Category NASA’S CONTRIBUTIONS TO AERONAUTICS

NASA’s long heritage of research in synthetic vision has generated use­ful concepts, demonstrations of key technological breakthroughs, and prototype systems and architectures that have influenced both the pri­vate and public sectors. Much of this work has been accomplished by small teams of dedicated researchers, often using creative approaches and management styles far removed from typical big management prac­tices. As this book goes to press, synthetic vision and advanced flight path guidance constitutes a critical piece of the Agency’s future work on Integrated Intelligent Flight Deck Technologies and related activi­ties aimed at fulfilling the promise of better air transportation and mil­itary airpower. While long-range institutional and national budgetary circumstances add greater uncertainties to the challenge of forecast­ing the future, it is clear that as the advent of blind-flying instrumenta­tion transformed aviation safety and utility in the interwar years, the advent of synthetic vision will accomplish the same in the first years of the 21st century, furnishing yet another example of the enormous and continuing contributions of NASA and its people to the advancement of aeronautics.

Ice formation on aircraft poses a serious flight safety hazard. Here a NASA technician measures ice deposits on a test wing in NASA’s Icing Research Tunnel, Lewis (now Glenn) Research Center, Ohio. NASA.

Joseph R. Chambers

Since the airplane’s earliest days, maintaining safe flight at low speeds and high angles of attack has been a stimulus for research. As well, ensuring that a military fighter aircraft has good high-angle-of-attack qualities can benefit its combat capabilities. NASA research has pro­vided critical guidance on configuration effects and helped usher in the advent of powerful flight control concepts.

T THE TIME THAT the National Aeronautics and Space Administration (NASA) absorbed the National Advisory Committee for Aeronautics (NACA), it also inherited one of the more challenging technical issues of the NACA mission: to "supervise and direct the scientific study of the problems of flight with a view to their practical solution.” Since the earliest days of heavier-than-air flight, intentional or inadvertent flight at high angles of attack (high alpha) results in the onset of flow separation on lifting surfaces, stabilizing fins, and aerodynamic controls. In such conditions, a poorly designed air­craft will exhibit a marked deterioration in stability, control, and flying qualities, which may abruptly cause loss of control, spin entry, and cat­astrophic impact with the ground.[1273] Stalling and spinning have been— and will continue to be—major areas of research and development for civil and military aircraft. In the case of highly maneuverable military aircraft, high-angle-of-attack characteristics exert a tremendous influ­ence on tactical effectiveness, maneuver options, and safety.

Some of the more notable contributions of NASA to the Nation’s military aircraft community have been directed at high-angle-of-attack technology, including the conception, development, and validation of advanced ground – and flight-test facilities; advances in related disci­plinary fields, such as aerodynamics and flight dynamics; generation
of high-alpha design criteria and methods; and active participation in aircraft development programs.[1274] Applications of these NASA contribu­tions by the industry and the Department of Defense (DOD) have led to a dramatic improvement in high-angle-of-attack behavior and asso­ciated maneuverability for the current U. S. military fleet. The scope of NASA activities in this area includes ground-based and flight research at all of its aeronautical field centers. The close association of NASA, industry, and DOD, and the significant advances in the state of the art that have resulted from common objectives, are notable achievements of the Agency’s value to the Nation’s aeronautical achievements.

As clearly evidenced by U. S. military experiences, the technical area of high-angle-of-attack/departure/spin behavior will continue to challenge design teams of highly maneuverable aircraft. The Nation has been for­tunate in assembling and maintaining unique expertise and facilities for the timely identification and resolution of problems that might have had a profound impact on operational capability or program viability. In the author’s opinion, several situations are emerging that threaten the tra­ditional partnerships and mutual resources required for advancing the state of the art in high-angle-of-attack technology for military aircraft.

The end of the Cold War has naturally resulted in a significant decrease in new military aircraft programs and the need for continued research in a number of traditional research areas. As technical person­nel exit from specialty areas such as high-angle-of-attack and spin behav­ior, the corporate knowledge and experience base that was the jewel in NASA’s crown rapidly erodes, and lessons learned become forgotten.

