Propeller Thrust Calculator
Calculate static aerodynamic thrust, exit airspeed, and absorbed shaft power for airplane, drone, and paramotor propellers.
Propeller Thrust Calculator
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What Is a Propeller Thrust Calculator?
A propeller thrust calculator uses actuator disk momentum theory and empirical aerodynamic blade lift formulas to compute the static thrust, propwash exit airspeed, and mechanical horsepower or wattage absorbed by a rotating propeller.
How to Use This Calculator
- Enter propeller diameter in inches.
- Enter propeller pitch in inches.
- Enter rotational speed in revolutions per minute (RPM).
- View resulting static thrust in grams, pounds, and Newtons alongside pitch exit airspeed.
Aerodynamic Propeller Thrust Equation
T = \frac{\pi}{2} \left(\frac{D}{2}\right)^2 \rho \cdot v_{\text{pitch}}^2 \quad ; \quad v_{\text{pitch}} = \frac{\text{RPM} \cdot P}{60}Where D is propeller diameter in meters, P is pitch in meters, rho is air density (1.225 kg/m³ at sea level), and v_pitch is theoretical fluid column exit velocity.
Worked Example
Scenario: A 10x4.5 inch propeller spinning at 8,500 RPM at standard sea level.
Diameter: 10 inches (0.254 m), Pitch: 4.5 inches (0.1143 m).
Pitch Exit Airspeed: ~36.3 mph (58.4 km/h).
Calculated Static Thrust: ~1,150 grams (~2.53 lbs / 11.3 N).
Shaft Power Absorbed: ~125 Watts.
Tips & Key Notes
- Thrust scales with the square of RPM and the 4th power of diameter. Increasing diameter creates far more thrust than increasing pitch for the same power.
- Static thrust decreases as the aircraft speeds up down the runway because the effective angle of attack of the propeller blades decreases.
- Square props (where pitch equals diameter, e.g. 8x8) may partially stall at static bench test conditions and deliver lower static thrust than in flight.
Frequently Asked Questions
Why does a larger diameter propeller produce more thrust per watt?
Larger propellers accelerate a larger volume of air more gently, which actuator disk theory proves minimizes kinetic energy wasted in the slipstream, maximizing propulsive efficiency.
What is static thrust versus dynamic thrust?
Static thrust is measured when the aircraft is stationary (zero airspeed). Dynamic thrust is the actual net forward pull produced when the airplane is moving at flight speed.
How does air density affect propeller thrust?
Thrust is directly proportional to air density. At higher altitudes or higher summer temperatures (high density altitude), propellers produce significantly less thrust.
What does propeller cavitation or stall mean?
If blade angle of attack is too steep (excessive pitch at zero forward speed), airflow detaches from the blade surface, creating aerodynamic stall and high noise with lost thrust.
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