Category NASA’S CONTRIBUTIONS TO AERONAUTICS

During that same month, the findings were released of what the FAAs offi­cial historical record details as its first joint research project with NASA.[188]

A year earlier, during May and June 1964, two series of flight tests were conducted using FAA aircraft with NASA pilots to study the haz­ards of light to moderate air turbulence to jet aircraft from several per­spectives. The effort was called Project Taper, short for Turbulent Air Pilot Environment Research.[189] In conjunction with ground-based wind tunnel runs and early use of simulator programs, FAA Convair 880 and

Boeing 720 airliners were flown to define the handling qualities of air­craft as they encountered turbulence and determine the best methods for the pilot to recover from the upset. Another part of the study was to determine how turbulence upset the pilots themselves and if any changes to cockpit displays or controls would be helpful. Results of the project presented at a 1965 NASA Conference on Aircraft Operating Problems indicated that in terms of aircraft control, retrimming the stabilizer and deploying the spoilers were "valuable tools,” but if those devices were to be safely used, an accurate g-meter should be added to the cockpit to assist the pilot in applying the correct amount of control force. The pilots also observed that initially encountering turbulence often cre­ated such a jolt that it disrupted their ability to scan the instrument dials (which remained reliable despite the added vibrations) and rec­ommended improvements in their seat cushions and restraint system.[190]

But the true value of Project Taper to making safer skyways may have been the realization that although aircraft and pilots under con­trolled conditions and specialized training could safely penetrate areas of turbulence—even if severe—the better course of action was to find ways to avoid the threat altogether. This required further research and improvements in turbulence detection and forecasting, along with the ability to integrate that data in a timely manner to the ATC system and cockpit instrumentation.[191]

Another NASA air traffic simulation tool, the Future ATM Concepts Evaluation Tool (FACET), was created to allow researchers to explore, develop, and evaluate advanced traffic control concepts. The system can operate in several modes: playback, simulation, live, or in a sort of hybrid mode that connects it with the FAAs Enhanced Traffic Management System (ETMS). ETMS is an operational FAA program that monitors and reacts to air traffic congestion, and it can also predict when and where conges­tion might happen. (The ETMS is responsible, for example, for keeping a plane grounded in Orlando because of traffic congestion in Atlanta.) Streaming the ETMS live data into a run of FACET makes the simula­tion of a new advanced traffic control concept more accurate. Moreover, FACET is able to model airspace operations on a national level, processing the movements of more than 5,000 aircraft on a single desktop computer, taking into account aircraft performance, weather, and other variables.[257]

Some of the advanced concepts tested in FACET include allowing aircraft to have greater freedom in maintaining separation on their own,[258] integrating space launch vehicle and aircraft operations into the

airspace, and monitoring how efficiently aircraft comply with ATC instructions when their flights are rerouted.[259] In fact, the last of these concepts was so successful that it was deployed into the FAA’s operational ETMS. NASA reports that the success of FACET has lead to its use as a simulation tool not only with the FAA, but also with sev­eral airlines, universities, and private companies. For example, Flight Dimensions International—the world’s leading vendor of aircraft sit­uational displays—recently integrated FACET with its already popu­lar Flight Explorer product. FACET won NASA’s 2006 Software of the Year Award.[260]

By the end of the Second World War, aviation was already well into the jet age, and man was flying yet higher and faster in his quest for space. During the years after the end of the war, human factors research con­tinued to evolve in support of this movement. A multiplicity of human and animal studies were conducted during this period by military, civil­ian, and Government researchers to learn more about such problems as acceleration and deceleration, emergency egress from high-speed jet aircraft, explosive decompression, pressurization of suits and cockpits,

and the biological effects of various types of cosmic rays. In addition, a significant amount of work concentrated on instrument design and cockpit display.[327]

During the years leading up to America’s space program, humans were already operating at the edge of space. This was made possible in large part by the cutting-edge performance of the NACA-NASA high­speed, high-altitude rocket "X-planes”—progressing from the Bell X-1, in which Chuck Yeager became the first person to officially break the sound barrier, on October 14, 1947, to the phenomenal hypersonic X-15 rocket plane, which introduced man to true space flight.[328]

