Design and development
The YF-22 and YF-23 were competing in the USAF’s Advanced Tactical Fighter (ATF) program, conceived in the early 1980s, to provide a replacement for the F-15 Eagle. Contracts for the two most promising designs were awarded in 1986.
The YF-23 was designed to meet USAF requirements for survivability, supersonic cruise (supercruise), stealth, and ease of maintenance. Designed with all-aspect stealth as a high priority, Northrop drew on the company’s experience with the B-2 Spirit and F/A-18 Hornet. The YF-23 was an unconventional-looking aircraft with trapezoidal wings, substantial area-ruling, and a V-tail. It introduced the novel feature of rear jet nozzle troughs lined with heat ablating tiles developed by Allison, which shielded the exhaust from infrared (IR) detection from below. All the control surfaces were coupled together via the Vehicle Management System to provide “net effect” aerodynamic control. The wing flaps and ailerons deflected inversely on either side to provide yaw, while the tail provided pitch. Aerodynamic braking was achieved by deflecting the flaps and ailerons on both sides simultaneously.
Although possessing an advanced design, in order to reduce costs and development, a number of F-15 Eagle components were utilized including the standard F-15 nose wheel unit and the forward cockpit of the F-15E Strike Eagle. Two aircraft were built. YF-23 #1 (PAV-1) was fitted with Pratt & Whitney YF119 engines, while YF-23 #2 (PAV-2) was fitted with General Electric YF120 engines. The YF-23 featured fixed nozzles. The first YF-23 was rolled out on 22 June 1990, and first flew on 27 August 1990. YF-23 #2 first flew on 26 October 1990.
The black YF-23 (PAV-1) was nicknamed “Black Widow II”, after the Northrop P-61 Black Widow of World War II and had a red hourglass marking resembling the underbelly marking of the black widow spider. The black widow marking was briefly seen under PAV-1 before being removed at the insistence of Northrop management. The gray colored YF-23 (PAV-2) was nicknamed “Gray Ghost”.
Both YF-23s were furnished in the configuration specified before the requirement for thrust reversing was dropped. The weapons bay was configured for weapons launch but no missiles were fired, unlike Lockheed’s demonstration aircraft. The YF-23s flew 50 times for a total of 65.2 hours. The YF-22 achieved Mach 1.58 in supercruise. The first YF-23 with P&W engines supercruised at Mach 1.43 on 18 September 1990 and the second YF-23 with GE engines reached Mach 1.6 on 29 November 1990. The flight testing demonstrated Northrop’s predicted performance values for the YF-23.
The YF-22 won the competition in April 1991. The YF-23 design was more stealthy and faster, but the YF-22 was more agile. It has been speculated in the aviation press that the YF-22 was also seen as more adaptable to the Navy’s Navalized Advanced Tactical Fighter (NATF), though as it turned out the US Navy abandoned NATF a few months later.
After losing the competition, both YF-23 prototypes were transferred from Northrop to NASA’s Dryden Flight Research Center, at Edwards AFB, California. The engines were removed. NASA had no plans to perform flight tests with the airframes, but a proposal was put forward to use one of the two aircraft to study strain gauge loads calibration techniques. The possible production configuration of the F-23A has never been publicly revealed.
- Northrop YF-23. (2009, May 13). In Wikipedia, The Free Encyclopedia. Retrieved 22:11, May 28, 2009, from http://en.wikipedia.org/w/index.php?title=Northrop_YF-23&oldid=289774104