WorldCat Identities

United States Army Aviation Research and Technology Activity

Works: 175 works in 232 publications in 1 language and 14,124 library holdings
Genres: Conference papers and proceedings 
Classifications: TJ184, 621.833
Publication Timeline
Most widely held works by United States
The effects of structural flap-lag and pitch-lag coupling on soft inplane hingeless rotor stability in hover by William G Bousman( Book )

3 editions published in 1990 in English and held by 191 WorldCat member libraries worldwide

A 1.62-m-diameter rotor model was tested in hover to examine the effects of structural flap-lag and pitch-lag coupling on isolated rotor blade lead-lag stability. Flap-lag coupling was introduced by inclining the principal axes of the blade structure up to 60 deg. Pitch-lag coupling ws obtained either alone or in combination with flap-lag coupling through the use of skewed flexural hinges. The principal results confirm the predictions of theory, and show that both structural flap-lag and pitch-lag coupling when used separately are beneficial to blade stability. Moreover, when the couplings are combined, the lead-lag damping is significantly greater than it would be if the individual contributions were superimposed. Pitch-flap coupling is shown to have only a minor effect on blade lead-lag damping. Differences between theory and experiment observed at zero blade pitch and flexure angles during the initial testing were determined in a second test to be caused by stand flexibility. Other differences between theory and experiment warrant further investigation
Performance data from a wind-tunnel test of two main-rotor blade designs for a utility-class helicopter by Jeffrey D Singleton( Book )

1 edition published in 1990 in English and held by 186 WorldCat member libraries worldwide

Matrix density effects on the mechanical properties of SiC/RBSN composites by Ramakrishna T Bhatt( Book )

1 edition published in 1990 in English and held by 184 WorldCat member libraries worldwide

The room temperature mechanical properties were measured for SiC fiber-reinforced reaction-bonded silicon nitride composites (SiC/RBSN) of different densities. The composites consisted of approx. 30 vol % uniaxially aligned 142 um diameter SiC fibers (Textron SCS-6) in a reaction-bonded Si3N4 matrix. The composite density was varied by changing the consolidation pressure during RBSN processing and by hot isostatically pressing the SiC/RBSN composites. Results indicate that as the consolidation pressure during RBSN processing and by hot isostatically pressing the SiC/RBSN composites. Results indicate that as the consolidation pressure was increased from 27 to 138 MPa, the average pore size of the nitrided composites decreased from 0.04 to 0.02 um and the composite density increased from 2.07 to 2.45 gm/cc. Nonetheless, these improvements resulted in only small increases in the first matrix cracking stress, primary elastic modulus, and ultimate tensile strength values of the composites. In contrast, HIP consolidation of SiC/RBSN resulted in a fully dense material whose first matrix cracking stress and elastic modulus values were approx. 15 and approx. 50 percent higher, respectively, the ultimate tensile strength values were approx. 40 percent lower than those for unHIPed SiC/RBSN composites. The modulus behavior for all specimens can be explained by simple rule-of-mixture theory. Also, the loss in ultimate strength for the HIP temperature. (SDW)
Inflow measurements made with a laser velocimeter on a helicopter model in forward flight( Book )

6 editions published in 1990 in English and held by 172 WorldCat member libraries worldwide

Identification of XV-15 aeroelastic modes using frequency-domain methods by C. W Acree( Book )

1 edition published in 1989 in English and held by 171 WorldCat member libraries worldwide

A flight-dynamic helicopter mathematical model with a single flap-lag-torsion main rotor by Marc D Takahashi( Book )

1 edition published in 1990 in English and held by 170 WorldCat member libraries worldwide

A mathematical model of a helicopter system with a single main rotor that includes rigid, hinge-restrained rotor blades with flap, lag, and torsion degrees of freedom is described. The model allows several hinge sequences and two offsets in the hinges. Quasi-steady Greenberg theory is used to calculate the blade-section aerodynamic forces, and inflow effects are accounted for by using a three-state nonlinear dynamic inflow model. The motion of the rigid fuselage is defined by six degrees of freedom, and an optional rotor rpm degree of freedom is available. Empennage surfaces and the tail rotor are modeled, and the effect of main-rotor downwash on these elements is included. Model trim, linearization, and time-integration operations are described and can be applied to a subset of the model in the rotating and nonrotating coordinate frame. A preliminary validation of the model is made by comparing its results with those of other analytical and experimental studies. This publication presents the results of research completed in November 1989
Correlation of Puma airloads : lifting-line and wake calculation( Book )

1 edition published in 1989 in English and held by 168 WorldCat member libraries worldwide

