Category NASA’S CONTRIBUTIONS TO AERONAUTICS

In the 1920s and 1930s, researchers in several wind tunnel and full-scale aircraft flight groups at Langley conducted analytical and experimental investigations to develop design guidelines to ensure satisfactory stability

and control behavior.[468] Such studies sought to develop methods to reli­ably predict the inherent flight characteristics of aircraft as affected by design variables such as the wing dihedral angle, sizes and locations of the vertical and horizontal tails, wing planform shape, engine power, mass distribution, and control surface geometry. The staff of the Free – Flight Tunnel joined in these efforts with several studies that correlated the qualitative behavior of free-flight models with analytical predictions of dynamic stability and control characteristics. Coupled with the results from other facilities and analytical groups, the free-flight results accel­erated the maturity of design tools for future aircraft from a qualita­tive basis to a quantitative methodology, and many of the methods and design data derived from these studies became classic textbook material.[469]

By combining free-flight testing with theory, the researchers were able to quantify desirable design features, such as the amount of wing – dihedral angle and the relative size of vertical tail required for satisfac­tory behavior. With these data in hand, methods were also developed to theoretically solve the dynamic equations of motion of aircraft and determine dynamic stability characteristics such as the frequency of inherent oscillations and the damping of motions following inputs by pilots or turbulence.

During the final days of model flight projects in the Free-Flight Tunnel in the mid-1950s, various Langley organizations teamed to quan­tify the effects of aerodynamic dynamic stability parameters on flying characteristics. These efforts included correlation of experimentally determined aerodynamic stability derivatives with theoretical predic­tions and comparisons of the results of qualitative free-flight tests with theoretical predictions of dynamic stability characteristics. In some cases, rate gyroscopes and servos were used to artificially vary the magnitudes of dynamic aerodynamic stability parameters such as yawing moment because of rolling.[470] In these studies, the free-flight model result served as a critical test of the validity of theory.

The helicopter drop-model technique has been used since the early 1950s to evaluate the spin entry behavior of relatively large unpowered mod­els of military aircraft. The objective of these tests has been to evaluate the relative spin resistance of configurations following various combi­nations of control inputs, and the effects of timing of recovery control inputs following departures. A related testing technique used to eval­uate spin resistance of spin entry evaluations of general aviation con­figurations employs remotely controlled powered models that take off from ground runways and fly to the test condition.

In the late 1950s, industry had become concerned over potential scale effects on long pointed fuselage shapes as a result of the XF8U-1

experiences in the Spin Tunnel, as discussed earlier. Thus, interest was growing over the possible use of much larger models than those used in spin tunnel tests, to eliminate or minimize undesirable scale effects. Finally, a major concern arose for some airplane designs over the launch­ing technique used in the Spin Tunnel. Because the spin tunnel model was launched by hand in a very flat attitude with forced rotation, it would quickly seek the developed spin modes—a very valuable output— but the full-scale airplane might not easily enter the spin because of con­trol limitations, poststall motions, or other factors.

One of the first configurations tested, in 1958, to establish the cred­ibility of the drop-model program was a 6.3-foot-long, 90-pound model of the XF8U-1 configuration.[519] With previously conducted spin tunnel results in hand, the choice of this design permitted correlation with the earlier tunnel and aircraft flight-test results. As has been discussed, wind tunnel testing of the XF8U-1 fuselage forebody shape had indi­cated that pro-spin yawing moments would be produced by the fuse­lage for values of Reynolds number below about 400,000, based on the average depth of the fuselage forebody. The Reynolds number for the drop-model tests ranged from 420,000 to 505,000, at which the fuse­lage contribution became antispin and the spins and recovery charac­teristics of the drop model were found to be very similar to the full-scale results. In particular, the drop model did not exhibit a flat-spin mode predicted by the smaller spin tunnel model, and results were in agree­ment with results of the aircraft flight tests, demonstrating the value of larger models from a Reynolds number perspective.

Success in applications of the drop-model technique for studies of spin entry led to the beginning of many military requests for evaluations of emerging fighter aircraft. In 1959, the Navy requested an evaluation of the McDonnell F4H-1 Phantom II airplane using the drop technique.[520] Earlier spin tunnel tests of the configuration indicated the possibility of two types of spins: one of which was steep and oscillatory, from which recoveries were satisfactory, and the other was fast and flat, from which recovery was difficult or impossible. As mentioned previously, the spin tunnel launching technique had led to questions regarding whether the airplane would exhibit a tendency toward the steeper spin or the more

dangerous flat spin. The objective of the drop tests was to determine if it was likely, or even possible, for the F4H-1 to enter the flat spin.

In the F4H-1 investigation, an additional launching technique was used in an attempt to obtain a developed spin more readily and to pos­sibly obtain the flat spin to verify its existence. This technique consisted of prespinning the model on the helicopter launch rig before it was released in a flat attitude with the helicopter in a hovering condition. To achieve even higher initial rotation rates than could be achieved on the launch rig, a detachable flat metal plate was attached to one wingtip of the model to propel it to spin even faster. After the model appeared to be rotating sufficiently fast after release, the vane was jettisoned by the ground-based pilot, who, at the same time, moved the ailerons against the direction of rotation to help promote the spin. The model was then allowed to spin for several turns, after which recovery controls were applied. In some aspects, this approach to testing replicated the spin tunnel launch technique but at a larger scale.

Results of the drop-model investigation for the F4H-1 are especially notable because it established the value of the testing technique to pre­dict spin tendencies as verified by subsequent full-scale results. A total of 35 flights were made, with the model launched 15 times in the pre­rotated condition and 20 times in forward flight. During these 35 flights, poststall gyrations were obtained on 21 occasions, steep spins were obtained on 10 flights, and only 4 flat spins were obtained. No recoveries were possible from the flat spins, but only one flat spin was obtained with­out prerotation. The conclusions of the tests stated that the aircraft was more susceptible to poststall gyrations than spins; that the steeper, more oscillatory spin would be more readily obtainable and recovery could be made by the NASA-recommended control technique; and that the like­lihood of encountering a fast, flat spin was relatively remote. Ultimately, these general characteristics of the airplane were replicated at full-scale test conditions during spin evaluations by the Navy and Air Force.

One of NASA’s first flight research studies was the X-15 program (1959— 1968). The program investigated flight at five or more times the speed of sound at altitudes reaching the fringes of space. Launched from the wing of NASA’s venerable Boeing B-52 mother ship, the North American X-15 was a true "aerospace” plane, with performance that went well beyond the capabilities of existing aircraft within and beyond the atmo­sphere. Long, black, rocket-powered, and distinctive with its cruci­form tail, the X-15 became the highest-flying airplane in history. In one flight, the X-15 flew to 67 miles (354,200 feet) above the Earth at a speed of Mach 6.7, or 4,534 mph. At those speeds and altitudes, the X-15 pilots, made up of the leading military and civilian aviators, had to wear pressure suits, and many of them earned astronaut’s wings. North American used titanium as the primary structural material and covered it with a new high-temperature nickel alloy called Inconel-X. The X-15 relied upon conventional controls in the atmosphere but used reaction – control jets to maneuver in space. The 199 flights of X-15 program generated important data on high-speed flight and provided valuable lessons for NASA’s space program.

The air traveling over the X-15 at hypersonic speeds generated enough friction and heat that the outside surface of the airplane reached 1,200 °F. A dozen Langley and Ames wind tunnels contributed to the X-15 program. The sole source of aerodynamic data for the X-15 came from tests generated in the pioneering Mach 6.8 11-Inch Hypersonic Tunnel developed by John Becker at Langley in the late 1940s. Fifty percent of the work conducted in the tunnel was for the X-15 program, which focused on aerodynamic heating, stability and control, and load

distribution studies. The stability and control investigations contributed to the research airplane’s distinctive cruciform tail. The 7- by 10-Foot High-Speed Wind Tunnel enabled the study of the X-15’s separation from the B-52 at subsonic speeds, a crucial phase in the test flight. At Ames, gun-launched models fired into the free-flight tunnels obtained shadowgraphs of the shock wave patterns between Mach 3.5 and 6, the performance regime for the X-15. The Unitary Plan Supersonic Tunnel generated data on aerodynamic forces and heat transfer. The Lewis Research Center facilities provided additional data on supersonic jet – plumes and rocket-nozzle studies.[595]

There was a concern that wind tunnel tests would not provide cor­rect data for the program. First, the cramped size of the tunnel test sec­tions did not facilitate more accurate full-scale testing. Second, none of NASA’s tunnels was capable of replicating the extreme heat gener­ated by hypersonic flight, which was believed to be a major factor in flying at those speeds. The flights of the X-15 validated the wind tunnel

testing and revealed that lift, drag, and stability values were in agree­ment with one another at speeds up to Mach 10.[596]

