Category NASA’S CONTRIBUTIONS TO AERONAUTICS

NASA essentially resumed in 1990 what had ended in 1981 with the termination of the SCR program. Enough time had elapsed since the U. S. SST political firestorm to suggest the possibility of developing a practical aircraft.[1108] Ironically, one of the justifications was concern that not only the Europeans but also the Japanese were studying a second – generation SST, one that could exploit reduced travel times to the Pacific rim countries, where U. S. overland sonic boom restrictions would not be such an economic handicap. A Presidential finding in 1986 during the Reagan Administration stated that research toward a supersonic com­mercial aircraft should be conducted. A consortium of NASA Research Centers continued research in conjunction with airframe manufacturers to work toward development of a High-Speed Civil Transport (HSCT), which would essentially become the 21st century SST. The development would incorporate lessons learned from previous SSTs and research con­ducted since 1981 and would be environmentally friendly. A test concept aircraft (TCA) configuration was established as a baseline for technology development studies. Cruise Mach number was to be Mach 2 to 2.5, and design range was to be 5,000 nautical miles, in deference to the Pacific Ocean traffic. Phase I of the SCR was to last 6 years, while concentrat­ing on such environmental issues as studies on ozone layer impact of an SST fleet and sideline community noise levels. Both areas required exten­sive propulsion system studies and probable advances in engine technol­ogy. Studies of the economics of an HSCT showed that the concept would be more practical if there were a reduction of a sonic boom footprint to the point where overland flight was permissible in some corridors. The Concorde boom average was 2 pounds per square foot, which was deemed unacceptable; the questions were what would be acceptable and how to achieve that level. Phase II was to be focused on development of specific technologies leading to HSCT as a practical commercial aircraft. The ini­tial goal was for a 2006 development decision target date.

The digital revolution has had a major impact on supersonic technol­ogy. The nonlinear physics of supersonic flow shock waves made control of a system difficult. But the advent of high-speed computer technology changed that. The improvement in the SR-71 fleet performance shown by the DAFICS, pioneered by NASA in the YF-12 program, showed the

operational benefits of digital controls. But in SCR, much effort centered on using the computational fluid dynamics (CFD) codes being developed to perform design tasks that traditionally required massive wind tun­nel testing.[1109] CFD could also be used to predict sonic boom propagation for configurations, once the basic physics of that propagation was better

understood. Another case study in this book addresses the details of the research that was conducted to provide that data. Flight tests included flights by an SR-71 over an instrumented ground array of microphones as in the 1960s that were also accompanied by instrumented chase aircraft that recorded the shock wave characteristics in free space at various dis­tances from the supersonic aircraft. These data were to be used to develop and validate the CFD predictions, just as supersonic flight-test data has traditionally been used to validate supersonic wind tunnel predictions.

Another flight research program devoted to SCR included a post-Cold War cooperative venture with Russia’s Central Institute of Aerohydromechanics (TsAGI) to resurrect and fly the Tu-144 SST of the 1970s.[1110] Equipped with new engines with more powerful turbofans, the Tu-144LL (the modified designation reflecting the Cyrillic abbreviation for flying laboratory) flew a 2-phase, 26-flight-test program in 1998 and 1999 at cruise Mach numbers to 2.15. All the flights were flown from Zhukovsky Flight Research Center outside Moscow, and NASA pilots flew on 3 of the sorties.[1111] Experiments investigated handling qualities, boundary layer characteristics, ground cushion effects of the large delta wing, cabin aerodynamic noise, and sideline engine noise.

Another flight research program of the 1990s was the NASA use of the arrow wing F-16XL. Flown over 13 months in 1995-1996, the 90-hour, 45-flight-test program was known as the Supersonic Laminar Flow Control program.[1112] A glove was fitted over the left wing of the air­craft, which had millions of microscopic laser-drilled holes. A suction system drew the turbulent supersonic boundary layer through the holes to attempt to create a laminar boundary layer with less friction drag. Flight Mach numbers up to Mach 2 showed that the concept was indeed effective at creating laminar flow. This was a significant finding for an HSCT, for which drag reduction at cruise conditions is so critical.[1113]