Of even more concern is the change in traditional working-level relationships between the NASA and DOD communities. During the term of NASA Administrator Daniel S. Goldin in the 1990s, NASA turned its priorities away from its traditional links with military aircraft R&D to the extent that long-time working-level relationships between NASA, indus­try, and DOD peers were ended. At the same time, aeronautics funding within the Agency was significantly reduced, and remaining aeronautics activities were redirected to civil goals. As a result of those programmatic decisions and commitments, NASA does not even highlight military – related research as part of its current mission. It has become virtually impossible for researchers and their peers in the military, industry, or DOD research laboratories to consider the startup of highly productive, unclassified military-related programs such as the NASA F/A-18 High – Angle-of-Attack Technology program.

Meanwhile, leaders in military services and research organiza­tions have now been replaced with many who are unfamiliar with the traditional NASA-military ties and accomplishments. Without those
relationships, the military R&D organizations have turned to hiring their own aeronautical talent and conducting major research undertakings in areas that were previously exclusive to NASA Centers.

Finally, one of the more alarming trends underway has been the massive closures of NASA wind tunnels, which have been the backbone of NASA’s ability to explore concepts and ideas and to respond to high – priority military requests and problem-solving exercises in specialty areas such as high-angle-of-attack technology.

In summary, this essay has discussed some of the advances made in high-angle-of-attack technology by NASA, which have contributed to a dramatic improvement in the capabilities of the Nation’s first-line mil­itary aircraft. Without these contributions, many of the aircraft would have been subject to severe operational restrictions, excessive develop­ment costs, significantly increased risk, and unacceptable accidents and safety-of-flight issues. In the current era of relative inactivity for devel­opment of new aircraft, it is critical that the resources required to pro­vide such technology be protected and nurtured for future applications.

Three important NASA research aircraft representing different approaches to V/STOL flight pass in review over NASA’s Ames Research Center. Left to right: the deflected lift QSRA, the tilt rotor XV-15, and the vectored-thrust Harrier. NASA.

While negotiations were underway in 1993, leading to the agreement between the United States and Russia to return a Tu-144D to flight status as a supersonic flying laboratory, the HSR Program Office selected NASA Dryden to establish a Project Office for all Tu-144 activ­ities. This initially involved developing a rapport with a British com­pany, IBP, Ltd., which served as the business representative for Tupolev, now known as the Tupolev Aircraft Company (or Tupolev ANTK) after the economic evolution in Russia in the 1990s. Ken Szalai and IBP’s Judith DePaul worked to establish an effective business relationship, and this paid dividends in the ensuing complex relationships involving NASA, Rockwell, McDonnell-Douglas, Boeing, Tupolev, and IBP. A degree of cooperation flourished at a level not always observed in NASA-Russian partnerships. Having a business intermediary such as IBP navigate the paths of international business helped ensure the success of the Tu-144 experiment, according to Dryden Tu-144 Project Manager Russ Barber.[1464]

Originally, the Tu-144 flight experiment was envisioned as a 6-month, 30-flight program.[1465] As events unfolded, the experiment evolved into a two-phase operation. This was due, in part, to the inevitable delays in an enterprise of this magnitude and complexity, to learning from the results of the initial experiments, and to data acquisition issues.[1466] By 1995, after two meetings in Russia, the HSR Program Office, Boeing, Rockwell, McDonnell-Douglas, and Tupolev established the requirements for returning a Tu-144D to flight and fabricating an instrumentation system capable of supporting the postulated lineup of experiments.[1467] [1468] From a list of some 50 proposed experiments, the NASA, industry, and Tupolev officials selected 6 flight experiments for inclusion (a 7th was later added).11

A somewhat complex international organization developed that, despite the superficial appearance of duplication, ended up working very smoothly. NASA Dryden represented the HSR Program Office as the overseer for all Tu-144 activity. Boeing was contracted to install the instrumentation system, a complex task with over 700 individual pressure transducers, accelerometers, thermocouples, boundary layer rakes, pressure belts, microphones, and other sensors. NASA Dryden installed a complex French-built Damien digital data acquisition system (DAS) for five of the original six experiments.[1469] The remaining experiment, a NASA Langley Structure/Cabin Noise experiment, used its own Langley-built DAS.[1470] In a sense, traditional roles had to be adjusted, because Boeing, as the contractor, directed NASA, as the Government Agency and supplier, when to provide the necessary sensors and DAS.[1471] Boeing and Tupolev would install the sensors, and NASA would then calibrate and test them. The Damien DAS ultimately became problem­atic and led to some erroneous data recording in Phase I.[1472]

Tupolev assumed the role of returning the selected Tu-144D, SSSR – 771114, to flight. This was no trivial matter. Even though 771114 had last flown in 1990, the engines were no longer supported and had to be replaced (as discussed in a subsequent section), which necessitated major modifications to the engine nacelles, elevons, and flight deck.[1473] As Tupolev was completing this work in 1995 and 1996, IBP acted as its business interface with NASA and Boeing.