These unique experimental rocket-propelled aircraft, devel­oped and flown from 1946 through 1968, were instrumental in helping scientists understand how best to sustain human life dur­ing high-speed, high-altitude flight.[329] One of the more important human factors developments employed in the first of this series, the Bell X-1 rocket plane, was the T-1 partial pressure suit designed by Dr. James Henry of the University of Southern California and produced by the David Clark Company.[330] This suit proved its worth during an August 25, 1949, test flight, when X-1 pilot Maj. Frank K. "Pete” Everest lost cabin pressure at an altitude of more than 65,000 feet. His pressure suit automatically inflated, and though it constricted him almost to the point of incapacitation, it nevertheless kept him alive until he could descend. He thus became the first pilot saved by the emergency use of a pressure suit.[331]

During the 1950s and 1960s, the NACA and NASA tested several additional experimental rocket planes after the X-1 series; however, the most famous and accomplished of these by far was the North American X-15. During the 199 flights this phenomenal rocket plane made from 1959 to 1968, it carried its pilots to unprecedented hypersonic speeds of nearly 7 times the speed of sound (4,520 mph) and as high as 67 miles above the Earth.[332] The wealth of information these flights continued to produce, nearly right up until the first piloted Moon flight, enabled tech­nology vital to the success of the NASA piloted space program.

One of the X-15 program’s more important challenges was how to keep its pilots alive and functioning in a craft traveling through space at hypersonic speeds. The solution was the development of a full – pressure suit capable of sustaining its occupant in the vacuum of space yet allowing him sufficient mobility to perform his duties. This innova­tion was an absolute must before human space flight could occur.

The MC-2 full-pressure suit provided by the David Clark Co. met these requirements, and more.[333] The suit in its later forms, the A/P-22S-2 and A/P-22S-6, not only provided life-sustaining atmospheric pressure, breathable oxygen, temperature control, and ventilation, but also a para­chute harness, communications system, electrical leads for physiolog­ical monitoring, and an antifogging system for the visor. Even with all these features, the pilot still had enough mobility to function inside the aircraft. By combining the properties of this pressure suit with those of the X-15 ejection seat, the pilot at least had a chance for emergency escape from the aircraft. This suit was so successful that it was also adapted for use in high-altitude military aircraft, and it served as the template for the suit developed by B. F. Goodrich for the Mercury and Gemini piloted space programs.[334]

The development of a practical spacesuit was not the only human factors contribution of the X-15 program. Its pioneering emphasis on the physiological monitoring of the pilot also formed the basis of that used in the piloted space program. These in-flight measurements and later analysis were an important aspect of each X-15 flight. The aero – medical data collected included heart and respiratory rates, electrocardio­graph, skin temperature, oxygen flow, suit pressure, and blood pressure.

Through this information, researchers were able to better under­stand human adaptation to hypersonic high-altitude flight.[335]

The many lessons learned from these high-performance rocket planes were invaluable in transforming space flight into reality. From a human factors standpoint, these flights provided the necessary testbed for ush­ering humans into the deadly environment of high-altitude, high-speed flight—and ultimately, into space.

Another hazardous type of human research activity conducted after World War II that contributed to piloted space operations was the series of U. S. military piloted high-altitude balloon flights conducted in the 1950s and 1960s. Most significant among these were the U. S. Navy Strato – Lab flights and the Air Force Manhigh and Excelsior programs.[336]

The information these flights provided paved the way for the design of space capsules and astronaut pressure suits, and they gained impor­tant biomedical and astronomical data.

The Excelsior program, in particular, studied the problem of emer­gency egress high in the stratosphere. During the flight of August 16, 1960, Air Force pilot Joseph Kittinger, Jr., ascended in Excelsior III to an altitude of 102,800 feet before parachuting to Earth. During this highest-ever jump, Kittinger went into a freefall for a record 4 minutes 36 seconds and attained a record speed for a falling human body out­side of an aircraft of 614 mph.[337] Although, thankfully, no astronaut has had to repeat this performance, Kittinger showed how it could be done.

