Skydiving Aerodynamics: 5 Equations You Must Know
Skydiving might seem chaotic, but behind the scenes, a few simple aerodynamic principles rule everything. If you understand these 5 key equations, you’ll grasp 99% of the physics that govern your descent, flight, and parachute deployment.
Let’s dive into them one by one:
1 & 2. Gliding Flight: The Fundamentals
In skydiving, we experience gliding flight without thrust. This is described by two force balance equations along and perpendicular to the flight path.
Along the flight path:
Perpendicular to the flight path:
Where:
T = Thrust (zero for a skydiver)
D = Drag
L = Lift
W = Weight
γ = Flight path angle (angle between the horizon and direction of motion)
Since T = 0 for a skydiver, we have:
Here’s the important part:
Drag (D) and weight (W) are positive quantities.
Thus, sin(γ)\sin(\gamma)sin(γ) must be negative.
A negative sine means that γ is an angle between 0° and -90°.
Mathematical conclusion:
γ < 0
Physical meaning:
You are always descending. Even with a parachute or a wingsuit, you are always trading altitude for horizontal distance.
3. Glide Ratio (Lift-to-Drag, L/D)
From the force balances, taking the ratio of lift to drag gives:
The glide ratio (L/D) tells you how efficiently you convert vertical descent into horizontal travel.
Deeper insights:
A better glide ratio means a flatter trajectory.
A typical belly-to-earth skydiver has an L/D around 0.3.
A skilled tracker can reach 1.0–1.2.
A modern wingsuit can achieve 2.5–3.5 or even higher.
Interesting point:
Changing small details can significantly alter L/D:
Tight jumpsuits reduce drag and improve L/D.
Arched body position improves stability but worsens L/D.
Reducing surface roughness (e.g., smooth fabrics) helps performance.
Example:
A wingsuit pilot with L/D = 3 jumping from 10,000 ft could glide about 30,000 ft horizontally (5.7 miles / 9.2 km) before landing.
4. Terminal Velocity
Terminal velocity is the steady speed you reach when the force of drag equals the force of gravity.
The formula is:
Breaking it down:
W = Total weight, including equipment.
ρ = Air density, which decreases with altitude.
S = Cross-sectional area exposed to airflow.
CD = Drag coefficient, depending on body shape and texture.
Real-world factors:
Tight suits reduce CDC_DCD, increasing terminal velocity.
Smaller surface area (e.g., head-down flying) significantly increases terminal speed.
Higher altitudes (lower ρ) increase terminal velocity by about 15–20% at typical skydiving heights.
Numerical Example:
Suppose:
Height: 5'11" (180 cm)
Weight: 176 lb (80 kg)
Surface area S ≈ 8 ft² (0.74 m²) in belly position
Drag coefficient CD ≈ 1.0
Air density at 10,000 ft ≈ 0.0020 slug/ft³
Using the formula above
Compared to about 120 mph (193 km/h) at sea level, that's a noticeable increase.
5. G-Forces During Parachute Opening
When you deploy your parachute, your body decelerates quickly. The G-forces you feel come from how rapidly your speed changes.
The formula to calculate G-forces is:
Where:
a = deceleration
g = gravity acceleration
Example:
Suppose you slow down from 120 mph (176 ft/s) to 15 mph (22 ft/s) in 2.5 seconds after deployment.
Then G-force experienced:
Result:
You feel approximately 1.9 G.
Important:
Typical openings produce between 1.5 and 3 G.
Very fast deployments ("hard openings") can cause up to 4–5 G, enough to stress your neck and parachute equipment.
Final Thoughts
Understanding these five equations gives you a huge advantage in skydiving.
You will be able to better adjust your body position, analyze your canopy flight, and make smarter equipment choices.
🔗 Related video: Watch my full explanation on YouTube!