In general, the HSR program funded the American effort. The cost to NASA for the Tu-144 flight experiment was $18.3 million for 27 flights. Boeing contributed $3.3 million, and it is estimated that Tupolev spent $25 million.[1474] Tupolev gained a fully instrumented and refurbished Tu-144, but unfortunately, after NASA canceled the HSR program in 1999, Tupolev could find no other customers for its airplane.

During the initial program definition and later during the aircraft modification, a number of HSR, Dryden, and Langley personnel made numerous trips to Zhukovsky. HSR managers coordinated program schedules and experiment details, Dryden personnel observed the return to flight efforts as well as the instrumentation modifications and pro­vided flight operations inputs, and Langley instrumentation technicians and researchers assisted with their experiment installation. Among the Dryden visitors to Zhukovsky was NASA research pilot Gordon Fullerton. Fullerton was the NASA pilot interface during these development years and worked with his Tupolev counterparts on flight deck and opera­tional issues. In an interview with the author, he recalled the many con­trasts in the program regarding the Russian and American methods of engineering and flight operations. Items worthy of minute detail to the Russians seemed trivial at times to the Americans, while American prac­tices at times resulted in confused looks from the Tupolev personnel. By necessity, because of a lack of computer assets, the Tupolev pilots, engi­neers, and technicians worked on a "back of the envelope” methodology. Involvement of multiple parties in decisions was thus restricted simply because of a lack of easy means to include them all. Carryovers from the Soviet days were still prevalent in the flightcrew distribution of duties, lack of flight deck instrumentation available to the pilots, and ground procedures that would be viewed as wholly inefficient by Western air­lines. Nevertheless, Tupolev produced an elegant airplane that could fly a large payload at Mach 2.[1475]

As the American and Russian participants gained familiarity, a spirit of trust and cooperation developed that ultimately contributed to the project’s success. The means of achieving this trust were uniquely Russian. As the various American delegations arrived in Moscow or Zhukovsky, they were routinely feted to gala dinners with copious sup­plies of freely offered vodka. This was in the Russian custom of becom­ing acquainted over drinks, during which inhibitions that might mask hidden feelings were relaxed. The custom was repeated over and over again throughout the program. Few occasions passed without a cele­bratory party of some degree: preflight parties, postflight parties, wel­coming parties, and farewell parties were all on the agenda. Though at times challenging for some of the American guests who did not drink,

these social gatherings were very effective at cementing friendships among two peoples who only a few years before uneasily coexisted, with all of their respective major cities targeted by the other’s missiles. To a person, the Americans who participated in this program realized that on a personal level, the Russians were generous hosts, loyal friends, and trusted colleagues. If nothing else, this was a significant accomplish­ment for this program.

Nineteen flights were completed by early 1998, achieving most of the original program goals. However, some data acquisition problems had rendered questionable some of the data from the six experiments.[1476] The HSR Program Office decided that it would be valuable to have United States research pilots evaluate the Tu-144 in order to develop corporate knowledge within NASA regarding SST handling qualities and to ascer­tain if the adverse handling qualities predicted by the data collected actu­ally existed. Furthermore, there were additional data goals developed since the inception of the program, and a seventh experiment was orga­nized. The resumption of the test flights was scheduled for September 1998. The HSR Program Office and Boeing selected Gordon Fullerton from Dryden and NASA research pilot Robert A. Rivers from Langley as the evaluation pilots. Fullerton had been the Dryden project pilot for the Tu-144 modification and refurbishment, and he was familiar with the Tupolev flightcrews and the airplane. Rivers had been the HSR project pilot for several years, had participated in every HSR flight simulation experiment, served on two HSR integrated test develop­ment teams, and had performed an extensive handling qualities eval­uation of the Concorde SST the previous year. To accompany them to Zhukovsky were two NASA flight control engineers, Timothy H. Cox from Dryden and E. Bruce Jackson from Langley, and Boeing Tu-144 project handling qualities engineer Norman H. Princen. Jackson had completed extensive work on flight control development for the HSCT Reference H model. During summer 1998, the team members worked together to develop a draft test plan, flew both the Ames and Langley 6-degree-of-freedom motion simulators with the Reference H model, and began studying the Tu-144 systems with the rudimentary information available in the United States at that time. On September 4, they departed for Zhukovsky.

