Category NASA’S CONTRIBUTIONS TO AERONAUTICS

After millions of years of birds having the sky to themselves, it only took 9 years from the time the Wright brothers first flew in 1903 for the first human fatality brought about by a bird striking an aircraft and caus­ing the plane to crash in 1912. Fast-forward to 1960, when an Eastern Air Lines plane went down near Boston, killing 62 people as a result of a bird strike—the largest loss of life from a single bird incident.[192]

With the growing number of commercial jet airplanes, faster aircraft increased the potential damage a small bird could inflict and the larger airplanes put more humans at risk during a single flight. The need to address methods for dealing with birds around airports and in the skies also rose in priority. So, on September 9, 1966, the Interagency Bird

Hazard Committee was formed to gather data, share information, and develop methods for mitigating the risk of collisions between birds and airplanes. With the FAA taking the lead, the Committee included rep­resentatives from NASA; the Civil Aeronautics Board; the Department of Interior; the Department of Health, Education, and Welfare; and the U. S. Air Force, Navy, and Army.[193]

Through the years since the Committee was formed, the avia­tion community has approached the bird strike hazard primarily on three fronts: (1) removing or relocating the birds, (2) designing aircraft components to be less susceptible to damage from bird strikes, and (3) increasing the understanding of bird habitats and migratory pat­terns so as to alter air traffic routes and minimize the potential for bird strikes. Despite these efforts, the problem persists today, as evidenced by the January 2009 incident involving a US Airways jet that was forced to ditch in the Hudson River. Both of its jet engines failed because of

bird strikes shortly after takeoff. Fortunately, all souls on board survived the water landing thanks to the training and skills of the entire flightcrew.[194]

NASA’s contributions in this area include research to character­ize the extent of damage that birds might inflict on jet engines and other aircraft components in a bid to make those parts more robust or forgiving of a strike,[195] and the development of techniques to iden­tify potentially harmful flocks of birds[196] and their local and seasonal flight patterns using radar so that local air traffic routes can be altered.[197]

Radar is in use to warn pilots and air traffic controllers of bird haz­ards at the Seattle-Tacoma International Airport. As of this writing, the FAA plans to deploy test systems at Chicago, Dallas, and New York air­ports, as the technology still needs to be perfected before its deploy­ment across the country, according to an FAA spokeswoman quoted in a Wall Street Journal story published January 26, 2009.[198]

Meanwhile, a bird detecting radar system first developed for the Air Force by DeTect, Inc., of Panama City, FL, has been in use since 2006 at NASA’s Kennedy Space Center to check for potential bird strike hazards before every Space Shuttle launch. Two customized marine radars scan the sky: one oriented in the vertical, the other in the horizontal. Together with specialized software, the MERLIN system can detect flocks of birds up to 12 miles from the launch pad or runway, according to a company fact sheet.

In the meantime, airports with bird problems will continue to rely on broadcasting sudden loud noises, shooting off fireworks, flashing strobe lights, releasing predator animals where the birds are nesting, or, in the worst case, simply eliminating the birds.

Making the skyways safer for aircraft to fly by reducing delays and lowering the stress on the system begins and ends with the short jour­ney on the ground between the active runway and the terminal gate. To better coordinate events between the air and ground sides, NASA devel­oped, in cooperation with the FAA, a software tool called the Surface Management System (SMS), whose purpose is to manage the move­ments of aircraft on the surface of busy airports to improve capacity, efficiency, and flexibility.[261]

The SMS has three parts: a traffic management tool, a controller tool, and a National Airspace System information tool.[262]

The traffic management tool monitors aircraft positions in the sky and on the ground, along with the latest times when a departing air­liner is about to be pushed back from its gate, to predict demand for taxiway and runway usage, with an aim toward understanding where backups might take place. Sharing this information among the traffic control tools and systems allows for more efficient planning. Similarly, the controller tool helps personnel in the ATC and ramp towers to bet­ter coordinate the movement of arriving and departing flights and to

advise pilots on which taxiways to use as they navigate between the runway and the gate.[263] Finally, the NAS information tool allows data from the SMS to be passed into the FAA’s national Enhanced Traffic Management System, which in turn allows traffic controllers to have a more accurate picture of the airspace.[264]

It is therefore abundantly evident that when the NACA handed over the keys of its research facilities to NASA on October 1, 1958, the Nation’s new space agency began operations with a large database of informa­tion relating to the human factors and human engineering aspects of piloted flight. But though this mass of accumulated knowledge and technology was of inestimable value, the prospect of taking man to the next level, into the great unknown of outer space, was a different prop­osition from any ever before tackled by aviation research.[339] No one had yet comprehensively dealt with such human challenges as the effects of long-term weightlessness, exposure to ionizing radiation and extreme temperature changes, maintaining life in the vacuum of space, or with­standing prolonged impact deceleration forces encountered by humans violently reentering the Earth’s atmosphere.[340]

NASA began operations in 1958 with a final parting report from the NACAs Special Committee on Space Technology. This report recommended several technical areas in which NASA should proceed with its human factors research. These included acceleration, high-intensity radiation in space, cosmic radiation, ionization effects, human information process­ing and communication, displays, closed-cycle living, space capsules, and crew selection and training.[341] This Committee’s Working Group on Human Factors and Training further suggested that all experimentation con­sider crew selection, survival, safety, and efficiency.[342] With that, America’s new space agency had its marching orders. It proceeded to assemble "the largest group of technicians and greatest body of knowledge ever used to define man’s performance on the ground and in space environments.”[343]

Thus, from NASA’s earliest days, it has pioneered the way in human – centered aerospace research and technology. And also from its begin­ning—and extending to the present—it has shared the benefits of this research with the rest of the world, including the same industry that contributed so much to NASA during its earliest days—aeronautics. This 50-year storehouse of knowledge produced by NASA human fac­tors research has been shared with all areas of the aviation community— both the Department of Defense (DOD) and all realms of civil avia­tion, including the Federal Aviation Administration (FAA), the National Transportation and Safety Board (NTSB), the airlines, general aviation, aircraft manufacturing companies, and producers of aviation-related hardware and software.