Yet another human research contribution from this period that proved to be of great value to the piloted space program was the series of impact deceleration tests conducted by U. S. Air Force physician Lt. Col. John P. Stapp. While strapped to a rocket-propelled research sled on a 3,500-foot track at Holloman Air Force Base (AFB), NM, Stapp made 29 sled rides during the years of 1947-1954. During these, he attained speeds of up to 632 mph, making him—at least in the eyes of the press— the fastest man on Earth, and he withstood impact deceleration forces of as high as 46 times the force of gravity. To say this work was haz­ardous would be an understatement. While conducting this research, Stapp suffered broken bones, concussions, bruises, retinal hemorrhages, and even temporary blindness. But the knowledge he gained about the effects of acceleration and deceleration forces was invaluable in delin­eating the human limitations that astronauts would have while exiting and reentering the Earth’s atmosphere.[338]

All of these flying and research endeavors involved great danger for the humans directly involved in them. Injuries and fatalities did occur, but such was the dedication of pioneers such as Stapp and the pilots of these trailblazing aircraft. The knowledge they gained by putting their lives on the line—knowledge that could have been acquired in no other way—would be essential to the establishment of the piloted space pro­gram, looming just over the horizon.

NASA established this project in 1996 to increase the capability of the Nation’s air transport activities. This program’s specific goal was to develop a set of "decision support tools” that would help air traffic service providers, aircrew members, and airline operations centers in streamlining gate-to-gate operations throughout the NAS.[431] Project personnel were tasked with researching and developing advanced

concepts within the air traffic management system to the point where the FAA and the air transport industry could develop a preproduction prototype. The program ended in 2004, but implementation of these tools into the NAS addressed such air traffic management challenges as complex airspace operations and assigning air and ground responsi­bilities for aircraft separation. Several of the technologies developed by this program received "Turning Goals into Reality” awards, and some of these—for example, the traffic management adviser and the collab­orative arrival planner—are in use by ATC and the airlines.[432]

Most of the free-flight model research conducted by NASA to evaluate dynamic stability and control within the flight envelope has focused on military configurations and a few radical civil aviation designs. This sit­uation resulted from advances in the state of the art for design methods for conventional subsonic configurations over the years and many expe­riences correlating results of model and airplane tests. As a result, trans­port design teams have collected massive data and experience bases for transports that serve as the corporate knowledge base for derivative air­craft. For example, companies now have considerable experience with the accuracy of their conventional static wind tunnel model tests for the prediction of full-scale aircraft characteristics, including the effects of Reynolds number. Consequently, testing techniques such as free-flight tests do not have high technical priority for such organizations.

The radical Blended Wing-Body (BWB) flying wing configuration has been a notable exception to the foregoing trend. Initiated with NASA sponsorship at McDonnell-Douglas (now Boeing) in 1993, the subsonic BWB concept carries passengers or payload within its wing structure to minimize drag and maximize aerodynamic efficiency.[503] Over the past 16 years, wind tunnel research and computational studies of various BWB configurations have been conducted by NASA-Boeing teams to assess cruise conditions at high subsonic speeds, takeoff and landing charac­teristics, spinning and tumbling tendencies, emergency spin/tumble recovery parachute systems, and dynamic stability and control.

By 2005, the BWB team had conducted static and dynamic force tests of models in the 12-Foot Low-Speed Tunnel and the 14- by 22-Foot Tunnel to define aerodynamic data used to develop control laws and con­trol limits, as well as trade studies of various control effectors available

on the trailing edge of the wing. Free-flight testing then occurred in the Full-Scale Tunnel with a 12-foot-span model.[504] Results of the flight test indicated satisfactory flight behavior, including assessments of engine – out asymmetric thrust conditions.

In 2002, Boeing contracted with Cranfield Aerospace, Ltd., for the design and production of a pair of 21-foot-span remotely piloted models of BWB vehicles known as the X-48B configuration. After con­ventional wind tunnel tests of the first X-48B vehicle in the Langley Full – Scale Tunnel in 2006, the second X-48B underwent its first flight in July 2007 at the Dryden Flight Research Center. The BWB flight-test team is a cooperative venture between NASA, Boeing Phantom Works, and the Air Force Research Laboratory. The first 11 flight tests of the 8.5- percent-scale vehicle in 2007 focused on low-speed dynamic stability and control with wing leading-edge slats deployed. In a second series of flights, which began in April 2008, the slats were retracted, and higher speed studies were conducted. Powered by three model aircraft turbojet engines, the 500-pound X-48B is expected to have a top speed of about 140 mph. A sequence of flight phases is scheduled for the X-48B with various objectives within each study directed at the technology issues facing the implementation of the innovative concept.

