As the year 1991 drew to a close, the program and its testers could take great satisfaction in what they had accomplished, including a final flight that year in the post-stall envelope up to 52° angle of attack. At this point, the two X-31 aircraft had flown 108 flights in 428 calendar days, roughly 1 flight every 4 days.15 But while this was, at first glance, a pretty impressive fly rate, it was still much less than the projected 100 flights in 325 days—0.30 flights per day—that was originally projected during test planning. Thus, though much
Flying Beyond the Stall
had, in fact, been accomplished, there was a feeling within the X-31 program office and test team that it was moving too slowly. It had taken over a year to achieve conventional envelope clearance and post-stall flight up to 52° angle of attack.16 While the engineers and test pilots were gradually expanding the envelope by flying in a controlled fashion well beyond the stall, the managers in Washington were struggling mightily to keep the program alive.
There were two fundamental reasons program personnel believed that the program was in trouble. As mentioned previously, the Navy (through NAVAIR) granted clearances for each test flight, starting with the very minimal envelope of 30,000 feet MSL, Mach 0.67, and 4 g’s that were set early in the program. The Navy’s procedure for flight-test clearance was largely developed for testing prototypes of operational aircraft, and the process was focused on minimizing program risk by taking a careful, incremental approach, building up only gradually to maximum performance. Rockwell, MBB, and DARPA all felt that this process was too slow for a purely experimental airplane program and that the slowness of progress itself was putting the program at risk, as there was a fear that program funding would dry up.
Furthermore, the Navy, while initially anointed with the job of military agent for DARPA in the X-31 program, had many overriding fiscal priorities that had a more immediate impact on their operational fleet aircraft, particu-larly in dealing with its aging F-14 Tomcat fleet (which was being converted to “Bombcats” after the Gulf War) and shepherding advanced models of the F/A-18 into service. So even as the X-31 flight-test program plodded along in 1991, there was a funding crisis developing, one in which the Navy could not be expected to go to any great lengths to support the tiny jet in the desert.
As a consequence, the DARPA program manager, Tack Nix, initiated talks with personnel at the NASA Ames-Dryden Flight Research Facility (now known as the Dryden Flight Research Center) about moving the X-31 flight-test program from Palmdale to the Dryden facility at Edwards AFB. Moving to Dryden had support from both DARPA and the German test establish-ment (WTD-61). Dryden possessed extensive flight-test facilities, including specialized control rooms and data-reduction facilities, and was in the midst of constructing a new building specifically designed for the integration of research teams and research components. This facility, the Integrated Test Facility (ITF), was designed specifically to support development of hardware and software, and the testing, analysis, and flight qualification of advanced aircraft having highly integrated flight and propulsion control systems. Another advantage was that this building offered a facility where program management, engineering support, and even the aircraft all could be located under one roof.
Other advantages to testing at Dryden were that the program would remain out west and have the benefits of the great weather and expansive R-2508
Into the Air: Initial Flight Testing
NASA Dryden Integrated Test Facility, 1991. (NASA DFRC)
flight-test range airspace that was available at Edwards AFB. In addition to the fact that the weather, on average, was poorer at NAS Patuxent River than at Edwards AFB, there also was the problem that the focus at Patuxent River was on programs that could have a direct bearing on higher-priority operational fleet aircraft, whereas the main focus at Dryden was on testing unconven-tional research airplanes. Therefore, in the daily scheduling battle for flight-test resources, the advantage would be at Dryden, where flight-testing this type of aircraft was the primary mission of the Center and not simply an “add on” to existing (and likely higher priority) operationally focused flight-test programs.
The ultimate type of testing that the X-31 would perform (i.e., dogfighting) was not something that Dryden typically did. They were used to performing in a more “pure research” mode. Dryden also was focused on data quality, not schedule pressures and airplane fly rate.
Very apparent to DARPA, which had just completed the X-29 program with NASA, was the financial benefit of testing at Dryden; this constituted, in fact, the biggest advantage of moving to Dryden. In the early 1990s, there were two different methods of accounting, or “charging,” for resources used in a flight-test program. One method was known as “institutional” funding, in which an organization received an annual budget amount for its operation and the organization’s managers determined how to support the various programs that were assigned to them. The other method was a “reimbursable” method whereby the flight-test customer was charged for each test resource as it was used.
Flying Beyond the Stall
The reimbursable method was often known as “full cost accounting” and was intended to provide managers and funding authorities (like Congress) with the knowledge of the real costs of a program. This method also expanded into charging program partners for the “services” provided to a program.
