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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,063 records · Page 59
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Speech recognition in advanced rotorcraft - Using speech controls to reduce manual control overload

An experiment has been conducted to ascertain the usefulness of helicopter pilot speech controls and their effect on time-sharing performance, under the impetus of multiple-resource theories of attention which predict that time-sharing should be more efficient with mixed manual and speech controls than with all-manual ones. The test simulation involved an advanced, single-pilot scout/attack helicopter. Performance and subjective workload levels obtained supported the claimed utility of speech recognition-based controls; specifically, time-sharing performance was improved while preparing a data-burst transmission of information during helicopter hover.

Vidulich, Michael A.↗
NASA NTRS1988

Euler solution of multiblade rotor flow

A numerical method for solving the Euler equations for multiblade rotors has been developed and some preliminary results reported. The numerical scheme is a combination of several recent methods and algorithm improvements, adapted to the particular requirements of rotor-body interactions. A cylindrical basic grid has been used to study conventional multiblade helicopter rotors. Test calculations have been made for two- and six-blade rotors in hover and for a two-blade rotor in forward flight, under transonic tip conditions but without lift. The results show good agreement with experimental data.

Chen, C. L.↗
NASA NTRS1989

A prediction of high-speed rotor noise

A combined computational (CFD) and integral approach solves the acoustic pressure fields of two high-speed helicopter rotors. A CFD code supplies boundary data to a non-linear type of Kirchhoff integral formulation to find the far-field pressures. Direct calculations of pressures are given by the CFD code up to the sonic cylinder where the Kirchhoff method takes over. This paper shows predictions and measurements of High-Speed Impulsive (HSI) noise in hover for two different rotor geometries. One rotor has a conventional rectangular planform, while the other rotor is highly swept and tapered. The swept rotor analysis forms the majority of this paper. Test data from both rotors are shown and compared with predictions for a range of tip Mach numbers from .85 to .95 (including delocalization). The correlation with the near-field pressures from the straight bladed experiment is excellent and good to excellent correlation is seen for the far-field pressures from both experiments.

Purcell, Timothy W.↗
NASA NTRS1989

Helicopters and VTOL. I

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.

Burks, John S.↗
NASA NTRS1988

Analytical modeling of helicopter static and dynamic induced velocity in GRASP

The methodology used by the General Rotorcraft Aeromechanical Stability Program (GRASP) to model the characteristics of the flow through a helicopter rotor in hovering or axial flight is described. Since the induced flow plays a significant role in determining the aeroelastic properties of rotorcraft, the computation of the induced flow is an important aspect of the program. Because of the combined finite-element/multibody methodology used as the basis for GRASP, the implementation of induced velocity calculations presented an unusual challenge to the developers. To preserve the modelling flexibility and generality of the code, it was necessary to depart from the traditional methods of computing the induced velocity. This is accomplished by calculating the actuator disk contributions to the rotor loads in a separate element called the air mass element, and then performing the calculations of the aerodynamic forces on individual blade elements within the aeroelastic beam element.

Kunz, Donald L.↗
NASA NTRS1989

Noise considerations for tiltrotor

A projection is made of the technology-development requirements faced by aircraft designers contemplating the evolution of V-22-type tilt-rotor aircraft technology into a civilian tilt-rotor commuter aircraft of the requisite scale and payload. These research challenges are noted to often involve the reduction of noise level to values tolerated by passengers within the cabin and communities in the vicinity of airports, especially during hover and in the course of transition from vertical to horizontal flight (and vice-versa). Noise-generation and noise-radiation characteristics research has been undertaken using the XV-15 tilt-rotor proof-of-concept aircraft.

Huston, Robert J.↗
NASA NTRS1989

Large-scale wind tunnel tests of an ejector-lift STOVL aircraft model

The initial results of a test program conducted on an ejector-augmented-lift STOVL aircraft design in the NASA-Ames 40-by-80-Foot Wind Tunnel has established the efficient performance of this full-scale aircraft realization of the propulsion-system configuration. It has also been noted that the generation of larger lift-augmentation ratios in this form than in component tests. In addition, it is found that configurations possessing thrust/weight ratios and wing loadings representative of current practice could, when outfitted with the present propulsion scheme, produce adequate level-flight acceleration through transition from VTOL hover to wingborne flight.

