Stealth turns 40: Looking back at the first flight of Have Blue

Invisible airplanes

Given the highly classified nature of the stealth program—it wouldn't be revealed in any form until a leak during the Carter administration, and it would remain largely secret until the F-117's starring role in the 1989 invasion of Panama and more public role in the 1990 Persian Gulf War—all of the testing of the Have Blue "vehicles" took place shrouded in secrecy. Ground tests were conducted at the Skunk Works' Burbank, California facility in early November of 1977, where the plane was carefully concealed and painted with camouflage to disguise its odd shape. And for flight-testing, the aircraft was partially disassembled and flown to Groom Lake (known in popular culture as "Area 51").

HB1001's December 1 first fight came just over a year and a half after Lockheed won the project. At the controls for that first flight was Lockheed test pilot Bill Park. The aircraft was followed by a T-38 chase plane flown by an Air Force F-15 pilot named Ken Dyson. The two would switch off between the two aircraft, and they were the only two pilots to ever fly the Have Blue aircraft.

The first plane would fly only 36 times before it was lost in a crash. In May of 1978, as Park was landing at the end of a test, the plane suddenly pitched upward—causing the two-rear landing gear to slam into the runway. One portion of the landing gear was damaged, and it would no longer fully extend, so Park was forced to eject when the plane ran out of fuel. Still, the first aircraft was considered a success, and its successor was almost complete.

The second aircraft "actually had all of the [stealth] technologies applied to it," Burnett said. It came with the addition of a radar absorbent coating and the removal of some of the less-stealthy equipment used on the first aircraft. HB1002, as it was designated, also incorporated improvements based on lessons learned from the first aircraft. HB1002 took its first flight on July 20, 1978, with Dyson at the stick—he would be the sole pilot to fly the second prototype for the full field testing of Have Blue against radar and air defense systems. In tests recounted by Rich, the only aircraft that ever showed up on air defense radars deployed in tests against Have Blue was the T-38 chase plane.

Almost a year after its first flight to the day, HB1002 crashed during its 52^nd flight. This time, the crash was caused by an exhaust leak that in turn caused a hydraulic line to fail, cascading into an engine fire and loss of control of the aircraft. Dyson safely ejected.

Nothing remains of either aircraft—what was left of them after their crashes was buried somewhere in the vast Nevada desert. "Yeah, they just took a bulldozer and hid the evidence, as it were," said Burnett. "There have been rumors over the years that people who were in the know have gone out trying to dig it up, but were not successful. But if there's any real truth to those rumors, I don't know. Then again, this was a program that was closely held, so there aren't a lot of spare parts lying around either. At the end of the program, they boxed the stuff up and sent it to that warehouse we see at the end of Indiana Jones."

Stealth legacy

Despite the loss of both aircraft, the Have Blue project was considered a success—and it led directly to the development of the F-117 Nighthawk. "Both were lost in flight test, but they became the basis—the lessons learned—for what needed to happen to produce the F-117," Burnett said.

Just as testing was beginning at Groom Lake in 1977, the Air Force awarded Lockheed a contract to develop a practical attack aircraft based on the technology, under the code name Senior Trend. The success of Have Blue's testing fed directly into the development of the F-117. But the translation would not be easy—manufacturing problems and other delays pushed back the first flight of what would be the first F-117 prototype to June of 1981.

While the F-117 was based largely on the same math that created Have Blue, there were a number of differences between the two—some simply because the F-117 had to accommodate two weapons bays and be an actual combat plane. "The F-117 is a much larger aircraft," Burnett said.

Other aspects of the design were based on the lessons learned from flight testing. "There was a large reduction in the leading edge sweep of the wing, for instance," Burnett explained. "Some of the trim of the vehicle—the shape of the closeout on the aft end of the vehicle, for instance—was modified so that we could get the pitching moment back where we wanted it." (A pitching moment here refers to the torque created on the aircraft aerodynamic forces that caused the sudden pitch during the fateful aborted landing of HB1001.)

Another modification was made to the pair of vertical control fins on the aircraft's tail. "They went from inboard canting to outboard canting based on our lessons learned," Burnett said. "The tails were much larger." There were changes in the cockpit layout as well, as the pilots had complained about the F-16 "side stick" in Have Blue. There was "a lot of detailed work on the exhaust system," he added.

Other aspects of the design changes were not as visible but just as important. One of these was how the aircraft's fly-by-wire system measured where the aircraft was pointing. Because of its unusual aerodynamics, the F-117 needed more direct measures of "air data" than the F-16 did, so additional control laws and sensor feedback systems had to be added into the fly-by-wire system.

The lineage of Have Blue extends far beyond the Nighthawk, however. The same math that was used in Echo 1 to help design Have Blue has been refined over the years, and the increased power of computing has made it possible to achieve the same (or better) results with designs with much more subtle geometry—math that resulted in the F-22 Raptor and F-35 Lightning II designs.

"While we had to use a very simple faceted shape back in the '70s," Burnett said, "our computers and our understanding of the equations that governed the physics have continued to evolve—not go through a revolutionary step change. And our materials we use have gone through more of an evolutionary change as well. So yes there is a lineage that can be traced back, the DNA is similar."

There's one other bit of DNA that's the same in the latest stealth aircraft Lockheed builds—some of the engineers that worked on them are veterans of the Have Blue program. Changing the way stealth works evidently earns you a bit of job security.