Category NASA’S CONTRIBUTIONS TO AERONAUTICS

By James Banke

The aerospace environment is a realm of extremes: low to high pres­sures, densities, and temperatures. Researchers have had the goal of improving flight efficiency and safety. Aircraft icing has been a prob­lem since the earliest days of flight and, historically, researchers have artfully blended theory, ground-and-flight research, and the use of new tools such as computer simulation and software modeling codes to ensure that travelers fly in aircraft well designed to confront this hazard.

NE FEBRUARY EVENING in the late 1930s, a young copilot strode across a cold ramp of the Nashville airport under a frigid moon­lit sky, climbing into a chilled American Airlines DC-2. The young airman was Ernest Gann, later to gain fame as a popular nov­elist and aviation commentator, whose best-remembered book, The High and the Mighty, became an iconic aviation film. His captain was Walter Hughen, already recognized by his peers as one of the greats, and the two men worked swiftly to ready the sleek twin-engine trans­port for flight. Behind them, eight passengers settled in, looked after by a flight attendant. They were bound for New York, along AM-23, an air route running from Nashville to New York City. Preparations com­plete, they taxied out and took off on what should have been a routine 4-hour flight in favorable weather. Instead, almost from the moment the airliner’s wheels tucked into the plane’s nacelles, the flight began to deteriorate. By the time they reached Knoxville, they were bucking an unanticipated 50-mile-per-hour headwind, the Moon had vanished, and the plane was swathed in cloud, its crew flying by instruments only. And there was something else: ice. The DC-2 was picking up a heavy load of ice from the moisture-laden air, coating its wings and engine cowlings, even its propellers, with a wetly glistening and potentially deadly sheen.[1197]

Suddenly there was "an erratic banging upon the fuselage,” as the propellers began flinging ice "chunks the size of baseballs” against the fuselage. In the cockpit, Hughen and Gann desperately fought to keep their airplane in the air. Its leading edge rubber deicing boots, which shattered ice by expanding and contracting, so that the airflow could sweep it away, were throbbing ineffectively: the ice had built up so thick and fast that it shrouded them despite their pulsations. Carburetor inlet icing was building up on each engine, causing it to falter, and only delib­erately induced back-firing kept the inlets clear and the engines run­ning. Deicing fluid spread on the propellers and cockpit glass had little effect, as did a hot air hose rigged to blow on the outside of the wind­shield. Worst of all, the heavy icing increased the DC-2’s weight and drag, slowing it down to near its stall point. At one point, the plane began "a sudden, terrible shudder,” perilously on the verge of a fatal stall, before Hughen slammed the throttles full-forward and pushed the nose down, restoring some margin of flying speed.[1198]

After a half hour of desperate flying that "had the smell of eternity” about it, the battered DC-2 and its drained crew entered clear skies. The weather around them was still foreboding, and so, after trying to return to Nashville, finding it was closed, and then flying about for hours searching for an acceptable alternate, they turned for Cincinnati, Hughen and Gann anxiously watching their fuel consumption. Ice— some as thick as 4 inches—still swathed the airplane, so much so that Gann thought, "Where are the engineers again? The wings should somehow be heated.” The rudder was frozen in place, and the elevators and ailerons (controlling pitch and roll) moveable only because of Hughen and Gann’s constant control inputs to ensure they remained free. At dawn they reached Cincinnati, where the plane, bur­dened by its heavy load of ice, landed heavily. "We hit hard,” Gann recalled,"and stayed earth-bound. There is no life left in our wings for bouncing.” Mechanics took "two hours of hard labor to knock the ice from our wings, engine cowlings, and empennage.” Later that day, Hughen and Gann completed the flight to New York, 5 hours late. In the remarks section of his log, explaining the delayed arrival, Gann simply penned "Ice.”[1199]

Gann, ever after, regarded the flight as marking his seasoning as an airman, "forced to look disaster directly in the face and stare it down.”[1200] Many others were less fortunate. In January 1939, Cavalier, an Imperial Airways S.23 flying boat, ditched heavily in the North Atlantic, breaking up and killing 3 of its 13 passengers and crew; survivors spent 10 cold hours in heaving rafts before being rescued. Carburetor icing while flying through snow and hail had suffocated two of its four engines, leaving the flying boat’s remaining two faltering at low power.[1201] In October 1941, a Northwest Airlines DC-3 crashed near Moorhead, MN, after the heavy weight of icing prevented its crew from avoiding terrain; this time 14 of 15 on the plane died.[1202]

