Is paragliding a dangerous sport?
Updated on June 23, 2001, then on July 12, 2007
Is ultralight flying a dangerous sport?
Jean-Pierre Petit
Former student of the National Superior School of Aeronautics in Paris.
...I can already picture fans of these sports reacting with alarm. One could indeed ask this question about any aerial sport, or any sport in general. It all depends on how it is practiced. Any reckless person could decide one fine day to cross the Mediterranean Sea in a drift boat or go rollerblading on a highway. The term "ultralight" encompasses what was formerly known as the "delta plane," hang gliding, powered hang gliding, and the ULM (motorized ultralight). These activities have one thing in common: they are subject to no regulation, unlike gliding, parachuting, or more generally, light aviation (&&& I wrote this in 2001. A reader will tell me if this situation has changed by 2007). No one can jump with a parachute they made themselves, nor practice this activity outside of duly accredited supervision (except when performing what is called "cliff jumping"). Still, accidents do happen in every sport. In gliding, the main danger is mid-air collision. That’s why all pilots and passengers are equipped with parachutes. These collisions can occur high in the sky when two gliders get too close while riding the same thermal current. Yet experienced pilots often prefer mountain flying. In "slope soaring," the glider flies close to terrain, taking advantage of lift created by wind blowing against a favorable slope. Another glider pilot might have had the same idea, at the same altitude but flying in the opposite direction. Gliders are white, and so is snow. It's not uncommon for two gliders to cross paths at 250 km/h, each spotting the other only at the last possible moment. Every year, people die in this game.
...In short, many sports are potentially dangerous. The key is knowing under what conditions they can be safely practiced, and understanding the limits of their safety margins. In the case of gliding, mountain slope soaring represents the highest risk. Those easily distracted should refrain.
...Parachuting can also result in serious injuries. Equipment has come a long way since the days when I made my first jumps at the end of the 1950s. It's still possible to have a bad opening (due to incorrect positioning or faulty folding). A quick clarification: in parachuting clubs, beginners fold their own parachutes, but the process is checked at two stages by an authorized inspector, who signs off on each jump related to each parachute. When parachutes reach the end of their useful life, they are reformatted and destroyed. They are not sold secondhand to just anyone (in ultralight flying, know that everything is sold without technical inspection &&& text written in 2001. But I assume this hasn't changed by 2007).
...When a parachute opens improperly, it’s called a "torch," with a descent speed of 25 m/s (50 m/s in free fall). A parachute in torch mode is a tangle of nylon fabric twisted in suspension lines, flailing above the parachutist without slowing their fall at all. In the past, one would then open their "ventral" parachute. The manual advised throwing it "as far away as possible" so it wouldn’t immediately tangle with the main parachute still in torch mode. Today, a handle system allows two actions: first, the malfunctioning parachute is jettisoned, then a smaller reserve parachute is deployed.
...Today, parachutes—once a luxury that didn’t exist before—are equipped with an automatic opening system that triggers at a certain barometric pressure threshold (i.e., at a minimum altitude) in case of distress. We’ve also increased the opening altitude from 600 to 800 meters. The era of death-defying low openings, the champions of low-altitude deployment, is over.
...There remains, for those who seek it, cliff jumping—away from prying eyes. But free fall itself is already a sport quite "hair-raising" enough. To add such danger deliberately, one must truly enjoy flirting with death.
Preliminary question: How do you manage to fly?
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Why and how do airplanes fly?
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...On one of the two CDs I distribute, you can find a comic strip, "L'Aspirisouffle", entirely dedicated to this subject. It explains in particular why an airplane wing, whose function is to push air downward, simultaneously experiences both drag and a nose-down pitching moment.
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The nose-down pitching moment of an airplane wing.
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...That’s why airplanes have tailplanes. These are set at a negative angle, counteracting the nose-down pitching moment caused by the wing, with the fuselage acting as a lever arm:
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The restoring moment from the tailplane balances the nose-down pitching moment of the airplane wing.
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...This system gives the airplane longitudinal stability. Indeed, if a disturbance changes its attitude by increasing the angle of attack, as shown below, the restoring moment from the tailplane will automatically bring the airplane back "into its flight lines."
How the tailplane counteracts an accidental nose-up pitch
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...We see that in the diagram above, the tailplane has become lifting, thus tending to make the airplane dive and return it to its original flight attitude.
...For this new, nose-up attitude to be stable (modulo an increase in engine power), the pilot would have had to "pull back on the stick" to recreate a nose-up moment via the tailplane, counteracting the nose-down moment from the wing.
Stabilized attitude of an airplane in a nose-up position
(stick pulled back, tailplane elevated upward)
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...If, starting from the initial stable flight configuration, a disturbance had "lowered the airplane’s nose," as shown here:
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Action of the tailplane to return an airplane to its flight lines after a dive caused by a gust.
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...the tailplane would automatically correct the aircraft’s attitude. Thus, we see how the tailplane tends to ensure the airplane’s aerodynamic stability, regardless of mass distribution.
...The lift force on the wing acts at a specific point called the center of pressure, located roughly at 25% of the wing’s chord:
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Position of the "center of pressure" of an airplane wing.
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...It is therefore recommended to place the airplane’s center of gravity at the wing’s center of pressure. This is how commercial airliners fly, in principle. ...But note that in this case, the horizontal stabilizer is negative-lift, maintaining the airplane in level flight at the cost of negative lift.
...When computer-assisted flight control appeared on French Airbus aircraft, fuel economy was sought by countering the wing’s nose-down pitching moment not with a counter-torque from the tailplane, but by shifting the airplane’s center of gravity (by moving a certain amount of fuel toward the rear). This results schematically in the following:
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Computer-piloted airliner (Airbus)
Horizontal stabilizer generating negative lift.
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...In this configuration, created during cruise at high altitude, the aircraft becomes harder to handle. Fuel is shifted toward the rear to facilitate the counter...