ALBERT

Description: The University of Kansas NASA/USRA Design Team worked on the design/evaluation of using 'family' concept in the case of a series of regional transport airplanes. Mission specifications for the four designs in the series are shown. Further design characteristics were specified as follows: (1) common cockpit instrumentation; (2) common structural and systems design (to as high a degree as possible); (3) jet-like ride quality and cabin environment; (4) identical handling qualities to allow for cross rating of pilots; and (5) low acquisition cost and low life-cycle costs

Description: The Advanced Aeronautics Design Program at The Ohio State University was to design a vehicle for hypersonic passenger flight across the Pacific Ocean. The specifications were as follows: (1) hypersonic flight; (2) range of 8000 nm; (3) passenger seating greater than 250; (4) operation from 15000 ft runways Mach number and altitude of operation were at the discretion of the design teams as were the propulsion system and type of fuel. The advanced aeronautics design sequence established specifically for this program consisted of a three quarter sequence as follows: Fall: ME 694 Senior Design Seminar - one quarter hour. Designers and specialists met one hour each week for ten weeks on relevant flight vehicle design topics. Winter: ME 515H Flight Vehicle Design - four quarter hours. Three design teams of six students each performed preliminary design studies of hypersonic configurations and potential propulsion systems. Each team's results were summarized in a final presentation to NASA Lewis Research Center personnel. The presentations resulted in the selection of the most promising design for additional development. Spring: AAE 516H Advanced Flight Vehicle Design - four quarter hrs. The class was reorganized to focus upon the specific design selected from the Winter configuration studies. Detailed analyses of thermal protection systems, costs, mission refinements, etc., completed the design task and final presentations were made to NASA Lewis Research Center staff.

Description: The Potential for V/STOL Aircraft Concepts for Air Transportation in the CALIFORNIA CORRIDOR in the 2010 time period is projected. The project description is to study the potential for V/STOL aircraft concepts in air transportation within the California Corridor, and emphasize V/STOL configurations that are innovative and unconventional in design for use in the 2010 time period. The project is consistent with the mission of the NASA/Ames Research Center and succeeding classes at Cal Poly can iterate and refine for meaningful results for NASA.

Description: A hypersonic transport aircraft design project was selected as a result of interactions with NASA Lewis Research Center personnel and fits the Presidential concept of the Orient Express. The Graduate Teaching Assistant (GTA) and an undergraduate student worked at the NASA Lewis Research Center during the 1986 summer conducting a literature survey, and relevant literature and useful software were collected. The computer software was implemented in the Computer Aided Design Laboratory of the Mechanical and Aerospace Engineering Department. In addition to the lectures by the three instructors, a series of guest lectures was conducted. The first of these lectures 'Anywhere in the World in Two Hours' was delivered by R. Luidens of NASA Lewis Center. In addition, videotaped copies of relevant seminars obtained from NASA Lewis were also featured. The first assignment was to individually research and develop the mission requirements and to discuss the findings with the class. The class in consultation with the instructors then developed a set of unified mission requirements. Then the class was divided into three design groups (1) Aerodynamics Group, (2) Propulsion Group, and (3) Structures and Thermal Analyses Group. The groups worked on their respective design areas and interacted with each other to finally come up with an integrated conceptual design. The three faculty members and the GTA acted as the resource persons for the three groups and aided in the integration of the individual group designs into the final design of a hypersonic aircraft.

Description: The design task for the Advanced Aeronautics Design Project at UCLA is to provide a design for a hypersonic trans-atmospheric vehicle capable of horizontal take-off and landing from conventional runways. To accomplish this task, students are developing unclassified, unrestricted generic hypersonic vehicle models. These models include aerodynamic, propulsive, and thermal effects. The models will be used in the 1987-1988 academic year for vehicle design emphasizing the use of trajectory studies to optimize the vehicle design. The design problem is being considered both in terms of conventional issues such as aerodynamics, propulsion, and thermal systems and also in terms of flight systems, flight controls, and flight testing. The goal of this program is to consider testing as an integral part of design.

Description: Transport fuselage section drop tests provided useful information about the crash behavior of metal aircraft in preparation for a full-scale Boeing 720 controlled impact demonstration (CID). The fuselage sections have also provided an operational test environment for the data acquisition system designed for the CID test, and data for analysis and correlation with the DYCAST nonlinear finite-element program. The correlation of the DYCAST section model predictions was quite good for the total fuselage crushing deflection (22 to 24 inches predicted versus 24 to 26 inches measured), floor deformation, and accelerations for the floor and fuselage. The DYCAST seat and occupant model was adequate to approximate dynamic loading to the floor, but a more sophisticated model would be required for good correlation with dummy accelerations. Although a full-section model using only finite elements for the subfloor was desirable, constraints of time and computer resources limited the finite-element subfloor model to a two-frame model. Results from the two-frame model indicate that DYCAST can provide excellent correlation with experimental crash behavior of fuselage structure with a minimum of empirical force-deflection data representing structure in the analytical model.

Description: The dynamic behavior of aircraft fuselage structures subject to various impact conditions was investigated. An analytical model was developed based on a self-consistent finite element (CFE) formulation utilizing shell, curved beam, and stringer type elements. Equations of motion were formulated and linearized (i.e., for small displacements), although material nonlinearity was retained to treat local plastic deformation. The equations were solved using the implicit Newmark-Beta method with a frontal solver routine. Stiffened aluminum fuselage models were also tested in free flight using the UTIAS pendulum crash test facility. Data were obtained on dynamic strains, g-loads, and transient deformations (using high speed photography in the latter case) during the impact process. Correlations between tests and predicted results are presented, together with computer graphics, based on the CFE model. These results include level and oblique angle impacts as well as the free-flight crash test. Comparisons with a hybrid, lumped mass finite element computer model demonstrate that the CFE formulation provides the test overall agreement with impact test data for comparable computing costs.

Description: The design task of high-speed passenger flight across the Pacific Ocean was addressed by four design teams of eight students each. Two teams examined hypersonic flight (Mach greater than 5) and two teams studied supersonic flight (Mach = 3). The specific task of the aircraft was to transport at least 250 passengers 6500 nautical miles while operating from airport runways of 15,000 feet. Four design concepts evolved; the supersonic designs--one a variable-sweep oblique wing and the other a cranked-arrow wing--use conventional turbine engines and liquid hydrocarbon fuels. The two hypersonic configurations, one with a variable-sweep wing and the other with a fixed, swept-wing planform, employ methane fueled, variable-cycle turbojet/ramjet propulsion systems. Both supersonic aircraft weigh less than 700,000 lbs at takeoff, while the variable-geometry hypersonic airplane is the heaviest at 1,100,000 lbs and weighs 170,000 lbs more than the fixed-wing hypersonic design. All the conceptual designs are shown to perform the transport mission, although development and operating cost estimates favor the supersonic designs over the hypersonic configurations.

