Category NASA’S CONTRIBUTIONS TO AERONAUTICS

NUSAT: 1985

NUSAT, a tiny satellite designed by Weber State College in northern Utah, was deployed into Earth orbit from the cargo bay of the Space Shuttle Challenger on April 29, 1985. Its purpose was to serve as a radar target for the FAA.

The satellite employed three L-band receivers, an ultra high frequency (UHF) command receiver, a VHF telemetry transmitter, associated antennas, a microprocessor, fixed solar arrays, and a power supply to acquire, store, and forward signal strength data from radar. All of that was packed inside a basketball-sized, 26-sided polyhedron that weighed about 115 pounds.[219]

NUSAT was used to optimize ground-based ATC radar systems for the United States and member nations of the International Civil Aviation Organization by measuring antenna patterns.[220]

Full-Scale Transport Controlled Impact Demonstration

This dramatic and elaborate crash test program of the early 1980s was one of the most ambitious and well-publicized experiments that NASA has conducted in its decades-long quest for increased aviation safety. In this 1980-1984 study, the NASA Dryden and Langley Research Centers joined with the FAA to quantitatively assess airline crashes. To do this, they set out to intentionally crash a remotely controlled Boeing 720 air­liner into the ground. The objective was not simply to crash the airliner, but rather to achieve an "impact-survivable” crash, in which many pas­sengers might be expected to survive.[369] This type of crash would allow a more meaningful evaluation of both the existing and experimental cabin safety features that were being observed. Much of the informa­tion used to determine just what was "impact-survivable” came from Boeing 707 fuselage drop tests conducted previously at Dryden’s Impact Dynamics Research Facility and a similar but complete aircraft drop conducted by the FAA.[370]

The FAA’s primary interest in the Controlled Impact Demonstration (CID, also sometimes jokingly referred to as "Crash in the Desert”) was to test an anti-misting kerosene (AMK) fuel additive called FM-9. This high – molecular-weight polymer, when combined with Jet-A fuel, had shown promise during simulated impact tests in inhibiting the spontaneous com­bustion of fuel spilling from ruptured fuel tanks. The possible benefits of this test were highly significant: if the fireball that usually follows an aircraft crash could be eliminated or diminished, countless lives might be saved. The FAA was also interested, secondarily, in testing new safety-related design features. NASA’s main interest in this study, on the other hand, was to measure airframe structural loads and collect crash dynamics data.[371]

Full-Scale Transport Controlled Impact Demonstration

A remotely controlled Boeing 720 airliner explodes in flame on December 1, 1984, during the Controlled Impact Demonstration. Although the test sank hopes for a new anti-misting kerosene fuel, other information from the test helped increase airline safety. NASA.

With these objectives in mind, researchers from the two agencies filled the seats of the "doomed” passenger jet with anthropomorphic dummies instrumented to measure the transmission of impact loads. They also fit­ted the airliner with additional crash-survivability testing equipment, such as burn-resistant windows, fireproof cabin materials, experimental seat designs, flight data recorders, and galley and stowage-bin attachments.[372]

The series of tests included 15 remote-controlled flights, the first 14 of which included safety pilots onboard. The final flight took place on the morning of December 1, 1984. It started at Edwards AFB, NV, and ended with the intentional crash of the four-engine jet airliner onto the bed of Rogers Dry Lake. The designated target was a set of eight steel posts, or cut­ters, cemented into the lakebed to ensure that the jet’s fuel tanks ruptured. During this flight, NASA Dryden’s Remotely Controlled Vehicle Facility research pilot, Fitzhugh Fulton, controlled the aircraft from the ground.[373]

The crash was accomplished more or less as planned. As expected, the fuel tanks, containing 76,000 pounds of the anti-misting kerosene jet fuel, were successfully ruptured; unfortunately, the unexpectedly

Full-Scale Transport Controlled Impact Demonstration

Instrumented test dummies installed in Boeing 720 airliner for the Controlled Impact Demonstration of December 1, 1984. NASA.

spectacular fireball that ensued—and that took an hour to extinguish— was a major disappointment to the FAA. Because of the dramatic fail­ure of the anti-misting fuel, the FAA was forced to curtail its plan to require the use of this additive in airliners.[374]

