Issued by Angus Pinkerton - Chairman of the Flying & Safety Committee 21November 2008.
All paraglider pilots, Instructors, Coaches and Safety Officers must READ, DIGEST AND TAKE ACTION onthe contents of this Notice and keep it for future reference.
If you hold a copy of the BHPA Technical Manual this notice must be inserted into it and retained until it iswithdrawn or superseded on instructions from the Chairman FSC.
PARAGLIDERS: 360 DEGREE TURNS AND
NOSE-DOWN SPIRAL DIVES
Following some recently reported incidents prompting further investigation, it has becomeapparent that it is possible for pilots to unintentionally enter a nose-down spiral dive from asustained 360 degree turn – and that recovery from this spiral can be difficult. Thesecharacteristics tend to be worse on the ‘safer’ low aspect ratio EN A, B, LTF (DHV) 1 and1 / 2 wings.
Once in a nose-down spiral dive extremely high ratesof descent – 14 to 27 m/s (approximately 30 to 60 mphstraight down) may be reached, along with forces of3g to 4g and airspeeds of up to 100km/h. Clearly anypilot inadvertently entering a nose-down spiral will findall of the above extremely disorientating. Whereas inmost situations a low aspect ratio wing (EN A, B, LTF(DHV) 1, 1 / 2 ) will ‘self-recover’ if the pilot lets up onthe controls, this is not the case in a nose-down spiral.
Reaching and activating an Emergency Parachutemay also be difficult whilst subject to high ‘g’ forces.
360 turn / Spiral dive mechanism:
If a 360 degree turn is continued for a revolution ortwo, without the airspeed and bank angle beingcontrolled, then the pilot will tend to swing out. Thesituation can then accelerate rapidly. The effectivepilot weight increases as centrifugal force increases,which increases the wing loading, which increases theairspeed, which increases the centrifugal force etc.
And as the pilot swings out, the pitch/roll/yaw axis ofthe paraglider tilts, with the result that the yawresulting from holding on inside brake now brings thenose further down, whilst the secondary effect (roll)keeps the glider rotating on the downward verticalcorkscrew path.
A 360 turn allowed to develop into a nosedown spiral
Instructors and Coaches should brief students and pilots in their care on the dangersoutlined above – especially if teaching 360’s, thermalling and ways of losing height beforecommencing a landing circuit. Students and pilots should be briefed when 360ing that 30degrees of bank angle is more than sufficient. The correct technique for normal 360ing is
to establish the turn using inside brake and weightshift and then, keeping these constant,to control the turn with outside brake so that a steady bank angle, airspeed and rate of turnis maintained. Initial 360s should be practised one at a time, then two at a time, and so on.
Normal angle of bank for 360 turns.
Pilots should avoid tight, high speed 360’s. 30 degrees of bank angle is more than enoughfor normal flight manoeuvres, including thermalling. The correct technique for a 360 turn isto establish the turn using inside brake and weightshift and then, keeping these constant,to control the turn with the outside brake so that a steady bank angle, airspeed and rate ofturn is maintained. Particularly when you are learning 360s, whilst maintaining a goodlookout, be aware of the horizon in the background and keep your inner wingtip at least 20degrees above it (20 degrees is the width of two fists held at arms stretch) – the straightahead view should be similar to that shown in the illustration. Use the controls asnecessary to maintain a steady bank angle and airspeed. Your first 360s should be carriedout one at a time, before linking them two at a time, and so on.
Emergency Actions: Getting out of a nose-down spiral dive
The key first step is to slow the glider by applying both brakes. Considerable
force may be required on the controls to do this – the brake pressure required
may be two, three or four times normal. As the glider slows the nose will come
up. Then it is important to keep the glider turning: completing another, wider,
circle in the initial direction (by raising the outside brake) is a good way of
dissipating the energy. Avoid exiting immediately to straight flight as you will have
considerable airspeed and energy, and this will result in a surging climb
followed by a dive which must be ‘damped’ out to prevent a possible collapse.
Nose-down spiral dives are a potentially dangerous manoeuvre and should be treated witha great deal of respect. They are however a valid emergency rapid descent technique forthose who are in current practice with their use – but recovery should always becompleted at least 300m (1000ft) above ground level. Pilots should seek skilled instructionbefore attempting this manoeuvre, on a course conducted in accordance with the BHPASIV Course Information Sheet.
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