Northrop Tacit Blue

The Northrop Tacit Blue was a technology demonstrator aircraft created to demonstrate that a low-observable stealth surveillance aircraft with a low-probability-of-intercept radar (LPIR) and other sensors could operate close to the forward line of battle with a high degree of survivability.

In December 1976, DARPA and the U.S. Air Force initiated the Battlefield Surveillance Aircraft-Experimental (BSAX) program, which was part of a larger Air Force program called Pave Mover.

Tacit Blue represented the "black" component in the larger "Assault Breaker" program, which intended to validate the concept of massed standoff attacks on advancing armoured formations using smart munitions.

Tacit Blue aimed to prove that a surveillance aircraft could persist for long periods over the front lines of the battlefield while collecting very high-fidelity intelligence and survive to repeat the task the next day. This was a huge departure from past spy aircraft like the SR-71, which took a snapshot in time.

Design

With a widely-spaced V-tail, a bulbous fuselage, and a large chine wrapping around the fuselage and giving it a boxy look from above or below, the Tacit Blue looked more bizarre than intimidating. Despite being engineered for low radar observability, this was not immediately apparent at first glance, and it lacked the matte black colour of other stealth aircraft. Those working in the program gave it the nickname “Whale” and “Alien School Bus.”

This resulted in a unique airframe shape with odd proportions, and correspondingly unique solutions had to be found to make it flyable. The wing, for example, was just over 48 feet in span and utilized the 1930s-era Clark Y airfoil.

Two Garrett ATF3-6 turbofan engines—like those used in the Dassault Falcon 20—were selected to power the Tacit Blue.

The aircraft made its first successful flight on February 5, 1982, in Area 51, at Groom Lake, Nevada, flown by Northrop test pilot Richard G. Thomas.

Another Tacit Blue test pilot, Ken Dyson, told CNN in 2014 that Northrop had manufactured additional major components for the jet, which amounted to half of a second plane. "If we lost one, we could have a second one up and flying in short order," Dyson said.

After reaching about 250 flight hours, the aircraft was placed in storage in 1985. In 1996, after Tacit Blue was declassified, it was placed on display at the National Museum of the United States Air Force at Wright-Patterson Air Force Base, near Dayton, Ohio and has been on display in the new fourth hangar at the museum since June 2016.

The program had a very small chain of command, which allowed them to do whatever they needed as long as it "didn't break federal law."

General Creech was bullish on the Tacit Blue concept but was worried that a stray MiG returning from a cross-enemy-lines combat mission could stumble upon it.

Tacit Blue's radar was nearly good enough to tell what type of vehicles it was detecting on the ground.

Infrared signature reduction was a big part of the design, with the deeply buried, dorsal inlet-fed twin Garrett ATF3 turbofan jet engines having a serpentine exhaust. This allowed the air to cool before exiting the aircraft and a specially treated 'platypus' tail allowed it to be cooled even more before leaving the confines of the aircraft's planform. The duct and tail arrangement reduced thrust, but it was an easy trade considering the mission set the aircraft was designed to achieve.

The Descendants

During Operation Desert Storm in 1991, the E-8 Joint Surveillance Target Attack Radar System, or Joint STARS, was first deployed. It uses the sensor systems that were originally developed for Tacit Blue, which allow it to determine the direction, speed and patterns of military activity of ground vehicles and helicopters.

The B-2 Spirit also grew from Tacit Blue’s low-observable yet aerodynamic features. The B-2 uses a combination of reduced infrared, acoustic, electromagnetic, visual and radar signatures, plus composite materials, special coatings and a unique wing design. This stealth design enables the bomber to penetrate enemy areas while flying at high altitudes, which provide a bird’s-eye view with minimal chance of being caught.

Global Hawk is an unmanned aircraft system designed to fly at high altitudes in order to provide near-real-time intelligence, surveillance and reconnaissance. While it has been through several iterations since it debuted in 1998, the Block 30 Global Hawk carries sophisticated imaging and electronic signals sensors for situational awareness and intelligence-gathering over large geographic areas.

Specifications

General characteristics

Crew: 1

Length: 55 ft 10 in (17.02 m)

Wingspan: 48 ft 2 in (14.68 m)

Height: 10 ft 7 in (3.23 m)

Airfoil: Clark Y mod.

Gross weight: 30,000 lb (13,608 kg)

Powerplant: 2 × Garrett ATF3-6 turbofan engines, 5,440 lbf (24.2 kN) thrust each

Performance

Maximum speed: 250 kn (290 mph, 460 km/h)

Service ceiling: 25,000–30,000 ft (7,600–9,100 m) operating altitude

Thrust/weight: 0.36