Even when nothing went wrong, flying in ice was unsettling. Trans World Airlines Captain Robert "Bob” Buck, who became aviation’s most experienced, authoritative, and influential airman in bad weather fly­ing, recalled in 2002 that

A typical experience in ice meant sitting in a cold cockpit, windows covered over in a fan-shaped plume from the lower aft corner toward the middle front, frost or snow covering the inside of the windshield frames, pieces as large as eight inches growing forward from the wind­shield’s edges outside, hunks of ice banging against the fuselage and the airplane shaking as the tail swung left and right, right and left, and the action was transferred to the rudder pedals your feet were on so you felt them saw back and forth beneath you The side winds were frosted, but you could wipe them clear enough for a look out at the engines. The nose cowlings collected ice on their lead­ing edge, and I’ve seen it so bad that the ice built forward until the back of the propeller was shaving it! But still the airplane flew. The indicated airspeed would slow, and
you’d push up the throttles for more power to overcome the loss but it didn’t always take, and the airspeed some­times went down to alarming numbers approaching stall.[1203]

Icing, as the late aviation historian William M. Leary aptly noted, has been a "perennial challenge to aviation safety.”[1204] It’s a chilling fact that despite a century of flight experience and decades of research on the ground and in the air, today’s aircraft still encounter icing conditions that lead to fatal crashes. It isn’t that there are no preventative measures in place. Weather forecasting, real-time monitoring of conditions via sat­ellite, and ice prediction software are available in any properly equipped cockpit to warn pilots of icing trouble ahead. Depending on the size and type of aircraft, there are several proven anti-icing and de-icing systems that can help prevent ice from building up to unsafe levels. Perhaps most importantly, pilot training includes information on recognizing icing con­ditions and what to do if an aircraft starts to ice up in flight. Unfortunately the vast majority of icing-related incidents echo a theme in which the pilot made a mistake while flying in known icing conditions. And that shows that in spite of all the research and technology, it’s still up to the pilot to take advantage of the experience base developed by NASA and others over the years.

In the very earliest days of aviation, icing was not an immediate con­cern. That all changed by the end of the First World War, by which time airplanes were operating at altitudes above 10,000 feet and in a variety of meteorological conditions. Worldwide, the all-weather flying needs of both airlines and military air service, coupled with the introduction of blind-flying instrumentation and radio navigation techniques that enabled flight in obscured weather conditions, stimulated study of icing, which began to take a toll on airmen and aircraft as they increasingly operated in conditions of rain, snow, and freezing clouds and sleet.[1205]

The NACAs interest in icing dated to the early 1920s, when America’s aviation community first looked to the Agency for help. By the early 1930s, both in America and abroad, researchers were examining the pro­cess of ice formation on aircraft and means of furnishing some sort of surface coatings that would prevent its adherence, particularly to wings, acquiring data both in actual flight test and by wind tunnel studies. Ice on wings changed their shape, drastically altering their lift-to-drag ratios and the pressure distribution over the wing. An airplane that was per­fectly controllable with a clean wing might prove very different indeed with just a simple change to the profile of its airfoil.[1206] Various mechan­ical and chemical solutions were tried. The most popular mechanical approach involved fitting the leading edges of wings, horizontal tails, and, in some cases, vertical fins with pneumatically operated rubber "de-icing” boots that could flex and crack a thin coating of ice. As Gann and Buck noted, they worked at best sporadically. Other approaches involved squirting de-icing fluid over leading edges, particularly over propeller blades, and using hot-air hoses to de-ice cockpit windshields.

Lewis A. "Lew” Rodert—the best known of ice researchers—was a driven and hard-charging NACA engineer who ardently pursued using heat as a means of preventing icing of wings, propellers, carburetors, and windshields.[1207] Under Rodert’s direction, researchers extensively instrumented a Lockheed Model 12 light twin-engine transport for icing research and, later, a larger and more capable Curtiss C-46 transport. Rodert and test pilot Larry Clausing, both Minnesotans, moved the NACAs ice research program from Ames Aeronautical Laboratory (today the NASA Ames Research Center) to a test site outside Minneapolis. There, researchers took advantage of the often-formidable weather con­ditions to assemble a large database on icing and icing conditions, and

on the behavior of various modifications to their test aircraft. These tests complemented more prosaic investigations looking at specific icing problems, particularly that of carburetor icing.[1208]