Scientists at NASA Ames Research Center have for many years been heavily involved with conducting research on visual technology for humans. The major areas explored include vision science, image

compression, imaging and displays, and visual human factors. Specific projects have investigated such issues as eye-tracking accuracy, image enhancement, metrics for measuring image quality, and methods to measure and improve the visibility of in-flight and air traffic control monitor displays.[433]

The information gained from this and other NASA-conducted research has played an important role in the development of such important and innovative human-assisting technologies as virtual reality goggles, helmet-mounted displays, and so-called glass cockpits.[434]

The latter concept, which NASA pioneered in the 1970s, refers to the replacement of conventional cockpit analog dials and gauges with a system of cathode ray tubes (CRT) or liquid crystal display (LCD) flatpanels that display the same information in a more readable and usable form.[435] Conventional instruments can be difficult to accurately read and monitor, and they are capable of providing only one level of information. Computerized "glass” instrumentation, on the other hand, can display both numerical and graphic color-coded readouts in 3-D format; furthermore, because each display can present several layers of information, fewer are needed. This provides the pilot larger and more readable displays. This technology, which is now used in nearly all airliners, business jets, and an increasing number of general-aviation aircraft, has improved flight safety and aircrew efficiency by decreasing workload, fatigue, and instrument interpretation errors.[436]

A related vision technology that NASA researchers helped develop is the head-up display.[437] This transparent display allows a pilot to view flight data while looking outside the aircraft. This is especially use­ful during approaches for landing, when the pilot’s attention needs to be focused on events outside the cockpit. This concept was originally developed for the Space Shuttle and military aircraft but has since been

adapted to commercial and civil aircraft, air traffic control towers, and even automobiles.[438]

The efforts of the NACA and NASA in developing and applying dynami­cally scaled free-flight model testing techniques have progressed through a truly impressive maturation process. Although the scaling relation­ships have remained constant since the inception of free-flight testing, the facilities and test attributes have become dramatically more sophis­ticated. The size and construction of models have changed from unpow­ered balsa models weighing a few ounces with wingspans of less than 2 feet to very large powered composite models with weights of over 1,000 pounds. Control systems have changed from simple solenoid bang-bang controls operated by a pilot with visual cues provided by model motions to hydraulic systems with digital flight controls and full feedbacks from an array of sensors and adaptive control systems. The level of sophisti­cation integrated into the model testing techniques has now given rise

to a new class of free-flight models that are considered to be integrated concept demonstrators rather than specific technology tools. Thus, the lines between free-flight models and more complex remotely piloted vehicles have become blurred, with a noticeable degree of refinement in the concept demonstrators.

Research activities at the NASA Dryden Flight Research Center vividly illustrate how far free-flight testing has come. Since the 1970s, Dryden has continually conducted a broad program of demonstrator applications with emphasis on integrations of advanced technology. In 1997, another milestone was achieved at Dryden in remotely piloted research vehicle technology, when an X-36 vehicle demonstrated the feasibility of using advanced technologies to ensure satisfactory flying qualities for radical tailless fighter designs. The X-36 was designed as a joint effort between the NASA Ames Research Center and the Boeing Phantom Works (previously McDonnell-Douglas) as a 0.28-scale pow­ered free-flight model of an advanced fighter without vertical or hori­zontal tails to enhance survivability. Powered by a F112 turbofan engine and weighing about 1,200 pounds, the 18-foot-long configuration used

a canard, split aileron surfaces, wing leading – and trailing-edge flaps, and a thrust-vectoring nozzle for control. A single-channel digital fly­by-wire system provided artificial stability for the configuration, which was inherently unstable about the pitch and yaw axes.[505]

The growing interest in and institutionalization of aeronautics in the late 19th century led to the creation of the wind tunnel.[531] English scien­tists and engineers formed the Royal Aeronautical Society in 1866. The group organized lectures, technical meetings, and public exhibitions, published the influential Annual Report of the Aeronautical Society, and funded research to spread the idea of powered flight. One of the more influential members was Francis Herbert Wenham. Wenham, a profes­sional engineer with a variety of interests, found his experiments with a whirling arm to be unsatisfactory. Funded by a grant from the Royal Aeronautical Society, he created the world’s first operating wind tunnel in 1870-1872. Wenham and his colleagues conducted rudimentary lift and drag studies and investigated wing designs with their new research tool.[532]

Wenham’s wing models were not full-scale wings. In England, University of Manchester researcher Osborne Reynolds recognized in 1883 that the airflow pattern over a scale model would be the same for its full-scale version if a certain flow parameter were the same in both cases. This basic parameter, attributed to its discoverer as the Reynolds number, is a measure of the relative effects of the inertia and viscosity of air flowing over an aircraft. The Reynolds number is used to describe all types of fluid flow, including the shape of flow, heat transfer, and the start of turbulence.[533]

While Wenham invented the wind tunnel and Reynolds created the basic parameter for understanding its application to full-scale aircraft, Wilbur and Orville Wright were the first to use a wind tunnel in the sys­tematic way that later aeronautical engineers would use it. The broth­ers, not aware of Wenham’s work, saw their "invention” of the wind tunnel become part of their revolutionary program to create a practical heavier-than-air flying machine from 1896 to 1903. Frustrated by the

poor performance of their 1900 and 1901 gliders on the sandy dunes of the Outer Banks—they did not generate enough lift and were uncontrol­lable—the Wright brothers began to reevaluate their aerodynamic cal­culations. They discovered that Smeaton’s coefficient, one of the early contributions to aeronautics, and Otto Lilienthal’s groundbreaking air­foil data were wrong. They found the discrepancy through the use of their wind tunnel, a 6-foot-long box with a fan at one end to generate air that would flow over small metal models of airfoils mounted on balances, which they had created in their bicycle workshop. The lift and drag data they compiled in their notebooks would be the key to the design of wings and propellers during the rest of their experimental program, which cul­minated in the first controlled, heavier-than-air flight December 17, 1903.[534]

Over the early flight and World War I eras, aeronautical enthusi­asts, universities, aircraft manufacturers, military services, and national governments in Europe and the United States built 20 wind tunnels. The United States built the most at 9, with 4 rapidly appearing during American involvement during the Great War. Of the European countries, Great Britain built 4, but the tunnels in France (2) and Germany (3) proved to be the most innovative. Gustav Eiffel’s 1912 tunnel at Auteiul, France, became a practical tool for the French aviation industry to develop high-performance aircraft for the Great War. At the University of Gottingen in Germany, aerodynamics pioneer Ludwig Prandtl designed what would become the model for all "modern” wind tunnels in 1916. The tunnel featured a closed circuit; a contraction cone, or nozzle, just before the test section that created uniform air velocity and reduced turbulence in the test section; and a chamber upstream of the test section that stilled any remaining turbulent air further.[535]

