WorldCat Identities

United States Army Aviation Research and Technology Activity

Overview
Works: 181 works in 252 publications in 1 language and 14,705 library holdings
Genres: Conference papers and proceedings 
Classifications: TL521.3.T4, 629.133352
Publication Timeline
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Most widely held works by United States
Acoustic measurements from a rotor blade-vortex interaction noise experiment in the German-Dutch wind tunnel (DNW) by R. M Martin( )

3 editions published in 1988 in English and held by 322 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
Stability of a rigid rotor supported on oil-film journal bearings under dynamic load by Bankim C Majumdar( )

3 editions published in 1987 in English and held by 297 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( )

2 editions published in 1989 in English and held by 295 WorldCat member libraries worldwide

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

2 editions published in 1989 in English and held by 284 WorldCat member libraries worldwide

Scaling effects in the static large defelction [i.e. deflection] response of graphite-epoxy composite beams by Karen E Jackson( )

2 editions published in 1989 in English and held by 283 WorldCat member libraries worldwide

Scaling effects in the large deflection response of graphite-epoxy composite beams was investigated. Eight different scale model beams ranging from 1/6 to full scale were subjected to an eccentric axial compressive load to promote large bending deformations and failures. Beams having laminate stacking sequences including unidirectional, angle ply, cross ply, and quasi-isotropic were tested to examine a wide variety of composite response and failure modes. The model beams were loaded under scaled test conditions until catastrophic failure. Data acquired included load, end displacement, and strain measurements, and qualitative failure measurements. The experimental data is compared to a large rotation beam analysis and a finite element model analysis
Reduction of blade-vortex interaction noise using higher harmonic pitch control( )

2 editions published in 1989 in English and held by 282 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
Inflow measurements made with a laser velocimeter on a helicopter model in forward flight( Book )

7 editions published in 1990 in English and held by 198 WorldCat member libraries worldwide

Aircraft crash survival design guide by Simula Inc( )

in English and held by 182 WorldCat member libraries worldwide

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 147 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 142 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 140 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)
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 127 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
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 126 WorldCat member libraries worldwide

Correlation of Puma airloads : lifting-line and wake calculation( Book )

1 edition published in 1989 in English and held by 123 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)
Applications of flight control system methods to an advanced combat rotorcraft( Book )

1 edition published in 1989 in English and held by 116 WorldCat member libraries worldwide

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 116 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)
Fuel-rich catalytic combustion of jet-A fuel : equivalence ratios 5.0 to 8.0 by Theodore A Brabbs( Book )

2 editions published in 1989 in English and held by 95 WorldCat member libraries worldwide

Fuel rich catalytic combustion (E.R.> 5.0) is a unique technique for preheating a hydrocarbon fuel to temperatures much higher than those obtained by conventional heat exchangers. In addition to producing very reactive molecules, the process upgrades the structure of the fuel by the formation of hydrogen and smaller hydrocarbons and produces a cleaner burning fuel by removing some of the fuel carbon from the soot formation chain. Temperatures higher than the 1200 K measured in a previous study with iso-octane (ref. 1) can be obtained by altering the air inlet temperature and/or the equivalence ratio (E.R.). The maximum temperature for the processed gases is probably 1350 K which is the threshold temperature for the formation of soot (ref. 2). This paper will describe the successful application of fuel-rich catalytic combustion to Jet-A, multicomponent fuel used in gas turbine combustors
The use of impact force as a scale parameter for the impact response of composite laminates by Wade C Jackson( Book )

1 edition published in 1992 in English and held by 94 WorldCat member libraries worldwide

Efficient fault diagnosis of helicopter gearboxes by H Chin( Book )

4 editions published in 1993 in English and held by 93 WorldCat member libraries worldwide

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 93 WorldCat member libraries 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

Languages
English (41)