The wind tunnels of NASA continued to reflect the Agency’s flexibil­ity in the development of craft that operated in and out of the Earth’s atmosphere. Specific components evaluated in the 9- by 6-Foot Thermal Structures Tunnel included the X-15 vertical tail, the heat shields for the Centaur launch vehicle and Project Fire entry vehicle, and components of the Hawk, Falcon, Sam-D, and Minuteman missiles. Researchers also subjected humans, equipment, and structures such as the Mercury Spacecraft to the 162-decibel, high-intensity noise at the tunnel exit. As part of Project Fire, in the early 1960s, personnel in the tunnel evalu­ated the effects of reentry heating on spacecraft materials.[597]

The Air Force’s failed X-20 Dyna-Soar project attempted to develop a winged spacecraft. The X-20 never flew, primarily because of bureaucratic entanglements. NASA researchers H. Julian Allen and Alfred J. Eggers, Jr., working on ballistic missiles, found that a blunt shape made reentry possible.[598] NASA developed a series of "lifting bodies”— capable of reentry and then being controlled in the atmosphere—to test unconventional blunt configurations. The blunt nose and wing-leading edge of the Space Shuttles that are launched into space and then glide to a landing after reentry, starting with Columbia in April 1981, owe their success to the lifting body tests flown by NASA in the 1960s and 1970s.

The knowledge gained in these programs contributed to the Space Shuttle of the 1980s. Analyses of the Shuttle reflected the tradition dating back to the Wright brothers of correlating ground, or wind tunnel, data with flight data. Langley researchers conducted an extended aerodynamic and aerothermodynamic comparison of hyper­sonic flight- and ground-test results for the program. The research team asserted that the "survival of the vehicle is a tribute to the over­all design philosophy, including ground test predictions, and to the designers of the Space Shuttle.”[599]

The latest NASA research program, called Hyper-X, investigated hypersonic flight with a new type of aircraft engine, the X-43A scramjet, or supersonic combustion ramjet. The previous flights of the X-15, the lifting bodies, and the Space Shuttle relied upon rocket power for hyper­sonic propulsion. A conventional air-breathing jet engine, which relies upon the mixture of air and atomized fuel for combustion, can only pro­pel aircraft to speeds approaching Mach 4. A scramjet can operate well

past Mach 5 because the process of combustion takes place at super­sonic speeds. Launch-mounted to the front of rocket booster from a B-52 at 40,000 feet, the 12-foot-long, 2,700-pound X-43A first flew in March 2004. During the 11-second flight, the little engine reached Mach 6.8 and demonstrated the first successful operation of a scramjet. In November 2004, a second flight achieved Mach 9.8, the fastest speed ever attained by an air-breathing engine. Much like Frank Whittle and Hans von Ohain’s turbojets and the Wrights’ invention of the airplane, the X-43A offered the promise of a new revolution in aviation, that of high-speed global travel and a cheaper means to access space.

The diminutive X-43A allowed for realistic testing at NASA Langley. First, it was at full-scale for the specific scramjet tests. Moreover, it served as a scale model for the hypersonic engines intended for future aerospace craft. The majority of the testing for the Hyper-X program occurred in the Arc-Heated Scramjet Test Facility, which was the primary Mach 7 scramjet test facility. Introduced in the late 1970s, the Langley facility generated the appropriate flows at 3,500 °F. Additional transonic and supersonic tests of 30-inch X-43A models took place in the 16-Foot Transonic Tunnel and the Unitary Plan Wind Tunnel.[600]

Researchers in the Langley Aerothermodynamics Branch worked on a critical phase of the flight: the separation of the X-43A from the Pegasus booster. The complete Hyper-X Launch Vehicle stack, consist­ing of the scramjet and booster, climbed to 20,000 feet under the wing of NASA’s Boeing B-52 Stratofortress in captive/carry flight. Clean sep­aration between the two within less than a second ensured the success of the flight. The X-43A, with its asymmetrical shape, did not facilitate that clean separation. The Langley team required a better aerodynamic understanding of multiple configurations: the combined stack, the X-43A and the Pegasus in close proximity, and each vehicle in open, free flight. The Langley 20-Inch Mach 6 and 31-Inch Mach 10 blow-down tunnels were used for launch, postlaunch, and free-flyer hypersonic testing.[601]

As noted earlier, the NACA research on aircraft performance began at the onset of the Agency. The steady progression of aircraft technology was matched by an equivalent progression in the understanding and com­prehension of aircraft motions, beginning with extensive studies of the loads, stability, control, and handling qualities fighter biplanes encoun­tered during steady and maneuvering flight.[807] At the end of the interwar period, NACA Langley researchers undertook a major evaluation of the flying qualities of American GA aircraft, though the results of that inves­tigation were not disseminated because of the outbreak of the Second World War and the need for the Agency to focus its attention on mili­tary, not civil, needs. Langley test pilots flew five representative aircraft, and the test results, on the whole, were generally satisfactory. Control effectiveness was, on the overall, good, and the aircraft demonstrated a desirable degree of longitudinal (pitch) inherent stability, though two of the designs had degraded longitudinal stability at low speeds. Lateral (roll) stability was likewise satisfactory, but "wide variations” were found in directional stability, though rudder inputs on each were sufficient to trim the aircraft for straight flight. Stall warning (exemplified by pro­gressively more violent airframe buffeting) was good, and each aircraft possessed adequate stall recovery behavior, though departures from controlled flight during stalls in turns proved more violent (the airplane rolling in the direction of the downward wing) than stalls made from wings-level flight. In all cases, aileron power was inadequate to maintain lateral control. Stall recovery was "easily made” in every case simply by pushing forward on the elevator. Overall, if some performance deficien­cies existed—for example, the tendency to spiral instability or the lack of lateral control effectiveness at the staff—such limitations were small compared with the dramatic handling qualities deficiencies of many early aircraft just two decades previously, at the end of the First World War. This survey demonstrated that by 1940 America had mastered the design of the practical, useful GA airplane. Indeed, such aircraft, built by the thousands, would play a critical role in initiating many young Americans into wartime service as combat and combat support pilots.[808]

During the Second World War, the NACA generated a new series of so-called Wartime Reports, complementing its prewar series of Technical

Reports (TR), Technical Memoranda (TM), and Technical Notes (TN). They subsequently had great influence upon aircraft design and engineering practice, particularly after the war, when applied to high-performance GA aircraft. The NACA studied various ways to improve aircraft performance through drag reduction of single-engine military fighter type aircraft and other designs resulting in improved handling qualities and increased air­speeds. The first Wartime Report was published in October 1940 by NACA engineers C. H. Dearborn and Abe Silverstein. This report described the test results that investigated methods for increasing the high speed for 11 single-engine military aircraft for the Army Air Corps. Their tests found inefficient design features on many of these airplanes indicating the desir­ability of analyzing and combining all of the results into a single paper for distribution to the designers. It highlighted one of the major problems afflicting aircraft design and performance analysis: understanding the inter­relationship of design, performance, and handling qualities.[809]

The NACA had long recognized "the need for quantitative design cri – terions for describing those qualities of an airplane that make up satis­factory controllability, stability, and handling characteristics,” and the individual who, more than any other, spurred Agency development of them was Robert R. Gilruth, later a towering figure in the devel­opment of America’s manned spaceflight program.[810] Gilruth’s work built upon earlier preliminary efforts by two fellow Langley research­ers, Hartley A. Soule (later chairman of the NACA Research Airplane Projects Panel that oversaw the postwar X-series transonic and super­sonic research airplane programs) and chief Agency test pilot Melvin N. "Mel” Gough, though it went considerably beyond.[811] In 1941, Gilruth and M. D. White assessed the longitudinal stability characteristics of 15 dif­ferent airplanes (including bombers, fighters, transports, trainers, and GA sport aircraft).[812] Gilruth followed this with another study, in partner­ship with W. N. Turner, on the lateral control required for satisfactory fly­ing qualities, again based on flight tests of numerous airplanes.[813] Gilruth capped his research with a landmark report establishing the require­ments for satisfactory handling qualities in airplanes, issued first as an Advanced Confidential Report in April 1941, then as a Wartime Report, and, finally, in 1943, as one of the Agency’s Technical Reports, TR-755. Based on "real-world” flight-test results, TR-755 defined what measured characteristics were significant in the definition of satisfactory flying qualities, what were reasonable to require from an airplane (and thus to establish as design requirements), and what influence various design features had upon the flying qualities of the aircraft once it entered flight testing.[814] Together, this trio profoundly influenced the field of flying qualities assessment.