Description: A study is presented on the planform effects of transport aircraft in the Mach 3 to 6 range. A request for proposal containing a baseline mission profile was common to four aircraft designs. These aircrafts were designed to perform the same mission in order to obtain conclusions regarding the performance of the aircraft. The four configurations include the blended-wing-body concept, jointed-wing concept, oblique-wing concept and the caret (waverider) concept. This paper presents the top-level performance trends common to the four configurations during high-speed flight. No conclusions are presented on the best planform as all the designs have positive and negative aspects. However, both the positive and negative features of the designs are identified.

Description: In 1986 NASA and USRA identified Cal Poly as one of seven 'Centers of Aircraft Design Education', and accepted a proposal from Cal Poly to conduct a three-year study of the potential for Lighter-Than-Air (LTA), Vertical Take-Off and Landing (VTOL), and Short Take-Off and landing (STOL) aircraft concepts for air transportation within the California corridor. The project emphasizes configurations that are both innovative and unconventional in design for use in the 2010 time period. The topic of LTA/VTOL/STOL aircraft was selected because it is consistent with the mission of the NASA Ames Research Center and is a broad topic that succeeding classes at Cal Poly can continue to iterate and refine to produce meaningful results for NASA. Along with studying the technical issues normally involved in any aircraft design problem, the topics of safety, noise, public acceptance, and economic viability in commercial operations are also addressed.

Description: Two high-speed civil transport (HSCT) design concepts are presented. Both transports are designed for a 5500-n.m. range with 300 passengers. The first design concept is a Mach 2.5, joined-wing, single-fuselage transport. The second design concept is a Mach-4.0, twin-fuselage, variable-sweep wing transport. The use of conventional hydrocarbon fuels is emphasized to reduce the amount of change required in current airport facilities. Advanced aluminums are used in the designs when possible to reduce material and production costs over more exotic materials. Methods to reduce airport noise, community noise, and fly-over noise are incorporated into the designs. In addition, requirements set forth by the Federal Aviation Regulations (FARs) have been addressed.

Description: As research continues in the development of an aircraft capable of travelling at hypersonic flight velocities, both the propulsion and thermal management systems stand out as areas requiring innovative technological breakthroughs. For propulsion, the difficulty involves efficiently compressing and combusting hydrogen in a supersonic stream, i.e., developing a viable scramjet with thermal management, the challenge lies in development of materials and active cooling systems capable of handling the enormous heat fluxes associated with hypersonic flight. This paper focuses on these problems and presents component designs for both an active cooling system and an all-external-compression scramjet. These systems are mated to a Mach-6 passenger cruise aircraft whose aerodynamic configuration was derived from an optimization of NASA windtunnel test results. The following outlines the development of the configuration and then focuses in on the design of the two component systems.

Description: UCLA's Advanced Aeronautic Design group focussed their efforts on design problems of an unmanned hypersonic vehicle. It is felt that a scaled hypersonic drone is necesary to bridge the gap between present theory on hypersonics and the future reality of the National Aerospace Plane (NASP) for two reasons: (1) to fulfill a need for experimental data in the hypersonic regime, and (2) to provide a testbed for the scramjet engine which is to be the primary mode of propulsion for the NASP. The group concentrated on three areas of great concern to NASP design: propulsion, thermal management, and flight systems. Problem solving in these areas was directed toward design of the drone with the idea that the same design techniques could be applied to the NASP. A 70 deg swept double-delta wing configuration, developed in the 70's at the NASA Langley, was chosen as the aerodynamic and geometric model for the drone. This vehicle would be air launched from a B-1 at Mach 0.8 and 48,000 feet, rocket boosted by two internal engines to Mach 10 and 100,000 feet, and allowed to cruise under power of the scramjet engine until burnout. It would then return to base for an unpowered landing. Preliminary energy calculations based on flight requirements give the drone a gross launch weight of 134,000 pounds and an overall length of 85 feet.

Description: The multiobjective programming techniques are important in the design of complex structural systems whose quality depends generally on a number of different and often conflicting objective functions which cannot be combined into a single design objective. The applicability of multiobjective optimization techniques is studied with reference to simple design problems. Specifically, the parameter optimization of a cantilever beam with a tip mass and a three-degree-of-freedom vabration isolation system and the trajectory optimization of a cantilever beam are considered. The solutions of these multicriteria design problems are attempted by using global criterion, utility function, game theory, goal programming, goal attainment, bounded objective function, and lexicographic methods. It has been observed that the game theory approach required the maximum computational effort, but it yielded better optimum solutions with proper balance of the various objective functions in all the cases.

Description: There are a number of helicopter design problems that are well suited to applications of numerical design optimization techniques. Adequate implementation of this technology will provide high pay-offs. There are a number of numerical optimization programs available, and there are many excellent response/performance analysis programs developed or being developed. But integration of these programs in a form that is usable in the design phase should be recognized as important. It is also necessary to attract the attention of engineers engaged in the development of analysis capabilities and to make them aware that analysis capabilities are much more powerful if integrated into design oriented codes. Frequently, the shortcoming of analysis capabilities are revealed by coupling them with an optimization code. Most of the published work has addressed problems in preliminary system design, rotor system/blade design or airframe design. Very few published results were found in acoustics, aerodynamics and control system design. Currently major efforts are focused on vibration reduction, and aerodynamics/acoustics applications appear to be growing fast. The development of a computer program system to integrate the multiple disciplines required in helicopter design with numerical optimization technique is needed. Activities in Britain, Germany and Poland are identified, but no published results from France, Italy, the USSR or Japan were found.

Description: An optimization study was performed to develop a minimum weight spreader bar to allow two helicopters to lift the same payload. With this arrangement, the maximum payload that can be lifted is almost doubled without the expense of designing and building a new helicopter. The concept has had some limited use by civil helicopter operators using small helicopters and has been demonstrated in large scale by two CH-54's which successfully lifted a total load of 20 ton. To this point, rather heavy available beams or tower structures have been used for the spreader bar. Since the weight of the bar not only detracts from payload but also adds to the logistics problem, there are more than the usual incentives to minimize weight. Since the design requirement is for classic beam column with uniform side loads resulting from bar weight and aerodynamic drag, the design problem is particularly amenable to optimization. A study has been performed at Sikorsky to establish the minimum weight for a spreader bar sized to carry a load equal to the capacity of two Army BLACK HAWK helicopters. Toward this end, a computer program was written to analyze the spreader bar deflections and stresses and coupled to the NASA developed CONMIN optimization routines.

