Calculator Inputs
Formula Used
Static thrust is estimated with the non-dimensional propeller coefficient method:
T = CT × ρ × n2 × D4 × Fb
T is thrust in newtons. CT is thrust coefficient. ρ is air density in kg/m³. n is revolutions per second. D is propeller diameter in meters. Fb is the optional blade correction factor.
Pitch speed is calculated as pitch × revolutions per second. Electrical power is voltage × current. Estimated shaft power is electrical power × motor efficiency.
Example Data Table
| Diameter | Pitch | RPM | Ct | Air Density | Voltage | Current | Use Case |
|---|---|---|---|---|---|---|---|
| 8 in | 4 in | 10500 | 0.095 | 1.225 | 11.1 | 18 | Light park flyer |
| 10 in | 4.5 in | 9000 | 0.105 | 1.225 | 11.1 | 22 | Trainer aircraft |
| 12 in | 6 in | 7600 | 0.115 | 1.18 | 14.8 | 30 | Payload platform |
| 15 in | 5.5 in | 6200 | 0.12 | 1.2 | 22.2 | 38 | Large electric model |
How To Use This Calculator
- Enter propeller diameter and pitch from the prop label.
- Measure loaded RPM with the actual battery and motor.
- Enter a thrust coefficient from prop data or a reasonable estimate.
- Add local air density, voltage, current, and efficiency.
- Select blade correction only for rough comparison work.
- Press Calculate to show results below the header.
- Use CSV or PDF export for your test records.
Engineering Guide
Why Static Thrust Matters
Static thrust is the pull a propeller makes while the aircraft is not moving. It helps builders compare motors, propellers, batteries, and gearing before flight. The value is useful for hover margin, launch confidence, payload checks, and early design screening. It is not a full wind tunnel result, but it gives a practical engineering estimate.
Inputs That Affect The Result
Diameter has a strong effect because thrust grows with the fourth power of diameter. RPM also matters greatly because thrust grows with the square of revolutions per second. Air density changes the answer too. A cold day near sea level usually gives more thrust than a hot day at altitude. Pitch mainly supports pitch speed and loading checks. Blade count can add pull, yet it also adds drag and current demand.
Reading The Output
The calculator reports thrust in newtons, grams force, kilograms force, and pounds force. It also shows disk area, disk loading, pitch speed, induced velocity, electrical input power, estimated shaft power, and thrust per watt. These numbers help you judge whether a setup is efficient or stressed. A high disk loading may give strong pull, but it can waste power and make control less gentle.
Engineering Use
Use the coefficient method when you have a known thrust coefficient from propeller data. Use the blade correction only as a broad comparison aid. Bench testing is still important because real propellers vary by brand, airfoil, stiffness, hub shape, and manufacturing quality. Motor timing, battery sag, ESC limits, and inlet obstruction also change the measured result.
Practical Tips
Measure RPM with the exact battery and propeller. Enter loaded voltage, not the label voltage. Use current from a wattmeter. Keep hands and loose items away from the propeller during tests. Compare several propellers at the same current limit. Choose the setup that gives enough thrust without overheating the motor, speed controller, or battery. Save the exported results with notes about temperature, altitude, and hardware. This makes future tuning faster and safer. Record propeller brand, blade material, and hub size. Small construction details can shift the coefficient. Treat every estimate as a starting point. Then confirm with a scale, tachometer, and wattmeter before committing to safe flight testing.
FAQs
1. What is static thrust?
Static thrust is the propeller pull measured while the aircraft is stationary. It is useful for launch, hover, payload, and early motor selection checks.
2. Is this calculator a replacement for bench testing?
No. It gives an engineering estimate. Real thrust depends on propeller design, battery sag, motor timing, airflow, and test stand accuracy.
3. What thrust coefficient should I use?
Use manufacturer test data when available. For rough estimates, many small RC propellers may fall near 0.08 to 0.13.
4. Why does diameter affect thrust so much?
The formula uses diameter to the fourth power. A small diameter change can greatly change calculated thrust, disk loading, and power demand.
5. Should I enable blade correction?
Enable it only for broad comparisons. If your thrust coefficient already comes from a tested propeller, leave blade correction disabled.
6. What is pitch speed?
Pitch speed estimates the forward speed suggested by propeller pitch and RPM. It does not include slip or aircraft drag.
7. Why can power margin look unrealistic?
Power margin can look unrealistic when coefficient, RPM, voltage, current, or efficiency inputs conflict. Check measured values before trusting the result.
8. Which units are used in the main formula?
The main formula uses meters, kilograms, seconds, revolutions per second, and newtons. The calculator converts common RC inputs automatically.