The design of an efficient aircraft or spacecraft involves the use of the wind tunnel. These tools simulate flight conditions, including Mach num­ber and scale effects, in a controlled environment. Over the late 19th, 20th, and early 21st centuries, wind tunnels evolved greatly, but they all incorporate five basic features, often in radically different forms. The main components are a drive system, a controlled fluid flow, a test sec­tion, a model, and instrumentation. The drive system creates a fluid flow that replicates flight conditions in the test section. That flow can move at subsonic (up to Mach 1), transonic (Mach 0.75 to 1.25), supersonic (up to Mach 5), or hypersonic (above Mach 5) speeds. The placement of a scale model of an aircraft or spacecraft in the test section via balances allows the measurement of the physical forces acting upon that model with test instrumentation. The specific characteristics of each of these compo­nents vary from tunnel to tunnel and reflect the myriad of needs for this testing technology and the times in which experimenters designed them.[529]

Wind tunnels allow researchers to focus on isolating and gather­ing data about particular design challenges rooted in the four main systems of aircraft: aerodynamics, control, structures, and propulsion. Wind tunnels measure primarily forces such as lift, drag, and pitching moment, but they also gauge air pressure, flow, density, and tempera­ture. Engineers convert those measurements into aerodynamic data to evaluate performance and design and to verify performance predic­tions. The data represent design factors such as structural loading and strength, stability and control, the design of wings and other elements, and, most importantly, overall vehicle performance.[530]

Most NACA and NASA wind tunnels are identified by their location, the size of their test section, the speed of the fluid flow, and the main design characteristic. For example, the Langley 0.3-Meter Transonic

Cryogenic Tunnel evaluates scale models in its 0.3-meter test section between speeds of Mach 0.2 to 1.25 in a fluid flow of nitrogen gas. A spe­cific application, 9- by 6-Foot Thermal Structures Tunnel, or the exact nature of the test medium, 8-Foot Transonic Pressure Tunnel, can be other characterizing factors for the name of a wind tunnel.

One man’s vision for the possibilities of new synthetic adhesives had a powerful impact on history. Before World War II, Geoffrey de Havilland had designed the recordbreaking Comet racer and Albatross airliner, both
made of wood.[670] Delivering a speech at the Royal Aeronautical Society in London in April 1935, however, de Havilland seemed to have already written off wooden construction. "Few will doubt, however,” he said, "that metal or possibly synthetic material will eventually be used universally, because it is in this direction we must look for lighter construction.”[671] Yet de Havilland would introduce 6 years later the immortal D. H. 98 Mosquito, a lightweight, speedy, multirole aircraft mass-produced for the Royal Air Force (RAF).

De Havilland’s decision to offer the RAF an essentially all-wooden aircraft might seem to be based more on logistical pragmatism than aerodynamic performance. After all, the British Empire’s metal stocks were already committed to building the heavy Lancaster bombers and Spitfire fighters. Wooden materials were all that were left, not to men­tion the thousands of untapped and experienced woodworkers.[672] But the Mosquito, designed as a lightweight bomber, became a success because it could outperform opposing fighters. Lacking guns for self-defense, the Merlin-powered Mosquito survived by outracing its all-metal opponents.[673] Unlike metal airplanes, which obtain rigidity by using stringers to con­nect a series of bulkheads,[674] the Mosquito employed a plywood fuselage that was built in two halves and glued together.[675] De Havilland used a new resin called Aerolite as the glue, replacing the casein-type resins that had proved so susceptible to corrosion.[676] The Mosquito’s construction technique anticipated the simplicity and strength of one-piece fuselage structures, not seen again until the first flight of Lockheed’s X-55 ACCA, nearly six decades later.

For most of the 1940s, both the Government and industry focused on keeping up with wartime demand for vast fleets of all-metal aircraft. Howard Hughes pushed the boundaries of conventional flight at the
time with the first—and ultimately singular—flight of the Spruce Goose, which adopted a fuselage structure developed from the same Haskelite material pioneered by Clark in the late 1930s.

