Under the dome “pilot”
Many skydivers believe that the angle of attack is equal to the angle at which the dome is located to the horizon. This is not true! The angle of attack is the angle between the plane of the wing chord and the direction of relative flow. The angle of attack is changed by turning the wing relative to the relative flow. The aircraft is using tail. Since there is no such thing on the dome, the only way to change the angle of its attack is to operate the control lines. When simultaneously pulling up both control lines, the pilot-suspended skider slides forward, as on a swing, towards the dome, because the larger dome in frontal projection creates more resistance and slows down when braking faster than the relatively smaller skydiver. As a result, the angle of attack for a while slightly increases, which gives rise to greater lift. With sufficient horizontal speed, the time during which this additional lifting force is produced can be quite long.
Note that in the above case, an increase in the angle of attack is achieved primarily due to the actual change in the relative flux with which the dome interacts as the parachutist moves forward – a complete analogy with what happens when you return from yourself a hang glider control knob. A change in the wing profile, which occurs as a result of working with brake keys, has an additional effect, but the first factor has a decisive role: if there is no forward weight shift of the skydiver, the angle of attack changes only slightly, and no additional lift is created – as is the case, for example with precision approach on the stagnant dome. With a well-made “cushion”, slow brake input leads to a gradual slowing down of the dome, while the parachutist constantly remains slightly biased towards the neutral position under the dome, which allows an increase in the angle of attack. As soon as all the energy given by the horizontal velocity is selected, the pilot, like a pendulum, moves back to the neutral position. Since the entire stock of translational speed is selected, the lifting force cannot be created, and a quick set of vertical speed begins until the dome accelerates horizontally or encounters the ground.
Now consider the angle cabrirovaniya dome, which is often confused with the angle of attack. This is the angle of tailing, which is set by mutual adjustment of the length of the lines. The pilot of the dome can also change it in flight, pulling the front or rear free ends of the harness. Pulling up the front free ends alters this cabling angle, but not the angle of attack. With a larger negative angle of tailing, the dome will pick up a greater vertical speed, but the direction of the relative flow remains practically unchanged, with the exception of the moments of the beginning of this maneuver and the exit from it. For most domes, the adjustment of the sling sets a cornering angle at which the dome moves forward by 3 meters as it descends one meter – the aerodynamic quality of the dome is said to be 3: 1. A smaller negative angle will improve aerodynamic quality and will cover a greater horizontal distance, but the price for this is a lower pressure inside the dome, which makes the profile of such a wing less stable during turbulence. In turn, a larger negative angle increases the speed of descent and the “pressurization” of the dome, but reduces the ability to plan, and sometimes leads to the loss of the “pillow”.