A cooperative program, undertaken by organizations in the United States, England, France, and Australia, assessed the strengths and weaknesses of four lifting-line/wake methods and three CFD methods by comparing their predictions with the data obtained in flight trials of a research Puma. The Puma has been tested in two configurations: a mixed-bladed rotor with instrumented rectangular-tip and swept-tip blades, and a configuration with four identical swept-tip blades. The present paper examines the results of the lifting-line predictions. The better lifting-line methods show good agreement with lift at the blade tip for the configuration with four swept tips; the moment is well- predicted at 0.92 R, but deteriorates outboard. The predictions for the mixed- bladed rotor configuration range from fair to good. The lift prediction is better for the swept-tip blade than for rectangular-tip blade, but the reasons for this cannot be determined because of the unmodeled effects of the mixed- bladed rotor. Keywords: Helicopter flight test; Computational fluid dynamics; Helicopter airloads correlation; Helicopter rotors; Rotor blades rotary wings. (edc)
Local delamination in laminates with angle ply matrix cracks by T. Kevin O'Brien( Book )

3 editions published in 1991 in English and held by 165 WorldCat member libraries worldwide

Applications of flight control system methods to an advanced combat rotorcraft( Book )

1 edition published in 1989 in English and held by 161 WorldCat member libraries worldwide

Advanced flight control system design, analysis, and testing methods are applied in an analytical and flight test evaluation of the Advanced Digital Optical Control System (ADOCS) demonstrator. This paper describes the knowledge gained about the implications of digital flight control system design for rotorcraft, and illustrates. The analysis of the resulting handling-qualities in the context of the proposed new handling-qualities specification for rotorcraft. Topics included are digital flight control design and analysis methods, flight testing techniques, ADOCS handling-qualities evaluation results, and correlation of flight test results with analytical models and the proposed handling- qualities specification. Evaluation of the ADOCS demonstrator indicated desirable response characteristics based on equivalent damping and frequency, but undesirably large effective time-delays. Piloted handling-qualities are desirable or adequate for all low, medium, and high pilot gain tasks; but handling-qualities are inadequate for ultra-high gain tasks such as slope and running landings. Correlation of these results with the proposed handling- qualities specification indicates good agreement for the bandwidth boundaries, but suggests the need for more stringent limits on allowable phase-delay. Analytical models based on emulation (s-plane) techniques compare favorably with flight extracted frequency-domain characteristics of the overall (end-to-end) ADOCS responses. Direct digital analysis procedures are necessary to characterize the intersample behavior of the actuator rate response
Review and analysis of the DNW/model 360 rotor acoustic data base by R. A Zinner( Book )

1 edition published in 1989 in English and held by 161 WorldCat member libraries worldwide

A comprehensive model rotor aeroacoustic data base was collected in a large anechoic wind tunnel in 1986. Twenty-six microphones were positioned around the azimuth to collect acoustic data for approximately 150 different test conditions. A dynamically scaled, blade-pressure-instrumented model of the forward rotor of the BH 360 helicopter simultaneously provided blade pressures for correlation with the acoustic data. High-speed impulsive noise, blade-vortex interaction noise, low-frequency noise, and broadband noise were all captured in this extensive data base. This paper presents trends in each noise source, with important parametric variations. The purpose of this paper is to introduce this data base and illustrate its potential for predictive code validation. (jes)
Stability of a rigid rotor supported on oil-film journal bearings under dynamic load by Bankim C Majumdar( Book )

3 editions published in 1987 in English and held by 152 WorldCat member libraries worldwide

Most published work relating to dynamically loaded journal bearings are directed to determining the minimum film thickness from the predicted journal trajectories. These do not give any information about the subsynchronous whirl stability of journal bearing systems since they do not consider the equations of motion. It is, however, necessary to know whether the bearing system operation is stable or not under such an operating condition. The purpose of the present paper is to analyze the stability characteristics of the system. A linearized perturbation theory about the equilibrium point can predict the threshold of stability; however it does not indicate postwhirl orbit detail. The linearized method may indicate that a bearing is unstable for a given operating condition whereas the nonlinear analysis may indicate that if forms a stable limit cycle. For this reason, a nonlinear transient analysis of a rigid rotor supported on oil journal bearings under (1) a unidirectional constant load, (2) a unidirectional periodic load, and (3) variable rotating load are performed. In this paper, the hydrodynamic forces are calculated after solving the time- dependent Reynolds equation by a finite difference method with a successive overrelaxation scheme. Using these forces, equations of motion are solved by the fourth-order Runge-Kutta method to predict the transient behavior of the rotor. With the aid of a high-speed digital computer and graphics, the journal trajectories are obtained for several different operating conditions. Keywords: Journal bearings; Stability; Dynamic loads; Bearings; Dynamics
Five year ground exposure of composite materials used on the Bell model 206L flight service evaluation by Donald J Baker( Book )

2 editions published in 1989 in English and held by 147 WorldCat member libraries worldwide

