Parachute Descent Rate Calculator

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Parachute Descent Rate Calculator

kg lbs
m² ft²
Flat Circular (Cd ≈ 0.75) Hemispherical (Cd ≈ 0.80) Cross / Cruciform (Cd ≈ 1.10) Ram-Air / Square Canopy (Cd ≈ 1.50) Conical (Cd ≈ 0.55)
Sea Level (1.225 kg/m³) 1,000m / 3,300ft (1.112 kg/m³) 2,000m / 6,600ft (1.007 kg/m³) 3,000m / 9,800ft (0.909 kg/m³)

Calculated Velocity

Meters per second 0.00 m/s
Feet per second 0.00 ft/s
Kilometers per hour 0.00 km/h
Miles per hour 0.00 mph

function calculateDescentRate() { var weight = parseFloat(document.getElementById("totalWeight").value); var weightUnit = document.getElementById("weightUnit").value; var area = parseFloat(document.getElementById("canopyArea").value); var areaUnit = document.getElementById("areaUnit").value; var Cd = parseFloat(document.getElementById("parachuteType").value); var rho = parseFloat(document.getElementById("airDensity").value); var gravity = 9.80665; if (isNaN(weight) || isNaN(area) || weight <= 0 || area 7) { safetyNote.innerText = "Warning: High descent rate (Hard landing potential)."; safetyNote.style.color = "#dc2626"; } else if (velocityMS > 5) { safetyNote.innerText = "Standard landing speed (Moderate impact)."; safetyNote.style.color = "#d97706"; } else { safetyNote.innerText = "Gentle descent rate (Soft landing potential)."; safetyNote.style.color = "#059669"; } document.getElementById("descentResult").style.display = "block"; }

Understanding Parachute Descent Rates

A parachute descent rate calculator is an essential tool for skydivers, hobbyist rocketeers, and drone pilots. It estimates the steady-state vertical velocity of an object falling under an open canopy. Knowing this speed is critical for ensuring a safe landing and preventing equipment damage or personal injury.

The Physics of the Calculation

The calculation is based on the terminal velocity equation, where the force of gravity equals the force of aerodynamic drag. The formula used is:

v = √((2 * m * g) / (ρ * Cd * A))

  • m (Mass): The total weight of the system (payload plus the parachute itself).
  • g (Gravity): Earth's gravitational acceleration (9.81 m/s²).
  • ρ (Air Density): The thickness of the air, which decreases as altitude increases.
  • Cd (Drag Coefficient): A dimensionless number representing how efficiently the parachute shape catches the air.
  • A (Surface Area): The total fabric area of the canopy.

Typical Drag Coefficients (Cd)

The shape of the parachute significantly impacts its drag efficiency:

Parachute Shape Typical Cd
Flat Circular 0.75 – 0.80
Hemispherical 0.80 – 0.90
Cruciform (Cross) 1.10 – 1.20
Ram-Air (Wing) 1.50 – 2.00

What is a Safe Descent Rate?

Safety depends on the fragility of the payload and the landing surface:

  • Human Skydivers: Typically target 5–7 m/s (16–23 ft/s). Values above this often require a "PLF" (Parachute Landing Fall) technique to avoid injury.
  • Model Rockets: Usually aim for 3–5 m/s to prevent the plastic airframe from cracking on impact.
  • Drones & UAVs: Often require slower rates (under 4 m/s) due to the delicate nature of gimbals and electronics.

Real-World Example Calculation

Suppose you have a payload weighing 100kg using a 30 m² hemispherical parachute (Cd 0.8) at sea level. The calculation would be:

Step 1: 2 * 100 * 9.81 = 1962
Step 2: 1.225 * 30 * 0.8 = 29.4
Step 3: √(1962 / 29.4) = 8.17 m/s

In this scenario, the landing would be quite hard (roughly equivalent to jumping off a 3.4-meter high wall), indicating that a larger canopy may be required for safety.

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