82 knots. At this attitude the aircraft was able to demonstrate controllability. Later analysis revealed that the aircraft could have maintained controlled, trimmed flight up to 70 degrees AoA. The wedge shapes of the nozzle flaps also reduce the infrared signature by flattening the exhaust plume and mixing it with shed vortices for cooling. On the YF-23, rather than a thrust-vectoring nozzle, the engine had a single-expansion ramp nozzle (SERN), with the top consisting of a variable external flap, or paddle, to control the nozzle area while the bottom was a fixed ramp. The engines were placed well forward of the trailing edge of the YF-23's aft fuselage, where each nozzle transitions to a trench on top of the aft fuselage that is lined with heat-resistant material. This allows the exhaust plume to be rapidly cooled before exiting the aircraft, significantly reducing the infrared signature particularly when viewed from below; the trenches in the aft deck were lined with tiles that were “transpiration cooled” from engine bleed air to withstand the heat of the exhaust. Applications Lockheed YF-22 Northrop YF-23 Specifications (YF120) See also References GE unveils ramjet design for shuttle Technology News Flight International 23/09/03 . External links GE/Allison/Rolls-Royce Team Developing YF120 Fighter Engine for JSF Aircraft Candidates. Press release GE Aviation (Sept 2, 1996). National Museum of the U.S. Air Force page on the YF120 Northrop YF-23 Enthusiast's site YF120 Low-bypass turbofan engines 1980s turbofan engines Abandoned military aircraft engine projects of the United States