A strategy began forming in 1972 with the launch of the Air Force-NASA Long Range Planning Study for Composites (RECAST), which focused priorities for the research projects that would soon begin.[700] That was pre­lude to what NASA research Marvin Dow would later call the "golden age of composites research,”[701] a period stretching from roughly 1975 until funding priorities shifted in 1986. As airlines looked to airframers for help, military aircraft were already making great strides with composite structure. The Grumman F-14 Tomcat, then the McDonnell-Douglas F-15 Eagle, incorporated boron-epoxy composites into the empennage skin, a primary structure.[702] With the first flight of the McDonnell-Douglas AV-8B Harrier in 1978, composite usage had drifted to the wing as well. In all,

about one-fourth of the AV-8B’s weight,[703] including 75 percent in the weight of the wing alone,[704] was made of composite material. Meanwhile, composite materials studies by top Grumman engineer Norris Krone opened the door to experimenting with forward-swept wings. NASA responded to Krone’s papers in 1976 by launching the X-29 technology demonstrator, which incorporated an all-composite wing.[705]

Composites also found a fertile atmosphere for innovation in the rotorcraft industry during this period. As NASA pushed the commer­cial aircraft industry forward in the use of composites, the U. S. Army spurred progress among its helicopter suppliers. In 1981, the Army selected Bell Helicopter Textron and Sikorsky to design all-composite airframes under the advanced composite airframe program (ACAP).[706]

Perhaps already eyeing the need for a new light airframe to replace the Bell OH-58 Kiowa scout helicopter, the Army tasked the contrac­tors to design a new utility helicopter under 10,000 pounds that could fly for up to 2 hours 20 minutes.[707] Bell first flew the D-292 in 1984, and Sikorsky flew the S-75 ACAP in 1985.[708] Boeing complemented their efforts by designing the Model 360, an all-composite helicopter airframe with a gross weight of 30,500 pounds.[709] Each of these projects provided the steppingstones needed for all three contractors to fulfill the design goals for both the now-canceled Sikorsky-Boeing RAH-66 Comanche and the Bell-Boeing V-22 Osprey tilt rotor. The latter also drove devel­opments in automated fiber placement technology, relieving the need to lay up by hand about 50 percent of the airframe’s weight.[710]

In the midst of this rapid progress, the makers of executive and "general” aircraft required neither the encouragement nor the finan­cial assistance of the Government to move wholesale into composite airframe manufacturing. While Boeing dabbled with composite spoil­ers, ailerons, and wing covers on its new 767, William P. Lear, founder of LearAvia, was developing the Lear Fan 2100—a twin-engine, nine – seat aircraft powered by a pusher-propeller with a 3,650-pound air­frame made almost entirely from a graphite-epoxy composite.[711] About a decade later, Beechcraft unveiled the popular and stylish Starship 1, an 8- to 10-passenger twin turboprop weighing 7,644 pounds empty.[712] Composite materials—mainly using graphite-epoxy and NOMEX sand­wich panels—accounted for 72 percent of the airframe’s weight.[713]

Actual performance fell far short of the original expectations dur­ing this period. Dow’s NASA colleagues in 1975 had outlined a strategy that should have led to full-scale tests of an all-composite fuselage and wing box for a civil airliner by the late 1980s. Although the dream was delayed by more than a decade, it is true that state of knowledge and
understanding of composite materials leaped dramatically during this period. The three major U. S. commercial airframers of the era—Boeing, Lockheed, and McDonnell-Douglas—each made contributions. However, the agenda was led by NASA’s $435-million investment in the Aircraft Energy Efficiency (ACEE) program. ACEE’s top goal, in terms of fund­ing priority, was to develop an energy-efficient engine. The program also invested greatly to improve how airframers control for laminar flow. But a major pillar of ACEE was to drive the civil industry to fundamentally change its approach to aircraft structures and shift from metal to the new breed of composites then emerging from laboratories. As of 1979, NASA had budgeted $75 million toward achieving that goal,[714] with the manufacturers responsible for providing a 10-percent match.

ACEE proposed a gradual development strategy. The first step was to install a graphite-epoxy composite material called Narmco T300/5208[715] on lightly loaded secondary structures of existing commercial aircraft in oper­ational service. For their parts, Boeing selected the 727 elevator, Lockheed chose the L-1011 inboard aileron, and Douglas opted to change the DC-10 upper aft rudder.[716] From this starting point, NASA engaged the manufac­turers to move on to medium-primary components, which became the 737 horizontal stabilizer, the L-1011 vertical fin, and the DC-10 vertical stabi­lizer.[717] The weight savings for each of the medium primary components was estimated to be 23 percent, 30 percent, and 22 percent, respectively.[718]

The leap from secondary to medium-primary components yielded some immediate lessons for what not to do in composite structural design. All three components failed before experiencing ultimate loads in initial ground tests.[719] The problems showed how different composite material could be from the familiar characteristics of metal. Compared to aluminum, an equal amount of composite material can support a heavier load. But, as experience revealed, this was not true in every con­dition experienced by an aircraft in normal flight. Metals are known to
distribute stresses and loads to surrounding structures. In simple terms, they bend more than they break. Composite material does the opposite. It is brittle, stiff, and unyielding to the point of breaking.

Boeing’s horizontal stabilizer and Douglas’s vertical stabilizer both failed before the predicted ultimate load for similar reasons. The brittle composite structure did not redistribute loads as expected. In the case of the 737 component, Boeing had intentionally removed one lug pin to simulate a fail-safe mode. The structure under the point of stress buck­led rather than redistributed the load. Douglas had inadvertently drilled too big of a hole for a fastener where the web cover for the rear spar met a cutout for an access hole.[720] It was an error by Douglas’s machin­ists but a tolerable one if the same structure were designed with metal. Lockheed faced a different kind of problem with the failure of the L-1011 vertical fin during similar ground tests. In this case, a secondary inter­laminar stress developed after the fin’s aerodynamic cover buckled at the attachment point with the front spar cap. NASA later noted: "Such secondary forces are routinely ignored in current metals design.”[721] The design for each of these components was later modified to overcome these unfamiliar weaknesses of composite materials.