Description: The optimization approach discussed is part of an ongoing effort to develop a general automated procedure for rotor blade design. This procedure can be used to determine the necessary geometric, structural, and material properties of a rotor system to achieve desired objectives relating to vibration, stress, and aerodynamic performance. The approach used for helicopter vibration is emphasized. Based on analytical studies performed at the United Technologies Research Center (UTRC), a simplified vibration analysis was developed to be used in conjunction with a forced response analysis in the optimization process. This simplified analysis improves the efficiency of the design process significantly. Results of applying this approach to the design of an existing rotor blade model are presented.

Description: This discussion summarizes the effort conducted by the BHTI Human Factors and Cockpit Arrangement group for a study and design of the integration of a cockpit control system for the AH 1T (TOW). The resulting design is a culmination of studies that were conducted using the existing configuration as a baseline and complementing it with new equipment and subsystems that fulfill the attack helicopter requirements for the foreseeable future. Of primary concern was the requirement to add a missile control system, with secondary considerations for improved NOE and night operations. In addition, growth capabilities for improved target acquisition, weapons delivery, and precise navigation was considered. Along with the addition of new equipment, the aircraft was assumed to have a central multiplex data bus system for information transfer throughout the aircraft and its subsystems.

Description: Nine research areas that are most critical to the issue of cockpits for the single pilot are discussed. Helicopter are addressed in this report. They are as follows: (1) automation priority issues; (2) increased complexity of systems; (3) cockpit workload highest in navigation; (4) auto hover and flight trim controls; (5) voice technology in integrated form; (6) systems must have visual and auditory declutter modes; (7) cockpit should be designed to be NBC resistant; and (8) considerations for spillover to civilian public service.

Description: Fundamental development issues, system requirements and improvements are reported for the HH-60D night hawk helicopter. The HH-60D mission requirements are for combat search and rescue (aerospace rescue and recovery service user based at Scott AFB) and special operations (special operations forces based at Hurlburt AFB). Cockpit design, computer architecture and software are described in detail.

Description: As a part of the EET aerodynamics program an out-of-house program was developed and monitored to provide theoretical procedures useful in the design of transport aircraft. The focus of the effort was to provide tools valid in the nonlinear transonic speed range. The effort was divided into two basic areas, inviscid configuration analysis and design procedures and viscous correction procedures.

Description: Improvements in cruise efficiency on the order of 15 to 40% are obtained by increasing the extent of laminar flow over lifting surfaces. Two methods of achieving laminar flow are being considered, natural laminar flow and laminar flow control. Natural laminar flow (NLF) relies primarily on airfoil shape while laminar flow control involves boundary layer suction or blowing with mechanical devices. The extent of natural laminar flow that could be achieved with consistency in a real flight environment at chord Reynolds numbers in the range of 30 x 10(6) power was evaluated. Nineteen flights were conducted on the F-111 TACT airplane having a NLF airfoil glove section. The section consists of a supercritical airfoil providing favorable pressure gradients over extensive portions of the upper and lower surfaces of the wing. Boundary layer measurements were obtained over a range of wing leading edge sweep angles at Mach numbers from 0.80 to 0.85. Data were obtained for natural transition and for a range of forced transition locations over the test airfoil.

Description: An analytical study was performed in order to assess relative performance and economic factors involved with alternative advanced fuel systems for future commercial aircraft operating with broad property fuels. Significant results, with emphasis on design practicality from the engine manufacturer' standpoint, are highlighted. Several advanced fuel systems were modeled to determine as accurately as possible the relative merits of each system from the standpoint of compatibility with broad property fuel. Freezing point, thermal stability, and lubricity were key property issues. A computer model was formulated to determine the investment incentive for each system. Results are given.

Description: Several problems related to the aeroelastic/aerodynamic optimization of a high speed helicopter compound rotor are discussed. The helicopter fuselage vibration problem, the effects of fuselage vibrations, the source of external and periodic air loads, typical airfoil environments and configurations, rotor dynamics, vibration reduction, and requirements for the rotor design optimization analysis are among the topics covered.

Description: Formal mathematical programing was applied to the aerodynamic rotor blade design process. The approach is to couple hover and forward flight analysis programs with the general-purpose optimization program CONMIN to determine the blade taper ratio, percent taper, twist distribution, and solidity which minimize the horsepower required at hover while meeting constraints on forward flight performance. Designs obtained using this approach for the blade of a representative Army helicopter compare well with those obtained using a conventional approach involving personnel-intensive parametric studies. Results from the present method can be obtained in 2 days as compared to 5 weeks required by the conventional procedure. Also the systematic manipulation of the design variables by the optimization procedure minimizes the need for the researcher to have a vast body of past experience and data in determining the influence of a design change on the performance.

Description: The main Army Helicopter Improvement Program (AHIP) mission is to navigate precisely, locate targets accurately, communicate their position to other battlefield elements, and to designate them for laser guided weapons. The onboard navigation and mast-mounted sight (MMS) avionics enable accurate tracking of current aircraft position and subsequent target location. The AHIP crewstation development was based on extensive mission/task analysis, function allocation, total system design, and test and verification. The avionics requirements to meet the mission was limited by the existing aircraft structural and performance characteristics and resultant space, weight, and power restrictions. These limitations and night operations requirement led to the use of night vision goggles. The combination of these requirements and limitations dictated an integrated control/display approach using multifunction displays and controls.

Description: A summary on heavy rain effects on aircraft aerodynamics validation of research and some wind shear accidents in which heavy rain were an important factor. Frost formation and what frost does to the lift and drag curves for an airfoil was examined. If frost could cause severe aerodynamic problems for both general aviation and transport aircraft due to its roughness, then heavy rain produce a similar result. The influencing parameters of heavy rain on an aircraft are studied. Sources of aerodynamic roughness due to rain and wind shear and heavy rain accidents are outlined.

Description: Meteorology impact on future aircraft design is discussed. Upcoming changes in both design and operations that will be influenced by the meteorological environment are outlined. Future and more nonconventional designs and meteorological impact brought about by operational changes over the next few years are examined.

Description: The connection between fuel consumption and weather data is discussed. Fuel efficient flights creating adequate near real time weather information are examined. The lack of highly resolved real time and near real time wind and temperature data at flight altitudes is investigated. The existing systems, which is based on twice a day balloon observations, supplemented by pilot reports or other occasional data, is not adequate for optimum flight planning. The impacts of upper winds and temperatures on fuel efficiency and flight planning are not widely appreciated and developing new weather products are considered.

