A method for determining the setpoint of the longitudinal airspeed and the setpoint of the longitudinal ground speed which are initialised at a current operating point of a rotary-wing aircraft depending on the exposure of said aircraft to the wind, said aircraft flying along a path T sol relative to the ground with a forward speed Va, said forward speed Va being able to be determined relative to the ground to form a ground speed V sol and relative to the air to form an airspeed V air, a longitudinal direction X extending from the rear of said aircraft towards the front of said aircraft, an elevation direction Z extending upwards perpendicularly to said longitudinal direction X and a transverse direction Y extending from right to left perpendicularly to said longitudinal direction X and elevation direction Z, said aircraft comprising: - an autopilot which generates control commands in accordance with predefined modes of operation and in accordance with flight setpoints, said control commands being capable of causing movements of said aircraft in rotation and/or in translation in said directions (X, Y, Z), - at least one control means which enables a pilot of said aircraft to pilot said aircraft by transparency during operation of said autopilot, - at least one computer, and - at least one memory storing characteristic speed curves of said aircraft, each characteristic speed curve corresponding to a flight phase of said aircraft and defining a setpoint of the longitudinal ground speed and a setpoint of the longitudinal airspeed corresponding to operating points of said aircraft as a function of a longitudinal speed of the relative wind to which said aircraft is subjected, each operating point being characterised by said setpoint of said longitudinal ground speed and said setpoint of said longitudinal airspeed, in a reference system with a longitudinal ground speed V solX of the aircraft on the ordinate and its longitudinal airspeed V airX on the abscissa, a flight phase corresponding to a flight of said aircraft during which a pilot of said aircraft does not cause any acceleration or deceleration of said aircraft along said longitudinal direction X, characterised in that - during an initialisation stage, for a current flight phase of said aircraft an initial characteristic speed curve is identified on which is located said current operating point of said aircraft, - said setpoints of said longitudinal airspeed and ground speed of said aircraft are determined for said current flight phase as a function of the variation of said total speed of the wind in said longitudinal direction X so that said current operating point of said aircraft is displaced on said initial characteristic speed curve, with a gradual shift from maintaining a longitudinal ground speed V solX of said aircraft at low forward speeds to maintaining a longitudinal airspeed V airX of said aircraft at high forward speeds, and - following a command by said pilot along said longitudinal direction for an acceleration or a deceleration of said aircraft, a new characteristic speed curve is identified on which is located said current operating point of said aircraft once said longitudinal airspeed V airX and ground speed V solX of said aircraft are stabilised and substantially constant. - an autopilot which generates control commands in accordance with predefined modes of operation and in accordance with flight setpoints, said control commands being capable of causing movements of said aircraft in rotation and/or in translation in said directions (X, Y, Z), - at least one control means which enables a pilot of said aircraft to pilot said aircraft by transparency during operation of said autopilot, - at least one computer, and - at least one memory storing characteristic speed curves of said aircraft, - during an initialisation stage, for a current flight phase of said aircraft an initial characteristic speed curve is identified on which is located said current operating point of said aircraft, - said setpoints of said longitudinal airspeed and ground speed of said aircraft are determined for said current flight phase as a function of the variation of said total speed of the wind in said longitudinal direction X so that said current operating point of said aircraft is displaced on said initial characteristic speed curve, with a gradual shift from maintaining a longitudinal ground speed V solX of said aircraft at low forward speeds to maintaining a longitudinal airspeed V airX of said aircraft at high forward speeds, and - following a command by said pilot along said longitudinal direction for an acceleration or a deceleration of said aircraft, a new characteristic speed curve is identified on which is located said current operating point of said aircraft once said longitudinal airspeed V airX and ground speed V solX of said aircraft are stabilised and substantially constant.