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Line 73: [[File:YF-23 exhaust.jpg|thumb|A rear view of a YF-23, showing its tile-lined exhaust channels|alt=Rear view of the YF 23, the two tile lined exhaust channels can be seen at the center, between the V tails]] It was powered by two [[turbofan]] engines, with each in a separate engine nacelle with [[S-duct]]s, to shield engine [[axial compressor]]s from [[radar]] waves, on either side of the aircraft's spine.{{Sfn|Sweetman|1991a|pp=42-44, 55}} The fixed-geometry inlets were trapezoidal in frontal profile, with special porous suction panels in front to absorb the turbulent [[boundary layer]] and vent it over the wings. Of the two aircraft built, the first YF-23 (PAV-1) had [[Pratt & Whitney F119|Pratt & Whitney YF119]] engines, while the second (PAV-2) was powered by [[General Electric YF120]] engines. The aircraft had single-expansion ramp nozzles (SERN) and, unlike the YF-22, did not employ [[thrust vectoring]].{{Sfn|Miller|2005|p=23}} As on the B-2, the exhaust from the YF-23's engines flowed through troughs lined with tiles that are “transpiration cooled” to dissipate heat and shield the engines from [[infrared homing]] (IR) missile detection from below.{{Sfn|Winchester|2005|pp=198-199}} The YF-23's propulsion and aerodynamics enabled it to cruise at over Mach 1.5 without afterburners.<ref name=":2">{{cite web |title=Northrop-McDonnell Douglas YF-23A Black Widow II |url=https://www.nationalmuseum.af.mil/Visit/Museum-Exhibits/Fact-Sheets/Display/Article/195766/northrop-mcdonnell-douglas-yf-23a-black-widow-ii/ |archive-url=https://web.archive.org/web/20230530132209/https://www.nationalmuseum.af.mil/Visit/Museum-Exhibits/Fact-Sheets/Display/Article/195766/northrop-mcdonnell-douglas-yf-23a-black-widow-ii/ |archive-date=30 May 2023 |work=National Museum of the U.S. Air Force}}</ref> [[File:Northrop McDonnell Douglas YF-23A PAV-1 87-0800 Black Widow II LEngineIntake R&D NMUSAF 25Sep09 (14414042127).jpg|thumb|YF-23 [[S-duct]] engine air intake with the porous suction panel in front|alt=A close up shot of the YF-23's S-duct engine air intake located below the right wing]] Line 101: The two contractor teams submitted evaluation results and their PSC proposals for full-scale development in December 1990,{{Sfn|Miller|2005|pp=38-39}} and on 23 April 1991, [[Donald Rice]], the [[United States Secretary of the Air Force|Secretary of the Air Force]] announced that the YF-22 team was the winner.{{Sfn|Jenkins|Landis|2008|p=234}} The Air Force also selected the Pratt & Whitney F119 engine to power the F-22 production version. The Lockheed and Pratt & Whitney designs were rated higher on technical aspects, considered lower risk (the YF-23 flew considerably fewer sorties and hours than its counterpart), and were considered to have more effective program management.<ref>{{cite report |url=https://www.afmc.af.mil/News/Article-Display/Article/2919261/flashback-northrop-yf-23-black-widow-ii/ |title=Flashback: Northrop YF-23 Black Widow II |author=Landis |first=Tony |date=1 February 2022 |publisher=Air Force Materiel Command History Office |archive-url=https://web.archive.org/web/20240523165544/https://www.afmc.af.mil/News/Article-Display/Article/2919261/flashback-northrop-yf-23-black-widow-ii/ |archive-date=23 May 2024 |url-status=live}}</ref>{{Sfn|Jenkins|Landis|2008|p=234}}{{Sfn|Miller|2005|pp=38-39}} It has been speculated in the aviation press that the Lockheed design was also seen as more adaptable as the basis for the Navy's NATF, but by FY 1992 the U.S. Navy had abandoned NATF.{{Sfn|Williams|2002|p=6}}{{Sfn|Miller|2005|p=76}} Following the competition, both YF-23s were transferred to NASA's [[Dryden Flight Research Center]] at [[Edwards Air Force Base|Edwards AFB]], California, without their engines.<ref name=NASA_DFRC/>{{Sfn|Winchester|2005|pp=198-199}} NASA planned to use one of the aircraft to study techniques for the calibration of predicted loads to measured flight results, but this did not happen.<ref name="NASA_DFRC">{{Cite web |date=1996-01-20 |title=YF-23 Photo Gallery |url=http://www.dfrc.nasa.gov/gallery/photo/YF-23/index.html |url-status=dead |archive-url=https://web.archive.org/web/19970605022423/http://www.dfrc.nasa.gov/gallery/photo/YF-23/index.html |archive-date=5 June 1997 |access-date=2024-06-13 |website=NASA Dryden Flight Research Center}}</ref> Both YF-23 airframes remained in storage until mid-1996 when they were transferred to museums, with PAV-2 briefly serving as a display model for the proposed FB-23 regional bomber in 2004.<ref name=NASA_DFRC/><ref>{{cite web |last=Landis |first=Tony |date=1 February 2022 |title=Flashback: Northrop YF-23 Black Widow II |url=https://www.afsc.af.mil/News/Article-Display/Article/2919531/flashback-northrop-yf-23-black-widow-ii/ |url-status=live |archive-url=https://web.archive.org/web/20240708223346/https://www.afsc.af.mil/News/Article-Display/Article/2919531/flashback-northrop-yf-23-black-widow-ii/ |archive-date=8 July 2024 |work=U.S. Air Force Sustainment Center}}</ref> ==Aircraft on display== | |||