Description: The interactions between the design and operation of aircraft fuel systems and the properties of alternative aircraft fuels are discussed. An overview of fuels system research and technology in terms of its rationale, its progress, and future plans is given. The measurement of ambient air temperatures for a wide range of seasonal and geographic variations, design studies on the use of fuels with increased as well as conventional freezing temperatures, the evaluation of fuel heating systems, and the low temperature behavior of fuels are among the topics discussed.

Description: Several examples of spacecraft systems fires are examined. Much of the design, manufacture, inspection, test, and operation of current high pressure oxygen components and systems has been driven by weight, cost, functional, and schedule requirements. As a result, little coordination has been expended on design for safe operation. While the number of oxygen related fires has not been large, their cost, including program losses and delays, has been very large. Most of these failures need not have occurred.

Description: The results of a study assessing the impact of using jet fuel with relaxed specification properties on an aircraft fuel system are given. The study objectives were to identify credible values for specific fuel properties which might be relaxed, to evolve advanced fuel system designs for airframe and engines which would permit use of the specified relaxed properties fuels, and to evaluate performance of the candidate advanced fuel systems and the relaxed property fuels in a typical transport aircraft. The study used, as a baseline, the fuel system incorporated in the Lockheed Tristar. This aircraft is powered by three RB.211-524 Rolls-Royce engines and incorporates a Pratt and Whitney ST6C-421 auxiliary power unit for engine starting and inflight emergency electrical power. The fuel property limits examined are compared with commercial Jet A kerosene and the NASA RFP fuel properties. A screening of these properties established that a higher freezing point and a lower thermal stability would impact fuel system design more significantly than any of the other property changes. Three candidate fuel systems which combine the ability to operate with fuels having both a high freeze point and a low thermal stability are described. All candidates employ bleed air to melt fuel freeze-out prior to starting the APU or an inoperable engine. The effects of incorporating these systems on aircraft weight and engine specific fuel consumption are given.

Description: Based on initial results obtained from the performance optimization code, a number of observations can be made regarding the utility of optimization codes in supporting design of rotors for improved performance. (1) The primary objective of improving the productivity and responsiveness of current design methods can be met. (2) The use of optimization allows the designer to consider a wider range of design variables in a greatly compressed time period. (3) Optimization requires the user to carefully define his problem to avoid unproductive use of computer resources. (4) Optimization will increase the burden on the analyst to validate designs and to improve the accuracy of analysis methods. (5) Direct calculation of finite difference derivatives by the optimizer was not prohibitive for this application but was expensive. Approximate analysis in some form would be considered to improve program response time. (6) Program developement is not complete and will continue to evolve to integrate new analysis methods, design problems, and alternate optimizer options.

Description: AAE 451 is the capstone course required of all senior undergraduates in the School of Aeronautics and Astronautics at Purdue University. During the past year the first steps of a long evolutionary process were taken to change the content and expectations of this course. These changes are the result of the availability of advanced computational capabilities and sophisticated electronic media availability at Purdue. This presentation will describe both the long range objectives and this year's experience using the High Speed Commercial Transport (HSCT) design, the AIAA Long Duration Aircraft design and a Remotely Piloted Vehicle (RPV) design proposal as project objectives. The central goal of these efforts was to provide a user-friendly, computer-software-based, environment to supplement traditional design course methodology. The Purdue University Computer Center (PUCC), the Engineering Computer Network (ECN), and stand-alone PC's were used for this development. This year's accomplishments centered primarily on aerodynamics software obtained from the NASA Langley Research Center and its integration into the classroom. Word processor capability for oral and written work and computer graphics were also blended into the course. A total of 10 HSCT designs were generated, ranging from twin-fuselage and forward-swept wing aircraft, to the more traditional delta and double-delta wing aircraft. Four Long Duration Aircraft designs were submitted, together with one RPV design tailored for photographic surveillance. Supporting these activities were three video satellite lectures beamed from NASA/Langley to Purdue. These lectures covered diverse areas such as an overview of HSCT design, supersonic-aircraft stability and control, and optimization of aircraft performance. Plans for next year's effort will be reviewed, including dedicated computer workstation utilization, remote satellite lectures, and university/industrial cooperative efforts.

Description: NASA and the USAF have conducted a program to investigate aircraft performance improvements utilizing a mission adaptive wing (MAW). The MAW was designed and developed for the AFTI/F-111 variable-sweep aircraft to provide a hydraulically driven, smooth, and continuous variable camber of the trailing and leading edges as a function of maneuvering requirements or of flight conditions. The remotely augmented vehicle facility (RAV) at the NASA DFRF, as utilized in the MAW investigations, is described. The RAV was a dedicated, ground based, general purpose facility capable of receiving a data stream downlinked from a test vehicle, processing this data stream in a digital computer, and transmitting processed data back to the test vehicle. It is shown that this method of flight testing provides a technique that can evaluate highly dynamic maneuvers.

Description: The validity of the room equation of Crocker and Price (1982) for predicting the cabin interior sound pressure level was experimentally tested using a specially constructed setup for simultaneous measurements of transmitted sound intensity and interior sound pressure levels. Using measured values of the reverberation time and transmitted intensities, the equation was used to predict the space-averaged interior sound pressure level for three different fuselage conditions. The general agreement between the room equation and experimental test data is considered good enough for this equation to be used for preliminary design studies.

Description: The paper discusses the development and ground testing of blades for the XV-15 tilt-rotor demonstrator aircraft. This work was performed under contract NAS2-11250 with NASA Ames Research Center. These blades, known as the Advanced Technology Blades (ATB), replace the rectangular, steel blades which were part of the XV-15 original design. The materials used in the primary structure of the ATB are fiberglass and high strain graphite epoxy laminates. This facilitates the use of 43 deg of nonlinear twist, a nonuniform tapered planform and thin airfoils required for aerodynamic efficiency. Instrumentation life is extended by encapsulating gages and wiring in the composite structure. Tip shells and cuff fairings are removable to provide access to tip weights and retention hardware; they are also replaceable with alternate research configurations. Extensive laboratory testing has validated predicted strength characteristics. Hover testing has demonstrated performance significantly superior to that predicted by contemporary methodology. Key elements of the test rig used for rotor performance measurement were developed as an ancillary part of the present program. The performance testing included measurement of near- and far-field noise. Induced inflow velocity distributions were also determined and photographs of tip vortex condensation trails were taken. These are providing guidance for modifications to hover peformance codes.

Description: During the 1985 thunderstorm season, three joint thunderstorm research flights were conducted within 100 n.mi. of NASA Langley by the NASA Storm Hazards F-106B and the FAA/USAF CV-580 research airplanes with ground-based weather radar measurements by NASA Wallops. This paper discusses the thunderstorm penetration capabilities of each airplane and the techniques used to safely place the two airplanes into the same thunderstorm cell for collection of correlated EM data. It is concluded that joint thunderstorm research operations of two aircraft with significantly dissimilar thunderstorm penetration capabilities are counterproductive to both airplanes.

