Avoiding the StallSpin Accident

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Avoiding the Stall/Spin Accident

• GLIDING FEDERATION OF AUSTRALIA

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Introduction

• The stall/spin accident has been with us since
  the days of the Wright brothers.
• In the early days, the terrifying "tailspin" was
  shrouded in mystery thus a high frequency of
  this type of accident was understandable.
• Today, even though the spin is well understood,
  we are still plagued with stall/spin accidents.

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Introduction

• However, if today's breed of pilot understands
  the spin, why do we still have so many stall/spin
  accidents?
• Perhaps the answer lies in stall/spin awareness
  and training - or rather the lack of it.

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Introduction

• The purpose of this lecture is threefold
• Alert pilots to the stall/spin hazard and the
  in-flight situations which lead to stalls and
  spins
• Explain the dynamics of the spin and spin
  recovery and
• Teach the most effective method of spin
  prevention-stall awareness.

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What is a Spin?

• A spin is a manoeuvre during which the glider
  descends rapidly in a helical movement about a
  vertical axis - the Spin Axis.

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What is a Spin?

• In some ways the spin resembles a spiral dive
  but there's a fundamental difference.

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What is a Spin?

• Throughout a spiral dive manoeuvre you have the
  glider under full aerodynamic control you can
  fly out at any time.

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What is a Spin?

• In a spin, the aerodynamic and inertial forces
  are in balance - which you have to upset in order
  to regain control.

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What is a Spin?

• If you have sufficient altitude at the start of
  the spin, fine! But if not... you may become a
  statistic!

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What Causes a Spin?

• A spin is caused by two primary factors
• the glider at or beyond the stall angle of
  attack and
• sideslip or yaw acting on the glider at or beyond
  the actual stall point.

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The Phases of a Spin

• A spin is divided into two phases-
• incipient and steady state.
• steady state or fully developed spin.

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The Incipient Spin

• The incipient phase is that portion after stall
  when the glider commences a spin-like motion.

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The Incipient Spin

• In this phase, the aerodynamic and the inertial
  forces have not achieved a balance.

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The Fully Developed Spin

• In the fully developed spin, the aerodynamic and
  the inertial forces are in balance.

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The Fully Developed Spin

• Attitude, angles and motions are repetitive from
  turn to turn.

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The Fully Developed Spin

• In a spin, the view looking out of the cockpit is
  generally a steep, nose-down attitude, with a
  yawing/rolling motion about the spin axis.

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The Fully Developed Spin

• The airspeed is near stall airspeed.

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The Fully Developed Spin

• The turn needle is fully deflected in the
  direction of the spin.

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The Fully Developed Spin

• The rate of descent is significant.

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The Fully Developed Spin

• The "g" force acting on a spinning glider is
  essentially One.

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The Fully Developed Spin

• The spin is a recoverable manoeuvre in gliders
  approved for spinning.

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The Fully Developed Spin

• Recovery does require altitude.

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The Fully Developed Spin
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The Fully Developed Spin
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Terminology

• Gravity, lift, thrust and drag are terms that are
  familiar to you.
• You also know the three axes of flight roll,
  pitch and yaw.
• To understand a spin, there are some other terms
  that you should be familiar with

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Relative airflow

• The speed and direction of the air that is
  approaching the glider.
• The velocity of the relative airflow and the
  airspeed of the glider are equal and opposite to
  each other.

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Angle of attack

• The angle formed by the relative airflow and the
  chord-line of the airfoil.

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Adverse yaw

• If you are near stall angle of attack and a wing
  drops, and you attempt to raise it by applying
  aileron alone, the aileron going down will
  increase the lift on the wing.

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Adverse yaw

• This increased lift increases the induced drag
  causing a yaw toward the down wing - this is
  adverse yaw.

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Adverse yaw

• The down wing, with an increase in total drag,
  becomes more stalled, producing even more roll
  and contributing to autorotation.

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Adverse yaw

• To prevent autorotation you must eliminate any
  slipping or turning input at the point of stall.
  Co-ordination of aileron and rudder is the key.

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When Are Spins Likely?

• Stall/spin is obviously more threatening under
  certain conditions such as low altitude.

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When Are Spins Likely?

• Potential stall/spin situations are part of
  virtually every flight you make.

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When Are Spins Likely?

• During your pre-flight inspection, ensure that
  the cockpit loading does not cause the centre of
  gravity limits to be exceeded.

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When Are Spins Likely?

• With insufficient ballast the C.G. will move aft
  of its proper location and you'll find that a
  steep climb may produce a departure stall.

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When Are Spins Likely?

• Even at altitude, an aft C.G. loading may result
  in your not having enough forward stick available
  to lower the angle of attack sufficiently to
  ensure stall/spin recovery.

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When Are Spins Likely?

• The solution, plan ahead-don't get trapped. If
  you find yourself in a potential spin situation
  and recognise it - lower the nose and regain
  speed!