The USAF had taken the SR-71 fleet out of service in 1990 because of cost concerns and opinions that its reconnaissance mission could be
better accomplished by other platforms, including satellites. This freed a number of Mach 3 cruise platforms equipped with advanced digital control systems for possible use by NASA in the SCR effort. Dryden Flight Research Center was allocated two SR-71As for research use and the sole SR-71B airframe for pilot checkout training. The crew­training simulator was also installed at Dryden. It was being updated to new computer technology when the financial ax fell yet again. Some research relevant to supersonic cruise was performed on the SR-71s. Handling qualities and cruise performance using the updated config­uration were evaluated. Despite the digital system, the use of an iner­tial vertical velocity indicator at Mach 3 was still found to be superior to the air-data-driven vertical velocity for precise altitude control.[1114] An experimental air-data system using lasers to sense angle of attack and sideslip rather than differential air pressure was also tested to confirm that it would function at the 80,000-foot cruise altitude. Several Sonic Boom Research Program flights were flown, as mentioned earlier, for in-flight sonic boom shock wave measurements. The SR-71 had to slow and descend from its normal cruise levels to accommodate the instru­mented chase aircraft. Like the YF-12, the SR-71 was again used as a platform for experiments. Several devices planned for satellite Earth observations were carried in the sensor bays of the SR-71 for observa­tions from above 95 percent of the Earth’s atmosphere. An ultraviolet camera funded by the Jet Propulsion Laboratory conducted celestial observations from the same vantage point.

The program that mainly funded retention of the airplanes was actu­ally in support of a proposed (later canceled) reuseable space launch vehicle, the Lockheed-Martin X-33. It would employ a revolutionary rocket engine, the Linear Aerospike Rocket Engine (LASRE). The engine used shock waves to contain the exhaust and increase thrust at a com­paratively light structural weight. For risk reduction, the SR-71 would have a fixture mounted atop the fuselage, on which would be installed a 12-percent model of the X-33 with engine for aerial tests. The fixture was installed, but the increased drag of the fixture plus the LASRE limited the maximum Mach number attainable to around Mach 2. The instal­lation was carried on several flights, but insuperable flight safety issues

meant that the engine never was fired on the aircraft.[1115] Funding ended with the demise of the SCR program. The final flight of the world’s only Mach 3 supersonic cruise fleet occurred as an overflight of the Edwards Air Force Base Open House on October 9, 1999. The staff of the Russian Test Pilot School furnished an indication of the unique cachet of the air­craft when they visited the USAF Test Pilot School at Edwards as part of a reciprocal exchange in the mid-1990s. They had earlier hosted the Americans in Moscow and allowed them to fly current Russian fighters. When asked what they would like to fly at Edwards, the response was the SR-71. T hey were told that was unfortunately impossible because of cost and because the SR was a NASA asset, but that a simulator flight might be arranged. Even so, these experienced test pilots welcomed the opportunity to sample the SR-71 simulator.

By 1999, much research work had been performed in support of the HSCT.[1116] Nevertheless, no breakthrough seemed to have been made that answered all the issues raised on a practical HSCT development deci­sion. One of the major contractor contributors had been McDonnell – Douglas, which became Boeing in the defense industry implosion of the 1990s.[1117] In 1999, Boeing withdrew further major financial support, as it saw no possibility of an HSCT before 2020. Also in 1999, NASA Administrator Daniel S. Goldin cut $600 million from the aeronautics budget to provide support for the International Space Station. These two actions essentially ended the SCR for the time being.

With its years of accumulated research about all aspects of icing—i. e., weather conditions that produce it, types of ice that form under vari­ous conditions, de-icing and anti-icing measures and when to employ them—NASA’s data would be useless unless they were somehow pack­aged and made available to the aviation community in a convenient manner so that safety could be improved on a daily basis. And so with desktop computers becoming more affordable, available, and increas­ingly powerful enough to crunch fairly complex datasets, in 1983, NASA researchers at what was still named the Lewis Research Center began developing a computer program that would at first aid NASA’s in-house researchers, but would grow to become a tool that would aid pilots, air traffic controllers, and any other interested party in the flight plan­ning process through potential areas of icing. The software was dubbed LEWICE, and version 0.1 originated in 1983 as a research code for in­house use only. As of the beginning of 2010, version 2.0 is the official cur­rent version, although a version 3.2.2 is in development, as is the first 0.1 version of GlennICE, which is intended to accurately predict ice growth under any weather conditions for any aircraft surface.[1243]

