Skydiving Body-Position Drag & Canopy Simulator

Body position (freefall)

Spread-eagle, max surface area facing the airflow.

Jump setup

Exit altitude 4000 m

Deploy altitude 1000 m

Skydiver mass 80 kg

Live readout

Altitude

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Velocity

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Air density ρ

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Phase

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Terminal v (now)

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Time elapsed

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How it works

Terminal velocity comes from balancing gravity against drag: mg = ½·ρ·v²·Cd·A. Changing body position changes the effective drag area Cd·A — belly-to-earth presents the most surface, head-down tracking presents the least. Air density ρ itself isn't constant: it falls with altitude following the barometric formula ρ(h) = ρ₀·exp(−h/H), so the same body position actually falls faster high up (thin air, less drag) and decelerates toward its sea-level terminal speed as it descends into denser air.

ρ(h) = 1.225 · exp(−h / 8500)  [kg/m³]
F_drag = ½ · ρ(h) · v² · (Cd·A)
a = g − F_drag/m   (opposing velocity)
v_terminal(h) = √(2mg / (ρ(h)·Cd·A))

Belly-to-earth — Cd·A ≈ 0.85 m², the classic "box man" position; terminal velocity ≈ 54 m/s (195 km/h) near sea level.
Head-down track — Cd·A ≈ 0.20 m², streamlined and diving forward; terminal velocity ≈ 95+ m/s (340+ km/h).
Delta glide — Cd·A ≈ 0.45 m², arms swept back for forward glide; terminal velocity ≈ 75 m/s, intermediate drag.
Canopy deployment — once you pull, drag area jumps to Cd·A ≈ 42 m² (an open parachute), so descent rate collapses toward a safe ~5–6 m/s within a couple of seconds.

The simulator integrates the real ODE numerically (RK-style sub-stepping) every frame, using the altitude-dependent ρ, so switching body position mid-fall genuinely changes acceleration in real time — it isn't a scripted animation.

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