Description: Four topics in landing gear dynamics are discussed. Three of these topics are subjects of recent research: tilt steering phenomenon, water spray ingestion on flooded runways, and actively controlled landing gear. The fourth topic is a description of a major facility recently enhanced in capability.

Description: Problems in using two-microphone sound-intensity (SI) measurements to measure structural transmission losses are investigated in experiments involving light-aircraft fuselage panels and windows. Both sound pressure (SP) and SI are measured near the passenger and door windows and panels of a single-engine aircraft and with these barriers removed, and the effect of increasing interior acoustic absorption and blocking flanking transmission paths is also tested. The results are presented graphically, and the SP measurements are used to indicate frequency ranges in which the two-microphone technique significantly underestimates SI. It is inferred that flanking paths and interior reverberation must be effectively suppressed in order to obtain accurate transmission-loss measurements.

Description: The analytical basis and the application of a Rotor/Airframe Comprehensive Aeroelastic Program (RACAP) are described in detail. The rationale behind each analytical choice is outlined and the modular procedure is described. The program is verified by application to the AH-1G helicopter. The applicability of various airload prediction models is examined, and both the steady and vibratory responses of the blade are compared with flight test data. Reasonable correlation is found between measured and calculated blade response, with excellent correlation for vibration amplitudes at various locations on the fuselage such as engine, pilot seat, and gunner. Within the analytical model, comparisons are drawn between an isolated blade analysis and a coupled rotor/fuselage model. The deficiency of the former in the context of the AH-1G is highlighted.

Description: Over the past several years the NASA Ames-Dryden Flight Research Facility at Edwards Air Force Base has developed a variety of flight flutter and ground test techniques which have been applied to an assortment of new or modified aerospace research vehicles. This paper presents a summary of these techniques and the experiences gained from these applications. Topics discussed include the roles of ground vibration testing, flight flutter testing, wind tunnel flutter model testing, predictive analyses, and aeroservoelastic considerations. Data are presented for a wide variety of aircraft, including remotely piloted vehicles, modern fighters with relaxed static stability and highly augmented flight control systems, aircraft modified for laminar flow control experiments, a glider modified for deep stall tests, and aircraft with skewed or forward swept wings. The conclusions include a brief discussion of future directions in flight flutter testing at Ames-Dryden.

Description: Attention is given to the ground proximity effects of a powered lift STOL aircraft, NASA's Quiet Short Haul Research Aircraft (QSRA); these effects have a profound influence on a landing's touchdown dispersion and sink rates, and must be determined with the greatest possible accuracy. The QSRA flight parameter values obtained by means of a small perturbation model for the trim flight condition out of ground effect, during a landing approach, are compared with flight test values, on the premise that any discrepancies between the two sets of values will be due to ground effect.

Description: A controlled impact demonstration (CID) program using a large, four engine, remotely piloted transport airplane was conducted. Closed loop primary flight control was performed from a ground based cockpit and digital computer in conjunction with an up/down telemetry link. Uplink commands were received aboard the airplane and transferred through uplink interface systems to a highly modified Bendix PB-20D autopilot. Both proportional and discrete commands were generated by the ground pilot. Prior to flight tests, extensive simulation was conducted during the development of ground based digital control laws. The control laws included primary control, secondary control, and racetrack and final approach guidance. Extensive ground checks were performed on all remotely piloted systems. However, manned flight tests were the primary method of verification and validation of control law concepts developed from simulation. The design development, and flight testing of control laws and the systems required to accomplish the remotely piloted mission are discussed.

Description: The purpose of Monte Carlo turbulence simulation is to add statistically accurate 'bumps' to aerospace vehicle flight simulation. Several recent improvements in the state of the art are reviewed and classified according to various characteristics affecting the realism of the simulation. Areas for future research are made clear by the classification scheme.

Description: The XV-15 Tilt-Rotor flight research program is described; it has resulted in the full-scale development of the Navy's MV-22A Osprey which will be the world's first operational tilt rotor aircraft. Proof-of-concept flight test objectives have been completed along with military service tests and demonstrations. NASA Ames and Bell Helicopter Textron are currently engaged in advanced flight research programs. The government flight test activity is dicussed. It includes hover tests both in ground effect (IGE) and out of ground effect (OGE) for performance, downwash and noise measurements, short-field takeoff and landing (STOL) evaluations, aeroelastic stability investigations, dynamic stability tests, and three-axis sidestick-controller development and evaluation. Advanced Technology Blades will be installed and evaluated under all flight conditions.

Description: It is announced that the X-29 forward-swept-wing (FSW) aircraft has been built, with flight testing under way and proceeding smoothly. The X-29 is a single-seat, single-engine supersonic aircraft that blends an optimized FSW, a close-coupled near-coplar canard, an F-5A forward fuselage module employing two side-mounted engine inlets, and a new aft fuselage. An F404-GE-400 engine with afterburner provides about 16,000 lb of thrust. The X-29 was designed to be near neutrally stable in the supersonic region to minimize drag; it becomes highly unstable transonically and subsonically, which dictates the use of a computerized fly-by-wire flight control system capable of stabilizing the aircraft. The X-29 advanced technology demonstrator began flight testing on Dec. 14, 1984; by Sept. 26, 1985, its envelope had been expanded to 0.75 Mach, 350 knots estimated airspeed, and 30,000 feet altitude. The aircraft has flown with very few problems and aerodynamic, structural, and control system results have correlated well with predictions. Areas where prediction and performance are not so well correlated are noted.

Description: The problems that were encountered in the dynamics of advanced rotor systems are described. The methods for analyzing these problems are discussed, as are past solutions of the problems. To begin, the basic dynamic problems of rotors are discussed: aeroelastic stability, rotor and airframe loads, and aircraft vibration. Next, advanced topics that are the subject of current research are described: vibration control, dynamic upflow, finite element analyses, and composite materials. Finally, the dynamics of various rotorcraft configurations are considered: hingeless rotors, bearingless rotors, rotors with circulation control, coupled rotor/engine dynamics, articulated rotors, and tilting proprotor aircraft.

Description: A testing status report is presented for the X-29 forward-swept-wing experimental aircraft, which integrates such advanced technologies as an aeroelastically tailored composite wing, a thin supercritical airfoil, three-surface pitch control, discrete variable camber, full-authority close-coupled canards, static instability, and digital fly-by-wire flight controls. X-29 flight test results to date raise several issues pertinent to the design of future combat aircraft flight control systems; for example, they bring into question the current MIL-8785C requirements on control system time delays.

