So DARPA turned to the U.S. Navy. But the Navy was moving slowly with X-31, averse to the kind of risk such a program came with.
“I had been working on [Michael Francis] for a couple years to try to get him to come to DARPA,” Allburn remembered. “The program was experiencing uncertain funding and delays. Mike did a bang up job.”
Francis came to DARPA from the Air Force Space Division (now Space and Missile Systems Center, Los Angeles AFB) in 1991 and grasped what needed to be done.
“Transferring the airplane from Rockwell at Palmdale [California] to NASA Dryden [Edwards AFB] was the way to go,” he said.
With NASA collaboration and the maneuver milestones created by Francis in place, progress came swiftly.
Said Francis, “Instead of a test plan calculated to be 12 years long we accomplished most of our original goals in six months!”
Greenlighted by Allburn in 1986, X-31 was the first international X-plane.
The X-31 EFM program logged a staggering 559 research flights. Along the way, two X-31 airframes graphically demonstrated the advantages Herbst had theorized in close-in dogfights. The X-31s soundly outperformed aircraft lacking thrust vectoring, using post-stall maneuvers to achieve a potential kill ratio of 30 to 1.
“We proved that thrust vectoring really was an advantage for this form of combat,” Francis said.
In addition, the X-31 program proved the viability of a (simulated) tailless fighter design and was one of the first experimental aircraft programs to introduce and employ helmet-mounted displays for pilots.
Unfortunately, one of the X-31s was lost in an accident in January 1995. The pilot, Karl-Heinz Lang, ejected safely before the aircraft crashed in the desert just north of Edwards AFB. An investigation indicated the crash resulted from ice accretion on the aircraft’s nose boom.
The X-31 EFM program logged a staggering 559 research flights. Along the way, two X-31 airframes graphically demonstrated the advantages Herbst had theorized in close-in dogfights. The X-31s soundly outperformed aircraft lacking thrust vectoring, using post-stall maneuvers to achieve a potential kill ratio of 30 to 1.
Though the EFM program concluded in 1995, the X-31 lived on. By 2000, the remaining airframe was transferred to NAS Patuxent River, Maryland, to undertake ESTOL (extremely short takeoff and landing) research for the U.S. Navy and the German government under the VECTOR program.
“I think we did more with X-31 than has been done with any X-plane,” Francis said. “We conquered the stall barrier more completely than any other airplane.”
X-45 J-UCAS
In 1992, Francis “started dabbling” with the “UTA concept” (Unmanned Tactical Aircraft) that would later yield the X-45 and become the $4 billion Joint Unmanned Combat Air Systems (J-UCAS) program.
As the X-31 EFM program came to a close, Mike Leahy was an Air Force major working at Wright Patterson AFB with the Directorate of Science and Technology, the acquisition arm that governed the Air Force Research Laboratory (AFRL). He had a background in manned robotics and taught robotics at the Air Force Institute of Technology.
“I saw what DARPA was doing with Global Hawk and Darkstar,” Leahy said, “and I kind of became the staff go-to guy for UAVs.”
Maj. Gen. Richard Paul, commander of AFRL at the time, told Leahy he wanted AFRL to be involved with X-45, and wanted Leahy to be the one doing it.
Still attached to AFRL, Leahy spent 1996 and 1997 working with initial DARPA X-45 program manager Larry Birckelbaw to craft what is arguably the most ambitious and capable unmanned combat aerial vehicle to date.
“We didn’t want to do a tech demonstrator,” Leahy explained. “Larry and I wanted something that was on a direct path to being a production system. We did operational studies and built them into the program. The contractor candidates needed to first prove that their system could accomplish a useful military mission. The one we picked was suppression of enemy air defenses [SEAD] because that was challenging and needed.”
“We picked a cost target for the program initially at one-third the cost of the Joint Strike Fighter,” Leahy said. “You had to be able to do the mission, do it affordably and use simulation for a lot of research.” They selected Boeing to build the X-45.
The year was 1999 and Birckelbaw decided to leave DARPA. Offered the opportunity to become the X-45 program manager, Leahy leapt at the opportunity.
“If you were in the field I was in at the time, this was your dream job. There are not many flight test programs where you can say you were there from concept to something that flew,” Leahy said.
DARPA’s X-45 program produced a UAV with tactical aircraft performance, which demonstrated formation flight, manned/unmanned teaming, and a coordinated strike against simulated radars and missile launchers. X-45 could be seen as the proof-of-concept vehicle for the unmanned combat air vehicle (UCAV) concept. NASA Dryden photo
Conducted in three phases, the X-45 program aimed to produce autonomous UCAVs that eventually would “fly in packs, searching for enemy anti-aircraft missile launchers, working together to destroy them under the supervision of a human operator, who could be located anywhere in the world,” said Leahy following the first flight of the X-45A on May 22, 2002, at NASA’s Dryden facility in California.
He remained DARPA’s X-45 PM for just one more flight, leaving to complete his senior military education at the Industrial College of the Armed Forces later in 2002. Reflecting on the program, he noted that X-45 was much more than a flight test vehicle.
“This wasn’t just an X-plane program,” Leahy said. “This was really a systems program. We were integrating existing things into a system in a way that had never been done before. You had to create something that could not be ignored.”
Ultimately, that’s just what X-45 did, becoming J-UCAS in 2003. By 2005, the effort had demonstrated formation flight with two X-45As, culminating in a “graduation combat demonstration” over the California desert in which the X-45As simulated a coordinated strike against radars and missile launchers.
Unfortunately, the J-UCAS program and the X-45A were consigned to history following the 2006 Quadrennial Defense Review, which unexpectedly ended the program.
“This wasn’t just an X-plane program,” Leahy said. “This was really a systems program. We were integrating existing things into a system in a way that had never been done before.”
Looking back, Leahy considered his time as X-45 program manager a highlight of his career.
“Seeing paper transform into reality with a living, breathing X-45 was really satisfying. And the people we had… everybody pulled together and was equally committed on both the government and Boeing sides. They were committed to success and being there.”
Each of these highly visible programs has contributed to future combat and civilian aircraft designs. For combat aircraft, the X-29 and X-31 demonstrated the advantages of unconventional planforms, tailless designs, thrust vectoring, and other technologies that contributed to high angle of attack maneuvering and “pointability” in a dogfight scenario. The technologies and systems demonstrated by DARPA directly influenced the requirements, and ultimately the designs for the F-22 and F-35 operational aircraft. The X-45 brought tactical aircraft performance, stealth qualities, and autonomy to the slow, pedestrian aircraft of the UAV world at the time, representing a giant step toward the realization of an unmanned, autonomous, combat air vehicle.
DARPA and experimental aircraft share a storied history, and the story surely has chapters to come. Consider the current Experimental Spaceplane program. If things go well, the nation eventually will have an entirely new class of spacecraft system that provides short-notice, low-cost access to space with aircraft-like operability, reliability, and cost-efficiency.