Principal Air - Flight Training / Charter in Canada

Principal Air - Flight Training / Charter in Canada, Learn to Fly


Unit D 30460 Liberator Ave. (Just past the Main Terminal)
Abbotsford International Airport
V2T 6H5
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Understanding the Spin

“ practice stalls and spins the ground only 
says “boo”; in the real thing it comes after you.

-Leighton Collins-

I remember all too well my first experience with a spin. We had been practicing slow flight and stalls when my instructor asked me to climb to 4000’ AGL. He took control of the aircraft and said, with a big smile, “I’m going to show you something.”

He abruptly pulled the nose up and jammed in full left rudder. The aircraft rolled up-side down; both doors popped open; the nose pointed straight down at the fields below. The world began to spin violently around; details in the fields below grew clearer in a big hurry.

He recovered from the manoeuvre and helped me close the doors. Turning to me he asked, “Are you OK?” “Not really,” I replied as I began to re-consider my decision to earn a pilot licence.

It may not have been the ideal manner in which to introduce a student pilot to the spin, but the experience certainly did leave a deep and lasting impression. I approached the spin manoeuvre with a less than enthusiastic attitude for some time.

Since then, I have taken some time to learn about the manoeuvre, to come to a better understanding of exactly what takes place during the event and to experience quite a number of spins in various aircraft.

If I understand how something works, what events will occur during a sequence and what positive steps I can take to rectify a problem, I find I am in a much better position to deal with it effectively.

In a paper presented at the NTSB General Aviation Accident Prevention Symposium, September 21-22, 2000, Rick Stowells writes, “In recent years, stall/spin accidents have accounted for roughly 12% of general aviation accidents but 25% of fatal accidents.”

The fact that one in four aviation fatalities is tied to the stall/spin is certainly an excellent argument for why spin training is included in pilot training in Canada.

Our friends south the line, in their wisdom, discontinued spin training in 1949 in favour of increased stall training and have hardly looked back since although a number of specialized schools do provide spin training for those interested in the manoeuvre. And, indeed, the number of stall/spin accidents reported in NTSB accident data since 1949 has decreased. 

While for many student pilots spin training is perhaps not a highlight of their training schedule, learning how to successfully and skilfully recognize the sequence of events leading up to the spin and how to prevent an inadvertent spin can save lives.

So, what exactly happens when we spin an aeroplane? 

We cause or allow an aeroplane to spin by allowing or inducing a stall aggravated by yaw. If an aeroplane is not allowed to stall it cannot spin. If it stalls without yaw movement, it cannot spin.

An aerodynamic stall results when a wing exceeds its critical angle of attack, regardless of airspeed or attitude. Normally, in training, we stall the aircraft at reduced airspeed at something approaching a normal flight attitude but airspeed and attitude are not the important factors. Angle of attack is.

If an aeroplane is stalled and at the same moment allowed or caused to yaw, the result is entry to an aerodynamic spin. Yaw may be induced in a variety of ways including improper use of rudder, incorrect use of ailerons, failing to compensate for engine torque, or from turbulence. Normally, in training, we intentionally and knowingly use rudder “incorrectly” to allow or produce the required yaw.  

Typically, unintentional spins occur during take-off or landing when rudder is not correctly applied to maintain coordinated flight or, during a climbing turn manoeuvre when the aircraft is allowed or caused to stall.

In level or descending flight, as the wings stall during a yawing movement, the outside wing, the wing opposite the direction of yaw, will be travelling through the air at a slightly faster speed with a slightly lower angel of attack than the inside wing. The inside wing stalls first and loses lift sooner than the outside wing. We experience this as a wing drop and learn during training that corrective steps must be taken quickly to prevent entering a spin.

In a climbing manoeuvre involving turn and thus yaw, the outside wing has a higher angle of attack and will stall first producing a spin in the opposite direction of the yawing movement. This is referred to as a departure stall as it typically occurs during the climb-out phase of flight—perhaps in an attempt to clear an obstacle, return to the aerodrome following an engine failure, or demonstrate our advanced piloting skills for the amazed onlookers on the ground. The departure stall/spin can be a very disorienting event, particularly if it comes as a surprise.

Initially, the rate of rotation about the normal axis, yaw, may be quite minimal, but it increases rapidly. This causes the inside wing, in the case of level or descending flight, or the outer wing, in the case of a climb, to become more deeply stalled. The aircraft drops its nose, increases its rate of yaw towards the more deeply stalled wing and begins to lose its forward momentum. Its flight path takes a more and more vertical trajectory increasing the angle of attack for both wings and the rate of yaw rotation.

