Drag-optimised ram-air duct and process for controlling a mass flow of ambient air or cooling air through a ram-air duct

A method for controlling a mass flow of ambient air or cooling air through a ram-air duct of an aircraft, the ram-air duct including:

• a ram-air inlet duct including an inlet,
• a ram-air outlet duct including an outlet and arranged downstream of the ram-air inlet duct and in fluid communication with the ram-air inlet duct,
• a first movable element located at the inlet of the ram-air inlet duct and adapted to set an inlet parameter of the inlet, wherein a smaller inlet parameter corresponds to a smaller flow cross-section of the inlet and a larger inlet parameter corresponds to a larger flow cross-section of the inlet, and
• a second movable element located at the outlet of the ram-air outlet duct and adapted to set an outlet parameter of the outlet, wherein a smaller outlet parameter corresponds to a smaller flow cross-section of the outlet and a larger outlet parameter corresponds to a larger flow cross-section of the outlet, and
• a control unit operatively coupled to actuators for moving the first and second movable elements,
• wherein the method comprises the following steps:
• a) defining a control range for the inlet parameter set by the first movable element so as to extend from a minimal inlet parameter up to a maximal inlet parameter,
• b) defining a control range for the outlet parameter set by the second movable element so as to extend from a minimal outlet parameter up to a maximal outlet parameter,
• c) defining a substantially linear function in such a manner that connects together with a constant, linear gradient the end values of the inlet parameter and of the outlet parameter at the minimal ends of the respective control ranges and the end values of the inlet parameter and of the outlet parameter at the maximal ends of the respective control ranges, thereby providing an outlet parameter corresponding to a value of the linear function for each inlet parameter,
• d) defining a control function that links together the outlet parameter and the inlet parameter so that an outlet parameter corresponding to a value of the control function is assigned to each inlet parameter, wherein the control function defines a gradient at the minimal inlet parameter that is less than the constant, linear gradient of the linear function and that is greater than or equal to zero, and
• e) implementing the control function with the control unit by actuating movements of the first and second movable elements according to the control function.