Enter Motor and Propeller Data
Example Data Table
| Build type | Prop | RPM | Ct | Cp | Voltage | Motors | Weight |
|---|---|---|---|---|---|---|---|
| Camera quad | 10 x 4.5 in | 8,500 | 0.10 | 0.045 | 14.8 V | 4 | 1.6 kg |
| Racing quad | 5 x 4.3 in | 18,000 | 0.095 | 0.052 | 22.2 V | 4 | 0.75 kg |
| Heavy lift | 15 x 5.5 in | 5,800 | 0.11 | 0.050 | 22.2 V | 6 | 4.2 kg |
Formula Used
Revolutions per second: n = RPM ÷ 60
Static thrust: T = Ct × ρ × n² × D⁴ × (1 − loss)
Propeller shaft power: P = Cp × ρ × n³ × D⁵
Torque: Q = P ÷ (2πn)
Available shaft power: Pa = V × I × motor efficiency × controller efficiency
Thrust-to-weight ratio: total thrust force ÷ aircraft weight force
Hover throttle estimate: aircraft weight force ÷ total thrust force × 100
These formulas estimate static conditions. Real thrust can change with propeller data, airflow, frame blockage, and temperature.
How to Use This Calculator
Enter the propeller diameter, pitch, loaded RPM, and coefficients. Use propeller test data when available. Add the battery voltage under load, current limit, efficiency values, motor count, and aircraft weight. Press the calculate button. Review thrust, current, torque, hover throttle, and reserve status.
Use the CSV button for spreadsheet records. Use the PDF button for a quick report. Bench test every final build before flight.
BLDC Motor Thrust Planning
A BLDC motor thrust calculation helps size a drone, ducted fan, or small electric aircraft. The result links motor speed, propeller diameter, air density, and propeller coefficients. It also checks electrical loading. This matters because static thrust alone can look safe. The motor may still overheat, pull excess current, or waste battery energy.
Why thrust is not one number
Static thrust changes with air density, propeller design, RPM, and installation losses. A larger propeller usually moves more air at lower RPM. A smaller propeller may need more speed. The thrust coefficient captures propeller behavior. The power coefficient estimates shaft power demand. Both values should come from propeller test data when possible.
Electrical checks for safer choices
This calculator compares propeller power demand with available shaft power. Available shaft power comes from voltage, current, controller efficiency, and motor efficiency. The tool also estimates torque, pitch speed, disk loading, and tip speed. These outputs help find weak points before a bench test.
Hover and flight estimates
For multirotors, total thrust must exceed aircraft weight. A thrust-to-weight ratio near one cannot hover with control authority. Many camera drones work better with a larger reserve. Racing builds often use a higher ratio. The hover throttle result estimates how hard the system works in steady lift. The battery runtime estimate uses current, capacity, and usable discharge. It is only a planning value. Real flight time changes with wind, maneuvers, payload, and battery age.
How to use the result
Start with measured RPM and propeller data. Enter realistic current limits from the motor and controller. Check that required shaft power stays below available shaft power. Then review thrust margin and hover current. If the margin is poor, choose a larger propeller, higher voltage, lower weight, or a stronger motor. Always confirm the final setup with a thrust stand and temperature checks.
Practical limits
Use conservative values for early design. Propeller coefficients vary by brand and blade shape. Guards, arms, ducts, and nearby surfaces reduce real thrust. Thin air also lowers lift at altitude. Leave space for wiring losses and heat. A safe setup should meet thrust needs without running at full throttle. Record test values, then update inputs for a tighter estimate.
FAQs
What is BLDC motor thrust?
It is the lifting or pushing force created when a brushless motor spins a propeller. The value depends on RPM, propeller size, air density, and propeller design.
Why do I need Ct and Cp?
Ct estimates thrust behavior. Cp estimates power demand. Use measured propeller data when possible. Generic values can help early planning, but they cannot replace a thrust stand test.
Can this calculator predict real flight time?
It gives a planning estimate. Real flight time changes with wind, throttle changes, payload, battery condition, temperature, and pilot style. Test flights are still needed.
What thrust-to-weight ratio should I use?
A ratio above 1 can lift. Many stable multirotors use more reserve. Camera drones may target moderate reserve. Racing drones often use a much higher ratio.
Why is loaded RPM important?
Loaded RPM is the speed while the propeller is installed. No-load RPM is higher and can overstate thrust. Use measured loaded RPM for better estimates.
What happens if current margin is negative?
The propeller may demand more current than the motor or controller limit. Use a smaller propeller, lower pitch, lower RPM, or stronger electrical parts.
Does air density affect thrust?
Yes. Lower air density reduces thrust. High altitude, heat, and humid air can reduce performance. Use a realistic density for your location and test day.
Is this safe for final aircraft design?
Use it for planning, comparison, and screening. Final designs need bench testing, temperature checks, vibration checks, and safe flight trials under controlled conditions.