In most other ways, however, the CID was a success. Of utmost importance were the lessons learned about crash survivability. New safety initiatives had been tested under realistic conditions, and the effects of a catastrophic crash on simulated humans were filmed inside the aircraft by multiple cameras and later visualized at the crash site. Analysis of these data showed, among many other things, that in a burn­ing airliner, seat cushions with fire-blocking layers were indeed supe­rior to conventional cushions. This finding resulted in FAA-mandated flammability standards requiring these safer seat cushions.[375] Another important safety finding that the crash-test data revealed was that the airliner’s adhesive-fastened tritium aisle lights, which would be of utmost importance during postcrash emergency egress, became dislodged and

nonfunctional during the crash. As a result, the FAA mandated that these lights be mechanically fastened, to maximize their time of usefulness after a crash.[376] These and other lessons from this unique research proj­ect have made commercial travel safer.

Effect of Reynolds Number

In the mid-1950s, the NACA encountered an unexpected aerodynamic scale effect related to the long fuselage forebodies being introduced at the time. This experience led to one of the more important and last­ing lessons learned in the use of free-spinning models for spin predic­tions. One particular project stands out as a key experience regarding this topic. As part of the ongoing military requests for NACA support of new aircraft development programs, the Navy requested Langley to conduct spin tunnel tests of a model of its new Chance Vought XF8U-1 Crusader fighter in 1955. The results of spin tunnel tests of a 1/25-scale model indicated that the airplane would exhibit two spin modes.[509] The first mode would be a potentially dangerous fast, flat spin at an angle of attack of approximately 87 degrees, from which recoveries were unsat­isfactory or unobtainable. The second spin was much steeper, with a lower rate of rotation, and recoveries would probably be satisfactory.

As the spin tunnel results were analyzed, Chance Vought engineers directed their focus to identifying factors that were responsible for the flat spin exhibited by the model. The scope of activities stimulated by the XF8U-1 spin tunnel results included, in addition to extended spin tunnel tests, one-degree-of-freedom autorotation tests of a model of the

XF8U-1 configuration in the Chance Vought Low Speed Tunnel and a NACA wind tunnel research program that measured the aerodynamic sensitivity of a wide range of two-dimensional, noncircular cylinders to Reynolds number.[510] The wind tunnel tests were designed and con­ducted to include variations in Reynolds number from the low values associated with spin tunnel testing to much higher values more repre­sentative of flight.

With results from the static and autorotation wind tunnel studies in hand, researchers were able to identify an adverse effect of Reynolds number on the forward fuselage shape of the XF8U-1 such that, at the relatively low values of Reynolds number of the spin tunnel tests (about

90,0 based on fuselage-forebody depth), the spin model exhibited a powerful pro-spin aerodynamic yawing moment dominated by forces produced on the forebody. The pro-spin moment caused an autorota­tive spinning tendency, resulting in the fast flat spin observed in the spin tunnel tests. As the Reynolds number in the tunnel tests was increased to values approaching 300,000, however, the moments produced by the forward fuselage reversed direction and became antispin, remaining so for higher values of Reynolds number. Fundamentally, the researchers had clearly identified the importance of cross-sectional shapes of mod­ern aircraft—particularly those with long forebodies—on spin charac­teristics and the possibility of erroneous spin tunnel predictions because of the low test Reynolds number. When the full-scale spin tests were conducted, the XF8U-1 airplane exhibited only the steeper spin mode and the fast, flat spin predicted by the spin model that had caused such concern was never encountered.

During and after the XF8U-1 project, Langley’s spin tunnel per­sonnel developed expertise in the anticipation of potential Reynolds number effects on the forebody, and in the art of developing methods to geometrically modify models to minimize unrealistic spin predic­tions, caused by the phenomenon. In this approach, cross-sectional shapes of aircraft are examined before models are constructed, and if the forebody cross section is similar to those known to exhibit scale effects at low Reynolds number, static tests at other wind tunnels are

conducted for a range of Reynolds number to determine if artificial devices, such as nose-mounted strakes at specific locations, can be used to artificially alter the flow separation on the nose at low Reynolds number and cause it to more accurately simulate full-scale conditions.[511]

In addition to the XF8U-1, it was necessary to apply scale-correction fuselage strakes to the spin tunnel models of the Northrop F-5A and F-5E fighters, the Northrop YF-17 lightweight fighter prototype, and the Fairchild A-10 attack aircraft to avoid erroneous predictions because of fuselage forebody effects. In the case of the X-29, a specific study of the effects of forebody devices for correcting low Reynolds number effects was conducted in detail.[512]

NACA-NASA’s Contribution to General Aviation

By Weneth D. Painter

Подпись: 8General Aviation has always been an essential element of American aeronautics. The NACA and NASA have contributed greatly to its efficiency, safety, and reliability via research across many technical disciplines. The mutually beneficial bonds linking research in civil and military aeronautics have resulted in such developments as the super­critical wing, electronic flight controls, turbofan propulsion, compos­ite structures, and advanced displays and instrumentation systems.