Description: Current research on vertical- or short-takeoff-and-landing (V/STOL) aircraft is concentrating on developing a multirole-capable fighter. Several V/STOL concepts being studied show a capability performing for short-takeoff and vertical-landing (STOVL) missions. This paper is concerned with a propulsion concept which promises added flexibility in mission performance: the hybrid-tandem fan. This propulsion concept is combined with four aircraft planforms and the performance of each is evaluated on a representative mission. The four aircraft planforms used in the study are a conventional wing-tail, a forward-swept wing and canard, a delta-wing and canard, and an oblique wing and tail. The mission was chosen so that the four aircraft all had approximately the same gross takeoff weight. The four designs are compared at various phases of the mission.

Description: Experimental data were obtained for the deicing characteristics of a stationary UH-1H helicopter blade which had been fitted with an electrothermal deicer assembly. The tests were run in the NASA Lewis Icing Research Tunnel, and yielded transient temperature responses for the substrate, heater and abrasion shield at selected positions around the blade. The data at the abrasion shield-ice interface clearly documented when melting, shedding or refreezing occurred. Comparisons were made between the experimental data and a one-dimensional numerical model. The agreement was generally very good, with the simulations being shown to be capable of predicting the transient temperature responses along with phase change and ice shedding. At many blade positions, the model was capable of accurately simulating the thermal response of the electrothermal deicer assembly.

Description: The total rotor isolation system (TRIS) is a six-degree-of-freedom helicopter rotor vibration isolation system that has been installed on a 206LM helicopter in order to demonstrate a better-than-90-percent isolation of the fuselage from main rotor forces and moments. The results thus far obtained indicate a 95-percent suppression of vibration levels from the rotor hub to the pilot's seat, with considerable weight savings over traditional antiresonant isolation concepts.

Description: The General Rotorcraft Aeromechanical Stability Program (GRASP), which is a hybrid between finite element programs and spacecraft-oriented multibody programs, is described in terms of its design and capabilities. Numerical results from GRASP are presented and compared with the results from an existing, special-purpose coupled rotor/body aeromechanical stability program and with experimental data of Dowell and Traybar (1975 and 1977) for large deflections of an end-loaded cantilevered beam. The agreement is excellent in both cases.

Description: This study considers the modification of existing aircraft to the folding tilt rotor (FTR) design configuration, and then addresses the vehicle design requirements necessary to demonstrate the FTR concept throughout the hover/transition high-speed envelope. Three potential candidates are considered: (1) the Bell/Boeing V-22 Osprey combined with either the existing TF-34 convertible engine or a conceptual convertible engine utilizing the torque-converter-coupled fan configuration; (2) a combination of the same powerplants with a modified Lockheed S-3A Viking; and (3) the NASA/Army/BELL XV-15 airframe mated with a conceptual generic turbofan engine with a fixed-pitch fan coupled to the engine by means of a torque converter. Required aircraft modifications are identified and recommended R&D efforts for engine/rotor/airframe integration are presented.

Description: The CH-47B variable-stability helicopter was used to evaluate a range of height-response configurations while performing a precision hover bob-up task. The purpose of the study was to assess the validity of results obtained in previous ground-based and in-flight simulations in the context of a precision bob-up task and to provide additional flight data for inclusion in revisions to specifications for helicopter handling qualities. Height response characteristics were implemented using explicit model-following techniques, and the resulting CH-47B dynamics were validated using time-domain and frequency-domain data-analysis methods. The tests complemented the previous investigations by providing detailed pilot comments and ratings, and performance and control-utilization data that relate exclusively to the hover bob-up task. The results are compared with those from previous investigations and with new criteria that have been proposed for handling qualities requirements for helicopters.

Description: Numerical optimization techniques are used to modify the dynamic response at a specified point(s) of a helicopter airframe structure due to a steady state narrow band excitation. Calculation of steady state vibration amplitude is reduced to the solution of linear equations with complex coefficients. The sensitivity of the dynamic amplitudes with respect to the structural parameter perturbations can be computed with the same technique as the one used in the static displacement sensitivity without requiring eigenvector sensitivity. Approximate models for critical structural responses are created based on the sensitivity data to reduce the amount of computational effort and to enable the design of structures of practical scale and complexity. This approach is general in that it accommodates static, dynamic, and frequency constraints simultaneously as long as their computational models are available. It can be used in optimizing mass distribution as well as stiffness modifications of practical structures.

Description: Acoustic near field data were collected with model single and twin jet nozzles to determine if closely spaced nozzles produce higher acoustic loading than do single nozzles. The tests were spurred by structural failure of the B-1 exhaust nozzle external flaps and similar damage on the F-15. The test was performed using two 5/8 in. ID pipes machined and placed side-by-side to mimic B-1 nozzles. A microphone mounted on the internozzle fairing measured acoustic levels near the nozzle exit plane. The nozzles oscillated significantly more than did a single nozzle over a wide range of nozzle pressure ratios. Acoustic levels in the dual jets exceeded single jet noise by as much as 20 dB, making acoustic resonance a definite candidate for structural damage in the twin jet configuration.

Description: Advanced flight management systems are being developed which are capable of calculating optimal 3-D and 4-D flight trajectories for arbitrary fuel and time costs. These systems require mathematical models of airplane performance in order to compute the optimal profiles. Mismodeled idle engine characteristics can result in descent trajectories requiring excessive throttle and/or speedbrake activity in order to achieve the desired end conditions. This paper evaluates the cost and fuel penalties, trajectory variations, and flight control requirements associated with typical idle engine modeling errors for a twin-jet transport airplane. Variations in idle power setting, thrust, fuel flow, and surge bleed operation were evaluated for a cruise/descent flight segment. The results of this analysis provide insight into the penalties associated with uncertainties in idle engine performance and suggest methods of modeling which minimize these penalties.

Description: Data on 637 direct lightning strikes and 117 close flashes observed by the NASA instrumented F-106B aircraft as part of the Storm Hazards Program at NASA Langley during 1980-1984 are compiled and analyzed, updating the report of Fisher and Plumer (1983). The airborne and ground-based measurement and recording apparatus and the flight and data-reduction procedures are described, and the results are discussed in terms of lightning-strike-conducive flight conditions and lightning attachment patterns. A peak strike rate of 2.1/min is found at altitude 38,000-40,000 ft and temperature below -40 C, with very few strikes below 20,000 ft. Four categories of swept-flash attachment pattern are identified, but it is pointed out that all exterior surfaces of the F-106B are potential attachment sites.

Description: The Rotor Systems Research Aircraft (RSRA) was flown in the airplane configuration. Eleven successful flights were made from May 8 to October 3, 1984. The takeoff and landing method was demonstrated and the resultant parameters were obtained. Control power data were obtained. In addition, main rotor hub drag, airplane configuration acoustics data, and aircraft stability data were obtained. Hub drag, acoustics, and stability will be separately reported in more detail. The tail rotor was installed for all tests.