Corsiglia, Victor↗
NASA NTRS1989

Transonic aeroelasticity analysis for rotor blades

A numerical method is presented for calculating the unsteady transonic rotor flow with aeroelasticity effects. The blade structural dynamic equations based on beam theory were formulated by FEM and were solved in the time domain, instead of the frequency domain. For different combinations of precone, droop, and pitch, the correlations are very good in the first three flapping modes and the first twisting mode. However, the predicted frequencies are too high for the first lagging mode at high rotational speeds. This new structure code has been coupled into a transonic rotor flow code, TFAR2, to demonstrate the capability of treating elastic blades in transonic rotor flow calculations. The flow fields for a model-scale rotor in both hover and forward flight are calculated. Results show that the blade elasticity significantly affects the flow characteristics in forward flight.

Chow, Chuen-Yen↗
NASA NTRS1989

NASA rotorcraft technology for the 21st century

Current and planned rotorcraft technology-related research at NASA's Ames, Lewis, and Langley research centers is discussed with a view to the fruits of these efforts beyond the year 2000. Examples of promising technologies are higher-harmonic and dynamic rotor controls, advanced structural composites, aerodynamics and acoustics simulation models for design predictions, automated flight controls, and high-reliability rotor drivetrains. The overall payoff from an integration of these technologies will allow safe automated flying in all weather conditions, as well as precision-hover and exceptionally low noise and vibration levels.

Albers, James A.↗
NASA NTRS1989

Integrated multidisciplinary design optimization of rotorcraft

The NASA/Army research plan for developing the logic elements for helicopter rotor design optimization by integrating appropriate disciplines and accounting for important interactions among the disciplines is discussed. The paper describes the optimization formulation in terms of the objective function, design variables, and constraints. The analysis aspects are discussed, and an initial effort at defining the interdisciplinary coupling is summarized. Results are presented on the achievements made in the rotor aerodynamic performance optimization for minimum hover horsepower, rotor dynamic optimization for vibration reduction, rotor structural optimization for minimum weight, and integrated aerodynamic load/dynamics optimization for minimum vibration and weight.

Adelman, Howard M.↗
NASA NTRS1989

Application of the wide-field shadowgraph technique to rotor wake visualization

The wide field shadowgraph technique is reviewed along with its application to the visualization of rotor wakes. In particular, current experimental methods and data reduction requirements are discussed. Sample shadowgraphs are presented. These include shadowgraphs of model-scale helicopter main rotors and tilt rotors, and full scale tail rotors, both in hover and in forward flight.

Norman, Thomas R.↗
NASA NTRS1989

Integrated multidisciplinary optimization of rotorcraft: A plan for development

This paper describes a joint NASA/Army initiative at the Langley Research Center to develop optimization procedures aimed at improving the rotor blade design process by integrating appropriate disciplines and accounting for important interactions among the disciplines. The paper describes the optimization formulation in terms of the objective function, design variables, and constraints. Additionally, some of the analysis aspects are discussed, validation strategies are described, and an initial attempt at defining the interdisciplinary couplings is summarized. At this writing, significant progress has been made, principally in the areas of single discipline optimization. Accomplishments are described in areas of rotor aerodynamic performance optimization for minimum hover horsepower, rotor dynamic optimization for vibration reduction, and rotor structural optimization for minimum weight.

Adelman, Howard M.↗
NASA NTRS1989

Acoustic design considerations: Review of rotor acoustic sources

It is not sufficient to optimize a rotor design in terms of a single noise level calculated for a single flight condition and a single measurement location. The various noise sources, their frequency content, amplitude, and directivity as a function of operating condition must be considered. A summary of the frequency ranges, directivity patterns and the most important operational and design parameters for major rotor noise sources is presented. It is difficult to generalize design requirements for rotor noise because the acoustic output varies so widely depending on the noise source, flight condition, measurement location, and frequency range. However, assuming the rotor must lift a fixed nominal payload and operate over a wide range of flight conditions, three general design guidelines can be stated: (1) minimize tip Mach number; (2) minimize blade thickness in the tip region; and (3) minimize gradients in the spanwise lift distribution in the tip region. Constraints on blade thickness, maximum values for hover tip Mach number, advancing tip Mach number and spanwise lift coefficient gradient will be specified during the aerodynamic, dynamic and structural optimization process. The rotor noise sources to be considered include the low frequency loading and thickness noise, and the higher frequency noise due to blade-vortex interactions (BVI). The analyses to be employed will include the comprehensive rotor analysis and design program CAMRAD and the rotor noise prediction program WOPWOP.

