PART 2, THE AERODYNAMICS OF A SPIN.
When an aircraft wing “stalls”, the airflow detaches from the wing and reduces lift and increases drag. The stall is the name given to this condition which is caused by the angle of attack (alpha) being excessive or going beyond critical. The speed this occurs at varies according to various factors including G, weight, power setting, air density etc. and is largely irrelevant from the pilots point of view as it is the critical alpha that is relevant, not the speed. It is convenient to know the approximate speed of reaching critical alpha at a certain configuration. In terms of aerobatics this will be a power off, 1 G condition at normal weight and normal height, clean stall. We know also that with power on, critical alpha will be at a lower speed, all other factors being equal. In the Extra 200, the aircraft we teach aerobatics and spinning in at the British Aerobatic Academy and what most of our tutorial will be based on, this is approximately 60kts.
If full left rudder is applied when the aircraft is stalled the yaw will cause the left wing to move backwards and the right wing forwards, the local airspeed difference will cause the right wing to rise and the left wing to drop and as the rudder is held in, this will continue. If the rudder were to be neutralised, at this very early stage, the spin would stop. This early stage where auto rotation has not become self-sustaining is known as the incipient spin.
With the rudder held in, the rolling and yawing movement will cause the left wing to have a greater angle of attack than the right, i.e. “be more stalled” and this will cause more drag and less lift which will cause the autorotation to be self-sustaining. This is known as a fully developed spin and occurs after a different number of rotations in different aircraft. It also occurs after a different number of rotations depending on how the spin is entered. In the Extra for example, if you enter the spin from significantly below the 1 G stalling speed, say 40 knots, it will take a long time to become fully developed and will be very slow to start spinning at all. This is because both wings will be heavily stalled and when rudder is applied, unless it is applied very vigorously, the lift difference between wings is not great so the aircraft just sinks with very little wing rise and therefore the alpha on each wing is not very different so autorotation is slow to develop.
From this description it is important to understand that the myth that if you let go of all the controls during a spin, it will recover itself, is wrong. This is only true if the spin is insipient and cannot be true, by definition, in a fully developed spin. What is certainly true in many aircraft is that the insipient stage can last a long time and during this period if you remove all control inputs, the aircraft will recover.
It is important to understand the effect of aileron. If you are spinning to the left and you apply right aileron, it will slow down recovery and increase the rate of rotation a little. This is because right aileron increases the angle of attack of the left wing and so reduces lift and increases drag which creates a stronger auto-rotative force. The effects of aileron vary according to aircraft type. In a Sukhoi 29 for example, full out spin aileron will prevent recovery. In an Extra it will significantly slow it down. The bottom line is to resist the natural instinct to use out spin aileron and consciously check the stick is neutral during recovery. The engine and propeller also have a big effect on the characteristics of a spin. If you are flying a lycoming powered aircraft, with a propeller that rotates to the right as seen from the pilots seat, then the gyroscopic force of propeller will lift the nose in a left hand spin. The amount of this force will vary according to the power setting. Therefore in all cases you must ensure the throttle is fully aft when entering a spin.
Later on I will write about flat spins, this is when we will push the throttle forward and thus flattening the spin, and inverted spin, this is where the aircraft enters inverted. It is the same as an erect spin except you are upside down and consequently the roll is opposite to yaw.
SPINNING PART 3, THE COMPETITION SPIN
A competition spin is a spin flown according to the judging criteria used in competitions. We will call everything else a normal spin.
If you make an error and end up inadvertently spinning, top of your priorities will be to recover and to do so without losing excessive height. Your immediate action should be to close the throttle and apply opposite rudder and relax back pressure followed by a little forward stick. In the “old days” we recommended that you should let go of the stick completely but some aircraft exhibit “Sticktion”, meaning the stick is sucked to out spin aileron and in these aircraft it is necessary to physically move the stick to the neutral position. The spin will stop almost immediately and as it stops you should neutralise rudder, apply power and ease out of the dive. Thats it, nothing more. Every aerobatic aircraft must be capable of recovering from a spin provided the C of G is within limits. Rule number 1 is to not fly aerobatics without confirming the weight and balance is within limits. If recovery does not happen you have done something wrong. Check that the ailerons are neutral and that you really have got full opposite rudder applied and the throttle really is closed. If that is the case and there is no indication the spin is going to stop, you must have the wrong rudder applied, so change feet, then of course the aircraft must recover.
It is important to understand that you should train with a good instructor before attempting solo spinning, or getting into a situation that could lead to solo spinning. I have seen many students in the heat of the moment make really basic errors that would have caused them embarrassment solo. The old adage, “aerobatics has never killed anyone, but hitting the ground often does” is true. Always practice with enough height for things to go wrong and have sufficient height to recover before reaching your minimum height which in the early days should be at least 1,000 feet agl.
In aerobatic competitions we fly in front of a team of “expert” judges. Each judge marks each figure out of 10, deducting one point per 5 degrees of error, and then each score for each figure is multiplied by a k factor representing the difficulty of the figure. A one turn spin has a k factor of 15, so the maximum points that you can score is 150.
Judging rules have evolved to ensure the pilots performance is rated. Wind correction is therefore not required in figures where it would be impossible. So for example, the vertical down line in a competition spin is not wind compensated and therefore the judges are simply looking for the aircraft to be vertical, not its track. We use the Zero Lift Axis (ZLA)of the aircraft to establish this.
Competition Spin judging criteria:
- Approach on heading in level flight, no roll or yaw height gain or loss is wrong, lose 1 point per 5 degrees off heading
- A clearly visible stall, the nose should drop without the aircraft climbing.
- Roll and yaw should begin concurrently and lead immediately to the spin. If it flicks or is forced then a PZ (perception zero) is awarded.
- The rotation should stop and the nose should drop to vertical ZLA (Zero Lift Axis) with aircraft on correct heading. Any aileron assistance will cause loss of points 1 point per 5 degrees off heading or off vertical. There must be no perceptible aileron roll to establish the correct final down-line axis.
- Rolls on the downline must follow the spin after a short pause they are not centred
- Execute a constant radius pull or push to horizontal flight on the correct heading
SPINNING PART 5, ADVANCED FRACTIONS
One and a Quarter and One and Three Quarter Turn Spins
When spinning, the trajectory is not vertically down but forward and down. This makes 1/4 and 3/4 fractions of spins more complicated because the heavy nose follows the trajectory after recovery causing, in a left spin, the right wing to be high and for a right spin the left wing will be high.
The aim, on spin recovery, is to draw a perfectly vertical line before coming level. If recovery after 1 turn, the wings should be perfectly level so the only effort required is to ensure it is exactly vertical in pitch. If it is a 1 1/4 or 1 3/4 turn spin to the left, because the trajectory is going to cause the heavy nose to swing through to the right causing the right wing to be high, you will need opposite rudder (right) to recover followed by left rudder to get the wings level again. This is quite demanding to master smoothly. Of course if you were in a right hand spin then you would use opposite rudder (left) followed by right rudder to get the wings level.
With practice you will find keeping in-spin rudder in until very late will take out a lot of the wing high error. The following recovery action works best for spins that are 1&1/4 or 1 &3/4 turns:
Full Power and almost full forward stick until the aircraft is pointing vertically down, in most cases almost no opposite rudder is required
Neutralise rudder on heading
Pull level at a suitable speed for the next figure.
Obviously this unconventional recovery technique needs some practice to perfect and the exact balance will vary from one aircraft type to another. It should be noted that it may not work at all in some aircraft types so should be practiced at height first!