Propeller Efficiency Calculator
Propeller efficiency is the ratio of useful thrust power delivered to the aircraft to the shaft power supplied by the engine. It is one of the key factors in determining aircraft range and cruise performance. This calculator computes propulsive efficiency from thrust, airspeed, and shaft power, and also calculates the advance ratio, thrust coefficient, and power coefficient. These dimensionless parameters are used in NACA propeller test series to characterize propeller performance independent of size and speed.
Propeller efficiency and advance ratio formulas
Thrust Power = T x V (watts)
eta_p = Thrust Power / Shaft Power = T x V / P
n = RPM / 60 (rev/s)
J = V / (n x D) (advance ratio, dimensionless)
CT = T / (rho x n^2 x D^4) (thrust coefficient)
These definitions follow the NACA propeller test series convention. Propulsive efficiency eta_p ranges from 0 to 1 (or 0% to 100%). Advance ratio J is the key parameter for propeller performance charts; efficiency peaks at the design J and falls off on either side. CT is dimensionless and characterizes thrust loading independently of propeller size.
Improving propeller efficiency
- Use a constant-speed propeller to maintain optimal advance ratio across altitudes and airspeeds.
- Keep propeller blades clean and free from nicks; surface roughness increases drag coefficient significantly.
- Operate at the engine's best-power mixture for climb and best-economy mixture for cruise to maximise shaft power per unit of fuel burned.
- Larger diameter, slower turning propellers are generally more efficient than small, fast-turning ones due to reduced tip losses.
- For feathering propellers: feathering minimizes drag during engine failure; ensure the governor and feathering mechanism are serviceable.
Propeller efficiency calculator: frequently asked questions
What is propeller efficiency?
Propeller efficiency (eta_p) is the ratio of thrust power output to shaft power input: eta_p = T x V / P, where T is thrust in Newtons, V is airspeed in m/s, and P is shaft power in watts. A perfectly efficient propeller would convert all shaft power to useful thrust power. Real propellers achieve 75-90% efficiency at their design point.
What is the advance ratio?
The advance ratio J = V / (n x D), where V is airspeed, n is propeller rotation speed in revolutions per second, and D is propeller diameter in metres. It is the non-dimensional forward speed of the aircraft relative to the propeller's rotational tip speed. Propeller efficiency curves are plotted against advance ratio in NACA/NASA propeller test reports.
Why does propeller efficiency decrease at low airspeed?
At low airspeed (low J), the propeller blades operate at a high effective angle of attack, producing significant drag relative to thrust. As airspeed increases toward the design advance ratio, efficiency rises to a peak. Beyond the design point, blades begin to operate below their optimal angle and efficiency drops again. This is why variable-pitch propellers are important for maintaining efficiency across a range of speeds.
What is thrust coefficient (CT)?
Thrust coefficient CT = T / (rho x n^2 x D^4), where T is thrust, rho is air density, n is rotation speed in rev/s, and D is diameter. It is a dimensionless measure of the thrust produced relative to the propeller disc loading. CT is tabulated as a function of advance ratio J for a given propeller in NACA propeller test series.
How do variable-pitch propellers improve efficiency?
A fixed-pitch propeller is optimized for one speed. A variable-pitch (constant-speed) propeller adjusts blade pitch to maintain the optimal advance ratio across a range of airspeeds and altitudes, keeping efficiency high through all phases of flight. Governors adjust pitch to maintain constant RPM as throttle and airspeed change.
Official sources
- NACA: NACA Technical Report 594: Efficiency of Propellers at Various Speeds.
- NASA Glenn Research Center: Propeller Work (NASA).
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.