In the late 1970s, all three manufacturers began working on the basic technology for the ultimate goal of the ACEE program: design­ing full-scale, composite-only wing and fuselage. Control surfaces and empennage structures provided important steppingstones, but it was expected that expanding the use of composites to large sections of the fuselage and wing could improve efficiency by an order of mag­nitude.[722] More specifically, Boeing’s design studies estimated a weight savings of 25-30 percent if the 757 fuselage was converted to an all­composite design.[723] Further, an all-composite wing designed with a metal-like allowable strain could reduce weight by as much as 40 per­cent for a large commercial aircraft, according to NASA’s design anal­ysis.[724] Each manufacturer was assigned a different task, with all three collaborating on their results to gain maximum results. Lockheed explored
design techniques for a wet wing that could contain fuel and survive light­ning strikes.[725] Boeing worked on creating a system for defining degrees of damage tolerance for structures[726] and designed wing panes strong enough to endure postimpact compression of 50,000 pounds per square inch (psi) at strains of 0.006.[727] Meanwhile, Douglas concentrated on meth­ods for designing multibolted joints.[728] By 1984, NASA and Lockheed had launched the advanced composite center wing project, aimed at designing an all-composite center wing box for an "advanced” C-130 airlifter. This project, which included fabricating two 35-foot-long structures for static and durability tests, would seek to reduce the weight of the C-130’s cen­ter wing box by 35 percent and reduce manufacturing costs by 10 percent compared with aluminum structure.[729] Meanwhile, Boeing started work in 1984 to design, fabricate, and test full-scale fuselage panels.[730]

Within a 10-year period, the U. S. commercial aircraft industry had come very far. From the near exclusion of composite structure in the early 1970s, composites had entered the production flow as both second­ary and medium-primary components by the mid-1980s. This record of achievement, however, was eclipsed by even greater progress in commer­cial aircraft technology in Europe, where the then-upstart DASA Airbus consortium had pushed composites technology even further.

While U. S. commercial programs continued to conduct demonstra­tions, the A300 and A310 production lines introduced an all-composite rudder in 1983 and achieved a vertical tailfin in 1985. The latter vividly demonstrated the manufacturing efficiencies promised by composite designs. While a metal vertical tail contained more than 2,000 parts, Airbus designed a new structure with a carbon fiber epoxy-honeycomb core sand­wich that required fewer than 100 parts, reducing both the weight of the structure and the cost of assembly.[731] A few years later, Airbus unveiled the A320 narrow body with 28 percent of its structural weight filled by
composite materials, including the entire tail structure, fuselage belly skins, trailing-edge flaps, spoilers, ailerons, and nacelles.[732] It would be another decade before a U. S. manufacturer eclipsed Airbus’s lead, with the introduction of the Boeing 777 in 1995. Consolidating experience gained as a major structural supplier for the Northrop B-2A bomber program, Boeing designed the 777, with an all-composite empennage one-tenth of the weight.[733] By this time, the percentage of composites integrated into a commercial airliner’s weight had become a measure of the manufactur­er’s progress in gaining a competitive edge over a rival, a trend that con­tinues to this day with the emerging Airbus A350/Boeing 787 competition.

As European manufacturers assumed a technical lead over U. S. rivals for composite technology in the 1980s, the U. S. still retained a huge lead with military aircraft technology. With fewer operational con­cerns about damage tolerance, crash survivability, and manufacturing cost, military aircraft exploited the performance advantages of com­posite material, particularly for its weight savings. The V-22 Osprey tilt rotor employed composites for 70 percent of its structural weight.[734] Meanwhile, Northrop and Boeing used composites extensively on the B-2 stealth bomber, which is 37-percent composite material by weight.

Steady progress on the military side, however, was not enough to sustain momentum for NASA’s commercial-oriented technology. The ACEE program folded after 1985, following several years of real prog­ress but before it had achieved all of its goals. The full-scale wing and fuselage test program, which had received a $92-million, 6-year budget from NASA in fiscal year 1984,[735] was deleted from the Agency’s spend­ing plans a year later.[736] By 1985, funding available to carry out the goals of the ACEE program had been steadily eroding for several years. The Reagan Administration took office in 1981 with a distinctly different view on the responsibility of Government to support the validation of com­mercial technologies.[737]

In constant 1988 dollars, ACEE funding dropped from a peak $300 million in 1980 to $80 million in 1988, with funding for validat­ing high-strength composite materials in flight wiped out entirely.[738] The shift in technology policy corresponded with priority disagree­ments between aeronautics and space supporters in industry, with the latter favoring boosting support for electronics over pure aeronautics research.[739]

In its 10-year run, the composite structural element of the ACEE program had overcome numerous technical issues. The most serious issue erupted in 1979 and caused NASA to briefly halt further studies until it could be fully analyzed. The story, always expressed in general terms, has become an urban myth for the aircraft composites commu­nity. Precise details of the incident appear lost to history, but the conse­quences of its impact were very real at the time. The legend goes that in the late 1970s, waste fibers from composite materials were dumped into an incinerator. Afterward, whether by cause or coincidence, a nearby electric substation shorted out.[740] Carbon fibers set loose by the inciner­ator fire were blamed for the malfunction at the substation.

The incident prompted widespread concerns among aviation engi­neers at a time when NASA was poised to spend hundreds of millions of dollars to transition composite materials from mainly space and military vehicles to large commercial transports. In 1979, NASA halted work on the ACEE program to analyze the risk that future crashes of increasingly composite-laden aircraft would spew blackout-causing fibers onto the Nation’s electrical grid.[741]

Few seriously question the potential benefits that composite mate­rials offer society. By the mid-1970s, it was clear that composites dra­matically raise the efficiency of aircraft. The cost of manufacturing the materials was higher, but the life-cycle cost of maintaining noncorrod­ing composite structures offered a compelling offset. Concerns about the economic and health risks poised by such a dramatic transition to a different structural material have also been very real.

It was up to the aviation industry, with Government support, to answer these vital questions before composite technology could move further.