During the past ten years, NASA has sponsored programs to build a data base and establish confidence in the long-term durability of advanced composite materials. Flight service experience is being obtained on primary and secondary structural components installed on commercial aircraft and from material specimens exposed at different locations. Although commercial aircraft and helicopters may fly in the same environment the behavior of composite materials on each vehicle may differ substantially. Most of the projected usage for composites in helicopter fuselage is Kevlar-49/epoxy with selective reinforcement of graphite/epoxy using 250 F curing epoxies. Most commercial aircraft are using 350 F cure graphite/epoxy systems with very little use of Kevlar/epoxy. Considering only the effects of moisture, materials in the minimum gage structure in most helicopter fuselage would reach equilibrium moisture content in a short time whereas the heavier gage structure on a commercial aircraft could take months to reach an equilibrium condition
Acoustic measurements from a rotor blade-vortex interaction noise experiment in the German-Dutch wind tunnel (DNW) by R. M Martin( Book )

3 editions published in 1988 in English and held by 99 WorldCat member libraries worldwide

Acoustic data are presented from a 40-percent-scale model of the four-bladed BO-105 helicopter main rotor, tested in a large aeroacoustic wind tunnel. Rotor blade-vortex interaction (BVI) noise data in the low-speed flight range were acquired using a traversing in-flow microphone array. The experimental apparatus, testing procedures, calibration results, and experimental objectives are fully described. A large representative set of averaged acoustic signals are presented
Integrated Technology Rotor Methodology Assessment Workshop : proceedings of a workshop by Integrated Technology Rotor Methodology Assessment Workshop( Book )

1 edition published in 1988 in English and held by 92 WorldCat member libraries worldwide

Theory of gearing by F. L Litvin( Book )

1 edition published in 1989 in English and held by 89 WorldCat member libraries worldwide

The author has significantly contributed to the goals of the NASA/ army transmission program by his accomplishments in the science of gearing and his authorship of this book. His work has provided a mathematical basis which improves our understanding of bevel gear geometry and the manufacturing procedure. His work has provided solutions to reduce gear noise and to enable a smoother transfer of power in helicopters. In summary, he has directly contributed to advance the state of the art in helicopter power transmission technology, and has made a significant contribution to NASA's research projects and to the public good. This book explains the most general problems of the theory of gearing, but it represents only a part of Dr. Litvins's accomplishments. His research contributions have improved (1) almost all types of gearing including spur, helical, hypoid, bevel, worm, and noncircular gears; (2) tools for gear manufacture; and (3) computer programs for simulation of meshing and contact. His theorems, methods for gear synthesis, and methods for gear generation represent a very significant contribution to the science of gearing
A real-time simulator of a turbofan engine by Jonathan S Litt( Book )

3 editions published in 1989 in English and held by 86 WorldCat member libraries worldwide

A real-time digital simulator of a Pratt and Whitney F100 engine has been developed for real-time code verification and for actuator diagnosis during full-scale engine testing. This self-contained unit can operate in an open-loop stand-alone mode ore as part of a closed-loop control system. It can also be used for control system design and development. Tests conducted in conjunction with the NASA Advanced Detection, Isolation, and Accommodation program show that the simulator is a valuable tool for real-time code verification and as a real- time actuator simulator for actuator fault diagnosis. Although currently a small perturbation model, advances in microprocessor hardware should allow the simulator to evolve into a real-time, full-envelope, full engine simulation
Scaling effects in the static large defelction [i.e. deflection] response of graphite-epoxy composite beams by Karen E Jackson( Book )

2 editions published in 1989 in English and held by 84 WorldCat member libraries worldwide

Correlation of puma airloads : evaluation of CFD prediction methods( Book )

2 editions published in 1989 in English and held by 84 WorldCat member libraries worldwide

Reduction of blade-vortex interaction noise using higher harmonic pitch control( Book )

2 editions published in 1989 in English and held by 83 WorldCat member libraries worldwide

An acoustics test using an aeroelastically scaled rotor was conducted to examine the effectiveness of higher harmonic blade pitch control for the reduction of impulsive blade-vortex interaction (BVI) noise. A four-bladed, 110 in. diameter, articulated rotor model was tested in a heavy gas (Freon-12) medium in the Transonic Dynamics Tunnel. Noise and vibration measurements were made for a range of matched flight conditions, where prescribed (open-loop) higher harmonic pitch was superimposed on the normal (baseline) collective and cyclic trim pitch. For the inflow-microphone noise measurements, advantage was taken of the reverberance in the hard walled tunnel by using a sound power determination approach. Initial findings from on-line data processing for three of the test microphones are reported for a 4/rev (4P) collective pitch control for a range of input amplitudes and phases. By comparing these results to corresponding baseline (no control) conditions, significant noise reductions (4- 5 dB) were found for low-speed descent conditions, where helicopter BVI noise was most intense. For other rotor flight conditions, the overall noise was found to increase. All cases show increased vibration levels
Aircraft crash survival design guide by Simula Inc( )

in English and held by 1 WorldCat member library worldwide

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Alternative Names

controlled identityUnited States. Army Aviation Research and Development Command

United States. Army Aviation Research & Technology Activity

United States. Army Aviation Systems Command. Aviation Research and Technology Activity

US Army Aviation Research and Technology Activity

English (40)