Patent ID: 8701385

Claim:
A method for operating a turboprop aircraft engine having a pusher propeller, comprising: providing an aircraft engine having a pusher propeller, a connecting structure positioned radially inwardly of the pusher propeller and connecting the pusher propeller to a drive and a nacelle surrounding a core flow duct of the engine, the nacelle having an outer boundary, an inner boundary and at least one cooling air duct extending from the outer boundary to the inner boundary, the pusher propeller having a diameter greater than a circumference of the nacelle and at least a portion of the connecting structure having a diameter smaller than the circumference of the nacelle; circumferentially enclosing an exhaust gas flow from the aircraft engine with an exhaust gas duct extending from an engine turbine to downstream of at least a portion of the connecting structure, wherein the inner boundary of the nacelle forms an outer boundary of the exhaust gas duct, the connecting structure being positioned axially at a position of the pusher propeller and extending radially outwardly of at least a portion of the exhaust gas duct at an axial position where the exhaust gas duct is axially aligned with the connecting structure; feeding cold air from an environment external to the aircraft engine through the at least one cooling air duct in the nacelle and mixing the cold air into the exhaust gas flow in the exhaust gas duct aft of the engine turbine and upstream of the connecting structure to cool the exhaust gas flow prior to reaching the connecting structure; retarding a flow velocity of the exhaust gas flow upon feeding of the cold air into the exhaust gas flow by continuously widening the exhaust gas duct from the at least one cooling air duct to the connecting structure, the exhaust gas duct being radially outwardly enclosed continuously from the at least one cooling air duct to downstream of at least a portion of the connecting structure; the cold air being at substantially a temperature of the external environment at a position that it is fed into the exhaust gas flow.