Description: This paper presents an application of multiple stepwise regression to the flight test data of a typical transport airplane. The flight test data was carefully preprocessed to eliminate aliasing, time skews and high frequency noise. The data consisted both of basic certification maneuvers, such as wind-up-turns and maneuvers suitable for parameter estimation, such as responses to elevator pulses and doublets. It is shown that the results of multiple stepwise regression techniques compare favorably with the results obtained from maximum likelihood estimation. Finally, it is concluded that multiple stepwise regression could be a fast economical way to estimate transport airplane aerodynamics.

Description: Performance of a 27-percent scale model of an advanced rotor designed for the AH-64 helicopter was measured in hover and at forward speeds of 50 to 130 knots. A baseline rotor, modeled after the current AH-64 rotor, was also tested to provide data for comparison. The investigation was conducted to validate procedures used at Langley to design rotors with increased performance potential and to provide a database for evaluation of current and future rotor systems. Both rotors were operated at full-scale tip speeds. Rotor thrust, forward speed, and ground height were varied for each rotor.

Description: Frequency-domain methods are used to extract the open-loop dynamics of the XV-14 tilt-rotor aircraft from flight test data for the cruise condition (V = 170 knots). The frequency responses are numerically fitted with transfer-function forms to identify equivalent model characteristics. The associated handling quality parameters meet or exceed Level 2, Category A, requirements for fixed-wing military aircraft. Step response matching is used to verify the time-domain fidelity of the transfer-function models for the cruise and hover flight conditions. The transient responses of the model and aircraft are in close agreement in all cases, except for the normal acceleration response to elevator deflection in cruise. This discrepancy is probably due to the unmodeled rotor rpm dynamics. The utility of the frequency-domain approach for dynamics identification and analysis is clearly demonstrated.

Description: A program for predicting the sound levels inside propeller driven aircraft arising from sidewall transmission of airborne exterior noise is validated through comparisons of predictions with both scale-model test results and measurements obtained in flight tests on a turboprop aircraft. The program produced unbiased predictions for the case of the scale-model tests, with a standard deviation of errors of about 4 dB. For the case of the flight tests, the predictions revealed a bias of 2.62-4.28 dB (depending upon whether or not the data for the fourth harmonic were included) and the standard deviation of the errors ranged between 2.43 and 4.12 dB. The analytical model is shown to be capable of taking changes in the flight environment into account.

Description: The Rotorcraft Dynamics Analysis was used to predict the aeroelastic responses of a representative X-Wing model with a 10-ft diameter rotor. The aeroelastic methodology used and the tests and assumptions involved are reviewed. Results are reported on the findings concerning control power and higher harmonic control in hover, transition flight, vibratory loads at forward speed, and responses in conversion. It is concluded that the analysis can give satisfactory predictions of X-Wing behavior.

Description: The weight of a hypersonic, airbreathing SSTO vehicle may be more critical than for any previous aerospacecraft; an evaluation is accordingly made of the development status and applicability of intermetallic compounds, metal-matrix composites, carbon-carbon composites, ceramics, and ceramic-matrix composites applicable to SSTO craft primary structures. Aerothermal, aerothermoelastic, and acoustic loads are high because the airbreathing SSTO vehicle must follow a high dynamic pressure trajectory in order to achieve the requisite propulsive efficiency. Attention is given to the prospects for integral cryogenic tankage and actively hydrogen-cooled airframe and engine structures.

Description: Experimental tests conducted on the fuselage of a single-engine Piper Cherokee light aircraft suggest that the cabin interior noise can be reduced by increasing the transmission loss of the dominant sound transmission paths and/or by increasing the cabin interior sound absorption. The validity of using a simple room equation model to predict the cabin interior sound-pressure level for different fuselage and exterior sound field conditions is also presented. The room equation model is based on the sound power flow balance for the cabin space and utilizes the measured transmitted sound intensity data. The room equation model predictions were considered good enough to be used for preliminary acoustical design studies.

Description: With the completion of the F-111 test-bed Mission Adaptive Wing (MAW) test program's manual flight control system, emphasis has been shifted to flight testing of MAW automatic control modes. These encompass (1) cruise camber control, (2) maneuver camber control, (3) maneuver load control, and (4) maneuver enhancement and load alleviation control. The aircraft is currently cleared to a 2.5-g maneuvering limit due to generally higher variable-incidence wing pivot loads than had been anticipated, especially at the higher wing-camber settings. Buffet is noted to be somewhat higher than expected at the higher camber settings.

Description: Performance projections into the next half-century of VTOL aircraft design are presently made on the basis of recent design trends. Attention is given to the technology-development and commercial prospects for tilt-rotor, thrust-vectoring hover, lighter-than-air, and speculative electromagnetic-propulsion, remotely-beamed power systems. Highly automated air traffic control systems are envisioned which will incorporate AI, satellite positioning, synthetic vision, obstacle detection/avoidance and fiber-optic transmission to safely manage giant airborne mass-transit commuter systems. It is expected that tilt-rotor aircraft will become the dominant VTOL configuration as time passes.

Description: The feasibility of operating tilting proprotor aircraft at high speeds is examined by calculating the performance, stability, and maneuverability of representative configurations. The rotor performance is examined in high speed cruise and in hover. The whirl flutter stability of the coupled wing and rotor motion is calculated in cruise. Maneuverability is examined in terms of the rotor thrust limit during turns in helicopter configuration. Rotor airfoils, rotor hub configuration, wing airfoil, and airframe structural weights representative of demonstrated advanced technology are considered. Key rotor and airframe parameters are optimized for high speed performance and stability. The basic aircraft design parameters are optimized for minimum gross weight. To provide a focus for the calculations, two high speed tiltrotor aircraft are considered: a 46-passenger civil transport and an air-combat/escort fighter, both with design speeds of about 400 knots. It is concluded that such high speed tiltrotor aircraft are quite practical.

Description: Two analytical procedures are discussed that are currently used to couple rotor and body equations. The first approach, a 'rotor-body iteration' procedure, is often used in flight dynamics simulations. In this approach, acceleration response at the hub interface between the rotor and body are calculated from the body set of equations. These hub acceleration responses are substituted into the rotor set of equations and the remaining rotor acceleration responses are calculated. These rotor responses are used to calculate the rotor hub loads which are transferred back to the body equations to initiate the next iteration. The second method is a 'fully coupled' equations approach that is used in finite element-based analyses. The body and rotor sets of equations are coupled using a kinematic constraint relation at the hub interface. This paper compares the advantages of the two approaches and shows where convergence problems occur in the rotor-body iteration procedure.

