Problems related to the trailing vortex hazard could be reduced in several ways, namely, (1) through improved understanding of the extent of the trailing vortex movement and persistence for different aircraft classes, modes of operation, and meteorological conditions, (2) by development of a way to monitor the trailing vortex position and wind intensity, particularly near the airfield, and (3) by development of a method to either discourage initial formation of high intensity vortices or encourage early breakup when once formed, through either aircraft design or artificially induced impedances.

NASA is continuing to work in each of these three categories. Flight tests to measure the velocities and persistence of vortices behind large transport aircraft are planned (top of Figure 21) using instrumented probe aircraft. These measurements, often done in cooperation with the USAF, are expected to provide a better understanding of vortex characteristics under different atmospheric conditions. Promising methods developed in the laboratory to either reduce vortex formation and intensity at the source or encourage early dissipation after formation will be further explored in flight tests. Other field tests will determine the movement and decay of vortices generated near the ground, as during landing and takeoff (bottom of Figure 21). Results from these tests will be useful for establishing safe separation distances between aircraft in the airport area, as well as a criterion for use in spacing of parallel runways in the design of new airports.

Laser velocimeters are being developed to permit remote measurement of vortex winds and provide the technological base for possible use of the velocimeter as an airport vortex monitoring system.

The test data accrued in all of these programs will be used to develop accurate nodels of vortex behavior. It is expected that the vortex models will be used to generate minimum safe separation between aircraft in the controlled air traffic systems and provide pilots with avoidance techniques.

AIRCRAFT OPERATING EXPERIENCES

One way to determine if aircraft are operating within the limits to which they were designed is to monitor the accelerations, speed and altitude ranges during routine operations. The NASA collects information on these parameters from recorders installed in commercial passenger and cargo transports, general aviation airplans, research type airplanes, and helicopters. The data from the commercial and general aviation airplanes are obtained through a coopertive effort with the aircraft manufacturers, airlines, and private owners. Figure 22 is a photograph of one of the recorders and a Boeing 747 in which it is installed. The data provides information on the ground/taxi and flight loads, airspeed and altitude operating practices, the turbulence environment experienced, and on unusual events, such as, loss of control in turbulence, collision avoidance maneuvers, and autopilot induced oscillations. This information is gathered on a continuing basis with recorders placed in aircraft flying over different geographical areas throughout the various seasons of the year. The data gathered is compared with the concepts used in design. The information identifies occurrences of unanticipated operational problems and provides trends useful in the design of new types of aircraft.

Continuing efforts are made to place the recorders in new type aircraft as they are placed in service. Operational experiences of aircraft used as executive transports, personal flying, commercial surveys, charter service, crop-dusting, and aerobatics, as well as those used in scheduled airline service, are being sampled.

FLIGHT TEST INSTRUMENTATION

Many of the laboratory and flight test programs aimed at solving operating problems require a wide range of instrumentation to sense such quantities as control positions, control forces, linear accelerators, velocity, angular pitch rates. vibrations, pressures, flow rates, etc. At times instruments used in these tests can be purchased off-the-shelf to meet the flight test engineers needs. Often modifications to available instruments or development of new instruments are needed. Many of the flight test systems require improvements to make them flight worthy and perform safely and accurately in severe environments.

Examples of instruments developed and applied in the past include the airplane flight recorder used to monitor the acceleration, speed and altitude of commercial airlines, which was previously discussed. Vanes mounted ahead of test aircraft on booms used to sense angle of attack changes have to withstand gusts and temperatures associated with supersonic flight. The laser velocimeter developed for remote sensing of atmosphere winds is another example.

Techniques to record the information on-board or telemeter the measurements to ground facilities are developed as needed. Digital techniques and technological innovations, such as microelectronics, are used to collect greater quantities of more precise data, and in a form compatible with automatic data processing techniques. A real-time ground readout of test measurements give the engineer a safety check on experimental progress and a check on experiment success, whether tests are made in the laboratory or in the air.

Frequently a major consideration is the location of the tests, whether near the research center or at some location far removed from sources of quick maintenance and repair. These types of instrumentation and data recording problems are resolved by the efforts funded in this area. The success of every experiment depends upon the quality of the instrumentation system.

CONCLUDING REMARKS

I have described operating problems caused by flight transportation's impingement on the quality of our environment (principally noise), operating problems caused by other aircraft (wake turbulence, congestion, ATC delays, etc.) operating problems caused by economic factors (the difficulty of providing frequent low-density, short-haul air transportation, for example) and operating problems caused by natural factors (clear air turbulence, slippery runways, storms, fog, etc.). I have also described the goals and many of the programs of the Aeronautical Operating Systems Division, a new organizational element of the Office of Advanced Research and Technology. The operating problems of flight transportation are more exacting and formidable than ever today. Through the programs I have described, conducted principally through our four research centers, and conducted in close collaboration with the DOT and the FAA, we plan to make a substantial contribution to the solution of these problems.

PREPARED STATEMENT OF MR. GEORGE C. DEUTSCH, DIRECTOR, MATERIALS AND STRUCTURES DIVISION, OFFICE OF ADVANCED RESEARCH AND TECHNOLOGY, NATIONAL AERONAUTICS AND SPACE ADMINISTRATION

INTRODUCTION

Mr. Chairman and Members of the Committee, in the recent OART reorganization, a new Division, the Materials and Structures Division, was created. The new Division combined the disciplines of "Materials" and "Structures" for both aeronautics and space and was a recognition of the fact that during the past several years these disciplines have become less and less distinct and, particularly with such new concepts as that of "composites" have tended to merge. Thus, the new Division recognizes the close interrelationships and interdependency between these important research and development areas and, by so doing, will facilitate the transfer of basic concepts about materials and structural designs to their ultimate application in aircraft and space vehicles. The Materials and Structures research and development program covers a broad range from very fundamental studies of the relationships between atoms and the theoretical analysis of static and dynamic stresses to the evolution of materials for specific aircraft and spacecraft usage and the prototype flight tests of components made from such materials.