But what was equally needed was a means of establishing a stan­dard measure for pilot assessment of aircraft handling qualities.

This proved surprisingly difficult to achieve and took a number of years of effort. Indeed, developing such measures took on such urgency and constituted such a clear requirement that it was one of the compelling reasons underlying the establishment of professional test pilot training schools, beginning with Britain’s Empire Test Pilots’ School established in 1943.[815] The measure was finally derived by two American test pilots, NASA’s George Cooper and the Cornell Aeronautical Laboratory’s Robert Harper, Jr., thereby establishing one of the essen­tial tools of flight testing and flight research, the Cooper-Harper rating scale, issued in 1969 in a seminal report.[816] This evaluation tool quickly replaced earlier scales and measures and won international acceptance, influencing the flight-test evaluation of virtually all flying craft, from light GA aircraft through hypersonic lifting reentry vehicles and rotor – craft. The combination of the work undertaken by Gilruth, Cooper, and

their associates dramatically improved flight safety and flight efficiency, and must therefore be considered one of the NACA-NASA’s major con­tributions to aviation.[817]

Despite the demands of wartime research, the NACA and its research staff continued to maintain a keen interest in the GA field, particularly as expectations (subsequently frustrated by postwar economics) antic­ipated massive sales of GA aircraft as soon as conflict ended. While this was true in 1946—when 35,000 were sold in a single year!—the post­war market swiftly contracted by half, and then fell again, to just 3,000 in 1952, a "boom-bust” cycle the field would, alas, all too frequently repeat over the next half-century.[818] Despite this, hundreds of NACA general-aviation-focused reports, notes, and memoranda were produced— many reflecting flight tests of new and interesting GA designs—but, as well, some already-classic machines such as the Douglas DC-3, which underwent a flying qualities evaluation at Langley in 1950 as an exer­cise to calculate its stability derivatives, and, as well, update and refine the then-existing Air Force and Navy handling qualities specifications guidebooks. Not surprisingly, the project pilot concluded, "the DC-3
is a very comfortable airplane to fly through all normal flight regimes, despite fairly high control forces about all three axes.”[819]

On October 4, 1957, Sputnik rocketed into orbit, heralding the onset of the "Space Age” and the consequent transformation of the NACA into the National Aeronautics and Space Administration (NASA). But despite the new national focus on space, NASA maintained a broad program of aeronautical research—the lasting legacy of the NACA—even in the shadow of Apollo and the Kennedy-mandated drive to Tranquility Base.

This included, in particular, the field of GA flying and handling qual­ities. The first report written in 1960 under NASA presented the status of spin research—a traditional area of concern, particularly as it was a killer of low-flying-time pilots—from recent airplane design as inter­preted at the NASA Langley Research Center, Langley, VA.[820] Sporadically, NASA researchers flight-tested new GA designs to assess their handling qualities, performance, and flight safety, their flight test reports frankly detailing both strengths and deficiencies. In December 1964, for exam­ple, NASA Flight Research Center test pilot William Dana (one of the Agency’s X-15 pilots) evaluated a Beech Debonair, a conventional-tailed derivative of the V-tail Beech Bonanza. Dana found the sleek Debonair a satisfactory aircraft overall. It had excellent longitudinal, spiral, and speed stability, with good roll damping and "honest” stall behavior in "clean” (landing gear retracted) configuration. But he faulted it for lack of rudder trim that hurt its climb performance, lack of "much warning, either by stick or airframe buffet” of impending stalls, and poor gear – down stall performance manifested by an abrupt left wing drop that hindered recovery. Finally, the plane’s tendency to promote pilot-induced oscillations (PIO) during its landing flare earned it a pilot-rating grade of "C” for landings.[821]

The growing recognition that GA technology had advanced far beyond the state of GA that had existed at the time of the NACA’s first qualitative examination of light aircraft handling qualities triggered one of the most significant of NASA’s GA assessment programs. In 1966, at the height of the Apollo program, pilots and engineers at the Flight Research Center performed an evaluation of the handling qualities of seven GA aircraft, expanding upon this study subsequently to include the handling qual­ities of other light aircraft and advanced control systems and displays. The aircraft for the 1966 study were a mix of popular single-and twin – engine, high-and low-wing types. Project pilot was Fred W. Haise (sub­sequently an Apollo 13 astronaut); Marvin R. Barber, Charles K. Jones, and Thomas R. Sisk were project engineers.[822]

As a group, the seven aircraft all exhibited generally satisfactory stability and control characteristics. However, these characteristics, as researchers noted,

Degraded with decreasing airspeed, increasing aft cen­ter of gravity, increasing power, and extension of gear and flaps.

The qualitative portion of the program showed the han­dling qualities were generally satisfactory during visual and instrument flight in smooth air. However, atmo­sphere turbulence degraded these handling qualities, with the greatest degradation noted during instrument landing system approaches. Such factors as excessive control-system friction, low levels of static stability, high adverse yaw, poor Dutch roll characteristics, and control-surface float combined to make precise instru­ment tracking tasks, in the present of turbulence diffi­cult even for experienced instrument pilots.

The program revealed three characteristics of specific airplanes that were considered unacceptable if encoun­tered by inexperienced or unsuspecting pilots: (1) A vio­lent elevator force reversal or reduced load factors in the landing configuration, (2) power-on stall character­istics that culminate in rapid roll offs and/or spins, and (3) neutral-to-unstable static longitudinal stability at aft center gravity.

A review indicated that existing criteria had not kept pace with aircraft development in areas of Dutch roll, adverse yaw, effective dihedral, and allowable trim changes with gear, flap and power. This study indicated that crite­ria should be specified for control-system friction and control-surface float.

This program suggested a method of quantitative eval­uating and handling qualities of aircraft by the use of pilot-work-load factor.[823]

As well, all of the aircraft tested had "undesirable and inconsistent placement of both primary flight instruments and navigational dis­plays,” increasing pilot workload, a matter of critical concern during precision instrument landing approaches.[824] Further, they all lacked good
stall warning (defined as progressively strong airframe buffet prior to stall onset). Two had "unacceptable” stall characteristics, one entering an "uncontrollable” left roll/yaw and altitude-consuming spin, and the other having "a rapid left rolloff in the power-on accelerated stall with landing flaps extended.”[825]

The 1966 survey stimulated more frequent evaluations of GA designs by NASA research pilots and engineers, both out of curiosity and some­times after accounts surfaced of marginal or questionable behavior. NASA test pilots and engineers found that while various GA designs had "gen­erally satisfactory” handling qualities for flight in smooth air and under visual conditions, they had far different qualities in turbulent flight and with degraded visibility. Control system friction, longitudinal and spiral instability, adverse yaw, combined lateral-directional "Dutch roll” char­acteristics, abrupt trim changes when deploying landing gear flaps, and adding or subtracting power all inhibited effective precision instrument tracking. Thus, instrument landing approaches quickly taxed a pilot, markedly increasing pilot workload. The FRC team explored applying advanced control systems and displays, modifying a light twin-engine

Piper PA-30 Twin Comanche business aircraft as a GA testbed with a flight-director display and an attitude-command control system. The result, demonstrated in 72 flight tests and over 120 hours of operation, was "a flying machine that borders on being perfect from a handling qual­ities standpoint during ILS approaches in turbulent air.” The team pre­sented their findings at a seminal NASA conference on aircraft safety and operating problems held at the Langley Research Center in May 1971.[826]

The little PA-30 proved a workhorse, employed for a variety of research studies including exploring remotely piloted vehicle technol­ogy.[827] During the time period of 1969-1972, NASA researchers Chester Wolowicz and Roxanah Yancey undertook wind tunnel and flight tests on it to investigate and assess its longitudinal and lateral static and dynamic stability characteristics.[828] These tests documented represen­tative state-of-the-art analytical procedures and design data for predict­ing the subsonic longitudinal static and dynamic stability and control characteristics of a light, propeller-driven airplane.[829] But the tests also confirmed, as one survey undertaken by North Carolina State University researchers for NASA concluded, that much work remained to be done to define and properly quantify the desirable handling qualities of GA aircraft.[830]

