Flight maneuvers and flight conditions (paraglider)
With a paraglider , various flight maneuvers and flight conditions can be flown through the use of the control lines ( brakes ), weight shift and the accelerator . In normal flight, a paraglider is flown with a slight brake so that the pilot receives feedback about the behavior of the paraglider via the control lines and, due to the increased angle of attack of the wing profile and higher internal pressure, becomes less sensitive to collapse in turbulent air currents.
Normal flight conditions
Minimum trip
The minimum travel characterizes the speed range in which the flow is just still present on the wing profile (approx. Point A in the graphic). Since changes in the angle of attack, for example when entering a thermal, can lead to a fall below the minimum speed and thus to a stall, this speed range is avoided during normal flights.
Slightest sinking
At the slightest sink (corresponds to point B in the graphic) the paraglider is braked so far that it loses the least amount of height per unit of time. This is achieved by gently braking the glider. The airspeed is slightly slower than the best glide.
Best glide
The longest distance is covered with the available height. Most modern glider models achieve the best gliding in the unbraked state. (Corresponds to point C in the graphic)
Accelerated flying
When accelerating, the angle of attack of the paraglider is reduced with the aid of the foot accelerator . This leads to a stepless increase in the flight speed ( True Air Speed ) of up to 25 km / h, but the glide angle deteriorates . This can be seen from the sharp drop in the velocity polar in the graphic.
In downwinds, the glide angle can be slightly improved by using the accelerator, because the area can be left more quickly with a stronger sink. In headwinds, the accelerator helps you to move forward better and to increase ground speed again. Undesirable side effect of the accelerated flight is a significant increase in the risk of Einklappungen the sail (for example by turbulence and / or thermal). The reactions of the paraglider to disturbances are also more extreme in accelerated flight than in non-accelerated flight.
Descent aids
Descent aids are flight maneuvers with the help of which you can reduce altitude very quickly in order to be able to land as quickly as possible or to clear a danger area e.g. B. to leave under a sucking cloud. This can be necessary when there are dangers - e.g. B. by an approaching thunderstorm - threaten. Mastering the descent aids is a prerequisite for safely flying the paraglider under thermal conditions.
A paraglider in normal flight typically loses 1 to 1.3 m height per second in calm air. This rate of descent can be increased significantly with the descent aids.
Big ears
Big ears is the easiest way to descend. The two outer ends of the umbrella are folded down by pulling the outer A-lines inwards. The advantage of big ears is that the paraglider flies straight ahead; you can thus leave a danger area. It can even be landed with big ears, for example to compensate for the updraft component during top landing. The "Big Ears" are a variant and are initiated by gripping the outer A-main lines or by pulling on 2 A-main lines. (Attention: both Big Ears methods should be flown e.g. as part of a safety training)
By reducing the wing area, the wing loading increases, the wing is more stable against collapsing in turbulence. However, the aerodynamic drag of the wing also increases, it flies more slowly and closer to the stall boundary . In order to counteract this and to increase the effectiveness of the sinking, the accelerator is usually also activated. Typical sink rates are 2.5 to 3.5 m / s, with accelerated big ears up to 4–6 m / s.
The big ears are initiated by pulling the outermost A-lines while the glider is not accelerated. The brake lines are held tight, the paraglider is controlled by shifting the pilot's weight. For most paragliders, it is sufficient to let go of the A-lines to take off; the ears pop open again, the glider goes into normal flight. If necessary, braking briefly on the respective wing side (pumps) can help with the diversion.
B stall
When B-stall is a stall provokes and the canopy drops vertically downward, with a typical rate of descent of 6-10 m / s. When viewed from the side, the paraglider takes on a typical V-shape.
The B-stall is initiated by symmetrically pulling down the risers on the B-level (second risers from the front). Avoid turning the canopy too much, as otherwise there is a risk of the pilot twisting it. The maneuver is ended by quickly releasing the B-risers so that the paraglider can pick up speed again. If the recovery is too slow, the glider can go into deep stall.
This maneuver is becoming increasingly less important, as it can only be used with the currently dominant three-line vehicles with considerable effort and high material loads.
Spiral dive
The spiral dive is the most effective descent aid with sink rates of 7 m / s for a moderately flown spiral dive and up to 25 m / s for aggressive flying. The course of the flight path resembles the shape of a corkscrew.