Pioneering work on plastic structures continued, with research­ers focusing on the basic foundations of the processes that would later gain wide application. For example, the NACA funded a study by the Laboratory for Insulation Research at the Massachusetts Institute of Technology (MIT) that would explore problems later solved by auto­claves. The goal of the MIT researchers was to address a difficulty in the curing process for thermoset plastics based on heating a wood-resin composite between hot plates. Because wood and resin were poor heat conductors, it would take several hours to raise the center of the mate­rial to the curing temperature. In the process, temperatures at the sur­face could rise above desired levels, potentially damaging the material even as it was being cured. The NACA-funded study looked for new ways to rapidly heat the material uniformly on the surface and at the cen­ter. The particular method involved inserting the material into a high- frequency electrical field, attempting to heat the material from the inside using the "dielectric loss of the material.”[677] This was an ambitious objec­tive, anticipating and appropriating the same principles used in micro­wave ovens for building aircraft structures. Not surprisingly, the study’s authors hoped to manage expectations. As they were not attempting to arrive at a final solution, the authors of the final report said their contribution was to "lay the groundwork for further development.” Their final conclusion: "The problem of treating complicated shapes remains to be solved.”[678]

Meanwhile, a Douglas Aircraft engineer hired shortly before World War II began would soon have a profound impact on the plastic com­posite industry. Brandt Goldsworthy served as a plastics engineer at Douglas during the war, where he was among the first to combine fiber­glass and phenolic resin to produce laminated tooling.[679] The invention did not spark radical progress in the aviation industry, although the
material was used to design ammunition chutes used to channel machine gun cartridges from storage boxes and into aircraft machine guns.[680] More noteworthy, after leaving Douglas in 1945 to start his own com­pany, Goldsworthy would pioneer the automation of the manufactur­ing process for composite materials. Goldsworthy’s invention of the pultrusion process in the 1950s would make durable and high-strength composites affordable for a range of applications, from cars to aircraft parts to fishing rods.[681]

As plastic composites continued to mature, the U. S. Army Air Corps began an ambitious series of experiments in the early 1940s on new com­posite material made from fiberglass-polyester blends. In the next two decades, the material would prove useful on aircraft as nose radomes and as both helicopter and propeller blades.[682] The combination of fiber­glass and polyester also proved tempting to the military as a potential new load-bearing structural material for aircraft. In 1943, researchers at Wright-Patterson Air Force Base fabricated an aft fuselage for the Vultee BT-15 basic trainer using fiberglass and a polyester material called Plaskon, with balsa used as a sandwich core material.[683] The Wright Field experiments also included the development of an outer wing panel made of cloth and cellulose acetate for a North American AT-6C.[684] The BT-15 experiment proved unsuccessful, but the plastic wing of the AT-6C was more promising, showing only minor wing cracks after 245 flight hours.[685]

Peter W. Merlin

For over a half century, NASA researchers have worked to make remotely piloted research vehicles to complement piloted aircraft, in the forms of furnishing cheap "quick look" design validations, under­taking testing too hazardous for piloted aircraft, and furnishing new research capabilities such as high-altitude solar-powered environmental monitoring. The RPRV has evolved to sophisticated fly-by-wire inherently unstable vehicles with composite structures and integrated propulsion.

INCE THE MID-1 990S, researchers at the National Aeronautics and Space Administration (NASA) have increasingly relied on unmanned aerial vehicles (UAV s) to fill roles traditionally defined by piloted aircraft. Instead of strapping themselves into the cockpit and taking off into the unknown, test pilots more often fly remotely piloted research vehicles (RPRVs) from the safety of a ground-based control sta­tion. Such craft are ideally suited to serve as aerodynamic and systems testbeds, airborne science platforms, and launch aircraft, or to explore unorthodox flight modes. NASA scientists began exploring the RPRV concept at Dryden Flight Research Center, Edwards, CA, in the 1960s. Since then, NASA RPRV development has contributed significantly to such technological innovations as autopilot systems, data links, and iner­tial navigation systems, among others. By the beginning of the 21st cen­tury, use of the once-novel RPRV concept had become standard practice.

