A control system configured to control an acceleration of an air vehicle which comprises a tiltable propulsion unit that is tiltable to provide a thrust whose direction is variable at least between a general vertical thrust vector direction and a general longitudinal thrust vector direction with respect to the air vehicle, the control system comprising: an input interface for receiving information indicative of a monitored airspeed of the air vehicle; and a control unit, configured to issue controlling commands to a controller of the tiltable propulsion unit for controlling the acceleration of the air vehicle, wherein the controlling of the acceleration comprises: in a first part of the acceleration, in which the tiltable propulsion unit provides thrust in the general vertical thrust vector direction: (a) controlling an operation of the at least one tiltable propulsion unit for providing lift to the air vehicle, and (b) controlling a modifying of a tilt angle of the tiltable propulsion unit with respect to a fuselage of the air vehicle, based on: (i) the monitored airspeed and (ii) an airspeed command; and following a tilting of the at least one tiltable propulsion unit, controlling in a second part of the acceleration an operation of the tiltable propulsion unit to provide thrust in the general longitudinal thrust vector direction for propelling the air vehicle, wherein the control unit comprises a pitch control module which is configured to issue a pitch command based on the monitored airspeed and the airspeed command and to control in the first part of the acceleration a modifying of a pitch angle of the air vehicle based on the pitch command, wherein the controlling of the modifying of the tilt angle is further based on the pitch command. an input interface for receiving information indicative of a monitored airspeed of the air vehicle; and a control unit, configured to issue controlling commands to a controller of the tiltable propulsion unit for controlling the acceleration of the air vehicle, wherein the controlling of the acceleration comprises: in a first part of the acceleration, in which the tiltable propulsion unit provides thrust in the general vertical thrust vector direction: (a) controlling an operation of the at least one tiltable propulsion unit for providing lift to the air vehicle, and (b) controlling a modifying of a tilt angle of the tiltable propulsion unit with respect to a fuselage of the air vehicle, based on: (i) the monitored airspeed and (ii) an airspeed command; and following a tilting of the at least one tiltable propulsion unit, controlling in a second part of the acceleration an operation of the tiltable propulsion unit to provide thrust in the general longitudinal thrust vector direction for propelling the air vehicle, wherein the control unit comprises a pitch control module which is configured to issue a pitch command based on the monitored airspeed and the airspeed command and to control in the first part of the acceleration a modifying of a pitch angle of the air vehicle based on the pitch command, wherein the controlling of the modifying of the tilt angle is further based on the pitch command. in a first part of the acceleration, in which the tiltable propulsion unit provides thrust in the general vertical thrust vector direction: (a) controlling an operation of the at least one tiltable propulsion unit for providing lift to the air vehicle, and (b) controlling a modifying of a tilt angle of the tiltable propulsion unit with respect to a fuselage of the air vehicle, based on: (i) the monitored airspeed and (ii) an airspeed command; and following a tilting of the at least one tiltable propulsion unit, controlling in a second part of the acceleration an operation of the tiltable propulsion unit to provide thrust in the general longitudinal thrust vector direction for propelling the air vehicle, wherein the control unit comprises a pitch control module which is configured to issue a pitch command based on the monitored airspeed and the airspeed command and to control in the first part of the acceleration a modifying of a pitch angle of the air vehicle based on the pitch command, wherein the controlling of the modifying of the tilt angle is further based on the pitch command.