T

HOUGH COMMONLY ASSOCIATED IN THE PUBLIC MIND with small private aircraft seen buzzing around local airports and air parks, the term "General Aviation” (hereafter GA) is primarily a definition of aircraft utilization rather than a classification per se of aircraft phys­ical characteristics or performance. GA encompasses flying machines ranging from light personal aircraft to Mach 0.9+ business jets, com­prising those elements of U. S. civil aviation which are neither certified nor supplemental air carriers: kit planes and other home-built aircraft, personal pleasure aircraft, commuter airlines, corporate air transports, aircraft manufacturers, unscheduled air taxi operations, and fixed-base operators and operations.

Overall, NACA-NASA’s research has profoundly influenced all of this, contributing notably to the safety and efficiency of GA worldwide. Since the creation of the NACA in 1915, and continuing after establishment of NASA in 1958, Agency engineers have extensively investigated design concepts for GA, GA aircraft themselves, and the operating environment and related areas of inquiry affecting the GA community. In particu­lar, they have made great contributions by documenting the results of various wind tunnel and flight tests of GA aircraft. These results have strengthened both industrial practice within the GA industry itself and the educational training of America’s science, technology, engineering, and mathematics workforce, helping buttress and advance America’s stature as an aerospace nation. This study discusses the advancements
in GA through a review of selected applications of flight disciplines and aerospace technology.

Early Transonic and Supersonic Research Approaches

The NACA’s applied research was initially restricted to wind tunnel work. The wind tunnels had their own problems with supersonic flow, as shock waves formed and disturbed the flow, thus casting doubt on the model test results. This was especially true in the transonic regime, from Mach

0. 8 to 1.2, at which the shock waves were the strongest as the super­sonic flow slowed to subsonic in one single step; this was called a "nor­mal” shock, referring to the 90-degree angle of the shock wave to the vehicle motion. Free air experiments were necessary to validate and improve wind tunnel results. John Stack at NACA Langley developed a slotted wind tunnel that promised to reduce some of the flow irregu­larities. The Collier Trophy was awarded for this accomplishment, but validation of the supersonic tunnel results was still lacking. Pending the development of higher-powered engines for full-scale in-flight experi­ments, initial experimentation included attaching small wing shapes to NACA P-51 Mustangs, which then performed high-speed dives to and beyond their critical Mach numbers, allowing seconds of transonic
data collection. Heavy streamlined bomb shapes were released from NACA B-29s, the shapes going supersonic during their 30-45-second trajectories, sending pressure data to the ground via telemetry before impact.[1055] Supersonic rocket boosters were fired from the NACA facil­ity at Wallops Island, VA, carrying wind tunnel-sized models of wings and proposed aircraft configurations in order to gain research data, a test method that remained fruitful well into the 1960s. The NACA and the United States Air Force (USAF) formed a joint full-scale flight-test program of a supersonic rocket-powered airplane, the Bell XS-1 (subse­quently redesignated the X-1), which was patterned after a supersonic

0. 50-caliber machine gun projectile with thin wings and tail surfaces. The program culminated October 14, 1947, with the demonstration of a controllable aircraft that exceeded the speed of sound in level flight. The news media of the day hailed the breaking of the "sound barrier,” which would lead to ever-faster airplanes in the future. Speed records popularized in the press since the birth of aviation were "made to be broken”; now, the speed of sound was no longer the limit.