Martin, Ruth M.↗
NASA NTRS1989

A CFD study of tilt rotor flowfields

The download on the wing produced by the rotor wake of a tilt rotor vehicle in hover is of major concern because of its severe impact on payload-carrying capability. In a concerted effort to understand the fundamental fluid dynamics that cause this download, and to help find ways to reduce it, computational fluid dynamics (CFD) is employed to study this problem. The thin-layer Navier-Stokes equations are used to describe the flow, and an implicit, finite difference numerical algorithm is the method of solution. The methodology is developed to analyze the tilt rotor flowfield. Included are discussions of computations of an airfoil and wing in freestream flows at -90 degrees, a rotor alone, and wing/rotor interaction in two and three dimensions. Preliminary results demonstrate the feasibility and great potential of the present approach. Recommendations are made for both near-term and far-term improvements to the method.

Fejtek, Ian↗
NASA NTRS1989

A survey of nonuniform inflow models for rotorcraft flight dynamics and control applications

The results of a brief survey of nonuniform inflow models was summarized for the calculation of induced velocities at and near a lifting rotor in and out of ground effect. The survey, conducted from the perspective of flight dynamics and control applications, covers a spectrum of flight conditions including hover, vertical flight, and low-speed and high-speed forward flight, and reviews both static and dynamic aspects of the inflow. A primary emphasis is on the evaluation of various simple first harmonic inflow models developed over the years, in comparison with more sophisticated methods developed for use in performance and airload computations. The results of correlation with several sets of test data obtained at the rotor out of ground effect indicate that the Pitt/Peters first harmonic inflow model works well overall. For inflow near the rotor or in ground effect, it is suggested that charts similar to those of Heyson/Katzoff and Castles/De Leeuw of NACA be produced using modern free-wake methods for use in flight dynamic analyses and simulations.

Chen, Robert T. N.↗
NASA NTRS1990

Three-dimensional viscous rotor flow calculations using a viscous-inviscid interaction approach

A three-dimensional viscous-inviscid interaction analysis was developed to predict the performance of rotors in hover and in forward flight at subsonic and transonic tip speeds. The analysis solves the full-potential and boundary-layer equations by finite-difference numerical procedures. Calculations were made for several different model rotor configurations. The results were compared with predictions from a two-dimensional integral method and with experimental data. The comparisons show good agreement between predictions and test data.

Chen, Ching S.↗
NASA NTRS1990

Performance Data from a Wind-Tunnel Test of Two Main-rotor Blade Designs for a Utility-Class Helicopter

An investigation was conducted in the NASA Langley Transonic Dynamics Tunnel to evaluate an advanced main rotor designed for use on a utility class helicopter, specifically the U.S. Army UH-60A Blackhawk. This rotor design incorporated advanced twist, airfoil cross sections, and geometric planform. For evaluation purposes, the current UH-60A main rotor was also tested and is referred to as the baseline blade set. A total of four blade sets were tested. One set of both the baseline and the advanced rotors were dynamically scaled to represent a full scale helicopter rotor blade design. The remaining advanced and baseline blade sets were not dynamically scaled so as to isolate the effects of structural elasticity. The investigation was conducted in hover and at rotor advance ratios ranging from 0.15 to 0.4 at a range of nominal test medium densities from 0.00238 to 0.009 slugs/cu ft. This range of densities, coupled with varying rotor lift and propulsive force, allowed for the simulation of several vehicle gross weight and density altitude combinations. Performance data are presented for all blade sets without analysis; however, cross referencing of data with flight condition may be useful to the analyst for validating aeroelastic theories and design methodologies as well as for evaluating advanced design parameters.

Singleton, Jeffrey D.↗
NASA NTRS1990

Preliminary design of a supersonic Short Takeoff and Vertical Landing (STOVL) fighter aircraft

The preliminary design study of a supersonic Short Takeoff and Vertical Landing (STOVL) fighter is presented. A brief historical survey of powered lift vehicles was presented, followed by a technology assessment of the latest supersonic STOVL engine cycles under consideration by industry and government in the U.S. and UK. A survey of operational fighter/attack aircraft and the modern battlefield scenario were completed to develop, respectively, the performance requirements and mission profiles for the study. Three configurations were initially investigated with the following engine cycles: a hybrid fan vectored thrust cycle, a lift+lift/cruise cycle, and a mixed flow vectored thrust cycle. The lift+lift/cruise aircraft configuration was selected for detailed design work which consisted of: (1) a material selection and structural layout, including engine removal considerations, (2) an aircraft systems layout, (3) a weapons integration model showing the internal weapons bay mechanism, (4) inlet and nozzle integration, (5) an aircraft suckdown prediction, (6) an aircraft stability and control analysis, including a takeoff, hover, and transition control analysis, (7) a performance and mission capability study, and (8) a life cycle cost analysis. A supersonic fighter aircraft with STOVL capability with the lift+lift/cruise engine cycle seems a viable option for the next generation fighter.

Cox, Brian↗