There is no substitute—wind tunnel and computer modeling notwith­standing—for actual flight data. The RPRV provides real-world results while providing the ground pilot with precisely the same responsibilities and tasks as if he were sitting in a cockpit onboard a research airplane. As in piloted flight-testing, the remote pilot is responsible for perform­ing data maneuvers, evaluating vehicle and systems performance, and reacting to emergency situations.

A ground pilot may, in fact, be considered the most versatile ele­ment of an RPRV system. Since experimental vehicles are designed to

venture into unexplored engineering territory, the remote pilot may be called upon to repeat or abort a test point, or execute additional tasks not included in the original flight plan. Not all unmanned research vehicles require a pilot in the loop, but having one adds flexibility and provides an additional level of safety when performing hazardous maneuvers.[880]

In 1989, engineers from NASA Ames Research Center and the Phantom Works, a division of McDonnell-Douglas—and later Boeing, following a merger of the two companies—began development of an agile, tailless aircraft configuration. Based on results of extensive wind tunnel test­ing and computational fluid dynamics (CFD) analysis, designers pro­posed building the X-36—a subscale, remotely piloted demonstrator—to validate a variety of advanced technologies. The X-36 project team con­sisted of personnel from the Phantom Works, Ames, and Dryden. NASA and Boeing were full partners in the project, which was jointly funded under a roughly fifty-fifty cost-sharing arrangement. Combined program cost for development, fabrication, and flight-testing of two aircraft was approximately $21 million. The program was managed at Ames, while Dryden provided flight-test experience, facilities, infrastructure, and range support during flight-testing.

The X-36 was a 28-percent-scale representation of a generic advanced tailless, agile, stealthy fighter aircraft configuration. It was about 18 feet long and 3 feet high, with a wingspan of just over 10 feet. A single

Williams International F112 turbofan engine provided about 700 pounds of thrust. Fully fueled, the X-36 weighed about 1,250 pounds.

The vehicle’s small size helped reduce program costs but increased risk because designers sacrificed aircraft system redundancy for lower weight and complexity. The subscale vehicle was equipped with only a single-string flight control system rather than a multiply redundant sys­tem more typical in larger piloted aircraft. Canards on the forward fuse­lage, split ailerons on the trailing edges of the wings, and an advanced thrust-vectoring nozzle provided directional control as well as speed brake and aerobraking functions. Because the X-36 was aerodynamically unsta­ble in both pitch and yaw, an advanced single-channel digital fly-by-wire control system was required to stabilize the aircraft in flight.[1013] Risks were mitigated by using a pilot-in-the-loop approach, to eliminate the need for expensive and complex autonomous flight control systems and the risks associated with such systems’ inability to correct for unknown or unfore­seen phenomena once in flight. Situational-awareness data were provided to the pilot’s ground station through a video camera mounted in the vehi­cle’s nose, a standard fighter-type head-up display, and a moving-map representation of the vehicle’s position.

Boeing project pilot Laurence A. Walker was a strong advocate for the advantages of a full-sized ground cockpit. When an engineer designs a control station for a subscale RPRV, the natural tendency might be to reduce the cockpit control and display suite, but Walker demonstrated that the best practice is just the opposite. In any ground-based cock­pit, the pilot will have fewer natural sensory cues such as peripheral vision, sound, and motion. Re-creating motion cues was impractical, but audio, visual, and HUD cues were re-created in order to improve situational awareness comparable to that of a full-sized aircraft.[1014] The X-36 Ground Control Station included a full-size stick, rudder pedals and their respective feel systems, throttle, and a full complement of mod­ern fighter-style switches. Two 20-inch monitors provided visual displays to the pilot. The forward-looking monitor provided downlinked video from a canopy-mounted camera, as well as HUD overlay with embedded flight-test features. The second monitor displayed a horizontal situation indicator, engine and fuel information, control surface deflection indi­cators, yaw rate, and a host of warnings, cautions, and advisories. An audio alarm alerted the pilot to any new warnings or cautions. A redun­dant monitor shared by the test director and GCS engineer served as a backup, should either of the pilot’s monitors fail.[1015] To improve the pilot’s ability to accurately set engine power and to further improve situational awareness, the X-36 was equipped with a microphone in what would have been the cockpit area of a conventional aircraft. Downlinked audio from this microphone proved to be a highly valuable cue and alerted the team, more than once, to problems such as screech at high-power settings and engine stalls before they became serious.