Fortunately, a key tool was rapidly maturing that made such anal­ysis far more attainable than it would have been just a few years pre­viously: the computer. Given a properly written analytical program, it had the ability to rapidly extract relevant performance parameters from flight-test data. Over several decades, estimating stability and control parameters from flight-test data had progressed through simple analog matching methodologies, time vector analysis, and regression analysis.[831] A joint program between the NASA Langley Research Center and the Aeronautical Laboratory of Princeton University using a Ryan Navion demonstrated that an iterative "maximum-likelihood minimum variance” parameter estimation procedure could be used to extract key aerodynamic parameters based on flight test results, but also showed that caution was warranted. Unanticipated relations between the various parame­ters had made it difficult to sort out individual values and indicated that prior to such studies, researchers should have a reliable mathematical model of the aircraft.[832] At the Flight Research Center, Richard E. Maine and Kenneth W. Iliff extended such work by applying IBM’s FORTRAN programming language to ease determination of aircraft stability and control derivatives from flight data. Their resulting program, a max­imum likelihood estimation method supported by two associated programs for routine data handling, was validated by successful analy­sis of 1,500 maneuvers executed by 20 different aircraft and was made available for use by the aviation community via a NASA Technical Note issued in April 1975.[833] Afterwards, NASA, the Beech Aircraft Corporation, and the Flight Research Laboratory at the University of Kansas col­laborated on a joint flight test of a loaned Beech 99 twin-engine com­muter aircraft, extracting longitudinal and lateral-directional stability derivatives during a variety of maneuvers at assorted angles of attack and in clean and flaps-down condition. "In general,” researchers con­cluded, "derivative estimates from flight data for the Beech 99 airplane were quite consistent with the manufacturer’s predictions.”[834] Another analytical tool was thus available for undertaking flying and handling qualities analysis.

In 1973, NASA and Air Force officials began exploring a project to develop technologies for advanced fighter aircraft. Several aerospace

contractors submitted designs for a baseline advanced-fighter concept with performance goals of a 300-nautical-mile mission radius, sus­tained 8 g maneuvering capability at Mach 0.9, and a maximum speed of Mach 1.6 at 30,000 feet altitude. The Los Angeles Division of Rockwell International was selected to build a 44-percent-scale, remotely piloted model for a project known as Highly Maneuverable Aircraft Technology (HiMAT). Testing took place at Dryden, initially under the leadership of Project Manager Paul C. Loschke and later under Henry Arnaiz.[945] The scale factor for the RPRV was determined by cost considerations, pay­load requirements, test-data fidelity, close matching of thrust-to-weight ratio and wing loading between the model and the full-scale design, and availability of off-the-shelf hardware. The overall geometry of the design was faithfully scaled with the exception of fuselage diameter and inlet – capture area, which were necessarily over-scale in order to accommodate a 5,000-pound-thrust General Electric J85-21 afterburning turbojet engine.

Advanced technology features included maximum use of lightweight, high-strength composite materials to minimize airframe weight; aero – elastic tailoring to provide aerodynamic benefits from the airplane’s
structural-flexibility characteristics; relaxed static stability, to provide favorable drag effects because of trimming; digital fly-by-wire controls; a digital integrated propulsion-control system; and such advanced aero­dynamic features as close-coupled canards, winglets, variable-camber leading edges, and supercritical wings. Composite materials, mostly graphite/epoxy, comprised about 95 percent of the exterior surfaces and approximately 29 percent of the total structural weight of the airplane. Researchers were interested in studying the interaction of the various new technologies.[946] To keep development costs low and allow for maxi­mum flexibility for proposed follow-on programs, the HiMAT vehicle was modular for easy reconfiguration of external geometry and propulsion systems. Follow-on research proposals included forward-swept wings, a two-dimensional exhaust nozzle, alternate canard configurations, active flutter suppression, and various control-system modifications. These options, however, were never pursued.[947] Rockwell built two HiMAT air vehicles, known as AV-1 and AV-2, at a cost of $17.3 million. Each was 22.5 feet long, spanned 15.56 feet, and weighed 3,370 pounds. The vehicle was carried to a launch altitude of about 40,000 to 45,000 feet beneath the wing of the NB-52B. Following release from the wing pylon at a speed of about Mach 0.7, the HiMAT dropped for 3 seconds in a preprogrammed maneuver before transitioning to control of the ground pilot. Research flight-test maneuvers were restricted to within a 50-nautical-mile radius of Edwards and ended with landing on Rogers Dry Lake. The HiMAT was equipped with steel skid landing gear. Maximum flight duration varied from about 15 to 80 minutes, depending on thrust requirements, with an average planned flight duration of about 30 minutes.

As delivered, the vehicles were equipped with a 227-channel data collection and recording system. Each RPRV was instrumented with 128 surface-pressure orifices with 85 transducers, 48 structural load and hinge-moment strain gauges, 6 buffet accelerometers, 7 propulsion sys­tem parameters, 10 control-surface-position indicators, and 15 airplane motion and air data parameters. NASA technicians later added more transducers for a surface-pressure survey.[948] The HiMAT project repre­sented a shift in focus by researchers at Dryden. Through the Vietnam era, the focal point of fighter research had been speed. In the 1970s, driven by a national energy crisis, new digital technology, and a chang­ing combat environment, researchers sought to develop efficient research models for experiments into the extremes of fighter maneuverability. As a result, the quest for speed, long considered the key component of suc­cessful air combat, became secondary.

HiMAT program goals included a 100-percent increase in aerody­namic efficiency over 1973 technology and maneuverability that would allow a sustained 8 g turn at Mach 0.9 and an altitude of 25,000 feet. Engineers designed the HiMAT aircraft’s rear-mounted swept wings, dig­ital flight-control system, and forward-mounted controllable canards to give the plane a turn radius twice as tight as that of conventional fighter planes. At near-sonic speeds and at an altitude of 25,000 feet, the HiMAT aircraft could perform an 8 g turn, nearly twice the capabil­ity of an F-16 under the same conditions.[949] Flying the HiMAT from the ground-based cockpit using the digital fly-by-wire system required con­trol techniques similar to those used in conventional aircraft, although design of the vehicle’s control laws had proved extremely challenging. The HiMAT was equipped with a flight-test-maneuver autopilot based on a design developed by Teledyne Ryan Aeronautical Company, which also developed the aircraft’s backup flight control system (with modifi­cations made by Dryden engineers). The autopilot system provided pre­cise, repeatable control of the vehicle during prescribed maneuvers so that large quantities of reliable test data could be recorded in a compar­atively short period of flight time. Dryden engineers and pilots tested the control laws for the system in simulations and in flight, making any nec­essary adjustments based on experience. Once adjusted, the autopilot was a valuable tool for obtaining high-quality, precise data that would not have been obtainable using standard piloting methods. The autopi­lot enabled the pilot to control multiple parameters simultaneously and to do so within demanding, repeatable tolerances. As such, the flight – test-maneuver autopilot showed itself to be a broadly applicable tech­nique for flight research with potential benefit to any flight program.[950]

The maiden flight of HiMAT AV-1 took place July 27, 1979, with Bill Dana at the controls. All objectives were met despite some minor dif­ficulty with the telemetry receiver. Subsequent flights resulted in acqui­sition of significant data and cleared the HiMAT to a maximum speed of Mach 0.9 and an altitude of 40,000 feet, as well as demonstrating a 4 g turning capability. By the end of October 1980, the HiMAT had been flown to Mach 0.925 and performed a sustained 7 g turn. The ground pilot was occasionally challenged to respond to unexpected events, includ­ing an emergency engine restart during flight and a gear-up landing.

AV-2 was flown for the first time July 24, 1981. The following week, Stephen Ishmael joined the project as a ground pilot. After several airspeed calibration flights, researcher began collecting data with AV-2.

On February 3, 1982, AV-1 was flown to demonstrate the 8 g maneu­ver capabilities that had been predicted for the vehicle. A little over 3 months later, researchers obtained the first supersonic data with the HiMAT, achieving speeds of Mach 1.2 and Mach 1.45. Research with both air vehicles continued through January 1983. Fourteen flights were completed with AV-1 and 12 with AV-2, for a total of 26 over 3% years.[951] The HiMAT research successfully demonstrated a synergistic approach to accelerating development of an advanced high-performance aircraft. Many high-risk technologies were incorporated into a single, low-cost vehicle and tested—at no risk to the pilot—to study interaction among systems, advanced materials, and control software. Design requirements dictated that no single failure should result in loss of the vehicle. Consequently, redundant systems were incorporated throughout the aircraft, including computer microprocessors, hydraulic and electri­cal systems, servo-actuators, and data uplink/downlink equipment.[952] The HiMAT program resulted in several important contributions to flight technology. The foremost of these was the use of new composite materials in structural design. HiMAT engineers used materials such as fiberglass and graphite epoxy composites to strengthen the airframe and allow it to withstand high g conditions during maneuverability tests. Knowledge gained in composite construction of the HiMAT vehicle strongly influenced other advanced research projects, and such materials are now used extensively on commercial and military aircraft.

