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