With this aircraft, we redefined the rule of designing and constructing an aircraft. In 2002, Boeing executive Jim Albaugh referred to a jet that appeared to belong in a sci-fi backlot, but nonetheless existed due to a very down-to-earth reason: demonstrate that low-observable design did not necessarily have to be accompanied by long and costly production development.
The YF-118G “Bird of Prey” demonstrated by Boeing was a single-seat, one-off stealth technology aircraft that was constructed to prove radar-defeating shaping and manufacturing techniques that could be scaled without the standard cost overheads. There was never a guiding passage to operational service, and its strange proportions, little wings, a beak-like nose, the inlet at the back, were all of a conscious experiment at trying what was practicable, what could be hurriedly constructed, and what could be replicated.
Process rather than performance was the greatest legacy of the project. In 38 flights, the plane acted as a flying test platform to one production philosophy that was heavily based on digital construction and reduced fabrication. The U.S. Air Force museum reports that the program was able to certified “large single-piece composite structures”, “virtual reality” on computerized design and assembly, and “disposable tooling”, a mix that was aimed at decreasing the number of parts and shortening build schedules without sacrificing on low-observable goals. That focus explains why the Bird of Prey was created based on what can be built in a consistent manner, smooth surface continuity, reduction of seams, and designs that could be built in large cohesive parts instead of intricate structures that were likely to be out of shape.
Others of the jet who are stealth-related can still be seen even in photographs. The museum emphasizes its “gapless” control surfaces, which are designed to merge into the wing without discontinuities which make it an intense radar return. It was also designed to have the dorsal intake such that the engine face was not exposed to the front, which is another conventional low-observable feature. Even the exaggerated chines, which have been likened to those of the SR-71, had a dual purpose: to provide lift and to aid in the control of the radar signature of the aircraft due to their precise shaping.
It was not merely a slogan to make the airframe “affordable”, but it was built into the decisions of the program. The aircraft employed “off the shelf” technology where it was able to, such as landing gear borrowed Beech King Air and Queen Air aircraft and the aircraft was not as complex as full up operational avionics. The museum fact sheet relates the control system as being all-manual without computer aids, a crude yet efficient method of keeping a demonstrator dedicated to its main goal: prove shaping and manufacturing concepts in flight.
It had a short program life by contemporary standards. It was a covert initiative between 1992 and 1999, first flown in the fall of 1996, but publicly disclosed in 2002 when the machinations behind it were no longer as delicate. At that point, it was already being stated: methods that had been tested on Bird of Prey were already trickling into subsequent Boeing projects, such as the X-32 Joint Strike Fighter demonstrators and the X-45 unmanned combat air vehicle program.
The single airframe is today in Dayton at the National Museum of the United States Air Force, a rarity among the “black” technology demonstrators to have survived and become a museum object. Its legacy is not so much a specific airplane form, nor that stealth could be created in a CAD system, assembled with fewer components, and produced with the same discipline which considers cost an engineering factor, not an afterthought.
