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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Airborne laser topographic mapping results

The results of terrain mapping experiments utilizing the National Aeronautics and Space Administration (NASA) Airborne Oceanographic Lidar (AOL) over forested areas are presented. The flight tests were conducted as part of a joint NASA/U.S. Army Corps of Engineers (CE) investigation aimed at evaluating the potential of an airborne laser ranging system to provide cross-sectional topographic data on flood plains that are difficult and expensive to survey using conventional techniques. The data described in this paper were obtained in the Wolf River Basin located near Memphis, TN. Results from surveys conducted under winter 'leaves off' and summer 'leaves on' conditions, aspects of day and night operation, and data obtained from decidous and coniferous tree types are compared. Data processing techniques are reviewed. Conclusions relative to accuracy and present limitations of the AOL, and airborne lidar systems in general, to terrain mapping over forested areas are discussed.

Krabill, W. B.↗
NASA NTRS1984

Rotorcraft flight-propulsion control integration

The parallel development of digital engine and flight controls for U.S. Army helicopters has made possible the future derivation of a fully integrated digital flight/propulsion control system. A NASA/Army research program has been undertaken to exploit these possibilities, ultimately yielding a generation of helicopters with exceptional agility and maneuverability in military roles and low pilot workloads in all-weather civil aviation missions. The program's three phases respectively address system modeling and analysis, flight hardware and software development, and flight evaluations aboard a research vehicle.

Mihaloew, J. R.↗
NASA NTRS1984

Flow of nitrogen-pressurized Halon 1301 in fire extinguishing systems

Halon 1301 which is a halocarbon fire extinguishing agent (CBrF3) used by the U.S. Army for vehicle fire suppression is discussed. Halon 1301 is discharged under nitrogen pressure, and the Halon-nitrogen mixture is a two phase, two component mixture that obeys compressible fluid laws and exhibits choking effects. A computer model was developed to analyze the discharge of Halon and nitrogen from a storage bottle through pipes and nozzles. The model agrees well with data from Halon 1301 discharge tests. The discharge time depends mainly on nozzle area and pipe volume, for given initial conditions. Graphs were developed for estimating discharge times. A nozzle employing multiple concentric converging/diverging nozzles was developed which gave hemispherical coverage.

Elliott, D. G.↗
NASA NTRS1984

Assessment of simulation fidelity using measurements of piloting technique in flight

The U.S. Army and NASA joined together on a project to conduct a systematic investigation and validation of a ground based piloted simulation of the Army/Sikorsky UH-60A helicopter. Flight testing was an integral part of the validation effort. Nap-of-the-Earth (NOE) piloting tasks which were investigated included the bob-up, the hover turn, the dash/quickstop, the sidestep, the dolphin, and the slalom. Results from the simulation indicate that the pilot's NOE task performance in the simulator is noticeably and quantifiably degraded when compared with the task performance results generated in flight test. The results of the flight test and ground based simulation experiments support a unique rationale for the assessment of simulation fidelity: flight simulation fidelity should be judged quantitatively by measuring pilot's control strategy and technique as induced by the simulator. A quantitative comparison is offered between the piloting technique observed in a flight simulator and that observed in flight test for the same tasks performed by the same pilots.

Clement, W. F.↗
NASA NTRS1983

Integrated Technology Rotor/Flight Research Rotor (ITR/FRR) concept definition study

Studies were conducted by Hughes Helicopters, Inc. (HHI) for the Applied Technology Laboratory and Aeromechanics Laboratory, U.S. Army Research and Technology Laboratories (AVRADCOM) and the Ames Research Center, National Aeronautics and Space Administration (NASA). Results of predesign studies of advanced main rotor hubs, including bearingless designs, are presented in this report. In addition, the Government's rotor design goals and specifications were reviewed and evaluated. Hub concepts were designed and qualitatively evaluated in order to select the two most promising concepts for further development. Various flexure designs, control systems, and pitchcase designs were investigated during the initial phases of this study. The two designs selected for additional development were designated the V-strap and flat-strap cruciform hubs. These hubs were designed for a four bladed rotor and were sized for 18,400 pounds gross weight with the same diameter (62 feet) and solidity (23 inch chord) as the existing rotor on the Rotor Systems Research Aircraft (RSRA).