LEWICE, which spelled out is the Lewis Ice Accretion Program, is a freely available desktop software program used by hundreds of people in the aviation community for purposes of predicting the amount, type, and shape of ice an aircraft might experience given a particular weather forecast, as well as what kind of anti-icing heat requirements may be necessary to prevent any buildup of ice from beginning. The software

runs on a desktop PC and provides its analysis of the input data within minutes, fast enough that the user can try out some different numbers to get a range of possible icing experiences in flight. All of the predic­tions are based on extensive research and real-life observations of icing collected through the years both in flight and in icing wind tunnel tests.[1244]

At its heart, LEWICE attempts to predict how ice will grow on an aircraft surface by evaluating the thermodynamics of the freezing pro­cess that occurs when supercooled droplets of moisture strike an air­craft in flight. Variables considered include the atmospheric parameters of temperature, pressure, and velocity, while meteorological parame­ters of liquid water content, droplet diameter, and relative humidity are used to determine the shape of the ice accretion. Meanwhile, the aircraft surface geometry is defined by segments joining a set of dis­crete body coordinates. All of that data are crunched by the software in four major modules that result in a flow field calculation, a parti­cle trajectory and impingement calculation, a thermodynamic and ice growth calculation, and an allowance for changes in the aircraft geom­etry because of the ice growth. In processing the data, LEWICE applies a time-stepping procedure that runs through the calculations repeat­edly to "grow” the ice. Initially, the flow field and droplet impingement characteristics are determined for the bare aircraft surface. Then the rate of ice growth on each surface segment is determined by applying the thermodynamic model. Depending on the desired time increment, the resulting ice growth is calculated, and the shape of the aircraft sur­face is adjusted accordingly. Then the process repeats and continues to predict the total ice expected based on the time the aircraft is flying through icing conditions.[1245]

The basic functions of LEWICE essentially account for the capa­bilities of the software up through version 1.6. Version 2.0 was the next release, and although it did not change the fundamental process or mod­els involved in calculating ice accretion, it vastly improved the robust­ness and accuracy of the software. The current version was extensively tested on different computer platforms to ensure identical results and also incorporated the very latest and complete datasets based on the most
recent research available, while also having its prediction results ver­ified in controlled laboratory tests using the Glenn IRT. Version 3.2— not yet released to date—will add the ability to account for the presence and use of anti-icing and de-icing systems in determining the amount, shape, and potential hazard of ice accretion in flight. Previously these variables could be calculated by reading LEWICE output files into other software such as ANTICE 1.0 or LEWICE/Thermal 1.6.[1246]

According to Jaiwon Shin, the current NASA Associate Administrator for the Aeronautics Research Mission Directorate, the LEWICE software is the most significant contribution NASA has made and continues to make to the aviation industry in terms of the topic of icing accretion. Shin said LEWICE continues to be used by the aviation community to improve safety, has helped save lives, and is an incredibly useful tool in the classroom to help teach future pilots, aeronautical engineers, traf­fic controllers, and even meteorologists about the icing phenomenon.[1247]

Initially envisioned as a nimble lightweight fighter with "carefree” maneu­verability, the F-16 was designed from the onset with reliance on the flight control system to ensure satisfactory behavior at high-angle-of – attack conditions.[1298] By using the concept of relaxed longitudinal sta­bility, the configuration places stringent demands on the flight control system. In addition to extensive static and dynamic wind tunnel testing in Langley’s tunnels from subsonic to supersonic speeds and free-flight model studies for high-angle-of-attack conditions and spinning, Langley and its partners from General Dynamics and the Air Force conducted in-depth piloted studies in a Langley simulator. The primary objective of the studies was to assess the ability of the F-16 control system to prevent loss of control and departures for critical dynamic maneuvers involving rapid roll rates at high angles of attack and low airspeeds.[1299] General Dynamics used the results of the study to modify gains in the F-16 flight control system and introduce new elements for enhanced departure prevention in production aircraft.

One of the more significant events in NASA’s support of the F-16 was the timely identification and solution to a potentially unrecoverable "deep-stall” condition. Analysis of Langley wind tunnel data at extreme angles of attack (approaching 90 degrees) and simulated maneuvers by pilots in the DMS during the earlier YF-16 program indicated that rapid roll maneuvers at high angles of attack could saturate the nose-down aerodynamic control capability of the flight control system, resulting in the inherently unstable airplane pitching up to an extreme angle of attack with insufficient nose-down aerodynamic control to recover to normal flight.[1300] The ability of the YF-16 to enter this dangerous condi­tion was demonstrated to General Dynamics and the Air Force, but aero­dynamic data obtained in other NASA and industry wind tunnel tests of different YF-16 models did not indicate the existence of such a problem.

