Before revision: Thermodynamics and Propulsion, main page where | border="0"|-| Va || is the freestream fluid velocity in m/s, typically the true airspeed of the aircraft or the water speed of the vessel|-| n || is the rotational speed of the propeller in revolutions per second|-| D || is the propeller's diameter in m| Helicopter rotors and cyclorotors The advance ratio μ is defined as: where {| border="0"|-| V∞ || is the free-stream fluid velocity in m/s, typically the true airspeed of the helicopter|-| Ω || is the rotor rotational speed in |-| r || is the rotor radius in m|} Significance Helicopters Single rotor helicopters are limited in forward speed by a combination of sonic tip speed and retreating blade stall.
After revision: Thermodynamics and Propulsion, main page where Helicopter rotors and cyclorotors The advance ratio μ is defined as: where {| border="0"|-| V∞ || is the free-stream fluid velocity in m/s, typically the true airspeed of the helicopter|-| Ω || is the rotor rotational speed in |-| r || is the rotor radius in m|} Significance Helicopters Single rotor helicopters are limited in forward speed by a combination of sonic tip speed and retreating blade stall.