Designers of the X-29 employed many design concepts developed for HiMAT, including the successful use of a forward canard and the rear-mounted swept wing constructed from lightweight composite mate­rials. Although the X-29’s wings swept forward rather than to the rear, the principle was the same. HiMAT research also brought about far – reaching advances in digital flight control systems, which can monitor and automatically correct potential flight hazards.[953]

Two users were looking to field airplanes in the 1960s with long range at high speeds. One organization’s requirement was high profile and the object of much debate: the United States Air Force and its continuing desire to have an intercontinental range supersonic bomber. The other organiza­tion was operating in the shadows. It was the Central Intelligence Agency (CIA), and it was aiming to replace its covert subsonic high-altitude recon­naissance plane (the Lockheed U-2). The requirement was simple; the ful­fillment would be challenging, to say the least: a mission radius of 2,500 miles, cruising at Mach 3 for the entire time, at altitudes up to 90,000 feet. The payload was to be on the order of 800 pounds, as it was on the U-2.

The evolution of both supersonic cruise aircraft was involved, much more so for the highly visible USAF aircraft that eventually appeared as the XB-70. The B-58 had given the USAF experience with a Mach 2 bomber, but bombing advocates (notably Gen. Curtis LeMay) wanted long range to go with the supersonic performance. As demonstrated in the classic Breguet range equation, range is a direct function of
lift-to-drag (L/D) ratio. The high drag at supersonic speeds reduced that ratio to the point where large fuel tanks were necessary, increas­ing the weight of the vehicle, requiring more lift, more drag, and more fuel. Initial designs weighed 750,000 pounds and looked like a "3-ship formation.” NACA research on the XF-92 had suggested a delta wing design as an efficient high-speed shape; now, a paper written by Alfred Eggers and Clarence Syvertson of Ames published in 1954 studied sim­ple shapes in the supersonic wind tunnels. They noted that, by mount­ing a wing atop a half cylindrical shape, they could use the pressure increase behind the shape’s shock wave to increase the effective lift of the wing.[1066] A lift increase of up to 30 percent could be achieved. This con­cept was dubbed "compression lift”; more recently, it is referred to as the "wave rider” concept. Using compression lift principles, North American Aviation (NAA) proposed a 6-engined aircraft weighing 500,000 pounds loaded that could cruise at Mach 2.7 to 3 for 5,000 nautical miles. The aircraft would have a delta wing, with a large underslung shape hous­ing the propulsion system, weapons bay, landing gear, and fuel tanks. A canard surface behind the cockpit would provide trim lift at super­sonic speeds. To provide additional directional stability at high speeds, the outer wingtips would fold to either 25 or 65 degrees down. Although reducing effective wing lifting surface, it would have an additional ben­efit of further increasing compression lift caused by wingtip shocks reflecting off the underside of the wing. Because of the 900-1,100-degree sustained skin temperature at such high cruise speeds, the aircraft would be made of titanium and stainless steel, with stainless steel honeycomb being used in the 6,300-square-foot wing to save weight.[1067]

Original goals were for the XB-70, as it was designated, to make its first flight in December 1961, after contract award to NAA in January 1958. But the development of the piloted bomber was colliding with the missile and space age. The NACA now became the National Aeronautics and Space Administration (NASA), and the research organization gained the mission of directing the Nation’s civilian space program, as well as its traditional aeronautics advancement focus. For military aviation, the development of reliable intercontinental ballistic missiles (ICBM)

В-70 AERODYNAMIC FEATURES

DELTA WING

DROOPED LEAOING EDGES 4 “COMPRESSION LIFT’

BLC GUTTER

North American Aviation (NAA) XB-70 Valkyrie. NASA.

promised delivery of atomic payloads in 30 minutes from launch. The deployment by the Soviet Union of supersonic interceptors armed with supersonic air-to air missiles and belts of Mach 3 surface-to-air missiles (SAM) increasingly made the survivability of the unescorted bomber once again in doubt. The USAF clung to the concept of the piloted bomber, but in the face of delays in manufacturing the airframe with its new mate­rials, increasing program costs, and the concerns of the new Secretary of Defense Robert S. McNamara, the program was scaled back to an experimental program with only four (later three, then two) aircraft to be built. The Air Force’s loss was NASA’s gain; a limited test program of 180 hours was to be flown, with the USAF and NASA sharing the cost and the data. At last, a true supersonic cruise aircraft would be avail­able for the NACA’s successor to study in the sky. The long-awaited first flight of XB-70 No. 1 occurred before a large crowd at Palmdale, CA, on September 21, 1964. But the other shadow supersonic cruise aircraft had already stolen a march on the star of the show.

In February 1964, President Lyndon Johnson revealed to the world that the United States was operating an aircraft that cruised at Mach 3 at latitudes over 70,000 feet. Describing a plane called the A-11, the ini­tial press release was misleading—deliberately so. The A-11 name was a misnomer; it was a proposed design for the CIA spy plane that was never
built, as it had too large a radar cross section. The photograph released was of a slim, long aircraft with two huge wing-mounted engines: the two-seat USAF interceptor version, known as the YF-12. Only three were built, and they were not put into production. The "A-11” that was flying was actually known as the A-12 and was the single-seat low-radar cross-section design plane built in secret by the Lockheed team led by Kelly Johnson, designer of the original U-2. Built almost exclusively of titanium, the aircraft had to be extremely light to achieve its altitude goal; its long range also dictated a high fuel fraction. The twin J58 turbojets had to remain in afterburner for the cruise portion, which dictated even higher-temperature materials than titanium and unique attention to the thermal environment of the vehicle.[1068] [1069]

The USAF ordered a two-seat reconnaissance version of the A-12, designated the SR-71 and duly announced by the President in summer 1964, before the Presidential election. The single-seat A-12 existence was kept secret for another 20 years at CIA insistence, which had a signifi­cant impact on NASA’s flight test of the only other Mach 3 piloted air­craft besides the XB-70. Later known collectively known as Blackbirds, a fleet of 50 Mach 3 cruise airplanes were built in the 1960s and oper­ated for over 25 years. But the labyrinth of secrecy surrounding them severely hampered acquisition by NASA of an airplane for research, much less investigating their technical details and publishing reports. This was unfortunate, as now the United States was committed to not only a space race, but also a global race for a new landmark in aviation technology: a practical supersonic jet airliner, more popularly known as the Supersonic Transport (SST). The emerging NASA would be a major participant in this race, and in 1964, the other runners had a headstart.

In 1997, in response to a White House Commission on Aviation Safety and Security, NASA created the Aviation Safety Program. SVS fit per­fectly within the goals of this program, and the NASA established a SVS project under AvSp, commencing on October 1, 1999. Daniel G. Baize, who had led the XVS element of the Flight Deck ITD Team during the HSR program, continued in this capacity as Project Manager for SVS under AvSP. He wasn’t the only holdover from HSR: most of the tal­ented researchers from HSR XVS moved directly to similar roles under AvSP and were joined by their Langley LVLASO colleagues. Funding for FL.5 transitioned from HSR to AvSP, effectively making FL.5 the first of many successful AvSP SVS flight tests.

Langley’s SVS research project consisted of eight key technical areas: database rendering, led by Jarvis "Trey” Arthur, III, and Steve Williams; pathway concepts, led by Russell Parrish, Lawrence "Lance” Prinzel, III, Lynda Kramer, and Trey Arthur; runway incursion prevention systems, led by Denise R. Jones and Steven D. Young; controlled flight into terrain (CFIT) avoidance using SVS, led by Trey Arthur; loss of control avoid­ance using SVS, led by Douglas T. Wong and Mohammad A. Takallu; data­base integrity, led by Steven D. Young; SVS sensors development, led by Steven Harrah; and SVS database development, led by Robert A. Kudlinski and Delwin R. Croom, Jr. These individuals were supported by numerous NASA and contractor researchers and technicians, and by a number of ded­icated industry and academia partners.[1173] By any measure, SVS development was moving forward along a broad front at the turn of the 21st century.

The first flight test undertaken under the SVS project occurred at the Dallas-Fort Worth International Airport (DFW) in September and October 2000. It constituted the culmination of Langley’s LVLASO project,
demonstrating the results of 7 years of research into surface display con­cepts for reduced-visibility ground operations. Because funding for the LVLASO experiment had transitioned to the AvSP, SVS Project Manager Dan Baize decided to combine the LVLASO elements of the test with continued SVS development. SVS was by now bridging the ground oper – ation/flight operation regimes into one integrated system, although at DFW, each was tested separately.