Description: A coupling method for efficient vibration mode analysis of aircraft with multiple external store configurations is presented. A set of low-frequency vibration modes, including rigid-body modes, represent the aircraft. Each external store is represented by its vibration modes with clamped boundary conditions, and by its rigid-body inertial properties. The aircraft modes are obtained from a finite-element model loaded by dummy rigid external stores with fictitious masses. The coupling procedure unloads the dummy stores and loads the actual stores instead. The analytical development is presented, the effects of the fictitious mass magnitudes are discussed, and a numerical example is given for a combat aircraft with external wing stores. Comparison with vibration modes obtained by a direct (full-size) eigensolution shows very accurate coupling results. Once the aircraft and stores data bases are constructed, the computer time for analyzing any external store configuration is two to three orders of magnitude less than that of a direct solution.

Description: The application of an experimental flight test maneuver autopilot test technique for collecting aerodynamic and structural flight research data on a highly maneuverable aircraft is described in this paper. This technique, which was developed to increase the quality and quantity of data obtained during flight test, was applied to the highly maneuverable aircraft technology (HiMAT) vehicle. A primary flight experiment was to verify the design techniques used to develop the HiMAT aerodynamics and structures. This required the performance of maneuvers for collection of large quantities of high-quality pressure distribution, loads, and wing and canard deflection data. Flight data obtained while executing these research maneuvers are presented to demonstrate the effectiveness of this new technique.

Description: Rotorcraft noise includes turbofan engine noise components, as well as noise from the main and tail rotors that is conditioned by the aircraft's various operational modes. Both of the rotors generate loading noise and broadband noise. Another noise contributor is blade/vortex interaction noise, which results when shed vortices are encountered by a following blade, releasing impulsive acoustic energy. Attention is presently given to the experimental and developmental initiatives to be made by a NASA/industry five-year program that began in 1983. Aeroacoustic data acquired from experiments conducted in NASA facilities can be used in the development of empirical noise prediction methods, in the improvement of existing noise prediction methodology, in the evaluation of proposed reduced noise designs, and in the establishment of useful scaling relationships for selected noise-generating mechanisms.

Description: This short paper will demonstrate that the separation of altitude and flight path angle dynamics using singular perturbation techniques for a transport fuel optimization problem results in an unacceptable oscillation in altitude. A technique for damping this oscillation by adding a penalty term to the cost function for the optimization problem will be discussed. This technique will be compared with a different approach that linearizes the altitude and flight path angle boundary layers.

Description: The characteristics of a proposed SST are described. The proposed aircraft is to have two engines and an arrow-wing design, a passenger capacity of 250, and attain speeds of Mach 2.7. The low fineness ratio, low-aspect ratio wing planform, different engine nacelles location, and improved lift-to-drag ratio of the aircraft contribute to attaining an economical supersonic cruise. The proposed structural design and materials for the aircraft are examined; the material and design are to be applicable to high Mach and high temperature. Changes in the SST propulsion system, the nozzle designs, and landing and takeoff procedures to improve the operation of the aircraft are discussed.

Description: The hover performance of three full-scale rotors was measured at the Ames Outdoor Aerodynamic Research Facility. The rotors, all designed for tilt-rotor aircraft, were the original metal blades for the XV-15 Tilt Rotor Research Aircraft, a set of composite, advanced technology blades for the XV-15, and a 0.658-scale model of the proposed V-22A Osprey (JVX) rotor. The composite advanced technology blades for the XV-15 were tested with several alternate blade root and blade tip configurations. This paper presents the performance of these three rotors, shows the effects of tip Mach number and root and tip configuration changes on rotor performance, and presents data on rotor wake velocity distributions and tip vortex geometry. Measured rotor performance is compared with theoretical predictions, and the discrepancies are discussed.

Description: Seven controller mechanisms and several tip geometries were proposed and evaluated in the course of a free tip rotor development program which integrated those components into a model rotor system for wind tunnel testing. After a rigid whirl test was run to determine controller mechanism performance and structural integrity, a second whirl test was performed with a model rotor incorporating a selected controller design and a selected tip platform to determine the transient behavior of the tips in response to aerodynamic excitation. The results obtained demonstrate that a swept, tapered tip with a tension-torsion strap controller furnished satisfactory mechanical operation, achieved the specified output torque, possessed a low spring rate, and had fast and stable response to excitation.

Description: A procedure based on a modified stepwise regression and several selection criteria is presented for the determination of airplane model structure from flight data. The aerodynamic force and moment coefficients in an airplane model are expresed either as polynomials in output and input variables or as a combination of splines. The procedure is demonstrated in three examples by attempting to determine a local, extended and global model. Some of the resulting models are verified by using the maximum likelihood estimation or by examining model prediction capabilities.

Description: Information on the exterior electromagnetic environment of an aircraft when it is struck by lightning has been obtained during thunderstorm penetrations with an F-106B aircraft. Electric and magnetic fields were observed, using mainly time-derivative type sensors, with bandwidths to 50 MHz. Lightning pulse lengths ranging from 25 ns to 7 microsec have been recorded. Sufficient high-frequency content was present to excite electromagnetic resonances of the aircraft, and peaks in the frequency spectra of the waveforms in the range 7 to 23 MHz are in agreement with the resonant frequencies determined in laboratory scale-model tests. Both positively and negatively charged strikes were experienced, and most of the data suggest low values of peak current.

Description: The AFTI/F-16 flight test program is summarized, and several design issues of general interest are addressed. A brief description is given of the test vehicle, its flight control modes, and the flight envelopes in which testing was performed. Flight test results are summarized by addressing benefits experienced in flight control task-tailoring, handling qualities in mission tasks, aircraft structure considerations, digital flight control system performance, and human factors. Finally, several design issues relevant to future fighter aircraft are examined, including degraded flight control, system complexity, simplex information in redundant systems, and single failure propagation in redundant systems.

Description: Several recent helicopter vibration reduction research programs are described. Results of studies of blade design parameters in rotor vibratory response and of an advanced blade design for reduced vibration are examined. An optimization approach to develop a general automated procedure for rotor blade design is described, and analytical results for an articulated rotor operating at a steady 160 kt flight condition are reported. The use of a self-adaptive controller to implement higher harmonic control in closed-loop fashion is addressed, and a computer simulation used to evaluate and compare the performance of alternative algorithms included in the generic active controller is discussed. Results are presented for steady level flight conditions, short-duration maneuvers, blade stresses and rotor performance, blade-appended aeroelastic devices, vibratory airloads, wake-induced blade airloads, and airloads from blade motions, the interaction of rotor and fuselage, and the interaction of rotor and empennage.