The war’s end brought Rodert a richly deserved Collier Trophy, American aviation’s most prestigious award, for his thermal de-icing research, particularly the development and validation of the concept of air-heated wings.[1209] By 1950, a solid database of NACA research existed on icing and its effects upon propeller-driven airplanes.[1210] This led many to conclude that the "heroic era” of icing research was in the past, a judg­ment that would prove to be wrong. In fact, the problems of icing merely changed focus, and NACA engineers quickly assessed icing implications for the civil and military aircraft of the new gas turbine and transonic era.[1211] New high-performance interceptor fighters, expected to acceler­ate quickly and climb to high altitudes, had icing problems of their own, typified by inlet icing that forced performance limitations and required imaginative solutions.[1212] When first introduced into service, Bristol’s otherwise-impressive Britannia turboprop long-range transport had persistent problems caused by slush ice forming in the induction system of its Proteus turboprop engines. By the time the NACA evolved into the

National Aeronautics and Space Administration in 1958, the fundamen­tal facts concerning the types of ice an aircraft might encounter and the major anti-icing techniques available were well understood and widely in use. In retrospect, as impressive as the NACA’s postwar work in icing was, it is arguable that the most important result of NACA work was the establishment of ice measurement criteria, standards for ice-prevention systems, and probabilistic studies of where icing might be encountered (and how severe it might be) across the United States. NACA Technical Notes 1855 (1949) and 2738 (1952) were the references of record in estab­lishing Federal Aviation Administration (FAA) standards covering aircraft icing certification requirements.[1213]

Early NACA research on stalling and spinning in the 1920s quickly con­cluded that the primary factors that governed the physics of stall behav­ior, spin entry, and recovery from spins were very complicated and would require extensive commitments to new experimental facilities for stud­ies of aerodynamics and flight motions. Over the following 85 years, efforts by the NACA and NASA introduced a broad spectrum of spe­cialized tools and analysis techniques for high-angle-of-attack condi­tions, including vertical spin tunnels, pressurized wind tunnels to define the impact of Reynolds number on separated flow phenomena, special free-flight model test techniques, full-scale aircraft flight experiments, theoretical studies of aircraft motions, piloted simulator studies, and unique static and dynamic wind tunnel aerodynamic testing capability.[1275]

By the 1930s, considerable progress had been made at the NACA Langley Memorial Aeronautical Laboratory on obtaining wind tunnel aerodynamic data on the effectiveness of lateral control concepts at the stall and understanding control effects on motions.[1276] A basic understand­ing began to emerge on the effects of design variables for biplanes of the era, such as horizontal and vertical tail configurations, wing stagger,
and center-of-gravity location on spinning. Flight-testing of stall char­acteristics became a routine element of handling quality studies. In the race to conquer stall/spin problems, however, simplistic and regretta­ble conclusions were frequently drawn.[1277]

The sudden onset of World War II and its urgency for aeronauti­cal research and development overwhelmed the laboratory’s plodding research environment and culture with high-priority requests from the military services for immediate wind tunnel and flight assessments, as well as problem-solving activities for emerging military aircraft. At that time, the military perspective was that operational usage of high-angle – of-attack capability was necessary in air combat, particularly in classic "dogfight” engagements wherein tighter turns and strenuous maneu­vers meant the difference between victory and defeat. Tactical effective­ness and safety, however, demanded acceptable stalling and spinning behavior, and early NACA assessments for new designs prior to indus­try and military flight-testing and production were required for every new maneuverable aircraft.[1278] Spin demonstrations of prototype aircraft by the manufacturer were mandatory, and satisfactory stall character­istics and recoveries from developed spins required extensive testing by the NACA in its conventional wind tunnels and vertical spin tunnel.

The exhausting demands of round-the-clock, 7-day workweeks left very little time for fundamental research, but researchers at Langley’s Spin Tunnel, Free-Flight Tunnel, Stability Tunnel, and 7- by 10-Foot Tunnels initiated a series of studies that resulted in advancements in high-angle-of-attack design procedures and analysis techniques.[1279]

The advent of vertical flight required mastery of aerodynamics, pro­pulsion, and flight control technology. In the evolution of flight charac­terized by progressive development of the autogiro, helicopter, and various convertiplanes, the NACA and NASA have played a predom­inant role. NASA developed the theoretical underpinning for vertical flight, evaluated requisite technologies and research vehicles, and expanded the knowledge base supporting V/STOL flight technology.

