Category NASA’S CONTRIBUTIONS TO AERONAUTICS

In 1993, responding to anticipated increases in air travel demand, NASA established a Terminal Area Productivity program to increase airliner throughput at the Nation’s airports by at least 12 percent over existing levels of service. TAP consisted of four interrelated subelements: air traf­fic management, reduced separation operations, integration between aircraft and air traffic control (ATC), and Low Visibility Landing and Surface Operations (LVLASO).[1145]

Of the four Agency subelements, the Low Visibility Landing and Surface Operations project assigned to Langley held greatest signifi­cance for SVS research. A joint research effort of Langley and Ames Research Centers, LVLASO was intended to explore technologies that could improve the safety and efficiency of surface operations, includ­ing landing rollout, turnoff, and inbound and outbound taxi; making better use of existing runways; and thus making obvious the need for expensive new facilities and the rebuilding and modification of older ones.[1146] Steadily increasing numbers of surface accidents at major air­ports imparted particular urgency to the LVLASO effort; in 1996, there had been 287 incidents, and the early years of the 1990s had witnessed 5 fatal accidents.[1147]

LVLASO researchers developed a system concept including two technologies: Taxiway Navigation and Situational Awareness (T-NASA) and Rollout Turnoff (ROTO). T-NASA used the HUD and NAV display moving map functions to provide the pilot with taxi guidance and data link air traffic control instructions, and ROTO used the HUD to guide the pilot in braking levels and situation awareness for the selected run­
way turnoff. LVLASO also incorporated surface surveillance concepts to provide taxi traffic alerting with cooperative, transponder-equipped vehicles. LVLASO connected with potential SVS because of its airport database and GPS requirements.

In July and August 1997, NASA Langley flight researchers undertook two sequential series of air and ground tests at Atlanta International Airport, using a NASA Boeing 757-200 series twin-jet narrow-body transport equipped with Langley-developed experimental cockpit displays. This permitted surface operations in visibility conditions down to a runway visual range (RVR) of 300 feet. Test crews included NASA pilots for the first series of tests and experienced airline captains for the second. All together, it was the first time that SVS had been demon­strated at a major airport using a large commercial jetliner.[1148]

LVLASO results encouraged Langley to continue its research on integrating surface operation concepts into its SVS flight environment studies. Langley’s Wayne H. Bryant led the LVLASO effort, assisted by a number of key researchers, including Steven D. Young, Denise R. Jones, Richard Hueschen, and David Eckhardt.[1149] When SVS became a focused project under AvSP in 1999, these talented researchers joined their col­leagues from the HSR External Vision Systems project.[1150] While LVLASO technologies were being developed, NASA was in the midst of one of the largest aeronautics programs in its history, the High-Speed Research Program. SVS research was a key part of this program as well.

After sporadic research at advancing the state of the art in high­speed aerodynamics in the 1970s, the United States began to look at both supersonic and hypersonic cruise technologies more seriously in the mid – 1980s. Responding to a White House Office of Science and Technology Policy call for research into promoting long-range, high-speed aircraft, NASA awarded contracts to Boeing Commercial Airplanes and Douglas Aircraft Company in 1986 for market and technology feasibility studies
of a potential High-Speed Civil Transport. The speed spectrum for these studies spanned the supersonic to hypersonic regions, and the areas of study included economic, environmental, and technical considerations. At the same time, LaRC conducted its own feasibility studies led by Charles M. Jackson, Chief of the High-Speed Research Division; his dep­uty, Wallace C. Sawyer; Samuel M. Dollyhigh; and A. Warner Robbins. These and follow-on studies by 1988 concluded that the most favorable candidate considering all factors investigated was a Mach 2 to Mach 3.2 HSCT with transpacific range.[1151]

NASA created the High-Speed Research program in 1990 to investigate technical challenges involved with developing a Mach 2+ HSCT. Phase I of the HSR program was to determine if major environmental obstacles could be overcome, including ozone depletion, community noise, and sonic boom generation. NASA and its industry partners determined that the state of the art in high-speed design would allow mitigation of the ozone and noise issues, but sonic boom mitigation remained elusive.[1152]

