SPIN RECOVERY AND SPIN TRAINING by Mal Beard

SPORT AEROBATICS May 1997 has some very interesting reports on spin accidents.  Between 1984 to 1994 there were twelve upright spin and five inverted spin accidents.  Of these, eleven were intentional entries, while six were unintentional. Since 1994 there have been many more spin accidents.

Near Eagle Point Oregon On 14 December 1996, a Bellanca 8KCAB Super Decathlon intentionally entered an inverted spin [to the right ???] by the application of left rudder at an altitude of 7200 feet. After three revolutions the flying instructor asked the student, who was a commercial pilot to assist with the rudder.  The student noted that right rudder pedal was full forward and applied left rudder.  This action prompted the following response from the instructor “not that rudder” where upon full right rudder was re applied. The student then took hold of the control stick, which was in the full forward position and moved it aft about four inches.  He could not feel any control input from the instructor on the stick.  Upon releasing the stick it returned to the full forward position. There was no power applied throughout the entry or recovery attempt. The instructor instructed the student to “bail out” which he did about 250 feet above the ground. At the point of impact the rudder was still fully deflected to the right. The aircraft impacted the ground in an inverted spin killing the instructor, who was still strapped in. There was no indication of any flight control or structural failure.

What caused this accident to occur? Pilot error due to lack of experience in spin recovery was the probably cause.  This can be broken down as follows. Pilot disorientation, in regard to the direction of yaw!, and or incorrect recovery technique! Throughout this discussion and to avoid confusing you, the physics of a spinning a/c will be treated as seen by an outside observer.  They do not change regardless of the a/c attitude. ie. Spinning Upright or Spinning Inverted.  It is only the pilots point of view that changes. Control inputs discussed will be from the pilots point of view. ie. right rudder means using your right foot etc. As the spin was initiated by applying left rudder at the point of stall, it must be assumed that the a/c was spinning inverted to the right,  [as viewed by an outside observer].  Remember, the physical forces acting on a spinning aeroplane do not change direction, regardless of the a/c attitude. [ie. upright or inverted]. If the a/c was in fact spinning to the right, the application of full right rudder and letting go of the control stick should have being sufficient for the aircraft to recover.  This statement is based on the “Muller-Beggs Emergency Spin Recovery Technique”. It may just be possible that the a/c was in fact spinning to the left, in which case the pilots being disorientated in regard to the direction of rotation, and continuing to apply right rudder, would be holding the a/c in the spin, thus causing the crash.

During recovery and to avoid any confusion in regard to the direction of yaw during upright or inverted spins, look out over the nose and pick a point.  That point will move towards one wingtip or the other.  Stand on the corresponding rudder.  Another way of saying it is, to stand on the same rudder as the wing that is moving forward across the horizon. If you do not look out over the nose, but allow your head to move back during an inverted spin, you may perceive the yaw to be in the opposite direction, leading to the incorrect rudder being applied to affect a recovery.  This error may occur if the a/c attitude is not flat, and as you are hanging upside down, it is very easy to look down at the ground behind the centre of rotation, thus seeing the yaw in the wrong direction.

Another possible cause, may have been lack of positive control inputs during the attempted recovery.

 The Muller-Beggs Emergency Spin Recover Procedure

1.   Cut the throttle.
2.   Take your hand off the stick.
3.   Kick full opposite rudder until the spin stops.
4.     Neutralize rudder and pull out of dive.

However the proponents of this technique agree that it only works with some aircraft.  On some other a/c it will not work.  Question:  Are you flying an a/c in which this method of recovery will not work?  Was this recovery method a contributing factor in the Eagle Point accident?

Let’s take a closer look at the Muller-Beggs Recovery Procedure. 

Step One:  Cut the throttle:  This is quiet straight forward, and should not be an area of concern to us as long as we, “do close the throttle fully”.

Step Two:  Take your hand off the stick:  Also quiet easy to follow and works up to a point. In many a/c the point of non recovery may never be reached, even if the spin has gone flat and stable, and just releasing the stick is all that will be required to recover.