The X-36 had a very high roll rate and a mild spiral divergence. Because of its size, it was also highly susceptible to gusty wind condi­tions. As a result, the pilot had to spend a great deal of time watching the HUD, the sole source of attitude cues. Without kinesthetic cues to signal a deviation, anything taking the pilot’s focus away from the HUD (such as shuffling test cards on a kneeboard) was a dangerous distrac­tion. To resolve the problem, the X-36 team designed a tray to hold test cards at the lower edge of the HUD monitor for easy viewing.[1016] Walker

piloted the maiden flight May 17, 1997. The X-36 flight-test envelope was limited to 160 knots to avoid structural failure in the event of a flight con­trol malfunction. If a mishap occurred, an onboard parachute was pro­vided to allow safe recovery of the X-36 following an emergency flight termination. Fortunately, the initial flight was a great success with no obvious discrepancies.

The second flight, however, presented a significant problem as the video and downlink signals became weak and intermittent while the X-36 was about 10 miles from the GCS at 12,000 feet altitude. As pro-^^^B^9 grammed to do, the X-36 went into lost-link autonomous operation, giv­ing the test team time to initiate recovery procedures to regain control.

The engineers were concerned, as each intermittent glimpse of the data showed the vehicle in a steeper angle of bank, well beyond what had yet been flown. Eventually, Walker regained control and made an unevent­ful landing. The problem was later traced to a temperature sensitivity problem in a low-noise amplifier.[1017] Phase I of the X-36 program pro­vided a considerable amount of data on real-time stability margin and parameter identification maneuvers. Automated maneuvers, uplinked to the aircraft, greatly facilitated envelope expansion, and handling qual­ities were found to be remarkably good.

Phase II testing expanded the flight envelope and demonstrated new software. New control laws and better derivatives improved stabil­ity margins and resulted in improved flying qualities. The final Phase II flight took place November 12, 1997. During a 25-week period, 31 safe and successful research missions had been made, accumulating a total of 15 hours and 38 minutes of flight time and using 4 versions of flight control software.[1018] In a follow-on effort, the Air Force Research Laboratory (ARFL) contracted Boeing to fly AFRL’s Reconfigurable Control for Tailless Fighter Aircraft (RESTORE) software as a dem­onstration of the adaptability of a neural-net algorithm to compensate for in-flight damage or malfunction of aerodynamic control surfaces.

Two RESTORE research flights were flown in December 1998, with the adaptive neural-net software running in conjunction with the orig­inal proven control laws. Several in-flight simulated failures of con­trol surfaces were introduced as issues for the reconfigurable control algorithm to address. Each time, the software correctly compensated

for the failure and allowed the aircraft to be safely flown in spite of the degraded condition.[1019] The X-36 team found that having a trained test pilot operate the vehicle was essential because the high degree of air­craft agility required familiarity with fighter maneuvers, as well as with the cockpit cues and displays required for such testing. A test pilot in the loop also gave the team a high degree of flexibility to address prob­lems or emergencies in real time that might otherwise be impossible with an entirely autonomous system. Design of the ground cockpit was also critical, because the lack of normal pilot cues necessitated devel­opment of innovative methods to help replace the missing inputs. The pilot also felt that it was vital for flight control systems for the subscale vehicle to accurately represent those of a full-scale aircraft.

Some X-36 team members found it aggravating that, in the minds of some upper-level managers, the test vehicle was considered expend­able because it was didn’t carry a live crewmember. Lack of redundancy in certain systems created some accepted risk, but process and safety awareness were key ingredients to successful execution of the flight – test program. Accepted risk as it extended to the aircraft and onboard systems did not extend to processes that included qualification testing of hardware and software.[1020] The X-36 demonstrator program was aimed at validating technologies proposed by McDonnell-Douglas (and later Boeing) for early concepts of a Joint Strike Fighter (JSF) design, as well as unmanned combat air vehicle (UCAV) proposals. Results were immediately applicable to the company’s X-45 UCAV demonstrator project.[1021]