Подпись: 10But the XS-1 flight in October was no more a practical solution to supersonic flight than the Wright brothers’ flights at Kitty Hawk in December 1903 were a director predecessor to transcontinental passen­ger flights. Rockets could produce the thrust necessary to overcome the drag of supersonic shock waves, but the thrust was of limited duration. Rocket motors of the era produced the greatest thrust per pound of engine, but they were dangerous and expensive, could not be throttled directly, and consumed a lot of fuel in a short time. Sustained supersonic flight would require a more fuel-efficient motor. The turbojet was an obvious choice, but in 1947, it was in its infancy and was relatively ineffi­cient, being heavy and producing only (at most) several thousand pounds of static thrust. Military-sponsored research continued on improving the efficiency and the thrust levels, leading to the introduction of after­burners, which would increase thrust from 10-30 percent, but at the expense of fuel flows, which doubled to quadrupled that of the more normal subsonic cruise settings. The NACA and manufacturers looked at another form of jet propulsion, the ramjet, which did away with the complex rotating compressors and turbines and relied on forward speed of the vehicle to compress the airflow into an inlet/diffuser, where fuel

would then be injected and combusted, with the exhaust nozzle further increasing the thrust.

Slip, Sliding Away

Before an aircraft can get into the winter sky and safely avoid the threat of icing, it first must take off from what the pilot hopes is a long, wide, dry runway at the beginning of the flight, as well as at the end of the flight. Likewise, NASA’s contributions to air safety in fighting the tyr­anny of temperature included research into ground operations. While NASA did not invent the plow to push snow off the runway, or flame­throwers to melt off any stubborn runway snow or ice, the Agency has been active in studying the benefits of runway grooves since the first civil runway was introduced in the United States at Washington National Airport in December 1965.[1260]

Runway grooves are intended to quickly channel water away from the landing strip without pooling on the surface so as to prevent

Подпись: 12 Slip, Sliding Away

hydroplaning. The 3-mile-long runway at the Shuttle Landing Facility is probably the most famous runway in the Nation and known for being grooved. Of course, there is little chance of snow or ice accumulating on the Central Florida runway, so when NASA tests runway surfaces for cold weather conditions it turns to the Langley Aircraft Landing Dynamics Facility at NASA’s Langley Research Center (LaRC) in Hampton, VA. The facility uses pressurized water to drive a landing-gear-equipped platform down a simulated runway strip, while cameras and sensors keep an eye on tire pressure, tire temperature, and runway friction. Another runway at NASA’s Wallops Flight Facility also has been used to test various sur­face configurations. During the mid-1980s, tests were performed on 12 different concrete and asphalt runways, grooved and non-grooved, includ­ing dry; wet; and snow, slush, and ice-covered surface conditions. More than 200 test runs were made with two transport aircraft, and more than 1,100 runs were made with different ground test vehicles. Ground vehi­cle and B-737 aircraft friction tests were conducted on grooved and non­grooved surfaces under wet conditions. As expected, grooved runway surfaces had significantly greater friction properties than non-grooved surfaces, particularly at higher speeds.[1261]

FAN-IN-WING AIRCRAFT HANDLING QUALITIES

The XV-5 was a proof-of-concept lift-fan aircraft and thus employed a completely "manual” powered-lift flight control system. The lack of an integrated powered-lift system required the pilot to manually control the aircraft flight-path through independent manipulation of stick, engine power, thrust vector angle and collective lift. This lack of an integrated powered-lift management system (and in particular, the conversion controls) was responsible for most of the adverse handling qualities of the aircraft. An advanced digital fly­by-wire control system must provide level one handling qualities, especially for integrated powered-lift management.

CONVERSION SYSTEM DESIGN

Подпись: 14The manually operated conversion system was the most exacting, interesting and potentially hazardous flight opera­tion associated with the XV-5. This type of "bang-bang” con­version system should not be considered for the SSTOVLF. Ideally, the conversion should consist of a fully reversible and continuously controllable process. That is, the pilot must be able to continuously control the conversion process. Good examples are the XV-15 Tilt Rotor, the X-22A and the AV-8 Harrier. Furthermore, the conversion of the SSTOVLF with an advanced digital flight control system should be fully decou­pled so that the pilot would not have to compensate for lift, attitude or speed changes. The conversion controller should be a single lever or beeper-switch that is safety-interlocked against inadvertent actuation. The conversion airspeed limit corridor must be wide enough to allow for operational flexi­bility and compensate for single-pilot operation where mis­sion demands can compete for pilot attention.