Much of NASA’s aerospace research overlaps various fields. For exam­ple, improving EMP tolerance of space-based systems involves studying plasma interactions in a high-voltage system operated in the ionosphere. But a related subject is establishing design practices that may have pre­viously increased adverse plasma interactions and recommending means of eliminating or mitigating such reactions in future platforms.

Standards for lightning protection tests were developed in the 1950s, under FAA and Department of Defense (DOD) auspices. Those studies mainly addressed electrical bonding of aircraft components and protec­tion of fuel systems. However, in the next decade, dramatic events such as the in-flight destruction of a Boeing 707 and the triggered responses of Apollo 12 clearly demonstrated the need for greater research. With advent of the Space Shuttle, NASA required further means of lightning protection, a process that began in the 1970s and continued well beyond the Shuttle’s inaugural flight, in 1981.

Greater interagency cooperation led to new research programs in the 1980s involving NASA, the Air Force, the FAA, and the government of France. The goal was to develop a lightning-protection design phi­losophy, which in turn required standards and guidelines for various aerospace vehicles.

NASA’s approach to lightning research has emphasized detection and avoidance, predicated on minimizing the risk of strikes, but then, if strikes occur nevertheless, ameliorating their damaging effects. Because early detection enhances avoidance, the two approaches work hand in glove. Translating those related philosophies into research and thence to design practices contains obvious benefits. The relationship between lightning research and protective design was noted by researchers for Lightning Technologies, Inc., in evaluating lightning protection for digi­tal engine control systems. They emphasized, "The coordination between the airframe manufacturer and system supplies in this process is fun­damental to adequate protection.”[176] Because it is usually impractical to perform full-threat tests on fully configured aircraft, lightning protec­tion depends upon accurate simulation using complete aircraft with full systems aboard. NASA, and other Federal agencies and military services, has undertaken such studies, dating to its work on the F-8 DFBW test­bed of the early 1970s, as discussed subsequently.

In their Storm Hazards Research Program (SHRP) from 1980 to 1986, Langley researchers found that multiple lightning strikes inject random electric currents into an airframe, causing rapidly changing magnetic fields that can lead to erroneous responses, faulty commands, or other "upsets” in electronic systems. In 1987, the FAA (and other nations’ avi­ation authorities) required that aircraft electronic systems perform­ing flight-critical functions be protected from multiple-burst lightning.

At least from the 1970s, NASA recognized that vacuum tube electron­ics were inherently more resistant to lightning-induced voltage surges than were solid-state avionics. (The same was true for EMP effects. When researchers in the late 1970s were able to examine the avionics of the Soviet MiG-25 Foxbat, after defection of a Foxbat pilot to Japan, they were surprised to discover that much of its avionics were tube-based, clearly with EMP considerations in mind.) While new microcircuitry obviously was more vulnerable to upset or damage, many new-generation aircraft would have critical electronic systems such as fly-by-wire control systems.

Therefore, lightning represented a serious potential hazard to safety of flight for aircraft employing first-generation electronic flight control architectures and systems. A partial solution was redundancy of flight controls and other airborne systems, but in 1978, there were few if any standards addressing indirect effects of lightning. That time, however, was one of intensive interest in electronic flight controls. New fly-by-wire aircraft such as the F-16 were on the verge of entering squadron service. Even more radical designs—notably highly unstable early stealth aircraft such as the Lockheed XST Have Blue testbed, the Northrop Tacit Blue, the Lockheed F-117, and the NASA-Rockwell Space Shuttle orbiter— were either already flying or well underway down the development path.

NASA’s digital fly-by-wire (DFBW) F-8C Crusader afforded a ready means of evaluating lightning-induced voltages, via ground simulation and evaluation of electrodynamic effects upon its flight control computer. Dryden’s subsequent research represented the first experimental investi­gation of lightning-induced effects on any FBW system, digital or analog.