Buoyed by these assessments, NASA commenced Phase II of the HSR program in 1995, in partnership with Boeing Commercial Airplane Group, McDonnell-Douglas Aerospace, Rockwell North American Aircraft Division, General Electric Aircraft Engines, and Pratt & Whitney as major industry participants. A comprehensive list of technical issues was slated for investigation, including sonic boom effects, ozone deple­tion, aero acoustics and community noise, airframe/propulsion integra­tion, high lift, and flight deck design. One of the earliest identified issues was forward visibility. Unlike the Concorde and the Tupolev Tu-144 Supersonic Transports, the drooping of the nose to provide forward visibility for takeoff and landing was not a given. By leaving the nose undrooped, engineers could make the final design thousands of pounds lighter. Unfortunately, to satisfy supersonic fineness ratio requirements, the postulated undrooped nose would completely obstruct the pilots’ forward vision. A solution had to be found, and the new disciplines of advanced cockpit electronic displays and high-fidelity sensors, in
combination with Langley’s HITS development, suggested an answer. A concept known as the External Vision System was developed, which was built around providing high-quality video signals to the flight deck to be combined with guidance and navigation symbology, creating a virtual out-the-window scene.[1153]

With the extensive general-aviation highway-in-the-sky experience at Langley, researchers began to expand their focus in the early 1990s to include more sophisticated applications to commercial and busi­ness aircraft. This included investigating the no-droop nose require­ments of the conceptual High-Speed Civil Transport, which lacked side windows and had such a forward-placed cockpit in relation to the nose wheel of the vehicle—over 50 feet separated the two—as to pose seri­ous challenges for precise ground maneuvering. As the High-Speed Research program became more organized, disciplines became grouped into Integrated Technology Development (ITD) Teams.[1154] An XVS ele­ment was established in the Flight Deck ITD Team, led by Langley’s Daniel G. Baize. Because the HSR program contained so many member organizations, each with its own prior conceptions, it was thought that the ITD concept would be effective in bringing the disparate organiza­tions together. This did not always lead to an efficient program or rapid progress. Partly, this was due to the requirement that consensus must be reached on all ITD Team decisions, a Skunk Works process in reverse. In the case of the XVS element, researchers from NASA Langley and NASA Ames Research Centers joined industry colleagues from Boeing, Douglas, Calspan, and others in designing a system from the bottom up.[1155]

Different backgrounds led to different choices for system design from the group. For example, at Langley, the HITS concept was favored with a traditional flight director, while at Ames, much work had been
devoted to developing a "follow me” aircraft concept developed by Ames researcher Richard Bray, in which an iconic aircraft symbol portrayed the desired position of the aircraft 5-30 seconds in the future. The pilot would then attempt to use the velocity vector to "follow” the leader aircraft. Subsequent research would show that choices of display symbology types profoundly coupled with the type of control law selected. Certain good display concepts performed poorly with certain good control law implementations. As the technology in both flight displays and digital fly-by-wire control laws advanced, one could not arbitrarily select one without considering the other. Flight tests in the United States Air Force (USAF)/Calspan Total In-Flight Simulator (TIFS) aircraft had shown that flightpath guidance cues could lead to pilot-induced oscilla­tions (PIOs) in the flare when control was dependent upon a flight con­trol system employing rate command control laws. For this reason, the Flight Deck and Guidance and Flight Controls (GFC) ITD Teams worked closely together, at times sharing flight tests to ensure that good concert existed between display and flight control architecture. To further help the situation, several individuals served on both teams simultaneously.

From 1994 to 1996, Langley hosted a series of workshops concern­ing concepts for commercial transports, including tunnel-, pathway-, and highway-in-the-sky concepts.[1156] The first two workshops examined potential display concepts and the maturity of underlying technologies, with attendees debating the merits of approaches and their potential utility. The final workshop, the Third XVS Symbology Workshop (September 4-5, 1996), focused on XVS applications for the HSCT. Led by the Flight Deck Integrated Display Symbology Team of Dr. Terrence Abbott and Russell Parrish, from Langley, and Andrew Durbin, Gordon Hardy, and Mary Kaiser, from Ames, the workshop provided an opportunity for participants from related ITD Teams to exchange ideas. Because the sensor image would be the primary means of traffic sepa­ration in VMC, display clutter was a major concern. The participants developed the minimal symbology set for the XVS displays to include the virtual out-the-window display and the head-down PFD. The theme of the workshop became, "Less is best, lest we obscure the rest.” [1157]

As flight tests would troublingly demonstrate, display clutter (excess symbology) would be one of several significant prob­lems revealed while evaluating the utility of displays for object (traffic) detection.