Reduced ground visibility has always constituted a risk in aircraft operations. On March 27, 1977, an experienced KLM 747 flight crew holding for takeoff clearance at Los Rodeos Airport, Tenerife, fell victim to a fatal combination of misunderstood communications and reduced ground visibility. Misunderstanding tower communications, the crew­members began their takeoff roll and collided with a Pan American 747 still taxiing on landing rollout on the active runway. This accident claimed 578 lives, including all aboard the KLM aircraft and still con­stitutes the costliest accident in aviation history.[1174] Despite the Tenerife disaster, runway incursions continued to rise, and the potential for fur­ther tragedies large and small was great. Incursions rose from 186 in 1993 to 431 in 2000, a 132-percent increase. In the first 5 months of 2000, the FAA and National Transportation Safety Board (NTSB) logged 158 incur­sions, an average of more than 1 runway incursion incident each day.[1175]

Recognizing the emphasis on runway incursion accident preven­tion, researchers evaluated a Runway Incursion Prevention System (RIPS), the key element in the DFW test. RIPS brought together advanced technologies, including surface communications, navigation, and sur­veillance systems for both air traffic controllers and pilots. RIPS uti­lized both head-down moving map displays for pilot SA and data link communication and an advanced HUD for real-time guidance. While

RIPS research was occurring on the ground, SVS concepts were being evaluated in flight for the first time in a busy terminal environment. This evaluation included a Langley-developed opaque HUD concept. Due to the high capacity of flight operations during normal hours at DFW, all research flights occurred at night. HSR veterans Lou Glaab, Lynda Kramer, Jarvis "Trey” Arthur, Steve Harrah, and Russ Parrish managed the SVS experiments, while LVLASO researchers Denise Jones and Richard Hueschen led the RIPS effort.[1176]

The successor to Langley’s remarkable ATOPS B-737 was a modi­fied Boeing 757, the Aries research airplane. Aries—a name suggested by Langley operations engineer Lucille Crittenden in an employee sug­gestion campaign—stood for Airborne Research Integrated Experiments System. For all its capabilities, Aries had a somewhat checkered his­tory. Like many new research programs, it provided systemic challenges to researchers that they had not encountered with the B-737. Indeed, Langley’s research pilot staff had favored a smaller aircraft than the 757, one that would be less costly and demanding to support. Subsequently, the 757 did prove complex and expensive to maintain, impacting the range of modifications NASA could make to it. For example, Aries lacked the separate mid-fuselage Research Flight Deck that had proven so adapt­able and useful in the ATOPS 737. Instead, its left seat of the cockpit (traditionally the "captain’s seat” in a multipilot aircraft) of was modi­fied to become a Forward Flight Deck research station. This meant that, unlike the 737, which had two safety pilots in the front cockpit while a test crew was using the Research Flight Deck, the 757 was essentially a "one safety pilot at the controls” aircraft, with the right-seat pilot per­forming the safety role and another NASA pilot riding in the center jump seat aft and between both the research and safety pilot. This increased the workload of both the research and safety pilots.[1177]

As configured for the DFW tests, Aries had an evaluation pilot in the left seat, a NASA safety pilot/pilot-in-command in the right seat, a secondary NASA safety pilot in the center jump seat, and the principal investigator in the second jump seat. The safety pilot monitored two com­munication frequencies and an intercom channel connected to the numer­ous engineers and technicians in the cabin. Because the standard B-757 flight deck instrumentation did not support the SVS displays, the SVS
researchers developed a portable SVS primary flight display that would be temporarily mounted over the pilot’s instrument panel. An advanced HUD was installed in the left-seat position as well, for use during final approach, rollout, turnoff, and taxi. The HUD displayed symbology relat­ing runway and taxiway edge and centerline detail, deceleration guid­ance, and guidance to gates and hold-short points on the active runway. As well, the Aries aircraft had multifunction display capability, includ­ing an electronic moving map (EMM) that could be "zoomed” to various scales and that could display the DFW layout, locations of other traffic, and ATC instructions (the latter displayed both in text and visual for­mats). Additionally, a test van outfitted with an Automatic Dependent Surveillance-Broadcast (ADS-B) Mode S radar transponder, an air traffic control Radio Beacon System (ATCRBS) transponder, a Universal Access Transceiver (UAT) data link, and a differential GPS was deployed to test sites and used to simulate an aircraft on the ground that could interact during various scenarios with the Aries test aircraft.[1178]

The DFW tests occurred in October 2000, with the Aries 757 interact­ing with the surrogate "airliner” van, and with the airport equipped on its east side with a prototype FAA ground surveillance system developed under the Agency’s runway incursion reduction program. Researchers were encouraged by the test results, and industry and Government eval­uation pilots agreed that SVS technologies showed remarkable potential, reflecting the thorough planning of the test team and the skill of the flight crew. The results were summarized by Denise R. Jones, Cuong C. Quach, and Steven D. Young as follows:

The measured performance of the traffic reporting technologies tested at DFW do meet many of the current requirements for surveillance on the airport surface. However, this is apparently not sufficient for a robust runway incursion alerting function with RIPS. This assessment is based on the observed rats of false alerts and missed detections. All false alerts and missed detections at DFW were traced to traffic data that was inac­curate, inconsistent, and/or not received in a timely manner….

All of the subject pilots were complimentary of the RIPS tested at DFW. The pilots stated that the system has the potential
to reduce or eliminate runway incursions, although human factors issues must still be resolved. Several suggestions were made regarding the alerting symbology which will be incorpo­rated into future simulation studies. The audible alert was the first display to bring the pilots’ attention to the incursion. The EMM would generally be viewed by the non-flying pilot at the time of an incursion since the flying pilot would remain heads up. The pilots stated that two-stage alerting was not necessary and they would take action on the first alert regardless. This may be related to the fact that this was a single pilot opera­tion and the subject pilot did not have the benefit of co-pilot support. In general, after an incursion alert was received, the subject pilots stated they would not want maneuver guidance during final approach or takeoff roll but would like guidance on whether to stop or continue when taxiing across a runway.

All of the pilots stated that, in general, the onboard alerts were generated in a timely manner, allowing sufficient time to react to the potential conflict. They all felt safer with RIPS onboard.[1179]

Almost exactly a year later, the SVS project deployed to a remote location for a major integrated flight test and demonstration of the Aries B-757, the third year in a row that the team had deployed for an offsite test. This time, the location was the terrain-challenged Eagle County Regional Airport near Vail, CO. Eagle-Vail is situated in a valley with mountains on three sides of the runway. It is also at an elevation of 6,540 feet, giving it a high-density altitude on hot summer days, which is not conducive to air­plane performance. Langley’s Aries B-757 was configured with two HUDs and four head-down concepts developed by NASA and its industry part­ner, Rockwell Collins. Enhanced Vision Systems were evaluated as well for database integrity monitoring and imaging the runway environment. Three differently sized head-down PFDs were examined: a "Size A” system, measuring 5.25 inches wide by 5 inches tall, such as flown on a conven­tional B-757-200 series aircraft; a "Size D” 6.4-inch-wide by 6.4-inch-tall display, such as employed on the B-777 family; and an experimental "Size X,” measuring 9 inches wide by 8 inches tall, such as might be flown on a future advanced aircraft.

Additionally, multiple radar altimeters and differential GPS receiv­ers gathered absolute altitude data to be used in developing database integrity monitoring algorithms.[1180]

Randy Bailey was NASAs Principal Investigator, joined by Russ Parrish, Dan Williams, Lynda Kramer, Trey Arthur, Steve Harrah, Steve Young, Rob Kudlinski, Del Croom, and others. Seven pilots from NASA, the FAA, the airline community, and Boeing evaluated the SVS concepts, with par­ticular attention to the terrain-challenged approaches. While fixed-base simulation had indicated that SVS could markedly increase flight safety in terrain-challenged environments, flight-test data had not yet been acquired under such conditions, aside from the limited experience of the Air Force-Calspan TIFS NC-131H trials at Asheville, NC, in September 1999. Of note was the ability of the B-757 to fly circling approaches under simulated instrument meteorological conditions (IMC) using the highly developed SVS displays. Until this test, commercial jet airplanes had not made circling approaches to Eagle-Vail under IMC.[1181] SVS were proving their merit in the most challenging of arenas, something evident in the comments of one evaluation pilot, who noted afterward:

I often commented to people over the years that I never ever flew a circling approach in the -141 [Lockheed C-141 Starlifter] that I was ever comfortable with, particularly at night. It always demanded a lot of attention. This was the first time I ever had an occasion of circling an approach with the kind of information I would love to have in a circling approach. Keeping me safe, I could see the terrain, taking me where I want to go, getting me all types of information in terms to where I am relative to the end of the runway. I mean it’s the best of all possible worlds in terms of safety.[1182]