A summary concluded:

Results are significant, both for this particular aircraft and for future generations of aircraft and other aero­space vehicles such as the Space Shuttle, which will employ digital FBW FCSs. Particular conclusions are: Equipment bays in a typical metallic airframe are poorly shielded and permit substantial voltages to be induced in unshielded electrical cabling. Lightning-induced volt­ages in a typical a/c cabling system pose a serious haz­ard to modern electronics, and positive steps must be taken to minimize the impact of these voltages on sys­tem operation. Induced voltages of similar magnitudes will appear simultaneously in all channels of a redun­dant system. A single-point ground does not eliminate lightning-induced voltages. It reduces the amount of diffusion-flux induced and structural IR voltage but per­mits significant aperture-flux induced voltages. Cable shielding, surge suppression, grounding and interface modifications offer means of protection, but successful design will require a coordinated sharing of responsibil­ity among those who design the interconnecting cabling and those who design the electronics. A set of transient control levels for system cabling and transient design levels for electronics, separated by a margin of safety, should be established as design criteria.[177]

The F-8 DFBW program is the subject of a companion study on electronic flight controls and so is not treated in greater detail here. In brief, a Navy Ling-Temco-Vought F-8 Crusader jet fighter was modi­fied with a digital electronic flight control system and test-flown at the NASA Flight Research Center (later the NASA Dryden Flight Research Center). When the F-8 DFBW program ended in 1985, it had made 210 flights, with direct benefits to aircraft as varied as the F-16, the F/A-18, the Boeing 777, and the Space Shuttle. It constituted an excellent exam­ple of how NASA research can prove and refine design concepts, which are then translated into design practice.[178]

The versatile F-106B program also yielded useful information on protection of digital computers and other airborne systems that trans­lated into later design concepts. As NASA engineer-historian Joseph Chambers subsequently wrote: "These findings are now reflected in lightning environment and test standards used to verify adequacy of protection for electrical and avionics systems against lightning hazards. They are also used to demonstrate compliance with regulations issued by airworthiness certifying authorities worldwide that require lightning strikes not adversely affect the aircraft systems performing critical and essential functions.”[179]

Similarly, NASA experience at lightning-prone Florida launch sites provided an obvious basis for identifying and implementing design practices for future use. A 1999 lessons-learned study identified design considerations for lightning-strike survivability. Seeking to avoid nat­ural or triggered lightning in future launches, NASA sought improve­ments in electromagnetic compatibility (EMC) for launch sites used by the Shuttle and other launch systems. They included proper grounding of vehicle and ground-support equipment, bonding requirements, and circuit protection. Those aims were achieved mainly via wire shielding and transient limiters.

In conclusion, it is difficult to improve upon D. L. Johnson and W. W. Vaughn’s blunt assessment that "Lightning protection assessment and design consideration are critical functions in the design and develop­ment of an aerospace vehicle. The project’s engineer responsible for lightning must be involved in preliminary design and remain an inte­gral member of the design and development team throughout vehi­cle construction and verification tests.”[180] This lesson is applicable to many aerospace technical disciplines and reflects the decades of experience embedded within NASA and its predecessor, the NACA, involving high-technology (and often high-risk) research, testing, and evaluation. Lightning will continue to draw the interest of the Agency’s researchers, for there is still much that remains to be learned about this beautiful and inherently dangerous electrodynamic phenomenon and its interactions with those who fly.

Recommended Additional Reading

In 2006, NASA’s Aeronautics Research Mission Directorate (ARMD) was reorganized. As a result, the projects that fell under ARMD’s Aviation Safety Program were restructured as well, with more of a focus on

aircraft safety than on the skies they fly through. Air traffic improvements in the new plan now fall almost exclusively within the Airspace Systems Program. The Aviation Safety Program is now dedicated to developing the principles, guidelines, concepts, tools, methods, and technologies to address four project areas: the Integrated Vehicle Health Management Project,[245] the Integrated Intelligent Flight Deck Technologies Project,[246] the Integrated Resilient Aircraft Control Project,[247] and the Aircraft Aging and Durability Project.[248]

The consideration of human factors in technology has existed since the first man shaped a wooden spear with a sharp rock to help him grasp it more firmly. It therefore stands to reason that the dimension of human factors has changed over time with advancing technology—a trend that has accelerated throughout the 20th century and into the current one.[296]

Man’s earliest requirements for using his primitive tools and weapons gave way during the Industrial Revolution to more refined needs in oper­ating more complicated tools and machines. During this period, the emer­gence of more complex machinery necessitated increased consideration of the needs of the humans who were to operate this machinery—even

if it was nothing more complicated than providing a place for the oper­ator to sit, or a handle or step to help this person access instruments and controls. In the years after the Industrial Revolution, human fac­tors concerns became increasingly important.[297]

As is apparent from the foregoing discussions, a recurring theme in NASA’s human factors research has been its dedication to improving aviation safety. The Agency’s many human factors research initiatives have contributed to such safety issues as crash survival, weather knowl­edge and information, improved cockpit systems and displays, security, management of air traffic, and aircraft control.[402]

