Shroud for a reversible thrust fan

In a shroud for a reversible thrust fan, the shroud having a inlet duct and an exhaust nozzle with the fan located there between, a system for increasing the efficiency of the exhaust nozzle when acting as an inlet duct when the fan is providing reverse thrust, the system comprising:

• a plurality of first slots spaced about the circumference of the exhaust nozzle in proximity to the rear end thereof, said slots extending from the exterior surface of the exhaust nozzle to the interior surface thereof;
• an airfoil pivotally mounted to the aft end of each said first slot having a portion of the top surface thereof conforming to the contour of the external surface of the exhaust nozzle and a bottom surface conforming to the internal surface of said exhaust nozzle, said airfoil movable from a closed position wherein said top surface thereof is aligned with the contour of the external surface of the exhaust nozzle to an open position aligned with the aft end of said slot;
• means to bias said airfoil toward said closed position;
• a plurality of second slots having an opening on the top external surface of the exhaust nozzle forward of the opening of said opening of said first slots and a rearward extending passage extending through the shroud and exiting into said passageway of said first slots;
• a second airfoil pivotally mounted to the forward end of said second slot having a top surface thereof conforming to the contour of the external surface of the exhaust nozzle, said second airfoil movable from a closed position wherein said top surface thereof is aligned with the contour of the external surface of the exhaust nozzle to an open position aligned with the forward end of said second slot;
• and
• second means to bias said second airfoil to said closed position.