With additional research required on SLDs and engine core ice accre­tion, new updates always in demand for the LEWICE software, and the still-unknown always waiting to be discovered, NASA maintains its research capability concentrated within the Icing Branch at GRC. The branch performs research activities related to the development of meth­ods for evaluating and simulating the growth of ice on aircraft surfaces, the effects that ice may have on the behavior of aircraft in flight, and the behavior of ice protection and detection systems. The branch is part of the Research and Technology Directorate and works closely with the staff of the Icing Research Tunnel and the Twin Otter Icing Research Aircraft. Its mission is to develop validated simulation methods—for use in both computer programmed and real-world experiments—suit­able for use as both certification and design tools when evaluating air­craft systems for operation in icing conditions. The Icing Branch also fosters the development of ice protection and ice detection systems by actively supporting and maintaining resident technical expertise, exper­imental facilities, and computational resources. NASA’s Aircraft Icing Project at GRC is organized into three sections: Design and Analysis Tools, Aircraft Ice Protection, and Education and Training.[1262]

NASA Langley became involved in the X-31 Enhanced Fighter Maneuverability (EFM) program in 1984, when mutual discussions with Rockwell International occurred regarding a fighter configuration capable of highly agile flight at extreme angles of attack. Known as the Super Normal Attitude Kinetic Enhancement (SNAKE) configuration, the design underwent exploratory testing in the Full-Scale Tunnel.[1319] The
early cooperative research study later led to a cooperative project using the Langley Full Scale Tunnel, the Langley Spin Tunnel, and the Langley Jet-Exit Test Facility. After DARPA and the West Germany government formally initiated the X-31 program, Langley and Dryden actively par­ticipated in the development of the configuration and flight tests of two X-31 demonstrators at Dryden from 1992 to 1995.

In the early SNAKE Langley-Rockwell study, Langley researchers assessed the high-angle-of-attack capabilities of the Rockwell-designed configuration that had been designed using computational methods with minimal use of wind tunnel tests. Preliminary evaluations in the full-scale tunnel disclosed that the configuration was unacceptable, being unsta­ble in pitch, roll, and yaw. Langley’s expertise in high-angle-of-attack stability and control contributed to modifications and revisions of the original configuration, eliminating the deficiencies of the SNAKE design.

Simultaneous with the SNAKE activities, several other events con­tributed to shaping what would become the X-31 program. First, the emerging recognition that thrust vectoring would provide unprece­dented levels of control for precision maneuvering at extreme angles of attack had led to joint Langley-Rockwell studies of jet-exit vanes sim­ilar to those previously discussed for the Navy F-14 experiments and the NASA F/A-18 HARV vehicle. The tests, which were conducted in the Langley Jet-Exit Test Facility, inspired Rockwell to include multi­axis thrust-vectoring paddles in the SNAKE configuration. Free-flight testing of the revised SNAKE configuration provided impressive proof that the vectoring paddles were extremely effective.

The second major activity was the strong advocacy of the West German Messerschmitt-Bolkow-Blohm (MBB) Company that asserted that high levels of agility for poststall flight conditions provided dom­inant capabilities for close-in air combat. With the support of DARPA, the X-31 EFM program was initiated in 1986 with a request that Langley be a major participant in the development program. Using the NASA Langley test facility assets for free-flight model testing, spin testing, and drop-model testing uncovered several critical issues for the configuration.

One issue was the general character of inherent poststall motions that might be encountered in the aircraft flight program. Results indi­cated that the X-31 might have marginal nose-down control for recovery from high-angle-of-attack maneuvers, and that severe unstable wing – rock motions would be exhibited by the configuration, resulting in a violent, disorienting roll departure and an unrecoverable inverted stall

condition. With these inputs, the X-31 design team worked to configure the flight control system for maximum effectiveness and to prevent the foregoing problems, even without thrust vectoring. The value of these contributions from Langley cannot be understated, but equally impor­tant contributions were to come as the drop-model technique maintained operations during the full-scale aircraft flight-test program.