Though NASA’s involvement with aviation safety has been an impor­tant focus of its research activities since its earliest days, this involve­ment was formalized in 1997. In response to a report by the White House Commission on Aviation Safety and Security, NASA created its Aviation Safety Program (AvSP).[403] As NASA’s primary safety program, AvSP dedi­cated itself and $500 million to researching and developing technologies that would reduce the fatal aircraft accident rate 80 percent by 2007.[404]

In pursuit of this goal, NASA researchers at Langley, Ames, Dryden, and Glenn Research Centers teamed with the FAA, DOD, the aviation industry, and various aviation employee groups—including the Air Line Pilots Association (ALPA), Allied Pilots Association (APA), Air Transport Association (ATA), and National Air Traffic Controllers Association

(NATCA)—to form the Commercial Aviation Safety Team (CAST) in 1998. The purpose of this all-inclusive consortium was to develop an integrated and data-driven strategy to make commercial aviation safer.[405]

As highlighted by the White House Commission report, statistics had shown that the overwhelming majority of the aviation accidents and fatalities in previous years had been caused by human error—specifically, loss of control in flight and so-called controlled flight into terrain (CFIT).[406] NASA—along with the FAA, DOD, the aviation industry, and human factors experts—had previously formed a National Aviation Human Factors Plan to develop strategies to decrease these human- caused mishaps.[407] Consequently, NASA joined with the FAA and DOD to further develop a human performance research plan, based on the NASA-FAA publication Toward a Safer 21st Century—Aviation Safety Research Baseline and Future Challenges.[408] The new AvSP thus incor­porated many of the existing human factors initiatives, such as crew fatigue, resource management, and training. Human factors concerns were also emphasized by the program’s focus on developing more sophis­ticated human-assisting aviation technology.

To accomplish its goals, AvSP focused not only on preventing accidents, but also minimizing injuries and loss of life when they did occur. The program also emphasized collection of data to find and address problems. The comprehensive nature of AvSP is beyond the scope of this case study, but some aspects of the program (which, in 2005, became the Aviation Safety & Security Program, or AvSSP) with the greatest human factors implications include accident mitiga­tion, synthetic vision systems, system wide accident prevention, and aviation system monitoring and modeling.[409]

• Accident mitigation: The goal of this research is to find ways to make accidents more survivable to aircraft

occupants. This includes a range of activities, some of which have been discussed, to include impact tests, in­flight and postimpact fire prevention studies, improved restraint systems, and the creation of airframes better able to withstand crashes.

• Synthetic vision systems: Unrestricted vision is vital for a pilot’s situational awareness and essential for him to control his aircraft safely. Limited visibility contributes to more fatal air accidents than any other single factor; since 1990, more than 1,750 deaths have been attrib­uted to CFIT—crashing into the ground—not to men­tion numerous runway incursion accidents that have taken even more lives.[410]

• The traditional approach to this problem has been the development of sensor-based enhanced vision systems to improve pilot awareness. In 2000, however, NASA Langley researchers initiated a different approach. They began developing cockpit displays, termed Synthetic Vision Systems, which incorporate such technologies as Global Positioning System (GPS) and photo-realistic terrain databases to allow pilots to "see” a synthetically derived 3-D digital reproduction of what is outside the cockpit, regardless of the meteorological visibility. Even in zero visibility, these systems allow pilots to synthet­ically visualize runways and ground obstacles in their path. At the same time, this reduces their workload and decreases the disorientation they experience during low – visibility flying. Such systems would be useful in avoid­ing CFIT crashes, loss of aircraft control, and approach and landing errors that can occur amid low visibility.[411] Such technology could also be of use in decreasing the risk of runway incursions. For example, the Taxiway

Navigation and Situation Awareness System (T-NASA) was developed to help pilots taxiing in conditions of decreased visibility to "see” what is in front of them. This system allows them to visualize the runway by present­ing them with a head-up display (HUD) of a computer­generated representation of the taxi route ahead of them.[412]

• One of the most important synthetic vision sys­tems initiatives arose from the Advanced General Aviation Transport Experiments (AGATE) program, which NASA formed in the mid-1990s to help revi­talize the lagging general-aviation industry. NASA joined with the FAA and some 80 industry mem­bers, in part to develop an affordable Highway in the Sky (HITS) cockpit display that would enhance safety and pilot situational awareness. In 2000, such a system was installed and demonstrated in a small production aircraft.[413] Today, nearly every aviation manufacturer has a Synthetic Vision System either in use or in the planning stages.[414]

