Since World War 1 various countries had experimented with stealth technology. The concepts were there but the technology, not so much. That changed in the late 1970’s when the United States caught a break thanks to a mathematician by the name of Denys Overholser. Overholser, who while working for Lockheed, developed a computer program called Echo 1.
This new program was derived from a mathematical model first developed by a scientist in the Soviet Union. Thanks to Echo 1, it was now possible to predict the radar signature of a ”faceted” aircraft. A faceted aircraft has flat panels which are made from radar absorbing materials arranged at certain angles so that incoming radar waves are deflected away from the aircraft instead of bouncing them back towards the radar station. Thanks in part to the Echo 1 software, the engineers at Lockheed’s famed Skunk Works found that an aircraft made with faceted surfaces could indeed have a very low radar signature.
The Lockheed team put together a stealth concept demonstrator known as “Have Blue”. Because the engineers predicted that the flight characteristics would be unstable it was given the nickname “The Hopeless Diamond.” Thanks to new modern flight computers at that time, the successful Have Blue program would eventually morph into the world’s first true “Stealth” aircraft the F-117 Nighthawk. December of 1976 saw the joint DARPA (Defense Advanced Research Projects Agency) and the U.S. Air Force move forward with the Battlefield Surveillance Aircraft-Experimental (BSAX) program.
The BSAX program’s goal was to develop a stealth aircraft for real time surveillance of battlefield frontlines using the “Pave Mover” program, a low probability of intercept radar to provide a real-time Ground Moving Target Indicator (GMTI).
In conjunction with other sensors this aircraft would provide valuable information while maintaining a high survivability rate.
Northrop began working on the BSAX project which now went by the code name “Tacit Blue.” The aircraft was engineered around the Pave Mover radar system, as opposed to trying to mate the radar to an existing airframe. The fuselage was 55. 8 feet long with a 48.2 foot wingspan. It was powered by two Garrett ATF3 engines that were fed through a recessed top mounted, turbofan air inlet, located just in front of its two canted tails.
The lone pilot would not have been able to control the aircraft if not for the digital fly-by-wire system. The quadruple-redundant system was installed by Northrop to counter act its unwieldy flight characteristics. In 1996, John Cashen, an engineer for Northrop said ”You’re talking about an aircraft that at the time, was arguably the most unstable aircraft man had ever flown”.
Between February of 1982 and late 1985, the aircraft which is arguably the most successful stealth test evaluator, and predecessor to the modern family of stealth technology laden aircraft, flew more than 135 test flights, while logging roughly 250 hours of flight time. It was placed in storage until April of 1996 when Tacit Blue was then transferred to the United States Air Force museum at Wright-Patterson Air Force Base in Ohio. It was touted by both Northrop and US Air Force dignitaries as one of the most important stealth aircraft ever.