Avoiding the Stall_Spin Accident

8/14/2019 Avoiding the Stall_Spin Accident

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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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Attitude, angles and motions are

repetitive from turn to turn.


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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 airspeed is near stall airspeed.


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The turn needle is fully deflected in the

direction of the spin.


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The rate of descent is significant.


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The "g" force acting on a spinning glider

is essentially One.


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The spin is a recoverable manoeuvre in

gliders approved for spinning.


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Recovery does require altitude.


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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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Potential stall/spin situations are part of

virtually every flight you make.


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During your pre-flight inspection,

ensure that the cockpit loading does not

cause the centre of gravity limits to beexceeded.


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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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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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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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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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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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The second step is to regain flying

speed; and


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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

Documents

Avoiding the Stall_Spin Accident