• System wide accident prevention: This research, which focuses on the human causes of accidents, is involved with improving the training of aviation professionals and in developing models that would help predict human error before it occurs. Many of the programs address­ing this issue were discussed earlier in greater detail.[415]

• Aviation system monitoring and modeling (ASMM) proj­ect: This program, which was in existence from 1999 to 2005, involved helping personnel in the aviation indus­try to preemptively identify aviation system risk. This included using data collection and improved monitoring of equipment to predict problems before they occur.[416] One important element of the ASMM project is the Aviation Performance Measuring System (APMS).[417] In 1995, NASA and the FAA coordinated with the airlines to develop this program, which utilizes large amounts of information taken from flight data recorders to improve flight safety. The techniques developed are designed to use the data collected to formulate a situational aware­ness feedback process that improves flight performance and safety.[418]

• Yet another spinoff of ASMM is the National Aviation Operational Monitoring Service (NAOMS). This system­wide survey mechanism serves to quantitatively assess the safety of the National Airspace System and evaluate the effects of technologies and procedures introduced into the system. It uses input from pilots, controllers, mechanics, technicians, and flight attendants. NAOMS therefore serves to assess flight safety risks and the effec­tiveness of initiatives to decrease these risks.[419] APMS impacts air carrier operations by making routine mon­itoring of flight data possible, which in turn can allow evaluators to identify risks and develop changes that will improve quality and safety of air operations.[420]

• A similar program originating from ASMM is the Performance Data Analysis and Report and System (PDARS). This joint FAA-NASA initiative provides a

way to monitor daily operations in the NAS and to eval­uate the effectiveness of air traffic control (ATC) services. This innovative system, which provides daily analysis of huge volumes of real-time information, including radar flight tracks, has been instituted throughout the conti­nental U. S.136

The highly successful AvSP ended in 2005, when it became the Aviation Safety & Security Program. AvSSP exceeded its target goal of reducing air­craft fatalities 80 percent by 2007. In 2008, NASA shared with the other members of CAST the prestigious Robert J. Collier Trophy for its role in helping produce "the safest commercial aviation system in the world.”137 AvSSP continues to move forward with its goal of identifying and develop­ing by 2016 "tools, methods, and technologies for improving overall air­craft safety of new and legacy vehicles operating in the Next Generation Air Transportation System.”138 NASA estimates that the combined efforts of the ongoing safety-oriented programs it has initiated or in which it has participated will decrease general-aviation fatalities by as much as another 90 percent from today’s levels over the next 10-15 years.139

Spurred on by postwar interests in the variable-wing-sweep concept as a means to optimize mission performance at both low and high speeds, the NACA at Langley initiated a broad research program to identify the potential benefits and problems associated with the concept. The disap­pointing experiences of the Bell X-5 research aircraft, which used a sin­gle wing pivot to achieve variable sweep in the early 1950s, had clearly identified the unacceptable weight penalties associated with the con­cept of translating the wing along the fuselage centerline to maintain satisfactory levels of longitudinal stability while the wing sweep angle was varied from forward to aft sweep. After the X-5 experience, military interest in variable sweep quickly diminished while aerodynamicists at

Langley continued to explore alternate concepts that might permit vari­ations in wing sweep without moving the wing pivot location and with­out serious degradation in longitudinal stability and control.

After years of intense research and wind tunnel testing, Langley researchers conceived a promising concept known as the outboard pivot.[486] The basic principle involved in the NASA solution was to pivot the mov­able wing panels at two outboard pivot locations on a fixed inner wing and share the lift between the fixed portion of the wing and the movable outer wing panel, thereby minimizing the longitudinal movement of the aerodynamic center of lift for various flight speeds. As the concept was matured in configuration studies and supporting tests, refined designs were continually submitted to intense evaluations in tunnels across the speed range from supersonic cruise conditions to subsonic takeoff and landing.[487]

The use of dynamically scaled free-flight models to evaluate the sta­bility and control characteristics of variable-sweep configurations was an ideal application of the testing technique. Since variable-sweep designs are capable of an infinite number of wing sweep angles between the for­ward and aft positions, the number of conventional wind tunnel force tests required to completely document stability and control variations with wing sweep for every sweep angle could quickly become unacceptable. In contrast, a free-flight model with continually variable wing sweep angles could be used to quickly examine qualitative characteristics as its geome­try changed, resulting in rapid identification of significant problems. Free – flight model investigations of a configuration based on a proposed Navy combat air patrol (CAP) mission in the Full-Scale Tunnel provided a con­vincing demonstration that the outboard pivot was ready for applications.