Unfortunately, this proved to be the last major flight-test program flown on NASA’s B-757 aircraft. An incident during the Eagle-Vail test­ing had profound effects on its future, illustrating the weakness of not
having an independent Research Flight Deck separated from the Forward Flight Deck, which could be occupied by a team of "full-time” safety pilots. After the B-757 missed its approach at Eagle-Vail following a test run, its auto throttles disconnected, without being noticed by the busy flight crew. The aircraft became dangerously slow in the worst possible circumstances: low to the ground and at a high-density altitude. In the subsequent confusion during recovery, the evaluation pilot, unaware that Aries lacked the kind of Full Authority Digital Electronic Control (FADEC) for its turbofan engines on newer B-757s, inadvertently over­boosted both powerplants, resulting in an in-flight abort. The incident reflected as well the decision to procure the B-757 without FADEC engine controls and insufficient training of evaluation pilots before their sor­ties into the nuances of the non-FADEC airplane. The busy flight deck caused by the FFD design likely also played a role in this incident, as it likely did in previous, less serious events. Safety concerns raised by pilots over this and other issues resulted in the grounding of the B-757 in June 2003. Subsequent examination revealed that it had overloaded floor beams, necessitating costly repairs. Though these repairs were com­pleted during a 12-month period in 2004-2005, NASA retired it from service in 2005, bringing its far-too-brief operational career to an end.[1183]

In 2001, NASA Langley’s SVS project was organized into two areas: commercial and business aircraft and general-aviation. Randy Bailey had come to NASA from Calspan and became a Principal Investigator for CBA tests, and Lou Glaab assumed the same role for GA. Monica Hughes, Doug Wong, Mohammad Takallu, Anthony P. Bartolome, Francis G. McGee, Michael Uenking, and others joined Glaab in the GA program, while most of the other aforementioned researchers continued with CBA. Glaab and Hughes led an effort to convert Langley’s Cessna 206-H Stationaire into a GA SVS research platform. A PFD and NAV display were installed on the right side of the instrument panel, and an instrumentation pal­let in the cabin contained processors to drive the displays and a sophis­ticated data acquisition system.[1184]

SVS was particularly important for general aviation, in which two kinds of accidents predominated: controlled flight into terrain and loss

of horizon reference (followed by loss of aircraft control and ground impact).[1185] To develop a candidate set of GA display concepts, Glaab con­ceived a General-Aviation Work Station (GAWS) fixed-base simulator, similar to the successful Virtual Imaging Simulator for Transport Aircraft Systems simulator. Doug Wong and other team members helped bring the idea to reality, and GAWS allowed the GA researchers and evaluation pilots to design and validate several promising GA SVS display sets. The GA implementation differed from the previous and ongoing CBA work, in that SVS for the GA community would have to be far lower in cost, computational capability, and weight. A HUD was deemed too expensive, so the PFD would assume added importance. An integrated simulation and flight-test experiment using GAWS and the Cessna 206 known as Terrain Portrayal for Head-Down Displays (TP-HDD) was commenced in summer 2002. The flight test spanned August through October at Newport News and Roanoke, two of Virginia’s regional airports.[1186]

Both EBG and photorealistic displays were evaluated, and results indicated that equivalent performance across the pilot spectrum could

be produced with the less computationally demanding EBG concepts. This was a significant finding, especially for the computationally and economically challenged low-end GA fleet.[1187]

The SVS CBA team had planned a comprehensive flight test using the Aries B-757 for summer 2003 at the terrain-challenged Reno-Tahoe International Airport. This flight test was to have included flight and surface runway incursion scenarios and operations using integrated SVS displays, including an SVS HUD and PFD, RIPS symbology, hazard sensors, and database integrity monitoring in a comparative test with conventional instruments. The grounding of Aries ended any hope of completing the Reno-Tahoe test in 2003. Set back yet undeterred, the SVS CBA researchers looked for alternate solutions. Steve Young and his Database Integrity Monitoring Experiment (DIME) team quickly found room on NASA Ames’s DC-8 Airborne Science Platform in July and August for database integrity monitoring and Light Detection and Ranging (LIDAR) elevation data collection.[1188] At the same time, manag­ers looked for alternate airframes and negotiated an agreement with Gulfstream Aerospace to use a G-V business jet with Gulfstream’s Enhanced Vision System. From July to September 2004 at Wallops and Reno-Tahoe International Airport, the G-V with SVS CBA researchers and partners from Rockwell Collins, Gulfstream, Northrop Grumman, Rannoch Corporation, Jeppesen, and Ohio University evaluated advanced runway incursion technologies from NASA-Lockheed Martin and Rannoch Corporation and SVS display concepts from Langley and Rockwell Collins. Randy Bailey again was project lead. Lynda Kramer and Trey Arthur were Principal Investigators for the SVS display devel­opment, and Denise Jones led the runway incursion effort. Steve Young and Del Croom managed the DIME investigations, and Steve Harrah continued to lead sensor development.[1189]

The Reno flight test was a success. SVS technologies had been shown to provide a significant improvement to safe operations in reduced vis­ibility for both flight and ground operations. SVS CBA researchers and managers, moreover, had shown a tenacity of purpose in completing project objectives despite daunting challenges. The last SVS flight test was approaching, and significant results awaited.

In August and September 2005, Lou Glaab and Monica Hughes led their team of SVS GA researchers on a successful campaign to argue for the concept of equivalent safety for VMC operations and SVS in IMC. Russ Parrish, at the time retired from NASA, returned to lend his considerable talents to this final SVS experiment. Using the Langley Cessna 206 from the TP-HDD experiment of 2002, Glaab and Hughes employed 19 evaluation pilots from across the flight-experience spec­trum to evaluate three advanced SVS PFD and NAV display concepts and a baseline standard GA concept to determine if measured flight techni­cal error (FTE) from the low-experience pilots could match that of the highly experienced pilots. Additionally, the question of whether SVS dis­plays could provide VMC-like performance in IMC was explored. With pathway-based guidance on SVS terrain displays, it was found that the FTE of low-time pilots could match that of highly experienced pilots. Furthermore, for the more experienced pilots, it was observed that with advanced SVS displays, difficult IMC tasks could be done to VMC perfor­mance and workload standards. The experiment was carefully designed to allow the multivariate discriminant analysis method to precisely quan­tify the results. Truly, SVS potential for providing equivalent safety for IMC flight to that of VMC flight had been established. The lofty goals of the SVS project established 6 years previously had been achieved.[1190]

After the Reno SVS CBA flight test and spanning the termination of the SVS project in 2005, Randy Bailey, Lynda Kramer, Lance Prinzel and others investigated the integration of SVS and EVS capabilities in a comprehensive simulation test using Langley’s fixed-base Integrated Intelligent Flight Deck Technologies simulator, a modified Boeing 757 flight deck. Twenty-four airline pilots evaluated a HUD and auxiliary head-down display with integrated SVS and EVS presentations, where forward-looking infrared video was used as the enhanced vision signal.

The fusion here involved blending a synthetic database with the FLIR signal at eight discrete steps selectable by the pilot. Both FLIR and SV signals were imagery generated by the simulation computers. The results showed an increase in SA for all of the subject pilots. Surprisingly, obstacle runway incursion detection did not show significant improve­ment in either the SV, EV, or fused displays.[1191]

The SVS project formally came to an end September 30, 2005. Despite many challenges, the dedicated researchers, research pilots, and technicians had produced an enviable body of work. Numerous techni­cal papers would soon document the results, techniques employed, and lessons learned. From SPIFR’s humble beginnings, NASA Langley had designed an SVS display and sensor system that could reliably trans­form night, instrument conditions to essentially day VMC for commer­
cial airliners to single-engine, piston-powered GA aircraft. Truly, this was what NASA aeronautics was all about. And now, as the former SVS team transitioned to IIFDT, the researchers at JSC were once again about to take flight.

To support NASA’s ongoing goal of improving aviation safety, the Education and Training Element of the Aircraft Icing Project contin­ues to develop education and training aids for pilots and operators on the hazards of atmospheric icing. A complete list of current train­ing aids is maintained on the GRC Web site. Education materials are tailored to several specific audiences, including pilots, operators, and engineers. Due to the popularity of the education products, NASA can no longer afford to print copies and send them out. Instead, interested parties can download material from the Web site[1269] or check out the lat­est catalog from Sporty’s Pilot Shop, an internationally known source of professional materials and equipment for aviators.[1270]

Icing Branch Facilities

NASA’s groundbreaking work to understand the aircraft icing phenom­enon would have been impossible if not for a pair of assets available at GRC. The more historic of the two is the Icing Research Tunnel (IRT),

which began service in 1944 and, despite the availability of other wind tun­nels with similar capabilities, remains one of a kind. The other asset is the DHC-6 Twin Otter aircraft, which calls the main hangar at GRC its home.

