🪂Skydiving Simulator - Terminal Velocity, Freefall Time, Opening Shock

How to use Skydiving Simulator (Terminal Velocity & Opening Shock)

1. 1Choose a scenario or body position and adjust total mass, body C_d·A, exit and deployment altitudes
2. 2Set the canopy inflation time and effective C_d·A, then press Play or drag the time slider
3. 3Read the results: top speed and Mach, time to 95% of terminal speed, freefall time, opening shock and landing speed
4. 4Open the comparison tab, change the altitude to see how thinner air speeds things up, or enter a custom object

FAQ

What is a skydiver’s terminal velocity, and how long does it take to reach?

Terminal velocity is where drag balances weight: v_t = √(2mg/(ρC_dA)). A skydiver of about 90 kg falls at roughly 55 m/s (about 200 km/h) belly-to-earth and over 80 m/s head-down. Because drag grows with the square of speed, the approach slows near v_t; near sea level it takes about 10 seconds and some 300+ metres to reach 95% of it. Thinner air higher up gives a larger terminal speed, so after a 4000 m exit the speed overshoots slightly and then eases off as the air thickens.

How did Felix Baumgartner go supersonic?

He stepped off at about 39 km, where air density is under 0.5% of sea level and the terminal speed exceeds 1000 m/s, so drag barely slowed him and the first 40-odd seconds were close to free fall. Around 50 s, at 27–28 km, he reached 1357.6 km/h (377 m/s, Mach 1.25). After that the air grew dense enough that drag exceeded weight and he decelerated, feeling more than 1 g. The preset reproduces the peak speed with a single effective drag area, but the real jumper spun and changed position, so the freefall time differs from the record.

How hard is the parachute opening shock?

During opening the drag area grows from about 0.5 m² to tens of square metres within a few seconds, cutting speed from over 50 m/s to about 5 m/s, a deceleration of several g. The tool models inflation as C_dA growing with the square of time; a normal sport canopy gives about 3–5 g for a second or two. A shorter inflation time or a faster deployment speed means a harder opening, which is why modern ram-air canopies use a slider to slow the inflation.

Are falling raindrops and hailstones dangerous?

Terminal velocity caps their speed. A 2 mm raindrop falls at about 6.5 m/s; large drops flatten, and measured speeds top out near 9 m/s. A 2 cm hailstone reaches about 20 m/s and a 5 cm one about 30 m/s, enough to crack windscreens. Cloud droplets are only tens of micrometres across, with Reynolds numbers far below 1, so they sit in the Stokes regime where drag is proportional to speed and they fall a centimetre or two per second, which is why clouds float. A cat’s light body and large area give a terminal speed of only about 100 km/h, one reason cats sometimes survive long falls.

Why use C_d(Re) for spheres instead of a fixed drag coefficient?

The drag coefficient depends on the Reynolds number Re = ρvd/μ. Below Re ≈ 1 the flow is viscous Stokes flow with C_d = 24/Re, so drag is proportional to speed. Between about 10³ and 2×10⁵, C_d stays near 0.4–0.5 and drag goes as speed squared. Fog, drizzle and raindrops span these regimes, and a fixed C_d would get small droplets wrong by orders of magnitude. So the tool uses the Clift–Gauvin correlation for spheres and labels each object’s regime in the table.