Hughes, C. W.↗
NASA NTRS1985

Investigation of technology needs for avoiding helicopter pilot error related accidents

Pilot error which is cited as a cause or related factor in most rotorcraft accidents was examined. Pilot error related accidents in helicopters to identify areas in which new technology could reduce or eliminate the underlying causes of these human errors were investigated. The aircraft accident data base at the U.S. Army Safety Center was studied as the source of data on helicopter accidents. A randomly selected sample of 110 aircraft records were analyzed on a case-by-case basis to assess the nature of problems which need to be resolved and applicable technology implications. Six technology areas in which there appears to be a need for new or increased emphasis are identified.

Chais, R. I.↗
NASA NTRS1985

Wind-tunnel evaluation of a 21-percent-scale powered model of a prototype advanced scout helicopter

An exploratory wind tunnel investigation of a 21 percent scale powered model of a prototype advanced scout helicopter was conducted in the Langley 4 by 7 Meter Tunnel. The investigation was conducted to define the overall aerodynamic characteristics of the Army Helicopter Improvement Program (AHIP), to determine the effects of the rotor on the aerodynamic characteristics and to evaluate the effect of a mast mounted sight on the aircraft stability characteristics. Tests covered a range of thrust coefficients, advance ratios, angles of attack and angles of sideslip and were run for both rotor on and rotor off configurations. Results of the investigation showed that the prototype configuration was longitudinally unstable with angle of attack for all configurations tested. The instability was due to unfavorable interference effects between the horizontal tail and the wake shed from the engine pylon and rotor hub, which caused a loss of horizontal tail effectiveness. The addition of the mast mounted sight had little effect on the stability of the model, but it caused an alteration in the rotor lift distribution that resulted in substantial interference drag for the sight.

Phelps, A. E., III↗
NASA NTRS1984

Hydrological planning studies using Landsat-4 Thematic Mapper (TM)

NASA, in cooperation with the U.S. Army Corps of Engineers, is evaluating the capabilities of Landsat 4 Thematic Mapper (TM) data for environmental and hydrological applications. Attention is given to the results of studies conducted at the Clinton River Basin in Michigan and the eastern shore of the Chesapeake Bay in Maryland. In the former, the evaluation conducted was for the band combinations: (1) 2, 3, and 4; (2) 3, 4, and 5; (3) 3, 4, 5, and 6; and (4) all seven bands. In the latter case, Multispectral Scanner (MSS) and TM data were classified for combinations (1), (3) and (4). Wetland classification accuracy for the 7-band TM data in this study was found to be 9 percent higher than with MSS data, allowing more reliable and accurate monitoring.

Gervin, J. C.↗
NASA NTRS1985

Optimization methods applied to the aerodynamic design of helicopter rotor blades

This paper describes a formal optimization procedure for helicopter rotor blade designs which minimizes hover horsepower while assuring satisfactory forward flight performance. The approach is to couple hover and forward flight analysis programs with a general purpose optimization procedure. The resulting optimization system provides a systematic evaluation of the rotor blade design variables and their interaction, thus reducing the time and cost of designing advanced rotor blades. The paper discusses the basis for and details of the overall procedure, describes the generation of advanced blade designs for representative Army helicopters, and compares designs and design effort with those from the conventional approach which is based on parametric studies and extensive cross-plots.