With the ACEE program suspended to study concerns about the risks to electrical equipment, both NASA and the U. S. Air Force by 1978 had launched separate efforts to overcome these concerns. In a typi­cal aircraft fire after a crash, the fuel-driven blaze can reach tempera­tures between 1,800 to 3,600 degrees Fahrenheit (°F). At temperatures higher than 750 °F, the matrix material in a composite structure will burn off, which creates two potential hazards. As the matrix polymer transforms into fumes, the underlying chemistry creates a toxic mix­ture called pyrolysis product, which if inhaled can be harmful. Secondly, after the matrix material burns away, the carbon fibers are released into the atmosphere.[742]

These liberated fibers, which as natural conductors have the power to short circuit a power line, could be dispersed over wide areas by wind. This led to concerns that the fibers would could come into contact with local power cables or, even worse, exposed power substations, leading to widespread power blackouts as the fibers short circuit the electrical equipment.[743] In the late 1970s, the U. S. Air Force started a program to study aircraft crashes that involved early-generation composite materials.

Another incident in 1997 was typical of different type of concern about the growing use of composite materials for aircraft structures. A

U. S. Air Force F-117 flying a routine at the Baltimore airshow crashed when a wing-strut failed. Emergency crews who rushed to the scene extinguished fires that destroyed and damaged several dwellings, blan­keting the area with a "wax-like” substance that contained carbon fibers embedded in the F-117’s structures that could have otherwise been released into the atmosphere. Despite these precautions, the same fire­fighters and paramedics who rushed to the scene later reported becom­ing "ill from the fumes emitted by the fire. It was believed that some of these fumes resulted from the burning of the resin in the composite materials,” according a U. S. Navy technical paper published in 2003.[744]

Yet another issue has sapped the public’s confidence in compos­ite materials for aircraft structures for several decades. As late as 2007, the risk presented by lightning striking a composite section of an aircraft fuselage was the subject of a primetime investigation by Dan Rather, who extensively quoted a retired Boeing Space Shuttle engineer. The question is repeatedly asked: If the aluminum structure of a previous generation of airliners created a natural Faraday cage, how would composite materials with weaker properties for conductivity respond when struck by lightning?

Technical hazards were not the only threat to the acceptance of com­posite materials. To be sure, proving that composite material would be safe to operate in commercial service constituted an important endorse­ment of the technology for subsequent application, as the ACEE projects showed. But the aerospace industry also faced the challenge of estab­lishing a new industrial infrastructure from the ground up that would supply vast quantities of composite materials. NASA officials anticipated the magnitude of the infrastructure issue. The shift from wood to metal in the 1930s occurred in an era when airframers acted almost recklessly by today’s standards. Making a similar transition in the regulatory and business climate of the late 1970s would be another challenge entirely. Perhaps with an eye on the rapid progress being made by European com­petitors in commercial aircraft, NASA addressed the issue head-on. In 1980, NASA Deputy Administrator Alan M. Lovelace urged industry to "anticipate this change,” adding that he realized "this will take consid­erable capital, but I do worry that if this is not done then might we not, a decade from now, find ourselves in a position similar to that in which the automobile industry is at the present time?”[745]

Of course, demand drives supply, and the availability of the raw mate­rial for making composite aerospace parts grew precipitously through­out the 1980s. For example, 2 years before Lovelace issued his warning to industry, U. S. manufacturers consumed 500,000 pounds of com­posites every 12 months, with the aerospace industry accounting for half of that amount.[746] Meanwhile, a single supplier for graphite fiber, Union Carbide, had already announced plans to increase annual out­put to 800,000 pounds by the end of 1981.[747] U. S. consumption would soon be driven by the automobile industry, which was also struggling
to keep up with the innovations of foreign competition, as much as by the aerospace industry throughout the 1980s.

Robert Dale Reed, an engineer at NASA’s Flight Research Center (later renamed NASA Dryden Flight Research Center) at Edwards Air Force Base and an avid radio-controlled (R/C) model airplane hobbyist, was one of the first to recognize the RPRV potential. Previous drone air­craft had been used for reconnaissance or strike missions, flying a restricted number of maneuvers with the help of an autopilot or radio signals from a ground station. The RPRV, on the other hand, offered a versatile platform for operating in what Reed called "unexplored engineering territory.”[883] In 1962, when astronauts returned from space

in capsules that splashed down in the ocean, NASA and Air Force engineers were discussing a revolutionary concept for spacecraft reentry vehicles. Wingless lifting bodies—half-cone-shaped vehicles capable of controlled flight using the craft’s fuselage shape to produce stability and lift—could be controlled from atmospheric entry to gliding touchdown on a conventional runway. Skeptics believed such craft would require deployable wings and possibly even pop-out jet engines.

Reed believed the basic lifting body concept was sound and set out to convince his peers. His first modest efforts at flight demonstra­tion were confined to hand-launching small paper models in the hall­ways of the Flight Research Center. His next step involved construction, from balsa wood, of a 24-inch-long free-flight model.

The vehicle’s shape was a half-cone design with twin vertical – stabilizer fins with rudders and a bump representing a cockpit canopy. Elevons provided longitudinal trim and turning control. Spring-wired tricycle wheels served as landing gear. Reed adjusted the craft’s center of gravity until he was satisfied and began a series of hand-launched flight tests. He began at ground level and finally moved to the top of the NASA Administration building, gradually expanding the performance envelope. Reed found the model had a steep gliding angle but remained upright and landed on its gear.

He soon embarked on a path that presaged eventual testing of a full-scale, piloted vehicle. He attached a thread to the upper part of the nose gear and ran to tow the lifting body aloft, as one would launch a kite. Reed then turned to one of his favorite hobbies: radio-controlled, gas-powered model airplanes. He had previously used R/C models to tow free flight model gliders with great success. By attaching the towline to the top of the R/C model’s fuselage, just at the trailing edge of the wing, he ensured minimum effect on the tow plane from the motions of the lifting body model behind it.

