Directly translate measured propeller rotational speed (RPM) and dimensions into static and dynamic thrust.
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The RPM to Thrust Calculator provides a direct mathematical bridge between optical tachometer RPM measurements and static propulsive thrust. By entering propeller diameter, pitch, and rotational RPM, it outputs instantaneous thrust in grams, pounds, and Newtons.
T = K \cdot \rho \cdot D^4 \cdot \text{RPM}^2 \cdot \left(\frac{P}{D}\right)Thrust increases quadratically with RPM: doubling the rotational speed quadruples the generated aerodynamic thrust.
Scenario: An 8x4.5 propeller rotating at 12,000 RPM.
Diameter: 8", Pitch: 4.5", RPM: 12,000.
Calculated Static Thrust: ~1,120 grams (~2.47 lbs / 11.0 N).
Exit Airflow Velocity: ~51 mph (82 km/h).
Standard APC electric thin props have a safe ceiling of approximately 145,000 / Diameter (inches). For example, a 10-inch prop maximum safe speed is ~14,500 RPM.
No. Thrust scales with the square of RPM (RPM²), meaning doubling RPM produces approximately 4 times more thrust (while requiring roughly 8 times more power).
Tachometers count blade passes. If set to a 2-blade setting while testing a 4-blade prop, the reading will be doubled. Ensure blade count matches your tachometer setting.
Yes. As propeller tips approach the speed of sound (Mach 0.7 to 0.8, ~550–600 mph), shockwaves form, causing severe drag rise, deafening noise, and stalled thrust.
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