Walsh, J. L.↗
NASA NTRS1984

Assessment of simulation fidelity using measurements of piloting technique in flight

The U.S. Army and NASA have undertaken the systematic validation of a ground-based piloted simulator for the UH-60A helicopter. The results of previous handling quality and task performance flight tests for this helicopter have been used as a data base for evaluating the fidelity of the present simulation, which is being conducted at the NASA Ames Research Center's Vertical Motion Simulator. Such nap-of-the-earth piloting tasks as pop-up, hover turn, dash/quick stop, sidestep, dolphin, and slalom, have been investigated. It is noted that pilot simulator performance is significantly and quantifiable degraded by comparison with flight test results for the same tasks.

Ferguson, S. W.↗
NASA NTRS1985

Effect of measured material properties on the finite element analysis of an OH-58 composite tail boom

A static and dynamic finite element analysis is conducted on a U.S. Army OH-58 composite tail boom and compared with test data. The tail boom is a filament-wound graphite/epoxy monocoque structure. The structural design of the composite tail boom skin is based on 50-percent graphite fiber volume. However, material tests on representative samples of the tail boom skin reveal that the graphite fiber-volume fraction varied from 44.6 to 49.3 percent. To determine the effect of using measured material properties, static and dynamic finite element analyses are conducted for three fiber-volume conditions of 45, 48, and 50 percent. The static and dynamic model with the 45-percent fiber-volume graphite skins gives the closest agreement with test data.

Bowman, L. M.↗
NASA NTRS1985

Tradeoff analysis of technology needs for public service helicopters

The design requirements for a family or type of Public Service Helicopter (PSH) is examined which will satisfy the needs of municipal and state governments in the following mission areas: Emergency Medical Service--Airborne Rescue Squad; Law Enforcement; Search and Rescue; and Environmental Control (Fire Fighting, Pollution, Resource Management). The report compares both design and performance requirements as specified by the PSH user's group against current technological capabilities, RTOPS and US Army LHX design requirements. The study explores various design trade-offs and options available to the aircraft designer/manufacturer in order to meet the several criteria specified by the PSH user's group. In addition, the report includes a brief assessment of the feasibility of employing certain advanced rotorcraft designs to meet the stringent combination of operational capabilities desired by the Public Service Helicopter Users.

Bauchspies, J. S.↗
NASA NTRS1986

Aerodynamic characteristics of several current helicopter tail boom cross sections including the effect of spoilers

Aerodynamic characteristics were determined of three cylindrical shapes representative of tail boom cross sections of the U.S. Army AH-64, UH-60, and UH-1H helicopters. Forces and pressures were measured in a wind-tunnel investigation at the Langley Research Center. Data were obtained for a flow incidence range from -45 to 90 deg and a dynamic pressure range from 1.5 to 50 psf. These ranges provided data representative of full-scale Reynolds numbers and the full range of flow incidence to which these helicopter tail boom shapes would be subjected at low flight speeds. The effects of protuberances such as tail rotor drive-shaft covers and spoilers were evaluated. The data indicate that significant side loads on tail booms of helicopters can be generated and that the addition of spoilers can beneficially alter the side loads. Although an increase in vertical drag occurs, the net effect through reduction of tail rotor thrust required can be an improvement in helicopter performance.

Wilson, J. C.↗
NASA NTRS1986

Testing of YUH-61A helicopter transmission in NASA Lewis 2240-kW (3000-hp facility

A helicopter transmission that was being considered for the Army's Utility Tactical Transport Attack System (UTTAS) was tested in the NASA Lewis 2240-kW (3000-hp) test facility to obtain the transmission's operational data. The results will form a vibration and efficiency data base for evaluation similar-class helicopter transmissions. The transmission's mechanical efficiency was determined to be 98.7 percent at its rated power level of 2080 kW (2792 hp). At power levels up to 113 percent of rated the transmission displayed 56 percent higher vibration acceleration levels on the right input than on the left input. Both vibration signature analysis and final visual inspection indicated that the right input spiral-bevel gear had poor contact patterns. The highest vibration meter level was 52 g's rms at the accessory gear, which had free-wheeling gearsets. At 113 percent power and 100 percent rated speed the vibration meter levels generally ranged from 3 to 25 g's rms.