The scope of the ensuing YF-16 flight program was limited and did not allow for exploration of a potential deep-stall problem.

The early production F-16 configuration also indicated a deep-stall issue during Langley tests in the Full-Scale Tunnel, and once again, the data contradicted results from other wind tunnels. As a result, the Langley data were dismissed as contaminated with "scale effects,” and concerns over the potential existence of a deep stall were minimal as the aircraft entered flight-testing at Edwards Air Force Base. However, dur­ing zoom climbs with combined rolling motions, the specially equipped F-16 high-angle-of-attack test airplane entered a stabilized deep-stall condition, and after finding no effective control for recovery, the pilot was forced to use the emergency spin recovery parachute to recover the aircraft to normal flight. The motions and flight variables were virtually identical to the Langley predictions.

Because Langley’s aerodynamic model of the F-16 provided the most realistic inputs for the incident, a joint NASA, General Dynamics, and Air Force team aggressively used the DMS simulator at Langley to develop a piloting strategy for recovery from the deep stall. Under Langley’s leadership, the team conceived a "pitch rocker” technique, in which the pilot pumped the control stick fore and aft to set up oscillatory pitching motions that broke the stabilized deep-stall condition and allowed the aircraft to return to normal flight. The concept was demonstrated dur­ing F-16 flight evaluations and was incorporated in the early flight con­trol systems as a pilot-selectable emergency mode. Ultimately, the deep stall was eliminated by an increase in size of the horizontal tail (which was done for other reasons) on later production models of the F-16.

The value of Langley’s support in the area of high-angle-of-attack behavior for the F-16 represented the first step for advancing method­ology for fly-by-wire control systems with special capabilities for severe maneuvers at high angles of attack. The experience demonstrated the advantages of NASA’s involvement as a Government partner in develop­ment programs and the value of having NASA facilities, technical exper­tise, and experience available to design teams in a timely manner. The initial objective of carefree maneuverability for the F-16 was provided in a very effective manner by the NASA-industry-DOD team.

In 1957, Britain’s Hawker and Bristol firms began development of what would prove to be the most revolutionary V/STOL airplane developed to that point in aviation history, the P.1127. This aircraft program, begun

as a private development by two of Britain’s more respected companies, was the product of Sir Sidney Camm and Ralph Hooper of Hawker, and Stanley Hooker of Bristol. It eventually spawned a remarkable opera­tional aircraft that fought in multiple wars and served in the air forces and naval air services of many nations. Hawker had an enviable reputa­tion for designing high-performance aircraft, dating to the Sopwith fight­ers of the First World War, and Bristol had an equally impressive one in the field of aircraft propulsion. NATO’s Mutual Weapon Development Project (MWDP) supported the project as it evolved, and it drew heav­ily upon American support from John Stack of NASA and the Langley Research Center, and from the U. S. Marine Corps. (The P.1127 design was extensively tested in Langley’s 30-Foot by 60-Foot Full Scale Tunnel, and the 16-Foot Transonic Tunnel, helping identify and alleviate a poten­tially serious pitch-up problem exacerbated by power effects during tran­sition upon the original horizontal tail configuration).[1446] Powered by a

single Bristol Siddeley Pegasus 5 vectored-thrust turbofan of 15,000- pound thrust, the P.1127 completed its first tethered hover in October 1960, an untethered hover the next month, and, after extensive prepara­tion, its first transition from vertical to conventional in September 1961. As with the X-14 and other V/STOL testbeds, bleed air reaction nozzles were used for hover attitude control and, in the P.1127’s initial configu­ration, had no SAS. Low control power, aerodynamic suck-down, and marginal altitude control power made for a high pilot workload for this early Harrier predecessor. Even so, NACA researchers quickly realized that the P.1127 offered remarkable promise. NASA pilots Jack Reeder from Langley and Fred Drinkwater from Ames went to Europe to fly the P.1127 in June 1962, Reeder confiding afterward: "The British are ahead of us again.”[1447] His flight evaluation report noted:

The P. 1127 is not a testbed aircraft in the usual sense. It is advanced well beyond this stage and is actually an operational prototype, with which it is now possible to study the VSTOL concept in relation to military requirements by actual opera­tion in the field. The aircraft is easily controlled and has safe flight characteristics throughout the range from hover to air­plane flight. The performance range is very great; yet, conver­sions to or from low or vertical flight can be accomplished simply, quickly, and repeatedly.[1448]