NE OF THE MAJOR ACCOMPLISHMENTS in the history of avi­ation has been the development of practical Vertical Take-Off and Landing (VTOL) aircraft, exemplified by the emergence of the helicopter in the 1930s and early 1940s, and the vectored-thrust

jet airplane of the 1960s. Here indeed was a major challenge that con­fronted flight researchers, aeronautical engineers, military tacticians, and civilian planners for over 50 years, particularly those of the National Aeronautics and Space Administration (NASA) and its predecessor, the National Advisory Committee for Aeronautics (NACA). While perhaps not regarded by aviation aficionados as being as glamorous as the exper­imental craft that streaked to new speeds and altitudes, early vertical flight testbeds were likewise revolutionary at the other end of the perfor­mance spectrum, in vertical ascents and descents, low-speed controlla­bility, and hover, areas challenging accepted knowledge and practice in aerodynamics, propulsion, and flight controls and controllability.[1330]

The accomplishment of vertical flight was as challenging as inventing the airplane itself. Only four decades after Kitty Hawk were vertical take­off, hovering, and landing aircraft beginning to enter service. These were, of course, the first helicopters: successors to the interim rotary wing auto­giro that relied on a single or multiple rotors to give them Vertical/Short

Take-Off and Landing (V/STOL) performance. Before the end of the Second World War, the helicopter had flown in combat, proved its value as a life­saving craft, and shown its adaptability for both land – and sea-based operation.[1331] The faded promises of many machines litter the path to the modern V/STOL vehicle. The dedicated research accompanying this work nevertheless led to a class of flight craft that have expanded the use of civil and military aeronautics, saving the lives of nearly a half million people over the last seven decades. The oil rigger in the Gulf going on leave, the yachtsman waiting for rescue, and the infantryman calling in gunships to fend off attack can all thank the flight researchers, particularly those of the NACA and NASA, who made the VTOL aircraft possible.[1332]

Helicopters matured significantly during the Korean war, setting the stage for their pervasive employment in the war in Southeast Asia a decade later.[1333] Helicopters revolutionized warfare and became the iconic image of the Vietnam war. On the domestic front, outstanding helicop­ter research was being carried on at NASA Langley. Of particular note were the contributions of researchers and test pilots such as Jack Reeder, John P. Campbell, Richard E. Kuhn, Marion O. McKinney, and Robert

H. Kirby. In the late 1950s, military advisers realized how much of the Nation’s defense structure depended on a few large airbases and a few large aircraft carriers. Military interests were driven by the objective of achieving operations into and out of unprepared remotely dispersed sites independent of conventional airfields. Meanwhile, commercial air transportation organizations were pursuing ways to cut the amount of real estate required to accommodate new aircraft and long airstrips.[1334]

Since NASAs inception in 1958, its researchers at various Centers have advanced the knowledge base of V/STOL technology via many special­ized test aircraft and flying techniques. Some key discoveries include the realization that V/STOL aircraft must be designed with good Short Take­Off and Landing (STOL) performance capability to be cost-effective, and that, arguably, the largest single obstacle to the implementation of STOL powered-lift technology for civil aircraft is the increasingly objection­able level of aircraft-generated noise at airports close to populated areas.

But NASA interest in fixed wing STOL and VTOL convertiplanes predates formation of the Agency, going back to the unsuccessful com­bined rotor and wing design by Emile and Henry Berliner tested at College Park Airport, MD, in the early 1920s. In the late 1930s and early 1940s, NACA researcher Charles Zimmerman undertook pioneer­ing research on such craft, his interest leading to the Vought V-173, popularly known as the "Flying Flapjack,” because of its peculiar near­circular wing shape. It led to an abortive Navy fighter concept, the Vought XF5U-1, which was built but never flown. The V-173, however, contrib­uted notably to the emerging understanding of V/STOL aircraft chal­lenges and performance. Aside from this sporadic interest, the Agency’s research staff did not place great emphasis upon such studies until the postwar era. Then, beginning in the early 1950s, a veritable explosion of interest followed, with a number of design studies and flight-test

programs undertaken at Langley and Ames laboratories (later the NASA Langley and Ames Research Centers). This interest corresponded to ris­ing interest in the military in the possibility of vertical flight vehicles for a variety of missions.

