56,193 research outputs found
Concepts for a theoretical and experimental study of lifting rotor random loads and vibrations (the effects of some rotor feedback systems on rotor-body dynamics), Phase 7-A
The effects of three gyroless rotor feedback systems: (1) coning feedback, (2) proportional tilting feedback, and (3) a combination of these on the rotor-body dynamics of hingeless rotorcraft are studied with a simplified analytical model in the advance ratio range from 0 to .8. Combinations of feedback phase angles and control phase angles are selected to minimize control cross coupling and control sensitivity changes between low and high speed flight. For the feedback systems thus selected the effects of feedback gain and control actuator time lag on the stability both with fixed hub and in free flight is studied, whereby the rotorcraft is free in pitch, roll and vertical motion but otherwise restrained. For the free flight is studied, whereby the rotorcraft is free in pitch, roll and vertical motion but otherwise restrained. For the free flight conditions the effects of a horizontal tail are also determined in itself and in combination with the rotor feedback systems
Finite Element Stability Analysis for Coupled Rotor and Support Systems
The effects of fuselage motions on stability and random response were analytically assessed. The feasibility of adequate perturbation models from non-linear trim conditions was studied by computer and hardware experiments. Rotor wake-blade interactions were assessed by using a 4-bladed rotor model with the capability of progressing and regressing blade pitch excitation (cyclic pitch stirring), by using a 4-bladed rotor model with hub tilt stirring, and by testing rotor models in sinusoidal up or side flow
Concepts for a theoretical and experimental study of lifting rotor random loads and vibrations. Phase 6-A: Effects of blade torsion, of blade flap bending flexibility and of rotor support flexibility on rotor stability and random response
The effects of lifting rotor blade torsion, blade flap bending flexibility and rotor support flexibility on rotor stability and random response are described. The subjects discussed are: (1) blade representation and method of analysis, (2) random gust response statistics for coupled torsion-flapping rotor blade vibrations, (3) flap bending corrections to the rigid blade analysis of lifting rotors, and (4) effects of rotor support flexibility. The response of linear periodically time varying systems to random excitation is examined
Computer aided manual tracking
A scheme was developed to assist the human operator by augmenting an optic sight manual tracking loop with target rate estimates from a computer control algorithm which can either be a Kalman Filter or an alpha, beta, gamma filter. The idea is for the computer to provide rate tracking while the human operator is responsible for nullifying the tracking error. A simple schematic is shown to illustrate the implementation of this concept. A hybrid real-time man-in-loop simulation was used to compare the tracking performance of the same flight trajectory with or without this form of computer-aided track. Preliminary results show the advantage of computer-aided track against high speed aircraft at close range. However, good tracking before target state estimator maturity becomes more critical for aided track than without. Results are presented for a constant velocity flight trajectory
Spin-spin Correlation lengths of Bilayer Antiferromagnets
The spin-spin correlation length and the static structure factor for bilayer
antiferromagnets, such as YBaCuO, are calculated using field
theoretical and numerical methods. It is shown that these quantities can be
directly measured in neutron scattering experiments using energy integrated
two-axis scan despite the strong intensity modulation perpendicular to the
layers. Our calculations show that the correlation length of the bilayer
antiferromagnet diverges considerably more rapidly, as the temperature tends to
zero, than the correlation length of the corresponding single layer
antiferromagnet typified by LaCuO. This rapid divergence may have
important consequences with respect to magnetic fluctuations of the doped
superconductors.Comment: This paper supersedes cond-mat/9703138 and contains numerical
simulation results to compare against analytical results. 6 pages, 2
postscript figures (embedded), uses EuroPhys.sty and EuroMac
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