Mitchell, A. M.↗
NASA NTRS1986

Wind-tunnel acoustic results of two rotor models with several tip designs

A three-phase research program has been undertaken to study the acoustic signals due to the aerodynamic interaction of rotorcraft main rotors and tail rotors. During the first phase, two different rotor models with several interchangeable tips were tested in the Langley 4- by 7-Meter Tunnel on the U.S. Army rotor model system. An extensive acoustic data base was acquired, with special emphasis on blade-vortex interaction (BVI) noise. The details of the experimental procedure, acoustic data acquisition, and reduction are documented. The overall sound pressure level (OASPL) of the high-twist rotor systems is relatively insensitive to flight speed but generally increases with rotor tip-path-plane angle. The OASPL of the high-twist rotors is dominated by acoustic energy in the low-frequency harmonics. The OASPL of the low-twist rotor systems shows more dependence on flight speed than the high-twist rotors, in addition to being quite sensitive to tip-path-plane angle. An integrated band-limited sound pressure level, limited by 500 to 3000 Hz, is a useful metric to quantify the occurrence of BVI noise. The OASPL of the low-twist rotors is strongly influenced by the band-limited sound levels, indicating that the blade-vortex impulsive noise is a dominant noise source for this rotor design. The midfrequency acoustic levels for both rotors show a very strong dependence on rotor tip-path-plane angle. The tip-path-plane angle at which the maximum midfrequency sound level occurs consistently decreases with increasing flight speed. The maximum midfrequency sound level measured at a given location is constant regardless of the flight speed.

Martin, R. M.↗
NASA NTRS1986

Investigation of an advanced fault tolerant integrated avionics system

Presented is an advanced, fault-tolerant multiprocessor avionics architecture as could be employed in an advanced rotorcraft such as LHX. The processor structure is designed to interface with existing digital avionics systems and concepts including the Army Digital Avionics System (ADAS) cockpit/display system, navaid and communications suites, integrated sensing suite, and the Advanced Digital Optical Control System (ADOCS). The report defines mission, maintenance and safety-of-flight reliability goals as might be expected for an operational LHX aircraft. Based on use of a modular, compact (16-bit) microprocessor card family, results of a preliminary study examining simplex, dual and standby-sparing architectures is presented. Given the stated constraints, it is shown that the dual architecture is best suited to meet reliability goals with minimum hardware and software overhead. The report presents hardware and software design considerations for realizing the architecture including redundancy management requirements and techniques as well as verification and validation needs and methods.

Dunn, W. R.↗
NASA NTRS1985

Feasibility study for ergonomic analysis and design of future helicopter cockpit systems

The Army's light scout-attack helicopters (LHXs), planned for deployment in the 1990's, will fly nap-of-the-earth (NOE) missions in high threat environments, often under poor visibility and adverse atmospheric conditions, and probably with a one man crew. A procedure for the analysis of pilot workload that will identify and explicate the main characteristics of those LHX mission components holding overload potential is described. A principled, in-depth, explication of the cognitive demans of LHX piloting is essential to any effective effort to address the human factors issues. A task-analytic procedure that will yield the detail and organizstion needed to achieve these goals is examined.

Hawkins, H. L.↗
NASA NTRS1986

A new version of the helicopter aural detection program, ICHIN

NASA Langley Research Center personnel have conducted an evaluation of the helicopter aural detection program I Can Hear It Now (ICHIN version-5). This was accomplished using flight noise data of five helicopters, obtained from a joint NASA and U.S. Army acoustics measurement program. The evaluation consisted of presenting the noise data to a jury of 20 subjects and to the ICHIN-5 program. A comparative study was then made of the detection distances determined by the jury and predicted by ICHIN-5. This report presents the changes made in the ICHIN-5 program as a result of this comparative study. The changes represent current psychoacoustics and propagation knowledge.

Mueller, A. W.↗