Camm’s P.1127 led to the Hawker Kestrel F. G.A. Mk. 1, an interim "militarized” variant, nine of which undertook operational suitabil­ity trials with a NATO tripartite (U. K., U. S., and Federal Republic of Germany) evaluation squadron in 1965. The trials confirmed not only the basic performance of the aircraft, but also its military potential. So the Kestrel, in turn, led directly to a production military derivative, the Hawker Harrier G. R. Mk. 1—or, as known in U. S. Marine Corps service, the AV-8A. Eight of the Kestrel aircraft, designated XV-6A, remained in the United States for follow-on testing. NASA received two Kestrels, flying them in an extensive evaluation program at Langley with pilots

Jack Reeder, Lee H. Person, Jr., Robert Champine, and Perry L. Deal, under the supervision of project engineer Richard Culpepper.[1449]

Langley tunnel-testing and flight-testing revealed a number of defi­ciencies, though not of such magnitude as to detract from the impres­sion that the P.1127 was a remarkable accomplishment, and that it had tremendous potential for development. For example, a directional insta­bility was noticed in turning out of the wind, yaw control power was low but not considered unsafe, and pitch-trim changes occurred when leav­ing ground effect. The usual hot-gas ingestion problem could be circum­vented by maintaining a low forward speed in takeoff and landing. A static pitch instability was encountered at alphas greater than approxi­mately 15 degrees, and a large positive dihedral effect limited crosswind operations. Transition characteristics were outstanding, with only small trim changes required. Overall, low – and high-speed performance was excellent. Like any swept wing airplane, the Kestrel’s "Dutch roll” lateral – directional damping was low at altitude, requiring provision of a yaw damper. It had good STOL performance when the engine nozzles were deflected between purely vertical and purely horizontal settings. Indeed, this would later become one of the Harrier strike fighter’s strongest oper­ational qualities.[1450]

Like any operational aircraft, the Harrier went through progressive refinement. Its evolution coincided with the onset of advanced avionics, the emergence of composite structures, and NASA’s development of the supercritical wing. All were developments incorporated in the next gener­ation of Harrier, the AV-8B Harrier II, developed at the behest of the U. S

Marine Corps and adopted, in slightly different form, as the Harrier Mk. 5 by the Royal Air Force. As well, the AV-8B benefited from Langley research on optimum positioning of engine nozzles, trailing-edge flaps, and the wing, in order to obtain higher propulsive lift. (This jet age work mirrored much earlier work on optimum positioning of propellers, engines, and nacelles undertaken at Langley in the 1920s by the NACA).[1451]

Two AV-8A Harriers had been modified to serve as prototypes of the new Harrier II, these being designated YAV-8B. Though deceptively similar to the earlier AV-8A, the YAV-8B relied extensively on graphite epoxy composite structure and had a leading-edge extension at its wing – root and a bigger, supercritical wing. The first made its initial flight in November 1978, joined shortly afterward by the second. A year later, in November 1979, the second YAV-8B crashed after engine failure; its pilot ejected safely. However, flight-testing by contractor and service pilots confirmed that the AV-8B would constitute a significant advance over the earlier AV-8A for, during its evaluation program, "all performance requirements were met or exceeded.”[1452] Not surprisingly, the AV-8B entered production and squadron service with the U. S. Marine Corps, replacing the older Vietnam-legacy AV-8A.

In 1984, after the AV-8B entered operational service, the U. S. Marine Corps delivered the surviving YAV-8B to Ames so that Ames researchers could investigate advanced controls and flight displays, such as those that might be incorporated on future V/STOL combat systems called upon to conduct vertical envelopment assaults from small assault car­riers and other vessels in all-weather conditions. The study effort that followed built upon Ames’s legacy of V/STOL simulation studies, using both ground and flight simulators to evaluate a variety of guidance, con­trol, and display concepts, particularly the research of Vernon K. Merrick, Ernesto Moralez, III, Jeffrey A. Schroeder, and their associates.[1453] NASA designated the YAV-8B the V/STOL Systems Research Aircraft (VSRA). A team led by Del Watson and John D. Foster modifying it with digi­tal fly-by-wire controls for pitch, roll, yaw, thrust magnitude and thrust deflection, and programmable electronic head-up displays. Researchers subsequently flew the YAV-8B in an extensive evaluation of control