For example, the U. S. Navy sponsored two unsuccessful experimen­tal "Pogo” tail-sitting turboprop-powered VTOL fighters: the Lockheed XFV-1 and the Convair XFY-1. Only the XFY-1 subsequently operated in true VTOL mode, and flight trials indicated that neither represented a
reasonable approach to practical VTOL flight. The Air Force developed a pure-jet equivalent: the VTOL delta-winged Ryan X-13. Though widely demonstrated (even outside the Pentagon), it was equally impracticable.[1335] The U. S. Army’s Transportation and Research Engineering Command sponsored ducted-fan flying jeep and other saucerlike circular flying platforms by Avro and Hiller, with an equivalent lack of success. Overall, the Army’s far-seeing V/STOL testbed program, launched in 1956 and undertaken in cooperation with the U. S. Navy’s Office of Naval Research, advanced a number of so-called "VZ”-designated research aircraft explor­ing a range of technical approaches to V/STOL flight.[1336] NATO planners envisioned V/STOL close-air support, interdiction, and nuclear attack aircraft. This interest eventually helped spawn the British Aerospace Harrier strike fighter of the late 1960s and other designs that, though they entered flight-testing, did not prove suitable for operational service.[1337]

The United States Pilot Evaluation Team (USPET)[1477] arrived in Moscow on Sunday, September 6, 1998, and was met by Professor Alexander Pukhov and a delegation of Tupolev officials. (Ill fortune had struck the team when NASA Langley research pilot Robert Rivers severely broke his right leg and ankle 2 weeks before departure. Because visas for work in Russia required 60 days’ lead time and because no other pilot could be prepared in time, Rivers remained on the team, though it required a great deal of perseverance to obtain NASA approval. Tupolev pre­sented relatively few obstacles, by contrast, to Rivers’s participation.) Pukhov was the Tupolev Manager for the Tu-144 experiment and a for­mer engineer on the original design team for the airplane. At Pukhov’s insistence, USPET was billeted in Zhukovsky at the former KGB san­itarium. Sanitaria in the Soviet Union were rest and vacation spas for the various professional groups, and the KGB sanitarium was similar to a large hotel. The sanitarium was minutes from the Zhukovsky Air

Development Center and saved hours of daily commute time that oth­erwise might have been wasted had the team been housed in Moscow.

The next day began a very intense training period lasting 2 weeks but was punctuated September 15 by the first flight by American pilots, a subsonic sojourn. The training was complicated by the language differ­ences but was facilitated by highly competent Russian State Department translators. Nevertheless, humorous if not frustrating problems arose when nontechnical translators attempted to translate engineering and piloting jargon with no clear analogs in either language. The training consisted of one-on-one sitdown sessions with various Tu-144 systems experts using manuals and charts written in Russian. There were no English language flight or systems manuals for the Tu-144, and USPET’s attempt over the summer to procure a translated Tu-144 flight manual was unsuccessful. Training included aircraft systems, life support, and flight operations. Because flights would achieve altitudes of 60,000 feet and because numerous hull penetrations had occurred to accommodate the instrumentation system, all members of the flightcrew wore partial pressure suits. Because of the experimental nature of the flights, a man­ual bailout capability had been incorporated in the Tu-144. This involved dropping through a hatch just forward of the mammoth engine inlets. The hope was that the crewmember would pass between the two banks of engines without being drawn into the inboard inlets. Thankfully, this theory was never put to the test.

Much time was spent with the Tupolev flightcrew for the experi­ment, and great trust and friendship ensued. Tupolev chief test pilot Sergei Borisov was the pilot-in-command for all of the flights. Victor Pedos was the navigator, in actuality a third pilot, and Anatoli Kriulin was the flight engineer. Tupolev’s chief flight control engineer, Vladimir Sysoev, spent hours each day with USPET working on the test plan for each pro­posed flight. Sysoev and Borisov represented Tupolev in the negotiations to perform the maneuvers requested by the various researchers.[1478] An effective give-and-take evolved as the mutual trust grew. From Tupolev’s perspective, the Tu-144 was a unique asset, into which the fledgling free- market company had invested millions of dollars. It provided badly needed funds at a time when the Russian economy was struggling, and

the payments from NASA via Boeing and IBP were released only at the completion of each flight. The Tupolev crewmembers could not afford to risk the airplane. At the same time, they were anxious to be as coop­erative as possible. Careful and inventive planning resulted in nearly all of the desired test points being flown.

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

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