Remember however that Eric Muller stated that his emergency spin recovery method was suitable for most a/c.  What about the rest? A small number of a/c will require, in addition to closing the throttle and applying full opposite rudder [step one and step three], a positive lowering of the nose to affect a recovery, from any spin.  Two a/c that may fall into this category are the Chipmunk and the Zlin 526.  A few years ago a Zlin crashed in Australia killing an  A.A.C. member when it failed to recover from a spin. 

The Chipmunk also has the reputation of being an a/c that should be treated with a great deal of respect, particularly in regard to spins. According to Gordon Lee, shortly after its' introduction the Chipmunk had the distinction of having the worst crash record of any a/c on the Australian registrar.  It is suspected that pilots who had trained on the DH 82 got into spins and failed to recover, because unlike the Tiger Moth, the Chipmunk requires an exact and positive recovery technique. Most Chipmunk pilots are aware of the consequences of not making sure that the park brake is fully released, which can restrict the rudder travel, thus making recovery from a spin unlikely. Many pilots are also aware of the danger posed by foreign objects restricting control inputs and have heard the story of the bent penny.

Many more a/c, will require a positive lowering of the nose to recover, once spin is stable and flat or is accelerated [by adding power or using aileron etc.].  Some a/c that I have flown that fall into this category are Pitts S2A, Cessna 150 Aerobat, Cessna 152 Aerobat and the Bellanca 8KCAB Super Decathlon.  Remember, no two a/c will recover in exactly the same manner.  This may be due to different rigging, changes to the C of G position, and Mass Distribution etc..  An a/c that has been repainted a number of times over the old paint, will have an aft C of G due to the fact that the area to be repainted is larger behind the C of G and the weight of the extra paint applied.

The Mass Distribution, The Tail Damping Power Ratio [TDPR], and The Unshielded Rudder Volume Coefficient [URVC] are just some of the terms used by a/c designers to predict the Spin Recovery Design Requirements It is interesting to note that there are two sections to the resulting graph. “Recovery by rudder alone” and “Recovery by rudder and elevator” 

The first aerobatic a/c that I owned was a Pitts S2A VH KJG.  It was an a/c that required a positive lowering of the nose to recover from a flat inverted spin.  Unfortunately VH KJG was destroyed in 1980 in WA when it recovered from an unintentional  spin, too low to avoid hitting the ground, killing the pilot and passenger.

Step three: Kick full opposite rudder!  This also needs to be closely examined.

Opposite to what?  Yaw! Of course!.  But, which way are we yawing?.  “Eric Muller recommends the rudder with the most resistance”.  Some other pilots recommend “the rudder closest to you”, which may require looking down at your feet.  What if the other pilot or passenger is already applying rudder in the correct direction for recovery?.  Many times during instructing I have experienced students who have done the wrong thing with the controls, and to extend my life expectancy I had to take over.  The worst example that I know of happened to a friend of mine, who was giving instruction on forced landings in an Ultralight.  Upon closing the throttle to simulate engine failure, his student panicked and pushed forward on the control stick locking his arms in that position until the point of impact.  My friend Nev. who was in the rear seat recovered after a long stay in hospital.  The point is, before you blindly follow step three, make sure that you are making the correct control input.  Failure to do this may result in you inadvertently re-applying rudder into the spin.  This also may have been a possible cause in the December fourteen accident.

Should you have no visual outside reference, the Turn Coordinator will always indicate the correct direction of yaw [from the pilots point of view] even if you are inverted, allowing the correct recovery rudder to be applied.  If the needle is hard left, apply opposite “right” rudder.  Remember, rudder must always be applied opposite to yaw.  Do not pay any attention to the ball as this only indicates slip, not yaw, and may vary either way depending on the centre of rotation and type of spin that you are in.  ie. incipient, un-stable, stable, flat, etc.  One slight problem here, many aerobatic aircraft are not fitted with a turn and slip indicator.