The NASA Ames YAV-8B V/STOL Systems Research Aircraft. NASA.

system concepts and behavior, from decelerations to hover, and then from hover to a vertical landing, assessing flying qualities tradeoffs for each of the various control concepts studied and evaluating advanced guidance and navigation displays as well.[1454] In addition to NASA pilots, a range of Marine, Royal Air Force, McDonnell-Douglas, and Rolls-Royce test pilots flew the aircraft. Their inputs, combined with data from Ames’s Vertical Motion Simulator, helped researcher Jack Franklin develop flying qualities criteria and control system and display concepts sup­porting the Joint Strike Fighter program.[1455] With the conclusion of the

VSRA aircraft program in 1997, NASA Ames’s role in V/STOL research came to an end.

In conclusion, in spite of the many challenges revealed in these summaries of V/STOL aircraft, the information accumulated from the design, development, and flight evaluations has provided a useful data­base for V/STOL designs. It is of interest to note that even though most of the aircraft were deficient, to some degree, in terms of aerodynamics, propulsion systems, or performance, it was always possible to develop special operating techniques to circumvent these problems. For the most part, this review would indicate that performance and handling – qualities limitations severely restricted operational evaluations for all types of V/STOL concepts. It has become quite obvious that V/STOL air­craft must be designed with good STOL performance capability to be cost-effective, a virtue not shared by many of the aircraft researched by NASA. Further, flight experience has shown that good handling quali­ties are needed, not only in the interest of safety, but also to permit the aircraft to carry out its mission in a cost-effective manner. It was appar­ent also that SAS was required to some degree for safely carrying out even simple operational tasks. The question of how much control sys­tem complexity is needed for various tasks and missions is still unan­swered. Another area deserving of increased attention derives from the fact that most of the V/STOL aircraft studied suffered to some degree from adverse ground effects. In this regard, better prediction techniques are needed to avoid costly aircraft modifications or restricted opera­tional use. Finally, there is an important continued need for good test­ing techniques and facilities to ensure satisfactory performance and control before and during flight-testing.

Today, NASA’s investment in V/STOL technology promises to be a key enabling technology in making the airspace system more environmen­tally friendly and efficient. Cruise Efficient Short Take-Off and Landing Aircraft (CESTOL) and Civil Tilt Rotor (CTR) promise to expand the number of takeoff and landing locations, operating in terminal areas in a simultaneous noninterfering manner (SNI) with conventional traffic, relieving overtaxed hub airports. CESTOL-CTR aircraft avoid the air­space and runways required by commercial aircraft using steeply curved approach and departure paths, thus enabling greater system capacity, reducing delays, and saving fuel. To fulfill this vision, performance penal­ties associated with STOL capability requires continued NASA research
to mitigate.[1456] While much still remains to be accomplished, much has already been achieved, and the vision of future V/STOL remains vibrant and exciting. That it is constitutes an accolade to those men and women of NASA, and the NACA before, whose contributions made V/STOL air­craft a practical reality.

S THIS BOOK GOES TO PRESS, the National Aeronautics and Space Administration (NASA) has passed beyond the half cen­tury mark, its longevity a tribute to how essential successive Presidential administrations—and the American people whom they serve—have come to regard its scientific and technological expertise. In that half century, flight has advanced from supersonic to orbital veloc­ities, the jetliner has become the dominant means of intercontinental mobility, astronauts have landed on the Moon, and robotic spacecraft developed by the Agency have explored the remote corners of the solar system and even passed into interstellar space.

Born of a crisis—the chaotic aftermath of the Soviet Union’s space triumph with Sputnik—NASA rose magnificently to the challenge of the emergent space age. Within a decade of NASA’s establishment, teams of astronauts would be planning for the first lunar landings, accom­plished with Neil Armstrong’s "one small step” on July 20, 1969. Few events have been so emotionally charged, and none so publicly visible or fraught with import, as his cautious descent from the spindly lit­tle Lunar Module Eagle to leave his historic boot-print upon the dusty plain of Tranquillity Base.

In the wake of Apollo, NASA embarked on a series of space initia­tives that, if they might have lacked the emotional and attention-getting impact of Apollo, were nevertheless remarkable for their accomplish­ment and daring. The Space Shuttle, the International Space Station, the Hubble Space Telescope, and various planetary probes, landers, rov­ers, and flybys speak to the creativity of the Agency, the excellence of its technical personnel, and its dedication to space science and exploration.