Many of the studies are equally applicable to both aeronautics and space. For example, a new high temperature material is of considerable importance to space power plants as well as to advanced aircraft engines and a new and improved structural analysis method would prove to be of equal validity to both a new wing concept for an airplane and for the fuselage of the space shuttle.

This statement will describe the program in terms of specific examples of studies that are currently underway. The examples have been selected to exhibit both the scope and the depth of the program; and have been divided into those which are primarily motivated by NASA aeronautics program and those where the primary motivation and values lie with the NASA space program.

AERONAUTICAL MATERIALS AND STRUCTURES

One area of materials research on which much attention has been directed is that of polymeric materials (plastics). Everyone is aware of the growing use of these very versatile and attractive materials in aircraft. This is indicative of the growing sophistication of the science and technology in this field. One area of polymer science that has received increased attention of late is that of elastomeric materials. These elastic or rubbery materials are widely used in caulking, wire insulation, and protective coatings (or potting compounds) for electronic circuitry. The best commercial material for these applications today are the silicone polymers particularly where moderately high temperatures are encountered. The scientists at the NASA Marshall Space Flight Center have been studying alternate materials to further extend the maximum use temperature. One approach that they have been pursuing is to incorporate metallic atoms into the chemical structure. This is an extension to what was done with the commercial silicones. From this research they have evolved a semiorganic polymer with the forbidding name silphenylene-siloxane. The molecular structure is shown (schematically) in the upper left panel of Figure 1 (RR71-3757). It can be noted that the central atomic chain contains a considerable number of the metallic silicon atoms. The properties of this material after 24 hours at 315° C are illustrated in the lower half of the figure. In each panel the NASA polymer is compared to the best commercial polymer that is available. It can be noted that the NASA polymer exceeds the commercial polymer in tensile strength and, as indicated by the low weight loss, has greater thermal stability.

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This is only one of several polymeric materials incorporating the silphenylene structure which are being synthesized and whose properties are being investigated. For example, a silphenylene containing fluorine is being investigated for use as sealants for aircraft fuel tanks. It is felt that research of this type must be continued to provide the long time reliable operation that is being demanded from both civil and military aircraft.

The current emphasis on the reliable and low cost operation of aircraft has resulted in an increased emphases on research and development programs concerned with the reliable prediction of service lives. It is imperative that, for example, the accuracy with which the fatigue life of materials and devices operating at or near room temperature can be predicted. Similarly, the stressrupture and creep life of materials and structures which operate at high temperatures, and the rate of corrosion and degradation of those materials and structures which operate in hostile environments must be accurately anticipated. The next example will illustrate some progress in this direction for elastomeric materials of the type that were discussed above.

Figure 2 demonstrates the progress that has been made in predicting the degradation in mechanical properties as the material undergoes attack by a hostile environment. The solid line at the top of the figure shows how the mechanical properties vary with time, if no attack occurs. The material suffers a nominal degradation at the beginning, but performs satisfactorily for the required service life. For some time now, this type of behavior could be predicted theoretically and the mathematical relationship by which this is done is given above the line.* In actual use however, such hostile environments as oxygen, heat, and radiation all have adverse effects. The shaded area in the figure and the modified equation at the bottom of the figure is one that has been recently developed at the Jet Propulsion Laboratory and includes degradation parameters. As indicated

*In the equations in Figure 2 (RW71-3808) M(t) represents the mechanical properties; Me is a softening parameter; av the cross linking between polymeric chains; t is time; and is a variable related to the creep rate.

by the equation below this area, two mechanisms of degradation are taken into account; one is "scission," or fracturing of the long polymeric chains resulting in shorter segments with a consequent loss in mechanical properties: the other is cross-linking which results in higher molecular weight chains of atoms but is accompanied by a loss in ductility and toughness. The current research is aimed at understanding and controlling these phenomena so as to maintain satisfactory mechanical properties throughout the required service life. This basic understanding should also result in the achievement of another important goal of materials research, that of predicting from short-time tests the long livesperhaps even measured in years-that can be expected from these materials.

In addition to exploring new materials, the materials research program is equally concerned with studying widely accepted and used materials to determine the limits of their applicability. One such material that is being extensively studied is the titanium alloy 8-1-1. This alloy is being used successfully in many of today's jet engines. However, there is some concern about its usefulness in future engines which will operate at higher temperatures. Because of this, the Lewis Research Center has undertaken a broad research program in which they hope to: (1) simulate in the laboratory the actual operating conditions of advanced engines in service so that alloys can be readily evaluated, and (2) study the mechanism leading to stress-corrosion cracking. As data about this alloy becomes available, clues should also be obtained to permit modifying the alloy to reduce its susceptibility to stress corrosion cracking.

The left half of the Figure 3 (RW 71-3812) is a schematic diagram of a facility in use at Lewis Research Center that can simulate the stress-temperaturechemical environment and velocity of air that titanium compressor vanes will experience in advanced jet engines. The right hand side of the figure shows some test results obtained with this apparatus-test results which point to promising research approaches. The results indicate that the alloy in a still air test (bottom line) is far more susceptible to stress corrosion than it is in the high velocity air stream in which it must operate (middle line) and that this difference in behavior is maintained over a wide temperature range. The top line in the figure