-The Northrop TACIT BLUE, nicknamed the "Whale", on the ramp at the USAF Museum. | Photo: NMUSAF
FLIGHTLINE: 160 - NORTHROP YF-117D TACIT BLUE/"WHALE"
The TACIT BLUE technology demonstrator was developed by Northrop to explore low observable technology and techniques, as well as a "stealth" radar.
Beginning in the middle 1970s, the USAF established a program codenamed PAVE MOVER, which sought to develop an advanced airborne radar system for ground surveillance, incorporating ground moving target indicator (GMTI), fixed target indicator (FTI) target classification, and synthetic aperture radar technologies; Pave Mover would later culminate in the E-8 Joint Surveillance Target Attack Radar System (J-STARS), which was rushed into service during the 1991 Gulf War, and continues serving today. As part of Pave Mover, in December 1976 the USAF and DARPA jointly initiated a program known as the Battlefield Surveillance Aircraft-Experimental (BSAX), which had as its goal the development of an aircraft that could covertly provide radar imagery of the ground behind the front lines.
The Northrop Company's advanced programs group was granted the contract for the BSAX, which was given the program code TACIT BLUE and assigned the designation YF-117D to further obscure its true nature and purpose. The difficulty of incorporating the low-probability-of-intercept (LPI) resulted in a design radically different from the Lockheed HAVE BLUE demonstrator, which was shaped from flat plates. This approach proved to be unworkable for the fuselage shape required by the Pave Mover radar antenna, so Northrop was forced to develop more advanced curvilinear shaping, resulting in an aircraft described by Northrop personnel as an "alien school bus".
-A Prime Mover antenna on display at the National Electronics Museum. | Photo: Daderot
The Tacit Blue had a long, rectangular fuselage married to a straight, tapered wing and a V-tail. Although designed to test stealth technologies, the aircraft was built of largely standard construction and materials, chiefly aluminum. As with other tech demo aircraft, several components were sourced from existing aircraft, including landing gear from an F-5E, an ACES II ejection seat, and Garrett turbofans from an HU-25 Guardian. The engines were fed by a dorsal intake , and the exhaust was shielded by the tail. The Tacit Blue was wildly unstable in flight, requiring a quadruple-redundant fly-by-wire system to remain in flight.
-Orthograph of the Tacit Blue. | Illustration: Dr Dan Saranga
The Tacit Blue, nicknamed "Whale" by pilots and crew, was transported to Groom Lake, Nevada, site of the infamous Area 51 test facility, where such planes as the A-12 and captured Soviet MiGs were flown, and prepared for flight. The maiden flight of the aircraft was on 5 February 1982 by Northrop test pilot Richard Thomas, and proved that the aircraft did perform to expectations. Over the next three years the Whale flew 135 flights, logging some 250 hours in the air. Missions were conducted up to four times weekly, with multiple flights a day. Controllers for the radar system were located in ground stations during the flight tests, as the aircraft was only designed for the pilot.
-For some time, this was the only photo of the Tacit Blue in flight. | Photo: USAF
-The Tacit Blue in flight, from below. | Photo: USAF
-The Whale was never going to win beauty pageants, but demonstrated the theories and techniques behind its design. | Photo: USAF
Although only one Tacit Blue was completed, Northrop completed enough spares to possibly build a second aircraft, should the need arise. The program concluded in 1985, after which the Whale was placed into storage pending a new mission, preservation or disposal. Overall the aircraft could be considered a success, with the Whale having proved the curvilinear design would adequately shield the aircraft from radar, regardless of direction (unlike the F-117s flat-panel design), and that the LPI radar would be effective. The BSAX program, on the other hand, was a failure, as the aircraft was deemed to be not survivable on daytime missions when it would be most useful. Although functionally invisible on radar, the Whale was easily visible from the ground, meaning that it would have required fighter protection to complete its mission. Furthermore, the J-STARS aircraft proved to be more than capable of performing the mission intended for the BSAX, and was cheaper, had more endurance and could gather more data as well. Lessons learned from the Tacit Blue were incorporated into the B-2 Spirit, as well as the YF-23 and X-32, though neither were produced. Another beneficiary of the Whale's research was the AGM-137 TSSAM, which resembled the Tacit Blue turned upside-down, and would have used by the Army, Navy and USAF. Budgeting issues, inter-service rivalries and technological hurdles resulted in delays and more than doubled the cost per unit however, and the TSSAM was canceled in 1994.
-Infographic for the TSSAM. | Illustration: Northrop Grumman
The BSAX program was declassified in 1996, with the Tacit Blue itself being transported to the National Museum of the USAF in Dayton and placed on display. In 2016 it was moved to the new R&D Hangar, where it now sits beneath the Boeing Bird of Prey, which was given the false designation YF-118G.
-The cockpit of the Tacit Blue was relatively primitive, considering how advanced it was otherwise. | Photo: NMUSAF
-The Whale on display in the museum's new fourth hangar, home to its R&D collection. | Photo: NMUSAF
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