SKY DYVING -a family holiday fun
Sky diving or 'free-fall parachuting' is an advanced form of parachuting. In normal parachuting, the parachute opens immediately after the exit from the aircraft, whereas in skydiving, the jumper may fall free for thousands of feet before opening his parachute. Sky diving is not just. falling; it is 'flying'-the closest man has been able to come to free, unencumbered, non-mechanical individual flight. It grew out of the air-show demonstrations in the 1930s and the parachute tactics employed in World War II. The activity is also called 'sport parachuting'. A world championship is held every two years.
A sky dive jump can be made from about 1,200 meters to 30,000 meters. The terminal speed is between 175 to 300 kmph of air in lower altitude, and as high as 1100 kmph in higher altitudes, where the density of air is less.
A sky diver behaves like an aircraft at this high speed relative air-flow, and can move left, right, or increase/ decrease his speed. The various competitions are based on this skill.
Jumpers wear a highly maneuverable main parachute and a reserve parachute on a single harness. So also a helmet, jumpsuit, boots, non-fogging plastic goggles, gloves, altimeter, and a stopwatch. The wing-like canopy of the parachute, based on ram-air principle has approximately 2 sq. metres of area. As the canopy moves forward and down, air enters the holes in the leading edge to inflate and pressurize the wing. For a 70 kg jumper, one can expect a forward speed of 35 kmph, and. a glide angle of 70°. The canopy can be turned in any desired direction, but the wind component adds or subtracts to the forward speed, depending on the canopy direction. The advantage of forward speed is utilized for military operations, wherein a skydiver dropped at higher altitudes can maneuver to a target area without being detected.
Competitive Sky Diving
Most of us do skydiving for fun and excitement. But those who compete in the world championships have to practice for accuracy to land on the target. The criteria used in judging competitive contests are:
- Accuracy in landing near a marked target, usually a disk at the centre of a large cross.
- Style in free fall.
- Group free-fall link-ups, called 'relative work'.
- Landing accuracy is rated by the distance in metres or yards, from the centre of the target, to the point where the parachutist first touches ground. New types of parachutes that can be steered, improved methods of wind measurements, and increased skills among parachutists have resulted in some notable records, based on the average distance from the target in two or more successive jumps.
Style in Free Fall
Style in free fall is the way the contestant holds his body from the time and how he leaves the aircraft, until he opens the parachute-involving various points. All events start with the body on a pre-selected heading during free fall. The contestant loses points for buffeting (longitudinal body rocking), fishtailing (horizontal swaying), or if his body falls on the side. He is disqualified if his back turns towards the earth (except in controlled loops) or if his fall is disordered.
Rate of Descent
A skilled parachutist can increase or decrease his rate, of descent while maintaining his stability. A combination of controlled forward speed, controlled turns, and variable descent rate has enabled several sky divers to even pass a baton from one to another during a free fall. In relative work, 20 or more experts have met and linked hands in a circle, before separating in order to deploy their parachutes at a safe altitude of 762 metres.
Principles of Controlled Free Fall
There are four principles for controlled free fall, which everyone must understand:
If the body presents a symmetrical and convex surface to the air flow, it would achieve a position of balance or 'stability' as it falls. Preferably, the position should be face down, with arms and legs spread for that altitude, providing both a comforting view of the approaching earth, and a good launching platform for a back-mounted parachute.
A controlled deviation from that symmetrical altitude-such as the bending of one lower leg, or the dipping of a shoulder, or reaching forward with both arms, or even an angling of the palms of the hands-would initiate movement. Lateral turns, somersaults, barrel rolls, and the changes of basic position are all possible through this controlled loss of stability, and the re-distribution of the air pressure acting against the body surface.
By reducing the area of the body surface presented to the airflow-as in a head-down dive-the vertical speed would get increased.
By inclining the body surface at an angle to the vertical air flow, an element of horizontal 'thrust' could be added to the inevitable downward fall.
Free fallers thus can achieve stability: full control of body, altitude, limited control of vertical speed, limited control of horizontal direction. Mari in the mid 1950s began to fly.
Group free-fall link-ups is what is termed as 'relative work'. The new-found ability to stabilize the body in-flight, and then to exercise some degree of control over the speed and direction of fall inevitably lead skydivers to maneuver their bodies, in relation to each other. The early goal of this 'relative' free fall was for two jumpers to guide themselves to a mid-air meeting, whilst hurtling earthwards at a speed of 190 kmph. Baton passing became a craze amongst the skydivers. The Californian divers then started making a star in the sky-with six, then eight and then 10 men. Soon world championships started in making the 10-men star; 17.3 secs. was the fastest record in 1973 World Championships.
By 1976, 'sequential relative work', started by four and eight men, in forming first a pattern (say, a diamond) before opening their parachutes. And today with newer and newer types of parachutes coming in the market, accuracy in spot landing has increased. And in relative work, a 99-man star, a 124-man star and a 136-man sequence have quite easily been formed by international sky divers.
Skydiving was a demonstration sport in the Seoul Olympic Games, and is being given a full-fledged discipline in Olympics of the future.