For ground-based research it’s the IRT, the world’s largest refriger­ated wind tunnel. It has been used to contribute to flight safety under icing conditions since 1944. The IRT has played a substantial role in developing, testing, and certifying methods to prevent ice buildup on gas-turbine-powered aircraft. Work continues today in the investigation of low-power electromechanical deicing and anti-icing fluids for use on the ground, deicing and anti-icing research on Short Take Off and Vertical Landing (STOVL) rotor systems and certification of ice protec­tion systems for military and commercial aircraft. The IRT is a closed – loop, refrigerated wind tunnel with a 6- by 9-foot test section. It can generate airspeeds from 25 to more than 400 miles per hour. Models placed in the tunnel can be subjected to droplet sprays of varying sizes to produce the natural icing conditions.[1271]

For its aerial research, the Icing Branch utilizes the capabilities of NASA 607, a DHC-6 Twin Otter aircraft. The aircraft has undergone many modifications to provide both the branch and NASA a "flying laboratory” for issues relating to the study of aircraft icing. Some of the capabilities of this research aircraft have led to development of icing protection sys­tems, full-scale iced aircraft aerodynamic studies, software code valida­tion for ground-based research, development of remote weather sensing technologies, natural icing physics studies, and more.[1272]

The U. S. Navy funded the F/A-18E/F Super Hornet program in 1992 to design its next-generation fighter as a replacement for the canceled A-12 aircraft and the earlier legacy F/A-18 versions. Although some­what similar in configuration to existing F/A-18C aircraft, the new design was a larger aircraft with critical differences in wing design and other features that impact high-angle-of-attack behavior. Two of the first configuration design issues centered on the shape of the wing leading-edge extension and the ability to obtain crisp nose-down control for recovery at extreme angles of attack. Representatives of Langley’s high-angle-of-attack specialty areas were participants in a 15-member NASA-industry-DOD team who conducted wind tunnel studies and anal­yses that provided the basis for the final design of the F/A-18E/F LEX.[1324]

Aerodynamic stability and control characteristics for the Super Hornet for high-angle-of-attack conditions were conducted in the Full – Scale Tunnel to develop a database for piloted simulator evaluations using the Langley and Boeing simulators. Once again, the Spin Tunnel was used for identifying spin modes, spin recovery characteristics, an acceptable emergency spin recovery parachute, and measurement of rotational aerodynamic characteristics using the rotary-balance tech­nique. Langley used an extremely large (over 1,000 pounds) drop model for departure susceptibility and poststall testing at the NASA Wallops Flight Facility to provide risk reduction for the subsequent full-scale flight-test program.[1325]

One of NASA’s more critical contributions to the Super Hornet pro­gram began in March 1996, when a preproduction F/A-18E experienced an unacceptable uncommanded abrupt roll-off that randomly occurred at high angles of attack (below maximum lift) at transonic speeds and involved rapid bank angle changes of up to 60 degrees in the heart of the maneuvering envelope. Engineering analyses indicated that the wing drop was caused by a sudden asymmetric loss of lift on the wing, but the fundamental cause of the problem was not well understood. Following the formation of a DOD Blue Ribbon Panel, a research pro­gram was recommended to be undertaken to develop design methods to avoid such problems on future fighter aircraft. This recommenda­
tion was accepted, and a joint NASA and Navy Abrupt Wing Stall (AWS) program was initiated to conduct the research.[1326]

Meanwhile, extensive efforts by industry and the Navy were under­way to resolve the wing-drop problem through wind tunnel tests and "cut and try” airframe modifications during flight tests. Over 25 potential wing modifications were assessed, and computational fluid dynamics studies were undertaken without a feasible fix identified. Subsequently, the automatically programmed wing leading-edge flaps were examined as a solution. Typical of current advanced fighters, the F/A-18E/F uses flaps with deflection programs scheduled as functions of angle of attack and Mach number. A revised deflection schedule was adopted in 1997 as a major improvement, but the aircraft still exhibited less serious wing drops at many test conditions. As the Navy test and evaluation staff con­tinued to explore further solutions to wing drop, exploratory flight tests with the outer-wing fold fairing removed indicated that the wing drop had been eliminated. However, unacceptable performance and buffet characteristics resulted from removing the fairing.

Langley personnel suggested that passive porosity be examined as a more acceptable treatment of the wing fold area based on NASA’s exten­sive fundamental research. Subsequently evaluated by the Navy flight – test team, the porous fold doors became a feature of the production F/A-18E/F and permitted continued production of the aircraft.

With the F/A-18E/F wing-drop problem resolved, NASA and the Naval Air Systems Command began their efforts in the AWS research program that used a coordinated approach involving static and dynamic tests at Langley in several wind tunnels, piloted simulator studies, and compu­tational fluid dynamics studies conducted by the Navy and NASA. The scope of research focused on the causes and resolution of the unexpected wing drop that had been experienced for the preproduction F/A-18E/F and the wealth of aerodynamic wind tunnel and flight data that had been collected, but the program was intentionally designed to include assessments of other aircraft for validation of conclusions. The stud­ies included the F/A-18C and the F-16 (both of which do not exhibit wing drop) and the AV-8B and the preproduction version of the F/A-18E (which do exhibit wing drop at the extremes of the flight envelope).

After 3 years of intense research on the complex topic of transonic shock-induced asymmetric stall at high angles of attack, the AWS program produced an unprecedented amount of design information, engineering tools, and recommendations regarding developmental approaches to avoid wing drop for future fighters. Particularly signifi­cant output from the program included the development and validation of a single-degree-of-freedom free-to-roll wind tunnel testing technique for detection of wing-drop tendencies, an assessment of advanced CFD codes for prediction of steady and unsteady shock-induced separation at high angles of attack for transonic flight, and a definition of simulator model requirements for assessment and prediction of wing drop. NASA and Lockheed Martin have already applied the free-to-roll concept in the development of the wing geometry for the F-35 fighter.[1327]

Robert A. Rivers

The aeronautics community has always had a strong international flavor. This case study traces how NASA researches in the late 1990s used a Russian supersonic airliner, the Tupolev Tu-144LL — built as a visible symbol of technological prowess at the height of the Cold War—to derive supersonic cruise and aerodynamic data. Despite numerous technical, organizational, and political challenges, the joint research team obtained valuable information and engendered much goodwill.

N A COOL, CLEAR, AND GUSTY SEPTEMBER MORNING in 1998, two NASA research pilots flew a one-of-a-kind, highly modi­fied Russian Tupolev Tu-144LL Mach 2 Supersonic Transport (SST) side by side with a Tupolev test pilot, navigator, and flight engi­neer from a formerly secret Soviet-era test facility, the Zhukovsky Air Development Center 45 miles southeast of Moscow, on the first of 3 flights to be flown by Americans.[1458] These flights in Phase II of the joint United States-Russian Tu-144 flight experiments sponsored by NASA’s High-Speed Research (HSR) program were the culmination of 5 years of preparation and cooperation by engineers, technicians, and pilots in the largest joint aeronautics program ever accomplished by the two countries. The two American pilots became the first and only non­Russian pilots to fly the former symbol of Soviet aeronautics prowess, the Soviet counterpart of the Anglo-French Concorde SST.

They completed a comprehensive handling qualities evaluation of the Tu-144 while 6 other experiments gathered data from hundreds of onboard sensors that had been painstakingly mounted to the airframe
in the preceding 3 years by NASA, Tupolev, and Boeing engineers and technicians. Only four more flights in the program awaited the Tu-144LL, the last of its kind, before it was retired. With the removal from service of the Concorde several years later, the world lost its only supersonic passenger aircraft and witnessed the end of an amazing era.

This is the story of a remarkable flight experiment involving the United States and Russia, NASA and Tupolev, and the men and women who worked together to accomplish a series of unique flight tests from late 1996 to early 1999 while overcoming numerous technical, program­matic, and political obstacles. What they accomplished in the late 1990s cannot be accomplished today. There are no more Supersonic Transports to be used as test platforms, no more national programs to explore com­mercial supersonic flight. NASA and Tupolev established a benchmark for international cooperation and trust while producing data of incal­culable value with a class of vehicles that no longer exists in a regime that cannot be reached by today’s transport airplanes.[1459]