With the demise of the national SST program and the popular shift away from a supersonic airliner, a principal reason for funding super­sonic research disappeared. Nevertheless, NASA’s mission to advance aeronautics research dictated that a program should continue, although not necessarily at the previous urgency. It was obvious from the XB-70 flight test and the SST debate that the integration of the elements of a supersonic cruiser was more critical than for a subsonic aircraft. The shape of the aircraft dictated external shock wave formation, which not only changed drag but also had a major effect on the sonic boom foot­print on the ground. The shock waves within the air-breathing engine inlet had a major impact on propulsive efficiency, which affected range and had operational impact if the inlet was not operating at optimal efficiency. To integrate these elements in the design process required better knowledge of how accurate the engineers design tools were. Wind tunnel fidelity in predicting results when the models did not necessarily have the temperature or aeroelastic characteristics of a full-sized air­craft at the high-temperature cruise state required investigation. The same could be said for propulsion wind tunnel models.

NASA developed a research program known initially as Advanced Supersonic Technology (AST), which lasted from 1972 to 1981. (Because of political sensitivities, the name was changed to Supersonic Cruise Aircraft Research [SCAR] in 1974; the "Aircraft” word was deleted in 1979, to avoid connection with the contentious SST label, so it became SCR.)[1097]

The idea was to research the technical problems that had appeared during the SST development program and the XB-70 flight test. NASA Langley concentrated on refining a configuration for an advanced super­sonic cruise aircraft, and it was postulated to have a cruise speed of Mach 2.2, matching the Concorde that was entering service. Its size, payload, and range performance were also reduced in comparison with the 1963 configurations. The configuration often shown for the SCR research resembled the Boeing 2707-300, but Langley continued to favor a refine­ment of the SCAT 15F, with the arrow wing as the optimum high-speed shape. Unfortunately, without variable sweep, the arrow wing was ini­tially one of the worst low-speed shapes. Lewis Research Center stud­ies focused on a variable cycle engine (VCE) to study optimizing engine performance, including internal aerodynamics for various phases of flight, engine noise, and exhaust emission problems. Dryden and Ames did simulator studies mainly, with some uses of the XB-70 test data followed by the YF-12 test program data.

Funding for AST-SCAR-SCR was limited, mainly because of the SST fallout; nevertheless, SCAR conferences in 1976 and 1979 were well-attended and produced almost 1,000 papers.[1098] Nor was the only target application a transport. The USAF was exploring the possibility of a fighter aircraft using supersonic cruise for "global persistence” to operate deep behind the battlefront over the Central European battlefield; thus, the Air Force and its contractors were inter­ested in optimum supersonic performance in an aircraft with limited fuel. A conference at the Air Force Academy hosted by the Air Force Flight Dynamics Laboratory in February 1976 included papers on NASA research results and contractor studies that used NASA’s arrow wing to satisfy the supersonic mission requirements. The arrow wing was shown to have superior maximum L/D over the delta wing, to the point that Lockheed studies switched to it from their SST double delta configuration.[1099]

General Dynamics—later Lockheed Martin Tactical Aircraft Systems (LMTAS)—worked with NASA Langley in the early 1970s in the devel­opment of its highly maneuverable F-16 Fighting Falcon fighter.[1100] As interest developed in a supersonic cruise fighter in 1977, the company teamed with Langley researchers again to design an arrow wing for its F-16. Known as the Supersonic Cruise and Maneuverability Program (SCAMP), it resulted in the construction of two company-funded air­craft designated F-16XL, which first flew in 1982. Development of an arrow wing aircraft provided an opportunity to develop the features nec­essary to make the design practical, especially with regard to its low – speed and high-angle-of-attack characteristics. Although USAF interest shifted to the air-to-ground mission, resulting in purchase of the larger McDonnell-Douglas (later Boeing) F-15E Strike Eagle, the two shapely F-16XLs were the first flying testbeds for the arrow wing. (NASA shared in the data from the test program and wisely put the two aircraft in storage for possible future use, for they were later used to accomplish

notable work in refined aerodynamic studies, including supersonic lam­inar flow control.) The AST-SCAR-SCR program had essentially ended in 1981, as funding for NASA aeronautical research was cut because of the needs of the approaching Space Transportation System (STS, the Space Shuttle). Flight test for supersonic aircraft was too expensive. But one supersonic NASA flight-test program of the 1970s proved to be a spectacular success, one that contributed across a number of techni­cal disciplines: the Blackbirds.