6,606 research outputs found

    Effects of planform geometry on hover performance of a 2-meter-diameter model of a four-bladed rotor

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    Hover tests were conducted on three small scale rotors to evaluate the effects of blade planform taper on rotor hover performance. Tests were conducted on a rectangular swept-tip configuration, on a configuration with a 3 to 1 taper over the outboard 20 percent of the span, and on a configuration with a 5 to 1 taper over the outboard 20 percent of the blade span. The investigation covered a range of thrust coefficients from 0 to 0.0075 and a range of tip speeds from 300 to 600 ft/sec. The tests showed that both tapered configurations had better hover performance than the swept-tip rectangular configuration and that the 3 to 1 taper configuration was better than the 5 to 1 taper configuration. The test results were compared with predictions made with a prescribed wake analysis, a momentum analysis, and a simplified free wake analysis

    Helicopter Anti-Torque System Using Strakes

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    A helicopter is disclosed with a system for controlling main-rotor torque which reduces the power and size requirements of conventional anti-torque means. The torque countering forces are generated by disrupting the main rotor downwash flowing around the fuselage. The downwash flow is separated from the fuselage surface by a strake positioned at a specified location on the fuselage. This location is determined by the particular helicopter wash pattern and fuselage configuration, generally being located between 20 deg before top dead center (TDC) and 80 deg from TDC on the fuselage side to which the main rotor blade approaches during rotation. The strake extends along the fuselage from the cabin section to the aft end and can be continuous or separated for aerodynamic surfaces such as a horizontal stabilizer

    A Study of the Perception of Verbal Aggression in Black and White Females

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    The purpose of this study was to compare black and white females\u27 perceptions of verbal aggression. Eighty black and 80 white female participants read a short dialogue of two female college roommates engaged in a verbal interaction. One of these women was arbitrarily selected as the identified aggressor; the other, the target. Pilot studies had established that participants similar to those used in this study thought that the dialogue contained verbal aggression and that each of the persons was equally verbally aggressive. As the participants read the dialogue, they had access to drawings of the two women. The experimental conditions were manipulated to produce a 2 x 2 x 2 design: race of participant (black or white), race of aggressor (black or white), and race of target (black or white). The dependent measures of aggressiveness were three scales of the Interpersonal Behavior Survey (1980) and a combination of two scales from the Adjective Check List (1952). There was a main effect for race of participant, such that ratings of aggression made by white females were significantly higher than those made by black females. There were no main effects for either race of aggressor or race of target; and there were no interactions. Implications related to the socialization process of black and white females and suggestions for future research are discussed

    Tunable Transient Decay Times in Nonlinear Systems: Application to Magnetic Precession

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    The dynamical motion of the magnetization plays a key role in the properties of magnetic materials. If the magnetization is initially away from the equilibrium direction in a magnetic nanoparticle, it will precess at a natural frequency and, with some damping present, will decay to the equilibrium position in a short lifetime. Here we investigate a simple but important situation where a magnetic nanoparticle is driven non-resonantly by an oscillating magnetic field, not at the natural frequency. We find a surprising result that the lifetime of the transient motion is strongly tunable, by factors of over 10,000, by varying the amplitude of the driving field.Comment: EPL Preprin
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