Future ATM Concepts Evaluation Tool

Another NASA air traffic simulation tool, the Future ATM Concepts Evaluation Tool (FACET), was created to allow researchers to explore, develop, and evaluate advanced traffic control concepts. The system can operate in several modes: playback, simulation, live, or in a sort of hybrid mode that connects it with the FAAs Enhanced Traffic Management System (ETMS). ETMS is an operational FAA program that monitors and reacts to air traffic congestion, and it can also predict when and where conges­tion might happen. (The ETMS is responsible, for example, for keeping a plane grounded in Orlando because of traffic congestion in Atlanta.) Streaming the ETMS live data into a run of FACET makes the simula­tion of a new advanced traffic control concept more accurate. Moreover, FACET is able to model airspace operations on a national level, processing the movements of more than 5,000 aircraft on a single desktop computer, taking into account aircraft performance, weather, and other variables.[257]

Some of the advanced concepts tested in FACET include allowing aircraft to have greater freedom in maintaining separation on their own,[258] integrating space launch vehicle and aircraft operations into the

airspace, and monitoring how efficiently aircraft comply with ATC instructions when their flights are rerouted.[259] In fact, the last of these concepts was so successful that it was deployed into the FAA’s operational ETMS. NASA reports that the success of FACET has lead to its use as a simulation tool not only with the FAA, but also with sev­eral airlines, universities, and private companies. For example, Flight Dimensions International—the world’s leading vendor of aircraft sit­uational displays—recently integrated FACET with its already popu­lar Flight Explorer product. FACET won NASA’s 2006 Software of the Year Award.[260]

Advanced Air Transportation Technologies Program

NASA established this project in 1996 to increase the capability of the Nation’s air transport activities. This program’s specific goal was to develop a set of "decision support tools” that would help air traffic service providers, aircrew members, and airline operations centers in streamlining gate-to-gate operations throughout the NAS.[431] Project personnel were tasked with researching and developing advanced

Advanced Air Transportation Technologies Program

NASA’s Boeing 737 in 1987 after significant cockpit upgrades. Note its much more user-friendly "glass cockpit” display, featuring eight 8- by 8-inch color monitors. NASA.

concepts within the air traffic management system to the point where the FAA and the air transport industry could develop a preproduction prototype. The program ended in 2004, but implementation of these tools into the NAS addressed such air traffic management challenges as complex airspace operations and assigning air and ground responsi­bilities for aircraft separation. Several of the technologies developed by this program received "Turning Goals into Reality” awards, and some of these—for example, the traffic management adviser and the collab­orative arrival planner—are in use by ATC and the airlines.[432]

The Anatomy of a Wind Tunnel

The design of an efficient aircraft or spacecraft involves the use of the wind tunnel. These tools simulate flight conditions, including Mach num­ber and scale effects, in a controlled environment. Over the late 19th, 20th, and early 21st centuries, wind tunnels evolved greatly, but they all incorporate five basic features, often in radically different forms. The main components are a drive system, a controlled fluid flow, a test sec­tion, a model, and instrumentation. The drive system creates a fluid flow that replicates flight conditions in the test section. That flow can move at subsonic (up to Mach 1), transonic (Mach 0.75 to 1.25), supersonic (up to Mach 5), or hypersonic (above Mach 5) speeds. The placement of a scale model of an aircraft or spacecraft in the test section via balances allows the measurement of the physical forces acting upon that model with test instrumentation. The specific characteristics of each of these compo­nents vary from tunnel to tunnel and reflect the myriad of needs for this testing technology and the times in which experimenters designed them.[529]

Wind tunnels allow researchers to focus on isolating and gather­ing data about particular design challenges rooted in the four main systems of aircraft: aerodynamics, control, structures, and propulsion. Wind tunnels measure primarily forces such as lift, drag, and pitching moment, but they also gauge air pressure, flow, density, and tempera­ture. Engineers convert those measurements into aerodynamic data to evaluate performance and design and to verify performance predic­tions. The data represent design factors such as structural loading and strength, stability and control, the design of wings and other elements, and, most importantly, overall vehicle performance.[530]

Most NACA and NASA wind tunnels are identified by their location, the size of their test section, the speed of the fluid flow, and the main design characteristic. For example, the Langley 0.3-Meter Transonic

Cryogenic Tunnel evaluates scale models in its 0.3-meter test section between speeds of Mach 0.2 to 1.25 in a fluid flow of nitrogen gas. A spe­cific application, 9- by 6-Foot Thermal Structures Tunnel, or the exact nature of the test medium, 8-Foot Transonic Pressure Tunnel, can be other characterizing factors for the name of a wind tunnel.