8/14/2019 1996 - 1113 Tacit Blue

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DEFEN E

O u t o f t h e b la c k c o m e s T a c it R ON LOPEZ WASHINGTON D

T HE US AIR FORCE hastaken the wraps off another ofits classified stealth projects withth e unveiling ofthe Tacit Blue technology demonstrator. The TacitBlue was used to test low-observable technologies eventually used inthe Northrop Grumman B-2bomber and other stealthy aircraftand missile programmes.

The USAF/Defense AdvancedResearch Projects Agency TacitBlue stealth-technology demonstrator was successfully flown duringthe early 1980s, a few years after theHave Blue prototype of the Lockheed Martin F-117 stealth fighter

was used to test faceted surfaces,also to achieve low observability.Despite the relative age of the

programme, the USAF remainssensitive about various aspects ofth e Tacit Blue. The released imageshave been heavily doctored toremove some features and alter othe r s including the rear-fuselage section and wing leading edge.

The Tacit Blue represented thefirst attempt at using ...curved linear or Gaussian surfaces to achievesignature reduction , says Lt Gen

George Muellner, the principaldeputy for the US Air Force'sacquisition chief. He says that theaircraft's classified radar c ross-section was smaller than th at of a bat.

Initially, the project w as createdto demonstrate that a stealth surveillance aircraft with a low probability of interce pt (LPI) radar inthis case a Hug hes Aircraft ground-surveillance multi-mode radar and other sensors could operateclose to the forward line of battlewith a high degree of survivability.

Th e Tacit Blue w as an element o fthe Pave Mover programme w hichled to the Northrop Grumman E-8

h Tacit Blue splanform reveals t h upper-fuselage intake duct

Joint Surveillance Target AttackRadar System. The E-8 aircraftamilitarised Boeing 707 carries a7.3m long radar antenna, whichdisplays either moving or fixedground targets.

Early in the programme, theUSAF verified the LPI radar s capabilities, and decided that theground-surveillance mission couldbe achieved by using larger aircraftpatrolling 90km (50nm) back from

the front line.Th e U SAF then decided to use

the Tacit Blue as a generic testbedfor low-observable technology.

Th e emergence ofthe Tacit Bluewill fuel speculation as to whetherit was succeeded by anothermanned low-observable reconnaissance platform.

The single-seat, 13,620kg, TacitBlue was powered by two Allied-Signal (formerly Garrett) ATF3-6

Reed Business Publishing

Length: 17m Speed: U p t o l 5 0 k t 2 8 0 k m / h )

Height: 3.2m Crew:Wingspan: 14.7mWeight: 13,620kg

Powerplant: two AlliedSignal Engines ATF3- high-bypass turbofa n engines

high-bypass turbofan engines. Aquadruple-redundant digital flight-control system (FCS), built byGeneral Electric, w as installed.

Northrop won a sole-source

contract in 1978 and completedfabrication of the 17m-long TacitBlue demonstrator at Haw thorne,California, four years later.

A second airframe shell laterscrapped was constructed toserve as a back-up. The total programme cost $165 million, ofwhich prime contractor Northropreceived S i 3 6 million.

Th e aircraft had its maiden flighton 5 February, 1982, and subse-quendy logged 2 5 Oh in 13 5 daylightsorties over a three-year period.

Average mission dura tion w as 2.5h.Th e Tacit Blue w as flown at severalundisclosed locations, completed itsfina l flight on 14 February, 1985 andw as then stored.

In the released images, the TacitBlue features a straight, taperedwing with a V tail mounted on anoversized fuselage with a curvedshape. A single flush inlet o n the topof the fuselage provided air to itstwo turbofan pow erplants.

In the flight ests, the aircraft wasfound to be unstable in pitch andyaw, and relied on the GE FCS tostabilise the aircraft about the longitudinal and directional axes.

Five company and USAF testpilots flew Tacit Blue, saying that..:it responded well, but flew ike a

big aircraft .The USAF says that the Tacit

Blue can now be revealed becausetechnology resulting from the secretproject is in operational use in theNorthrop B-2 stealth bomber. Theterminated Northrop GrummanTri-Service Standoff Attack Mssile ,the Lockheed Martin F-22 fighterand the Lockheed Martin D arkstarUAV also gained from h e project. Q

FLIGHT INTERNATIONAL 8 - 14 May 19 96 17