The oblique wing concept (sometimes referred to as the "switch­blade wing” or "skewed wing”) had originated in the German design studies of the Blohm & Voss P202 jet aircraft during World War II and was pursued at Langley by R. T. Jones. Oblique wing designs use a single­pivot, all-moving wing to achieve variable sweep in an asymmetrical fashion. The wing is positioned in the conventional unswept position for takeoff and landings, and it is rotated about its single pivot point for high-speed flight. As part of a general research effort that included

theoretical aerodynamic studies and conventional wind tunnel tests, a free-flight investigation of the dynamic stability and control of a sim­plified model was conducted in the Free-Flight Tunnel in 1946.[488] This research on the asymmetric swept wing actually predated NACA wind tunnel research on symmetrical variable sweep concepts with a research model of the Bell X-1.[489] The test objectives were to determine whether such a radical aircraft configuration would exhibit satisfactory stability characteristics and remain controllable in the swept wing asymmetric state at low-speed flight conditions. The results of the flight tests, which were the first U. S. flight studies of oblique wings ever conducted, showed that the wing could be swept as much as 40 degrees without significant degradation in behavior. However, when the sweep angle was increased to 60 degrees, an unacceptable longitudinal trim change was experienced, and a severe reduction in lateral control occurred at moderate and high angles of attack. Nonetheless, the results obtained with the simple free – flight model provided optimism that the unconventional oblique wing concept might be feasible from a perspective of stability and control.

R. T. Jones transferred to the NACA Ames Aeronautical Laboratory in 1947 and continued his brilliant career there, which included his continuing interest in the application of oblique wing technology. In the early 1970s, the scope of NASA studies on potential civil supersonic transport configurations included an effort by an Ames team headed by Jones that examined a possible oblique wing version of the super­sonic transport. Although wind tunnel testing was conducted at Ames, the demise and cancellation of the American SST program in the early 1970s terminated this activity. Wind tunnel and computational studies of oblique wing designs continued at Ames throughout the 1970s for subsonic, transonic, and supersonic flight applications.[490] Jones stim­ulated and participated in flight tests of several oblique wing radio – controlled models, and a joint Ames-Dryden project was initiated to use a remotely piloted research aircraft known as the Oblique Wing Research Aircraft (OWRA) for studies of the aerodynamic characteris­tics and control requirements to achieve satisfactory handling qualities.

Growing interest in the oblique wing and the success of the OWRA remotely piloted vehicle project led to the design and low-speed flight demonstrations of a full-scale research aircraft known as the AD-1 in the late 1970s. Designed as a low-cost demonstrator, the radical AD-1 proved to be a showstopper during air shows and generated consider­able public interest.[491] The flight characteristics of the AD-1 were quite satisfactory for wing-sweep angles of less than about 45 degrees, but the handling qualities degraded for higher values of sweep, in agreement with the earlier Langley exploratory free-flight model study.

After his retirement, Jones continued his interest in supersonic oblique wing transport configurations. When the NASA High-Speed Research program to develop technologies necessary for a viable super­sonic transport began in the 1990s, several industry teams revisited the oblique wing for potential applications. Ames sponsored free-flight radio – controlled model studies of oblique wing configurations at Stanford University in the early 1990s. As a result of free-flight model contribu­tions from Langley, Ames, Dryden, and academia, major issues regarding potential dynamic stability and control problems for oblique wing con­figurations have been addressed for low-speed conditions. Unfortunately, funding for transonic and supersonic model flight studies has not been forthcoming, and high-speed studies have not yet been accomplished.

Efforts by the NACA and NASA over the last 80 years with applications of free-flying dynamic model test techniques have resulted in signifi­cant contributions to the civil and military aerospace communities. The results of the investigations have documented the testing techniques and lessons learned, and they have been especially valuable in defining critical characteristics of radical new configurations. With the passing of each decade, the free-flight techniques have become more sophis­ticated, and the accumulation of correlation between model and full – scale results has rapidly increased. In view of this technical progress, it

is appropriate to reflect on the state of the art in free-flight technology and the challenges and opportunities of the future.