RC Airplane Speed Calculator
Estimate theoretical RC airplane speed from propeller RPM and pitch, with an optional gear reduction between motor and propeller.
Propeller
Propeller shaft RPM. For a geared setup this is motor RPM ÷ gear ratio.
Speed unit
Result
Theoretical airspeed
68.2mph
(109.7 km/h)
Propeller RPM
12,000RPM
Theoretical pitch speed — real airspeed is lower because of propeller slip and airframe drag.
Formula
- 1.
Propeller RPM = Motor RPM / Gear Reduction Ratio (direct drive = 1) - 2.
Pitch Speed (mph) = Propeller RPM × Pitch (inches) / 1056 - 3.
km/h = mph × 1.609344
Worked example
- 1.Inputs: 12,000 RPM propeller, 6 inch pitch, direct drive.
- 2.Propeller advance = 12,000 × 6 = 72,000 inches per minute.
- 3.Pitch speed = 72,000 / 1056 ≈ 68.2 mph ≈ 109.8 km/h.
Assumptions and limits
- Real airspeed is lower: propeller slip, airframe drag, load and flight conditions all reduce it.
- Motor KV alone cannot predict real top speed — propeller RPM and pitch are the inputs that matter here.
- Treat the output as a theoretical pitch speed, not a flight-test number.
Related tools
Guides and concepts
FAQ
Can I just enter motor KV instead of prop RPM?
No — this tool needs propeller RPM. Multiply KV by pack voltage for theoretical motor RPM, then divide by your gear ratio if the motor is geared.
How close is pitch speed to real airspeed?
It is the theoretical ceiling. Slip and drag mean the real figure is lower, sometimes by 20–40%.
Assumptions
- Theoretical pitch speed is computed — no propeller slip or drag model.
- Optional reduction divides motor RPM into propeller RPM.
- Result is not a predicted real airspeed.