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Speed skydiving is a skydiving competition, sanctioned by the International Speed Skydiving Association, in which the goal is to achieve and maintain the highest possible terminal velocity. It was developed in the mid 2000s and is the fastest non-motorized sport on Earth. The speed, achieved by the human body in free fall, is a function of several factors; including the body's mass, orientation, and skin area and texture. In stable, belly-to-earth position, terminal velocity is about 200 km/h (120 mph). Stable freefall head down position has a terminal speed of 240–290 km/h (around 150–180 mph). Further minimization of drag by streamlining the body allows for speeds in the vicinity of 480 km/h (300 mph).
Participants compete for the best Meet Result and attempt to set World Records. A Meet Result is made up of 3 jumps from “regular” skydiving altitude : 4,000 meters (13,124 ft). Meet Results and World Records can only be set during a sanctioned ISSA competition.
The terminal velocity of a falling body occurs during free fall when the force due to gravity is exactly balanced by the force due to air resistance, such that the body experiences zero acceleration. The formula for terminal velocity (where buoyancy in air is negligible) is given by the thrust
- m is the mass of the falling object
- g is the acceleration due to gravity (9.8 m/s2)
- Cd is the drag coefficient (~0.7 for head down position, ~1 for belly-to-earth position)
- ρ is the density of the fluid through which the object is falling (1,23 kg/m3 for air at sea level, and ~0.99 kg/m3 at the middle of the measurement zone (2200m))
- A is the projected area of the object, or area cross-section (~0.18 m2 for head down position, ~0.7 for belly-to-earth position)
So, for a human in belly-to-earth position (A = 0.7 m2, m = 90 kg, Cd = 1) this gives 50.6 m/s, about the terminal velocity of the typical skydiver of 55 m/s.
The skydiver cannot increase their mass easily enough to significantly increase terminal velocity, and the skydiver's area cross-section is limited by their helmet and shoulders in a head-down dive position. The most significant difference comes from the skydiver reducing their coefficient of friction. The head-down body position has to be carefully managed to be as streamlined as possible, while special helmets and slick body suits reduce skin friction, which is a function of surface area and texture. The shape and rigidity of the suits also have to be designed to minimize the coefficient of drag. Finally, a skydiver must reach their maximum speed at as high an altitude as possible so that the density of air is at a minimum.
The International Speed Skydiving Association rules have altered over the years to accommodate the changes necessary. Some Speed Skydiving jargon involved is:
The Measurement Zone: A vertical kilometer where speed measurements are taken. It starts at 2,700 m and ends at 1,700 m above the ground
The Speed Measuring Device: Measurements are made by two free fall computers (Pro-Tracks) placed on the lateral webbing or in a line from it on the competitors rig.
Speed Measurement: Speed is averaged over the measurement zone using two Pro-Tracks.
Qualification Jump: Minimum qualification speed for men is 300 km/h and 250 km/h for women. The result is not used in the competition itself.
Qualified Competitor: One who has met or exceeded the speed requirements, or who has previously participated in a competition qualifies to compete.
Qualified Meet: No special conditions.
Out of Boundaries(OB): When the speed difference between 2 Pro-Tracks is greater than 30 km/h
Qualified Jump: Exit altitude is about 4,000 meters.
Meet Result: The average of the best competition jumps, depending on the number of rounds completed
The competition is held over a course of 3–4 days. Every competition consists of 6 individual rounds. The best 3 rounds are considered for the meet result (average speed). Out of bounds runs will result in a zero and there is no limitation to how many OBs a competitor can have, although they will affect the average result.
The judges in speed skydiving competitions are the speed measuring devices, although the ISSA race commission will check each competitor to ensure that their gear is acceptable. Anything found dangerous is prohibited, as are the use of weights. The Race Commission is elected before every meet and is composed of a representative of every country competing. Their job is to ensure that both the competition and competitors follow the rules. They have no authority to change the rules, and refer to the FAI/PC Sporting Code. There is also a download team responsible for measuring the device handling, data download, and documentation of the use of the devices.
Weather can have an extraordinary effect on a competition as well as individual divers. In the event of bad weather or air traffic circumstances, the exit altitude is lowered. In addition, thick cloud conditions may cause a delay in the jump time altogether.
- While none of these matter in free fall in the absence of friction by Newton's Laws, they are significant when dealing with air resistance.
- ISSA: ‘’What is...’’, page 1. International Speed Skydiving Association, 2010.
- OpenStax College (Feb 19, 2014). "Drag Forces" (PDF).
- "Standard Atmosphere Calculator".
- Elert, G: ‘’Speed of a Skydiver (Terminal Velocity’’, page1-9. The Physics Factbook, 2009.
- ISSA: ‘’ISSA Speed Skydiving Rules 2010’’, page 1-4. ISSA, 2010.