However, an aggressively flown spiral dive also means significant physical strain due to increasing g-forces . The reason lies in the pendulum system of the paraglider and the pilot: Due to the rapid turning movement (curve), the pilot, who hangs on the lines and risers about five to seven meters below the paraglider, commutes to the outside of the curve due to centrifugal force . It moves on the outer circular path at a speed of up to 70 km / h and more. From a certain rate of descent in the spiral dive, the glider falls on its nose , i.e. H. the entire front of the wing points downwards, the wing literally flies towards the ground.
The spiral dive is initiated by a turn that is flown ever tighter and the pilot clearly shifts his weight to the inside of the turn. This maneuvering maneuver is performed by braking on the outside of the curve and shifting weight to the outside of the curve. The inner brake should only be released in a controlled manner when exiting the spiral, in order to prevent the glider from accelerating further in the spiral. The glider converts excess travel energy into climbing for a short time after it has been released, while the pilot shuttles forward in the direction of flight. To reduce this, the spiral dive should be carried out slowly over several turns. Briefly braking on the inside of the curve also helps shortly before the end of the diversion.
Full stall (stall)
A full stall is no longer a common descent aid today. In the early years of paragliding , however, the full stall was definitely practiced. Nowadays, the full stall is only flown deliberately by experienced pilots in order to solve rope tangles (e.g. after a collapse). The reasons for this are, on the one hand, that the B-stall is preferred, and on the other hand, the higher dynamics of today's umbrellas. With a full stall, there is a risk that the glider will pick up speed again when the stall is closed with such force that the canopy will overtake the pilot forwards and the pilot will fall into his own paraglider.
This flight maneuver is initiated by consistent braking on both sides. The wing loses speed until the flow breaks off at the profile and the canopy empties. The pilot oscillates forward due to his inertia. He has the feeling that he is tipping backwards.
Held rattle
A rattle is provoked and held. The folded side leads to a higher air resistance and a turning movement to this side. The advantage is the lower physical stress than with a steep spiral with high sink rates. This flight condition is provoked by quickly and vigorously tearing down one of the front risers. As a rule, letting go of the shoulder strap is sufficient for recovery; if necessary, as with big ears, the respective side must be braked briefly (pumping).
Disturbed flight conditions
Side folding
Side collapses are partial lateral collapses of the paraglider, caused by the migration of the stagnation point at the leading edge of the paraglider. A part of the canopy collapses due to negative angles of attack and folds downwards. The result is an increase in resistance on the folded side with a more or less pronounced tendency to turn in this direction. By reducing the lift surface associated with this flight condition, the paraglider tries to compensate for the loss of lift by increasing the flight speed. This can lead to the canopy shooting forward.
This unwanted flight condition can be caused by turbulent air currents, e.g. B. Downdrafts in the lee, on the edge of thermal beards, wind shear or wake vortices from other aircraft.
Front folding
Einklappungen of the central leading edge portion are also carried negative angle of attack caused. This can be done by e.g. B. turbulence or a rapid advance of the paraglider ("falling out" from a thermal beard or after a full stall).
Stall (full stall)
Complete or almost complete breakdown of the lift-generating circulation on the paraglider . The trigger is when the maximum possible angle of attack of the profile is exceeded . The most frequent cause is falling below the minimum speed of the paraglider or flying in this area, coupled with the effect of turbulence. The umbrella collapses and brakes. Since the pilot is normally in a forward movement, he oscillates forward and tips backwards on his back. The re-opening of the cap takes place under circumstances after pilot action and significant loss of altitude.
Deep stall
Stable flight condition of the wing without moving forward. The aircraft sags almost vertically. The flow towards the sail is vertical from below. Triggers can be: Brake lines that are set too tightly (without freewheeling), aged or damaged and thus more air-permeable sail, changed trim (line lengths), deterioration of the profile due to moisture or similar (flight through rain showers). To exit, the pilot operates the accelerator or pushes the A-lines forward.
Spin
The spin is a stable flight condition, in which a side of the glider is in the stall, while the other continues to generate buoyancy. The paraglider rotates around the torn side. Depending on the design of the glider, active intervention by the pilot is required to end the process. More good-natured models lead the spin u. U. after a certain loss of altitude, while others cannot be freed from the tailspin. The spin can also be triggered by an incorrectly flown spiral dive .
See also
Web links
- P @ r @ 2000 - overview of most current and historical paraglider wings, including speed polar (in French, English)
literature
- Otto Voigt: Aerodynamics and flight mechanics of the paraglider . 2nd edition, Books on Demand GmbH 2003, ISBN 3-0344-0192-2