Tips for beginners – low turn
Starting from the very first jumps, skydivers are taught that a low turn is one of the main causes of accidents in parachuting. When turning, the vertical speed increases, and when it leaves it, it becomes horizontal. You need to be very careful in managing the energy of the turn, in order to avoid a collision with the ground. It does not matter if the turn was due to improvisation or a pre-planned maneuver, if contact with the surface occurs before the dome returns to normal, it can lead to serious injury or death.
Accidents are the result of two low turns. In the first case, an unplanned maneuver is an attempt to get away from an obstacle or other threat, often less serious (for example, landing on the wind). In the second, the reversal is carried out purposefully. Acceleration horizontally before landing is, of course, “high” for many skydivers, but they should be very familiar with the procedure for making such turns, as well as with the consequences that can be caused by an error in the calculation. And even conservative in terms of low turnings, skydawers should imagine the order of their execution in order to avoid the consequences of panic actions.
The design of any parachute wing follows simple principles. The slings of group A are shorter than the slings of group D, with the result that the nose of the dome is lowered. The dome slides down like a sled from a mountain whose slope is determined by adjusting the length of the lines. Forward movement contributes to the flow of air around the dome. The profile of the wing is set in such a way that the air pressure above the dome is lower than below it. The pressure difference creates lift. It is this lifting force that slows the rate of decline of the parachute-wing. Lift force can also be created due to the downward air flow – we will discuss this effect when we talk about the angle of attack. The lifting force of both types depends on the square of the translational speed – when doubling the speed, the lifting force increases four times. At a speed equal to zero, the lift force is zero! The ability of the wing to produce lift force deteriorates when there is a disturbance in the flow above it, such as, for example, when a wing profile is deformed or when the smoothness of the flow changes suddenly.
Before continuing, we introduce the basic terms to discuss the characteristics of a parachute-wing. The instructions of the manufacturers of domes often use the concepts of “angle of attack” and “relative flow”. These terms are borrowed from aviation theory and are quite suitable for talking about aircraft. Domes, however, lack a source of thrust (engine) and tail. Many domes have more differences than similar features in comparison with traditional aircraft, so we will redefine these concepts as applied to domes.