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The Launch

• Takeoffs have stall/spin potential.
• Just after leaving the ground and during the
  initial climb, a launch failure can be
  disturbing.

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The Launch

• Your instinct is to try to turn back. But if you
  do, you may well set up a stall/spin entry.
• If this occurs at low height recovery may be
  impossible.

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The Launch

• The solution is to lower the nose immediately to
  attain your safe speed near the ground, thereby
  preventing a stall or loss of control.

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The Launch

• It's always better to make an unscheduled
  outlanding under control than to stall, spin and
  crash out of control.

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Landings

• When landing you may encounter a crosswind that
  makes you overshoot the turn onto final.
• If you use excessive rudder pressure to turn the
  glider onto final whilst holding off bank, a
  slight increase in back elevator pressure may
  cause a stall.

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Landings

• The solution, plan ahead - don't get trapped.
• If you find yourself in such a situation and
  recognise it - lower the nose and regain speed!

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Landings

• If you are undershooting on final approach you
  may instinctively want to apply back pressure-try
  to hold the glider in the air.
• The safe thing is to maintain your approach speed
  closely (at least 1.5Vs) as you look for a
  possible touchdown spot.

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Landings

• Flying in the circuit or on short final, at 400
  to 500 feet above the surface, is no place to
  enter a spin that requires 400 or so feet for
  recovery after you apply control forces.

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Spin Recovery

• There are four classic steps for recovering from
  a spin.
• Apply rudder opposite to the direction of the
  spin.
• Neutralise the ailerons.
• As the rotation begins to stop, ease the elevator
  control forward to reduce the angle of attack and
  break the stall.
• As rotation stops, centralise the rudder and
  recover from the ensuing dive in the normal
  manner.

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Spin Recovery

• The best way to learn about a spin and spin
  recovery is by practice.

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Stall Awareness

• The most effective spin prevention is stall
  awareness.
• To be specific there are five cues that can warn
  you of an impending stall.

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Stall Awareness

• Vision is one. But its usefulness is limited to
  watching for a change of attitude.

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Stall Awareness

• Hearing can give you another cue. The sounds
  related to flight will increase as your speed
  increases, as you know. But if a stall is
  impending, the sounds lessen.

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Stall Awareness

• The third sign is Kinesthesis - muscle sense -
  the response of your body to the glider's changes
  of direction and speed. You can feel it. If you
  haven't already done so, you can develop the
  ability.

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Stall Awareness

• The fourth cue is the feeling of control
  pressures. As speed is reduced, control
  resistance to pressure becomes less and less.
  You can move the controls farther and farther
  without a corresponding change in glider
  attitude. Also, onset of airframe buffet may
  indicate the approach of a stall.

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Stall Awareness

• Last, but not least! Your flight instruments.
  The airspeed indicator warns you of impending
  stall, and indicates the actual stall.

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Stall Awareness - Summary

• Your sight, hearing and feeling are the means by
  which stall awareness enables you to sense an
  impending stall.

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Stall Awareness - Summary

• You can lose your awareness very quickly if your
  attention is lessened or lost by distraction -
  the major cause of inadvertent stalls.

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Stall Awareness - Summary

• Anything that takes your attention away from your
  number one responsibility, FLYING THE GLIDER, may
  lead to a stall.

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How do you prevent distraction?

• Develop a good scan pattern. You must keep your
  attention moving back and forth between flying
  the glider, the instruments and outside
  references.

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How do you prevent distraction?

• Remember the cardinal rule of flying
• Aviate (i.e., fly the aeroplane)
• Navigate and
• Communicate.

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How to handle the stall

• The first step is to positively reduce the angle
  of attack - generally by lowering the nose

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How to handle the stall

• The second step is to regain flying speed and

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How to handle the stall

• Third, co-ordinate your controls to regain full
  aerodynamic control of the glider.

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Know your glider

• At height, practice flying at minimum
  controllable airspeed and find out about-
• Your gliders attitude versus airspeed produced
• The trim required
• The effectiveness of controls and
• The effects of flap extension and retraction (if
  fitted).

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Know your glider

• Practice at minimum controllable airspeed will
  sharpen your stall avoidance ability.

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Summary

• You may not be able to avoid a stall/spin threat,
  but you should be able to avoid the condition by
  recognising it before it becomes a problem.

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Summary

• To increase your confidence, take some spin
  practice with an instructor in a glider that has
  been approved for intentional spinning.

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Summary

• Become proficient in flight at minimum
  controllable airspeed and re-acquaint yourself
  with how your glider reacts in stall recovery.

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Summary

• The key to the stall/spin problem is Stall
  Awareness. Know the warning signs, respond to
  them and go ahead and do what you have to do.

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Summary

• Remember - no stall - no spin!

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A presentation by
Christopher Thorpe Chief Flying
Instructor Beaufort Gliding Club