Flight-testing of the two X-31 aircraft began at Dryden in February 1992 under the direction of an International Test Organization (ITO) that included NASA, the U. S. Navy, the U. S. Air Force, Rockwell, the Federal Republic of Germany, and Deutsche Aerospace (formerly MBB). Two issues were encountered in the flight-test program, resulting in addi­tional test requirements from the supporting team of Langley research­ers. Early in the flight tests, pilots reported marginal nose-down pitch control and said that significant improvements would be necessary if the aircraft were to be considered an efficient weapon system for close – in combat. In a quick-response mode, Langley conducted evaluations of 16 configuration modifications to improve nose-down control in the Full-Scale Tunnel. From these tests, a decision was made to add strakes to the lower aft fuselage, and pilots of subsequent flight tests with the modified airplane reported that the problem was eliminated.

Another problem encountered in the X-31 flights at extreme angles of attack was the presence of large out-of-trim yawing moments with the potential to overpower corrective inputs from the pilot. After a depar­ture was unexpectedly experienced during a maneuvering flight near an angle of attack of 60 degrees, analysis of the flight records indicated that the departure had been caused by a large asymmetric yawing moment that was much larger than any predicted in subscale wind tunnel testing. The presence of asymmetric moments of this type had been well-known to the aeronautics community, including the fact that the phenomenon might be sensitive to the specific Reynolds number under consider­ation. Experience had shown that, for some configurations, the out-of­trim moments exhibited during subscale model tests might be larger than those exhibited at the full-scale conditions, and for other config­urations, opposite results might occur. In the case of the X-31, the full – scale aircraft exhibited significantly higher values.[1320]

The flight-test team sent an urgent request to Langley for solutions to the problem. Once again, tests in the full-scale tunnel were conducted of a matrix of possible airframe modifications, a candidate solution was identified, and real-time recommendations were made to the ITO. In these tunnel tests, a single nose strake was used to predict the maximum level of asymmetry for the airplane, and the solutions worked for that configuration. A pair of nose strakes designed in the tunnel tests was
implemented and, together with other modifications (grit on the nose boom and slight blunting of the fuselage nose tip), permitted the air­craft flight program to continue. This X-31 experience was noteworthy, in that it demonstrated the need for testing seemingly unimportant details at Reynolds numbers equivalent to flight.

The X-31 EFM program completed an X-plane record of 524 flights with 14 evaluation pilots from the sponsoring organizations.

The XV-5B demonstrated that lift-fan aircraft are capable of performing steep simulated instrument approaches with up to 20° flight-path angles. Once more, lack of an integrated powered-lift flight control system was the primary cause of adverse handling qualities and operational limitations. The SSTOVLF’s integrated powered-lift system must provide decou­pled flight path control for glide slope tracking where a sin­gle controller, such as a throttle-type lever is used for direct flight-path modulation while airspeed and/or angle-of-attack are held constant. Simulator evaluations of such systems have indicated significant improvements in handling qualities and reductions in pilot workload, an integrated powered-lift sys­tem a must in a single-piloted SSTOVF.

Evaluations of the XV-5B’s ability to perform simulated instrument landing approaches along a 10° glide slope revealed that pilots preferred to approach with a deck-parallel attitude (near-zero angle-of-attack) instead of using deck-level attitude (near 10° angle-of-attack) instead of 15°. Fan-stall boundary and random aerodynamic lift disturbances were cited as the causes.

SSTOVLF designers should encourage the development of lift – fans with increased angle-of-attack capability which would enhance Instrument Meteorological Conditions (IMC) oper­ational capability and improve safety.

All pilots that flew the XV-5 (the "XV-5 Fan Club”) were of the unanimous opinion that the conversion handling qualities of the Vertifan were completely unsatisfactory for IMC oper­ations. Trying to contend with the large power changes, atti­tude and altitude displacements, and abrupt airspeed changes while trying to fly instruments with the XV-5’s "manual” con­trol system was too much to handle. The enhanced operational flexibility requirement laid on the SSTOVLF requires that it have full IMC operational capability.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Dr. Richard P. Hallion

August 25, 2010

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