During my early flying career I posed the question, to Bill Cooper, who had taught me to fly and do basic aerobatics in a Victa Airtourer.  Bill how does one quickly determine the correct direction of yaw when in a spin?.  His response was, that if confused, “apply rudder in one direction, and that if this did not work, to then try the other rudder”.  Not to be out done I then asked, “what if we have just popped out of cloud and were in a spin at 1500 ft. AGL. and probably inverted?” - not much time to try rudder in one direction and if that did not work to then try the other rudder. His answer was to “look at the Turn coordinator”.  All right Bill, we have just got the S2A going and it is not fitted with a turn coordinator.  What are we going to use?.  This had prompted me to work out the technique of looking out over the nose. 

Every pilot should sit down and spend the time visualizing  what you can expect to see and how to interpret these visual clues.

Question:  what is the difference between a “Turn Coordinator” and a “Turn And Balance”,[“Turn And Bank” to some people]? 

Advanced Spinning 

As you can see this is a very long and involved subject. Most Aerobatic pilots know that a stable spin can be flattened out by two main methods. 

Power and aileron.
The application of power in an a/c with the propeller rotating clockwise [as seen from the pilots point of view] when yawing [spinning]to the left will cause the nose to rise.  The smaller and lighter the a/c, and the larger the power output, the greater the tendency. will be for the a/c nose to rise.  This is due to gyroscopic precision.  Because we are causing the yaw to the left by applying left rudder, the rotating force is being felt as a force acting forward at three o’clock position of the propeller arc and then processing around the propeller arc ninety degrees in the direction of rotation, resulting in a force acting forward at the six o’clock position, thus forcing the nose of the a/c to rise.  If the same a/c is rotating to the right the nose will be forced down by the application of power.  In a/c that have the propeller rotating in the opposite direction ie. anti-clockwise the tendency will be for the nose to rise when yawing [spinning] to the right, and to lower the nose when yawing [spinning]to the left.  Remember, During recovery from a spin make sure that the throttle is fully closed. 

Out-Spin Aileron
Let me tell the story and why I have so much respect for spins, and why thorough spin training by properly qualified instructors is essential.  After I had rebuilt VH KJG in 1978, there were no suitably experienced instructors to give me the necessary training that I required, so I obtained a copy of Neil Williams book “Aerobatics”.  After reading the appropriate chapter on spinning I proceeded solo to the training area and 6500 ft.  After placing the aircraft into a left spin, I applied outspin aileron and went flat as expected.  So far, so good, I thought. At 5000 ft. I tried to recover.  To my dismay, the spin got a lot, lot faster.  I went through the recovery procedure once or twice more [I am not sure of the exact number of times].

Step One:  ailerons neutral and close the throttle .  Step Two:  apply full opposite rudder.  Step Three:  stick forward.  By this time I was giving some serious thought to the prospect of having to jump.  I decided to give it one more try, and in doing so looked out and spotted the right aileron still deflected up very slightly, only about a 1/4 of an inch.  This prompted me to push the stick over to the left {use inspin aileron] and guess what happened?

Subsequently I worked out that:  I already knew the correct rudder application for recovery [due to the direction of rudder used for entry].  I was very hasty when lowering the nose [I had worked out that I was going to need forward stick to recover before leaving the ground] and probably shielded the rudder and “unloaded” during the recovery.  This caused the rate of yaw to increase dramatically.  I did not centralize the ailerons fully for the recovery phase. [although I had not thought about using in-spin aileron to assist during the recovery prior to going up, I was able to do so at the time].

The recovery altitude was approx. 2000 ft. on Q.N.H. and only about 1000 ft. Agl.  I do not like my chances had I decided to jump.  The use of in-spin aileron to assist during the recovery is recommended in the book Flight Unlimited by Eric Muller.  This is a good technique in most a/c.  Neil Williams recommends ailerons neutral in his book.

Let’s look at the physics involved in using out-spin aileron during a stall/spin.  If an a/c is at the point of a wings level stall and the pilot perceives a roll to the left, and tries to oppose the roll by applying right aileron it is likely that the roll to the left will accelerate uncontrollably.  This is due to the left aileron deflecting down as the stick is moved to the right, thus increasing the Angle of Attack well beyond the already near critical angle, thus increasing the drag and reducing lift.  At the same time the right aileron is deflecting up thus maintaining lift and reducing drag.  Auto-rotation or an uncontrolled roll followed by yaw to the left is the end result.

