avoiding the stall_spin accident
TRANSCRIPT
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Avoiding the Stall/SpinAccident
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" wasshrouded 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 isthreefold:
1. Alert pilots to the stall/spin hazard andthe in-flight situations which lead to stallsand spins;
2. Explain the dynamics of the spin and spin
recovery; and3. 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 gliderdescends 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 gliderunder 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! Butif not... you may
become a statistic!
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What Causes a Spin?
A spin is caused by two primary
factors:
1. the glider at or beyond the stall angle ofattack; and
2. 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:-
1. incipient and steady state.
2. 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 motionabout 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 familiarwith:
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Relative airflow
The speed and direction of the air thatis approaching the glider.
The velocity of the relative airflow andthe airspeed of the glider are equal andopposite 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 ailerongoing down will increase the lift on the
wing.
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Adverse yaw
This increased lift
increases the
induced dragcausing 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 andcontributing 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 ofaileron 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 beexceeded.
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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 adeparture 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 theangle 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 bedisturbing.
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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 astall 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 ofcontrol.
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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 backelevator 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 situationand 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 theglider 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 400or so feet for recovery after you apply
control forces.
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Spin Recovery
There are four classic steps for recoveringfrom a spin.1. Apply rudder opposite to the direction of the spin.
2. Neutralise the ailerons.
3. As the rotation begins to stop, ease the elevatorcontrol forward to reduce the angle of attack andbreak the stall.
4. As rotation stops, centralise the rudder andrecover from the ensuing dive in the normalmanner.
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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 thatcan 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 andspeed. 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 becomesless 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, andindicates 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 impendingstall.
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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 ofinadvertent 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 astall.
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How do you preventdistraction?
Develop a good scan pattern. You
must keep your attention moving back
and forth between flying the glider, theinstruments and outside references.
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How do you preventdistraction?
Remember the cardinal rule of flying:Aviate (i.e., fly the aeroplane);
Navigate; andCommunicate.
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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 minimumcontrollable airspeed and find out
about:-1. Your gliders attitude versus airspeed
produced;
2. The trim required;
3. The effectiveness of controls; and4. 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 itbefore 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 forintentional spinning.
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Summary
Become proficient in flight at minimum
controllable airspeed and re-acquaint
yourself with how your glider reacts install 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 dowhat you have to do.
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Summary
Remember: - no stall - no spin!
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A presentation by
Christopher ThorpeChristopher Thorpe
Chief Flying InstructorChief Flying Instructor
Beaufort Gliding ClubBeaufort Gliding Club