Reed conducted his flight tests at Sterk’s Ranch in nearby Lancaster while his wife, Donna, documented the demonstrations with an 8-millimeter motion picture camera. When the R/C tow plane reached a sufficient altitude for extended gliding flight, a vacuum timer released the lifting body model from the towline. The lifting body demonstrated stable flight and landing characteristics, inspir­ing Reed and other researchers to pursue development of a full-scale,

piloted lifting body, dubbed the M2-F1.[884] Reed’s R/C model experiments provided a low-cost demonstration capability for a revolutionary con­cept. Success with the model built confidence in proposals for a full – scale lifting body. Essentially, the model was scaled up to a length of 20 feet, with a span of 14.167 feet. A tubular steel framework pro­vided internal support for the cockpit and landing gear. The outer
shell was comprised of mahogany ribs and spars covered with plywood and doped cloth skin. As with the small model, the full-scale M2-F1 was towed into the air—first behind a Pontiac convertible and later behind a C-47 transport for extended glide flights. Just as the models paved the way for full-scale, piloted testing, the M2-F1 served as a pathfinder for a series of air-launched heavyweight lifting body vehi­cles—flown between 1966 and 1975—that provided data eventually used in development of the Space Shuttle and other aerospace vehicles.[885]

By 1969, Reed had teamed with Dick Eldredge, one of the origi­nal engineers from the M2-F1 project, for a series of studies involving modeling spacecraft-landing techniques. Still seeking alternatives to splashdown, the pair experimented with deployable wings and paraglider concepts. Reed discussed his ideas with Max Faget, director of engineer­ing at the Manned Spacecraft Center (now NASA Johnson Space Center) in Houston, TX. Faget, who had played a major role in designing the Mercury, Gemini, and Apollo spacecraft, had proposed a Gemini-derived vehicle capable of carrying 12 astronauts. Known as the "Big G,” it was to be flown to a landing beneath a gliding parachute canopy.

Reed proposed a single-pilot test vehicle to demonstrate paraglider­landing techniques similar to those used with his models. The Parawing demonstrator would be launched from a helicopter and glide to a land­ing beneath a Rogallo wing, as used in typical hang glider designs. Spacecraft-type viewports would provide visibility for realistic simula­tion of Big G design characteristics.[886] Faget offered to lend a borrowed Navy SH-3A helicopter—one being used to support the Apollo program— to the Flight Research Center and provide enough money for several Rogallo parafoils. Hugh Jackson was selected as project pilot, but for safety reasons, Reed suggested that the test vehicle initially be flown by radio control with a dummy on board.

Eldredge designed the Parawing vehicle, incorporating a generic ogival lifting body shape with an aluminum internal support structure, Gemini-style viewing ports, a pilot’s seat mounted on surplus shock struts from Apollo crew couches, and landing skids. A general-aviation auto­pilot servo was used to actuate the parachute control lines. A side stick controller was installed to control the servo. On planned piloted flights, it would be hand-actuated, but in the test configuration, model airplane servos were used to move the side stick. For realism, engineers placed an anthropomorphic dummy in the pilot’s seat and tied the dummy’s hands in its lap to prevent interference with the controls. The dummy and airframe were instrumented to record accelerations, decelerations, and shock loads as the parachute opened.

The Parawing test vehicle was then mounted on the side of the heli­copter using a pneumatic hook release borrowed from the M2-F2 lifting body launch adapter. Donald Mallick and Bruce Peterson flew the SH-3A to an altitude of approximately 10,000 feet and released the Parawing test vehicle above Rosamond Dry Lake. Using his R/C model controls, Reed guided the craft to a safe landing. He and Eldredge conducted 30 successful radio-controlled test flights between February and October 1969. Shortly before the first scheduled piloted tests were to take place, however, officials at the Manned Spacecraft Center canceled the project. The next planned piloted spacecraft, the Space Shuttle orbiter, would be designed to land on a runway like a conventional airplane does. There was no need to pursue a paraglider system.[887] This, however, did not spell the end of Reed’s paraglider research. A few decades later, he would again find himself involved with paraglider recovery systems for the Spacecraft Autoland Project and the X-38 Crew Return Vehicle tech­nology demonstration.

Hyper III: The First True RPRV

In support of the lifting body program, Dale Reed had built a small fleet of models, including variations on the M2-F2 and FDL-7 concepts. The M2-F2 was a half cone with twin stabilizer fins like the M2-F1 but with the cockpit bulge moved forward from midfuselage to the nose. The full-scale heavyweight M2-F2 suffered some stability problems and eventually crashed, although it was later rebuilt as the M2-F3 with an additional vertical stabilizer. The FDL-7 had a sleek shape (somewhat resembling a flatiron) with four stabilizer fins, two horizontal, and two that were canted outward. Engineers at the Air Force Flight Dynamics Laboratory at Wright-Patterson Air Force Base, OH, designed it with hypersonic-flight characteristics in mind. Variants included wingless ver­sions as well as those equipped with fixed or pop-out wings for extended gliding.[888] Reed launched his creations from a twin-engine R/C model

plane he dubbed "Mother,” since it served as a mother ship for his lifting body models. With a 10.5-foot wingspan, Mother was capable of lofting models of various sizes to useful altitudes for extended glide flights. By the end of 1968, Reed’s mother ship had successfully made 120 drops from an altitude of around 1,000 feet.

One day, Reed asked research pilot Milton O. Thompson if he thought he would be able to control a research airplane from the ground using an attitude-indicator instrument as a reference. Thompson thought this was possible and agreed to try it using Reed’s mother ship. Within a month, at a cost of $500, Mother was modified, and Thompson had success­fully demonstrated the ability to fly the craft from the ground using the instrument reference.[889] Next, Reed wanted to explore the possibility of flying a full-scale research airplane from a ground cockpit. Because of his interest in lifting bodies, he selected a simplified variant of the FDL-7 configuration based on research accomplished at NASA Langley Research Center. Known as Hyper III—because the shape would have a lift-to-drag (L/D) ratio of 3.0 at hypersonic speeds—the test vehicle had a 32-foot-long fuselage with a narrow delta planform and trapezoidal
cross-section, stabilizer fins, and fixed straight wings spanning 18.5 feet to simulate pop-out airfoils that could be used to improve the low-speed glide ratio of a reentry vehicle. The Hyper III RPRV weighed about

1,0 pounds.[890]

Reed recruited numerous volunteers for his low-budget, low – priority project. Dick Fischer, a designer of R/C models as well as full-scale homebuilt aircraft, joined the team as operations engineer and designed the vehicle’s structure. With previous control-system engineering experience on the X-15, Bill "Pete” Peterson designed a control system for the Hyper III. Reed also recruited aircraft inspector Ed Browne, painter Billy Schuler, crew chief Herman Dorr, and mechan­ics Willard Dives, Bill Mersereau, and Herb Scott.