The use of out-spin aileron during a spin has a similar affect, thus increasing the drag on the into-spin wing and reducing the drag on the other wing [the forward moving wing], causing the rate of rotation to increase dramatically.  This is why the ailerons should be neutralized during the recovery from a spin, and why all pilots are taught not to use any aileron during stall training to avoid an un-intentional spin.

While Eric Muller recommends the use of in-spin aileron as part of a normal spin recovery,. in some a/c it may have an adverse affect.  The use of inspin aileron in a Cessna 150/152 Aerobat has the opposite affect to what you would expect.  Inspin aileron causes the spin to go flat.

This is the result of the very effective Frieze Ailerons that are fitted to the Cessna wing creating a lot more drag on the aileron that is deflected up.[inside aileron with inspin aileron applied]

In the Cessna 150/152 outspin aileron will cause the spin to stop. The reverse airflow through the propeller will cause the motor to stop rotating, just to add a bit of extra excitement and to further raise your heart rate.

In the unlikely event that you find yourself spinning inverted in the Cessna it is likely that the use of out-spin aileron will have the normal affect of flattening the spin while in-spin aileron will help during the recovery.  This is due to the frieze aileron being in-effective when spinning inverted, as the hinge point of the ailerons is on the top surface of the Cessna wing, a smooth surface is maintained when the wing is inverted regardless of aileron deflection, and A of A should come back into play. Due to a lack of an inverted oil system in the Cessna 150A/152A I have being unable to flight test the above theory inverted, although the use of in-spin aileron to flatten the upright spin has being tested over a number of years and a countless number of spins. 

A word of warning to anyone contemplating flat spinning the Cessna 150A/152A.  A positive hands on spin recovery will be required.  Allow several rotations for the recovery  to be effective.  Also allow for an air restart as the motor will probably have stopped rotating.  About 6000 feet plus minimum starting altitude.

Question.  During inverted spinning, what constitutes “Out Spin Aileron”?
As previously stated the physics remain the same to an outside observer.  To initiate an inverted spin to the left we can stall the a/c inverted and apply right rudder.  This causes the left wing to move forward.  As we are inverted the left wing is already on the right hand side as seen by an outside observer, thus the a/c enters a spin to the left.  The pilot is still holding forward stick and right rudder with the a/c spinning to the left [rolling and yawing to the left]. To apply outspin aileron the pilot would attempt to roll the a/c to the right. That is, apply aileron in the same direction as the rudder being used to initiate the spin. Left aileron applied while holding the a/c in an inverted spin to the left with right rudder and forward stick would qualify as In Spin Aileron. If you are a bit confused, use the analogy that Neil Williams did of a pilot sitting on the belly of an inverted a/c and flying it with an extended control stick.  Simply stated, if you are spinning inverted to the left, using right rudder, then right stick is out spin aileron. During recovery, stick in the same direction as the recovery rudder, is in-spin aileron.  Can you see why it is so important to work out the correct rudder application. 

Unloading is a term used to describe a method of reducing drag and increasing the rate of rotation during spins and snap rolls.  All a pilot has to do is to unload is move the stick towards the neutral or central position rather than holding full forward or full back stick once a spin or snap roll is underway.  As both of these manoeuvres require the angle of attack to remain over critical too much unloading will un-stall the a/c thus stopping the manoeuvre.

 To summarize:

Situation awareness is critical when undertaking spin training.
The sky above is as useless as the runway behind.
The standard spin recovery is:
·        Close the throttle and ailerons neutral.
·        Identify the direction of yaw and apply full opposite rudder. Sufficient time must be allowed for the rudder to take affect.
·        Lower the nose. Progressively move the stick from aft, to full forward, when spinning upright, or from forward, to full aft, when spinning inverted. Do not rush lowering the nose, and expect a fully developed spin to take up to three or four rotations to stop spinning.
·        When the rotation stops, neutralize the controls, roll to wings level, and then ease out of the dive.
If the spin continues, go to your backup plan. ie. apply inspin aileron/outspin aileron as appropriate to your type of a/c.
Before embarking on your spin training lesson you should review your spin awareness checklist, including emergencies.