The institutional method was the method in use at that time for many NASA Centers, including Dryden. The method used by the military, including NAS Patuxent River and contractors, was the reimbursable method. Therefore, Dryden could absorb the overhead cost of its personnel and support services into its institutional overhead, saving the X-31 program an enormous amount of money. When the International Test Organization (ITO) was created for the X-31, Dryden Director Ken Szalai could decide what charges to pass through to the ITO. For example, there were no charges to the ITO for building space, NASA engineers and test pilots, or NASA chase aircraft and their fuel costs.
The ITO was charged, though, for the additional computers required to build the X-31 simulator at Dryden and any necessary new equipment that was specific to the X-31 program.17 It has been noted that, through Dryden, NASA contributed the equivalent of $14.9 million to the X-31 program in terms of indirect (personnel and support services) support.18
As might be expected, the Navy’s flight-test community was less happy with the plans to move to Dryden, as they had expected to undertake post-stall envelope expansion at Patuxent River. At this time, the plan was still to move the aircraft back to Patuxent for the tactical utility portion of the program. As noted above, DARPA and WTD-61 were in favor of the move, but Rockwell and MBB had some hesitancy with the prospect of going to Dryden. Rockwell’s experience with Dryden during the HiMAT program, and both companies’
close observation of the X-29 program, was that NASA could become so involved in the details of doing the research that schedules and progress often slowed considerably. On the other hand, Dryden had considerable experience in conducting flight tests of nonproduction research aircraft, and since flight clearance authority was to transfer from the Navy to Dryden, it was felt that the flight clearance process could potentially proceed much faster than the rate being experienced.
Even so, there were a few even within NASA who remained unconvinced that moving the X-31 to Dryden was a good move. This minority felt that the tactical utility emphasis of the X-31 made the program a better fit for the military test community rather than NASA, whose main interest (in their view) was pure research data gathering. However, NASA Dryden—and the NACA High-Speed Flight Station that had preceded it—had long engaged in programs directly related to tactical utility, including the extensive pitch-up studies NACA had undertaken on combat aircraft such as the F-86 in the 1950s. At the time this minidebate occurred, Dryden was in the midst of two
Into the Air: Initial Flight Testing
Grumman X-29 forward-swept wing test bed. (AFFTC)
other high-AOA programs: the X-29 forward-swept wing, which had just fin-ished its flights, and the F/A-18 High Alpha Research Vehicle. The X-29 was a DARPA research program with Dryden as the responsible test organization that had as its primary objective an understanding of the benefits and risks of aircraft configurations having forward-swept wings. While flight at high angles of attack was not the primary objective of this program, the X-29 was operated at angles of attack up to 52°.
The F/A-18 HARV was an F/A-18 modified with paddles similar to the X-31’s; however, the installation on the F/A-18 HARV was very heavy, and while the F/A-18 HARV did yeoman work in exploring the high-AOA regime, including three-dimensional thrust vectoring, it did not have the performance of the X-31. The X-31 had a 40 percent higher thrust-to-weight ratio, a 35 per-cent lower wing loading, a 30 perper-cent higher maximum g-limit, and twice the thrust-vectoring control power of the F/A-18 HARV. Thus, the X-31 offered NASA engineers the ability to explore areas of thrust-vectoring flight at very high angles of attack that they could not achieve with either the X-29 or the F/A-18 HARV. This was the part of the X-31 program that was attractive to the Dryden engineers.19
As the test team at Palmdale was slowly expanding the flight envelope for the X-31, DARPA in mid-1991 had made the decision to move the program to Dryden and make both NASA and the Air Force partners in the program.
Flying Beyond the Stall
NASA F/A-18 High Alpha Research Vehicle, 1996. (NASA DFRC)
On January 20, 1992, both X-31 aircraft flew in formation, piloted by Fred Knox and Dietrich Seeck, on a ferry flight from Palmdale to the Dryden facility at Edwards AFB, just 40 miles away. It would turn out that this was the only time that both aircraft were flown together.20
Shortly after the move took place, the reticent industry members’ resis-tance melted away. This was because of two NASA managers who saw the reticence and understood why it was there. These two, Ken Szalai (director of Dryden) and Gary Trippensee (the designated NASA X-31 program manager), dedicated themselves to doing things differently to support the X-31 goals and objectives. They deftly managed their own team to change to the “new”
approach and proved true to their word, becoming stalwarts of the program.