The craft was built in the Flight Research Center’s fabrication shops. Frank McDonald and Howard Curtis assembled the fuselage, consist­ing of a Dacron-covered, steel-tube frame with a molded fiberglass nose assembly. LaVern Kelly constructed the stabilizer fins from sheet aluminum. Daniel Garrabrant borrowed and assembled aluminum wings from an HP-11 sailplane kit. The vehicle was built at a cost of just $6,500 and without interfering with the Center’s other, higher-priority projects.[891] The team managed to scrounge and recycle a variety of items for the vehicle’s control system. These included a Kraft uplink from a model airplane radio-control system and miniature hydraulic pumps from the Air Force’s Precision Recovery Including Maneuvering Entry (PRIME) lifting body program. Peterson designed the Hyper III control system to work from either of two Kraft receivers, mounted on the top and bottom of the vehicle, depending on signal strength. If either malfunctioned or suffered interference, an electronic circuit switched control signals to the operating receiver to actuate the elevons. Keith Anderson modified the PRIME hydraulic actuator system for use on the Hyper III.

The team also developed an emergency-recovery parachute sys­tem in case control of the vehicle was lost. Dave Gold, of Northrop, who had helped design the Apollo spacecraft parachute system, and John Rifenberry, of the Flight Research Center life-support shop, designed a system that included a drogue chute and three main parachutes that would safely lower the vehicle to the ground onto its landing skids. Pyrotechnics expert Chester Bergener assumed responsibility for the drogue’s firing system.[892] To test the recovery system, technicians mounted the Hyper III on a flatbed truck and fired the drogue-extraction system while racing across the dry lakebed, but weak radio signals kept the three main chutes from deploying. To test the clustered main parachutes, the team dropped a weight equivalent to the vehicle from a helicopter.

Tom McAlister assembled a ground cockpit with instruments iden­tical to those in a fixed-base flight simulator. An attitude indicator displayed roll, pitch, heading, and sideslip. Other instruments showed air­speed, altitude, angle of attack, and control-surface position. Don Yount and Chuck Bailey installed a 12-channel downlink telemetry system to record data and drive the cockpit instruments. The ground cockpit sta­tion was designed to be transported to the landing area on a two-wheeled trailer.[893] On December 12, 1969, Bruce Peterson piloted the SH-3A heli­copter that towed the Hyper III to an altitude of 10,000 feet above the lakebed. Hanging at the end of a 400-foot cable, the nose of the Hyper III had a disturbing tendency to drift to one side or another. Reed real­ized later that he should have added a small drag chute to stabilize the craft’s heading prior to launch. Peterson started and stopped forward flight several times until the Hyper III stabilized in a forward climb atti­tude, downwind with a northerly heading.

As soon as Peterson released the hook, Thompson took control of the lifting body. He flew the vehicle north for 3 miles, then reversed course and steered toward the landing site, covering another 3 miles. During each straight course, Thompson performed pitch doublets and oscilla­tions in order to collect aerodynamic data. Since the Hyper III was not equipped with an onboard video camera, Thompson was forced to fly on instruments alone. Gary Layton, in the Flight Research Center con­trol room, watched the radar data showing the vehicle’s position and relayed information to Thompson via radio.

Dick Fischer stood beside Thompson to take control of the Hyper III just before the landing flare, using the model airplane radio­control box. Several miles away, the Hyper III was invisible in the hazy sky as it descended toward the lakebed. Thompson called out altitude read­ings as Fischer strained to see the vehicle. Suddenly, he spotted the lifting body, when it was on final approach just 1,000 feet above the ground. Thompson relinquished control, and Fischer commanded a slight left roll to confirm he had established radio contact. He then leveled the aircraft and executed a landing flare, bringing the Hyper III down softly on its skids.

Thompson found the experience of flying the RPRV exciting and chal­lenging. After the 3-minute flight, he was as physically and emotionally drained as he had been after piloting first flights in piloted research air­craft. Worries that lack of motion and visual cues might hurt his pilot­ing performance proved unfounded. It seemed as natural to control the Hyper III on gauges as it did any other airplane or simulator, respond­ing solely to instrument readings. Twice during the flight, he used his experience to compensate for departures from predicted aerodynamic characteristics when the lift-to-drag ratio proved lower than expected, thus demonstrating the value of having a research pilot at the controls.[894]

Military UAVs are easily adapted for civilian research missions. In November 2006, NASA Dryden obtained a civilian version of the General Atomics MQ-9 Reaper that was subsequently modified and instrumented for research. Proposed missions included supporting Earth science research, fabricating advanced aeronautical technology, and develop­ing capabilities for improving the utility of unmanned aerial systems.

The project team named the aircraft Ikhana, a Native American Choctaw word meaning intelligent, conscious, or aware. The choice was considered descriptive of research goals NASA had established for the aircraft and its related systems, including collecting data to better under­stand and model environmental conditions and climate and increasing the ability of unpiloted aircraft to perform advanced missions.

The Ikhana was 36 feet long with a 66-foot wingspan and capable of carrying more than 400 pounds of sensors internally and over 2,000 pounds in external pods. Driven by a 950-horsepower turboprop engine, the aircraft has a maximum speed of 220 knots and is capable of reaching

altitudes above 40,000 feet with limited endurance.[1038] Initial experiments included the use of fiber optics for wing shape and temperature sens­ing, as well as control and structural loads measurements. Six hairlike fibers on the upper surfaces of the Ikhana’s wings provided 2,000 strain measurements in real time, allowing researchers to study changes in the shape of the wings during flight. Such sensors have numerous appli­cations for future generations of aircraft and spacecraft. They could be used, for example, to enable adaptive wing-shape control to make an aircraft more aerodynamically efficient for specific flight regimes.[1039] To fly the Ikhana, NASA purchased a Ground Control Station and satellite communication system for uplinking flight commands and downlink­ing aircraft and mission data. The GCS was installed in a mobile trailer and, in addition to the pilot’s remote cockpit, included computer work­stations for scientists and engineers. The ground pilot was linked to the aircraft through a C-band line-of-sight (LOS) data link at ranges up to 150 nautical miles. A Ku-band satellite link allowed for over-the-horizon control. A remote video terminal provided real-time imagery from

the aircraft, giving the pilot limited visual input.[1040] Two NASA pilots, Hernan Posada and Mark Pestana, were initially trained to fly the Ikhana. Posada had 10 years of experience flying Predator vehicles for General Atomics before joining NASA as an Ikhana pilot. Pestana, with over