This process—called autorotation—tends to be self sustaining: the faster the aeroplane rotates about its normal axis the greater the difference in lift produced by the wings. The aeroplane begins to rotate about its normal axis and assume a helical, vertical flight path causing the details of the ground below to become increasingly clear and the pilot to become increasingly interested.o:p>

At the moment of stall, as we remember from ground school, the centre of pressure—the point through which lift acts—after moving forward as we approach the critical angle of attack moves rapidly aft causing the nose of the aircraft to pitch downward, further increasing our vertical movement and providing momentum to increase our rate of rotation about the normal axis.

As the aeroplane assumes a more and more vertical flight path, both wings become deeply stalled: their angles of attack increase with the inside wing remaining more deeply stalled than its outside brother or sister increasing the tendency to autorotation.

In a light, training aeroplane, within something like 4 to 6 seconds, approximately the first two turns about the normal axis, the machine establishes itself in a fully developed spin. The attitude the aircraft assumes depends on a number of factors including the location of its centre of gravity. The farther forward the centre of gravity the more the aircraft will tend to assume a nose down attitude.  

An extreme aft centre of gravity may result in the aeroplane failing to put its nose down sufficiently to allow recovery from the spin. Kids, don’t try this at home. 

Once established in a fully developed spin, the nose has a tendency to pitch upward and the machine establishes a repeating pattern of yawing, rolling and pitching as it continues to turn about its normal axis and descend in a helical and vertical flight path. 

This fully developed stage of the spin is maintained by a balance between aerodynamic and inertial forces and movements and is, in its own way, a quite stable condition. 

The aeroplane continues to yaw about the normal axis as a result of the differential lift produced by the wings: the outside wing is less stalled and produces more lift than the inside wing. The inside wing, having a higher angle of attack produces more drag, maintaining the autorotation tendency. The aircraft pitches nose up/nose down as a result of the aerodynamic and inertial forces produced by the yawing motion.  

Inertial pitching results from the changing rate of rotation about the normal axis. As the nose drops the rotation rate of the aircraft accelerates inducing an increased tendency for the nose to rise which, in turn, slows the rate of rotation resulting in the nose pitching downward. 

If you would like to experience this first hand on the ground try this trick suggested to my by one of my mentors, Bob: stand with your arms loosely at your sides. Begin to spin around, rotate about your “normal axis”. You will notice as your rate of rotation increases there is an increasing tendency for your arms to raise themselves—inertial pitch. As your arms rise, you will note increased difficulty in maintaining rate of rotation. The tendency is to slow down the rate of rotation which then results in your arms returning to your sides.

As the aircraft increases and decreases its rate of rotation through inertial force changes, the differential lift produced by the wings increases and decreases as well, resulting in a rhythmic rolling movement 

So, there we are in a stable condition of rhythmic movements involving pitch, roll and yaw as we descend in a helical and vertical flight path toward the ground below.

To recover from the spin, it is necessary to upset this stable and interesting condition.

Normally, we choose to achieve recovery through positive control inputs. Most training aircraft are designed to recover on their own if we simply release the pro-spin inputs: full rudder and full elevator. Positive recovery techniques simply accelerate the recovery process which is normally considered useful. It also allows the pilot to feel useful and needed and serves to boost his or her self confidence. As interesting as the spin manoeuvre is, we generally do not choose to prolong it any longer than necessary.

Consult your aircraft POH for the recommended technique for spin recovery. Of course, for intentional spins we would choose to use an aircraft that is both approved for spins and in the required condition of weight and balance.

For most training aircraft we can use the acronym PARE to remind us of the spin recovery procedure. P is for power; A is for aileron; R is for rudder; E is for elevator. If we have any flaps deployed on entry, we want to retract them immediately after diagnosing spin entry. Flaps reduce our nose down attitude flattening the spin and making recovery more difficult, and we may easily exceed Vfe on recovery. Having flaps deployed may result in structural damage to the machine.

To recover: flaps up; power idle; ailerons neutral; rudder initially full in the opposite direction to the spin then neutral as soon as autorotation stops; elevator reduce input as required to break the stall. We now find ourselves in a power-off dive and can easily recover the aircraft to a normal flight condition 

Spin training is interesting and, at times, quite focusing. If we understand what is happening and why and what we need to know and do about the situation, we can find ourselves much more comfortable about the whole process. The key knowledge and skill-set training is designed to give a pilot is recognition of the conditions and symptoms leading up to spin entry and the necessary techniques for preventing those conditions leading to the fully developed spin. If we can avoid ever experiencing inadvertent spin entry we will increase our opportunities to participate in flying for a much longer time to come. Enjoy