But there is another aspect to NASA, one that is too often hidden in an age when the Agency is popularly known as America’s space agency and when its most visible employees are the astronauts who courageously

rocket into space, continuing humanity’s quest into the unknown. That hidden aspect is aeronautics: lift-borne flight within the atmosphere, as distinct from the ballistic flight of astronautics, out into space. It is the first "A” in the Agency’s name, and the oldest-rooted of the Agency’s tech­nical competencies, dating to the formation, in 1915, of NASA’s lineal predecessor, the National Advisory Committee for Aeronautics (NACA). It was the NACA that largely restored America’s aeronautical primacy in the interwar years after 1918, deriving the airfoil profiles and con­figuration concepts that defined successive generations of ever-more – capable aircraft as America progressed from the subsonic piston era into the transonic and supersonic jet age. NASA, succeeding the NACA after the shock of Sputnik, took American aeronautics across the hyper­sonic frontier and onward into the era of composite structures, elec­tronic flight controls and energy-efficient flight.

As with the first in this series, this second volume traces con­tributions by NASA and the post-Second World War NACA to aeronautics. The surveys, cases, and biographical examinations pre­sented in this work offer just a sampling of the rich legacy of aero­nautics research having been produced by the NACA and NASA. These include

• Atmospheric turbulence, wind shear, and gust research, subjects of crucial importance to air safety across the spectrum of flight, from the operations of light general – aviation aircraft through large commercial and super­sonic vehicles.

• Research to understand and mitigate the danger of light­ning strikes upon aerospace vehicles and facilities.

• The quest to make safer and more productive skyways via advances in technology, cross-disciplinary integration of developments, design innovation, and creation of new operational architectures to enhance air transportation.

• Contributions to the melding of human and machine, via the emergent science of human factors, to increase the safety, utility, efficiency, and comfort of flight.

• The refinement of free-flight model testing for aero­dynamic research, the anticipation of aircraft behavior, and design validation and verification, complementing traditional wind tunnel and full-scale aircraft testing.

• The evolution of the wind tunnel and expansion of its capabilities, from the era of the slide rule and subsonic flight to hypersonic excursions into the transatmosphere in the computer and computational fluid dynamics era.

• The advent of composite structures, which, when cou­pled with computerized flight control systems, gave air­craft designers a previously unknown freedom enabling them to design aerospace vehicles with optimized aero­dynamic and structural behavior.

• Contributions to improving the safety and efficiency of general-aviation aircraft via better understanding of their unique requirements and operational circum­stances, and the application of new analytical and tech­nological approaches.

• Undertaking comprehensive flight research on sustained supersonic cruise aircraft—with particular attention to their aerodynamic characteristics, airframe heating, use of integrated flying and propulsion controls, and eval­uation of operational challenges such as inlet "unstart,” aircrew workload—and blending them into the predomi­nant national subsonic and transonic air traffic network.

• Development and demonstration of Synthetic Vision Systems, enabling increased airport utilization, more effi­cient flight deck performance, and safer air and ground aircraft operations.

• Confronting the persistent challenge of atmospheric icing and its impact on aircraft operations and safety.

• Analyzing the performance of aircraft at high angles of attack and conducting often high-risk flight-testing to study their behavior characteristics and assess the value of developments in aircraft design and flight control technologies to reduce their tendency to depart from controlled flight.

• Undertaking pathbreaking flight research on VTOL and V/STOL aircraft systems to advance their ability to enter the mainstream of aeronautical development.

• Conducting a cooperative international flight-test program to mutually benefit understanding of the potential, behav­ior, and performance of large supersonic cruise aircraft.

As this sampling—far from a complete range—of NASA work in aeronautics indicates, the Agency and its aeronautics staff spread across the Nation maintain a lively interest in the future of flight, benefitting NASA’s reputation earned in the years since 1958 as a national reposi­tory of aerospace excellence and its legacy of accomplishment in the 43-year history of the National Advisory Committee for Aeronautics, from 1915 to 1958.

As America enters the second decade of the second century of winged flight, it is again fitting that this work, like the volume that precedes it, be dedicated, with affection and respect, to the men and women of NASA, and the NACA from whence it sprang.

Dr. Richard P. Hallion

August 25, 2010

TH