4,0 flight hours in numerous aircraft types, had never flown a UAS prior to his assignment to the Ikhana project. He found the experience an exciting challenge to his abilities because the lack of vestibular cues and peripheral vision hinders situational awareness and eliminates the pilot’s ability to experience such sensations as motion and sink rate.[1041]

Building on experience with the Altair unpiloted aircraft, NASA devel­oped plans to use the Ikhana for a series of Western States Fire Mission flights. The Autonomous Modular Sensor (AMS), developed by Ames, was key to their success. The AMS is a line scanner with a 12-band spec­trometer covering the spectral range from visible to the near infrared for fire detection and mapping. Digitized data are combined with navi­gational and inertial sensor data to determine the location and orienta­tion of the sensor. In addition, the data are autonomously processed with geo-rectified topographical information to create a fire intensity map.

Data collected with AMS are processed onboard the aircraft to provide a finished product formatted according to a geographical infor­mation systems standard, which makes it accessible with commonly available programs, such as Google Earth. Data telemetry is downlinked via a Ku-band satellite communications system. After quality-control assess­ment by scientific personnel in the GCS, the information is transferred to NASA Ames and then made available to remote users via the Internet.

After the Ikhana was modified to carry the AMS sensor pod on a wing pylon, technicians integrated and tested all associated hardware and systems. Management personnel at Dryden performed a flight read­iness review to ensure that all necessary operational and safety con­cerns had been addressed. Finally, planners had to obtain permission from the FAA to allow the Ikhana to operate in the national airspace.[1042]

The first four Ikhana flights set a benchmark for establishing cri­teria for future science operations. During these missions, the aircraft traversed eight western U. S. States, collecting critical fire information and relaying data in near real time to fire incident command teams on the ground as well as to the National Interagency Fire Center in Boise, ID. Sensor data were downlinked to the GCS, transferred to a server at Ames, and autonomously redistributed to a Google Earth data visualization capability—Common Desktop Environment (CDE)—that served as a Decision Support System (DSS) for fire-data integration and information sharing. This system allowed users to see and use data in as little as 10 minutes after it was collected.

The Google Earth DSS CDE also supplied other real-time fire – related information, including satellite weather data, satellite-based fire data, Remote Automated Weather Station readings, lightning-strike detection data, and other critical fire-database source information. Google Earth imagery layers allowed users to see the locations of man­made structures and population centers in the same display as the fire information. Shareable data and information layers, combined into the CDE, allowed incident commanders and others to make real-time strategy decisions on fire management. Personnel throughout the U. S. who were involved in the mission and imaging efforts also accessed the CDE data. Fire incident commanders used the thermal imagery to develop management strategies, redeploy resources, and direct operations to critical areas such as neighborhoods.[1043] The Western States UAS Fire Missions, carried out by team members from NASA, the U. S. Department of Agriculture Forest Service, the National Interagency Fire Center, the NOAA, the FAA, and General Atomics Aeronautical Systems, Inc., were a resounding success and a historic achievement in the field of unpiloted aircraft technology.

In the first milestone of the project, NASA scientists developed improved imaging and communications processes for delivering near-real-time information to firefighters. NASA’s Applied Sciences and Airborne Science programs and the Earth Science Technology Office developed an Airborne Modular Sensor with the intent of dem­onstrating its capabilities during the WSFM and later transitioning those capabilities to operational agencies.[1044] The WSFM project team repeatedly demonstrated the utility and flexibility of using a UAS as a tool to aid disaster response personnel through the employment of various platform, sensor, and data-dissemination technologies related to improving near-real-time wildfire observations and intelligence-gathering techniques. Each successive flight expanded capa­bilities of the previous missions for platform endurance and range, number of observations made, and flexibility in mission and sensing reconfiguration.

Team members worked with the FAA to safely and efficiently inte­grate the unmanned aircraft system into the national airspace. NASA pilots flew the Ikhana in close coordination with FAA air traffic control­lers, allowing it to maintain safe separation from other aircraft.

WSFM project personnel developed extensive contingency man­agement plans to minimize the risk to the aircraft and the public, including the negotiation of emergency landing rights agreements at three Government airfields and the identification and documentation of over 300 potential emergency landing sites.

The missions included coverage of more than 60 wildfires through­out 8 western States. All missions originated and terminated at Edwards Air Force Base and were operated by NASA crews with sup­port from General Atomics. During the mission series, near-real-time data were provided to Incident Command Teams and the National Interagency Fire Center.[1045] Many fires were revisited during some mis­sions to provide data on time-induced fire progression. Whenever possible, long-duration fire events were imaged on multiple mis­sions to provide long-term fire-monitoring capabilities. Postfire burn – assessment imagery was also collected over various fires to aid teams in fire ecosystem rehabilitation. The project Flight Operations team built relationships with other agencies, which enabled real-time flight plan changes necessary to avoid hazardous weather, to adapt to fire priorities, and to avoid conflicts with multiple planned military GPS testing/jamming activities.

Critical, near-real-time fire information allowed Incident Command Teams to redeploy fire-fighting resources, assess effectiveness of containment operations, and move critical resources, personnel, and equipment from hazardous fire conditions. During instances in which blinding smoke obscured normal observations, geo-rectified thermal- infrared data enabled the use of Geographic Information Systems or data visualization packages such as Google Earth. The images were col­lected and fully processed onboard the Ikhana and transmitted via a communications satellite to NASA Ames, where the imagery was served on a NASA Web site and provided in the Google Earth-based CDE for quick and easy access by incident commanders.

The Western States UAS Fire Mission series also gathered crit­ical, coincident data with satellite sensor systems orbiting overhead, allowing for comparison and calibration of those resources with the more sensitive instruments on the Ikhana. The Ikhana UAS proved a versatile platform for carrying research payloads. Since the sensor pod could be reconfigured, the Ikhana was adaptable for a variety of research projects.[1046]

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.