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Multiple-orifice throttle valve is not subject to cold welding in a vacuum environment and is compatible with strong oxidizing fluid. The valve is of all metal construction using simple components that do not slide or rotate and excludes static or dynamic seals.
The application of the Scott effect to the dynamics of galactic and stellar rotation is investigated. Efforts were also made to improve the sensitivity and stability of torque measurements and understand the microscopic mechanism that causes the Scott effect.
A two degrees-of-freedom (TDF) rate integrating gyro in the strapdown mode is a candidate for attitude sensing in a spacecraft navigation system, since it provides an additional axis of information for a relatively small increase in hardware complexity. A type of gyro which has not been fully exploited is of the dry, tuned, TDF design, in which the spring constant of the suspension system is effectively cancelled by the dynamic antispring of a swiveling, rotating, gimbal. The use of this unconventional gyro in a digital rebalance loop was investigated.
The dynamics of four important farfield rotating blade noise sources are summarized and techniques for noise reduction are discussed. These four noise areas include the role of unsteady blade surface loads on rotational noise, the effect of turbulent inflow on the radiated broadband noise of an airfoil, the influence of the trailing vortex on impulsive noise and tail rotor noise, and the effect of blade geometry on high-speed impulsive noise. These noise mechanisms occur to varying degrees on both helicopter rotors and propellers. Considerable theoretical work was done in the area of high-speed impulsive noise resulting from the geometry of the rotating blade system. Both model and full-scale experimental correlation of helicopter and propeller high-speed noise are presented. The effect of blade number and airfoil thickness distribution in reducing the high-speed noise is shown.
This paper investigates the physics of meteoroid breakup in the atmosphere and its implications for the observed features of strewn fields. There are several effects which cause dispersion of the meteoroid fragments: gravity, differential lift of the fragments, bow shock interaction just after breakup, centripetal separation by a rotating meteroid, and possibly a dynamical transverse separation resulting from the crushing deceleration in the atmosphere. Of these, it is shown that gravity alone can produce the common pattern in which the largest crater occurs at the downrange end of the scatter ellipse. The average lift-to-drag ratio of the tumbling fragments must be less than about 0.001, otherwise small fragments would produce small craters downrange of the main crater, and this is not generally observed. The cross-range dispersion is probably due to the combined effects of bow shock interaction, crushing deceleration, and possibly spinning of the meteoroid. A number of terrestrial strewn fields are discussed in the light of these ideas, which are formulated quantitatively for a range of meteoroid velocities, entry angles, and crushing strengths. It is found that when the crater size exceeds about 1 km, the separation between the fragments upon landing is a fraction of their own diameter, so that the crater formed by such a fragmented meteoroid is almost indistinguishable from that formed by a solid body of the same total mass and velocity.
An analysis is made of the influence of landing gear deflection characteristics on aircraft performance on the ground up to rotation. A quasi-steady dynamic equilibrium state is assumed, including other simplifying assumptions such as calm air conditions and normal aircraft lift and drag. Ground incidence is defined as the angle made by the mean aerodynamic chord of the wing with respect to the ground plane, and equations are given for force and balance which determine the quasi-equilibrium conditions for the aircraft during ground roll. Results indicate that the landing gear deflections lead to a substantial increase in the angle of attack, and the variation in the ground incidence due to landing gear flexibility could be as much as + or - 50%, and the reduction in tail load requirements almost 25%.
The effects of face coning on seal performance are evaluated with particular regard to the energy saving potential of convex conedface end seals as indicated by torque reduction. Experiments were conducted using a conventional carbon flat-face pusher-type seal, a coned-face pusher-type seal, coned-face bellows-type seal, and a modified coned-face pusher-type seal intended for dynamically unstable operation, with shaft rotation at up to 8000 rpm, pressures of up to 2758 kPa, and a petroleum-based turbine oil as lubricant. Torque at the seal interface is found to be reduced by 42% when the standard flat-face seal is replaced by a coned seal, although the leakage of the cone-face seal was 11 times greater. Reduction of seal balance from 76.1 to 51.3% resulted in an additional 44% reduction in torque, although at the expense of excessive leakage, but did not produce unstable operation. Face temperatures were reduced by 33-56 C and wear was also reduced greatly on the cone face seals. Seal performance is noted to be in agreement with analytical calculations.
It is shown that, for floated satellite gradiometers subject to very low levels of unmodeled forces and torques, dynamic estimation can dramatically reduce rotation correction errors. The filter structure is developed, and the value of factorization techniques is examined. Numerical examples are given for a few practical cases using plausible instrument ensembles. To achieve these early results, great simplifications have been made, and important error sources have been suppressed.
A recursive Newton-Euler procedure is presented for the formulation and solution of manipulator dynamical equations. The procedure includes rotational and translational joints and a topological tree. This model was verified analytically using a planar two-link manipulator. Also, the model was tested numerically against the Walker-Orin model using the Shuttle Remote Manipulator System data. The hinge accelerations obtained from both models were identical. The computational requirements of the model vary linearly with the number of joints. The computational efficiency of this method exceeds that of Walker-Orin methods. This procedure may be viewed as a considerable generalization of Armstrong's method. A six-by-six formulation is adopted which enhances both the computational efficiency and simplicity of the model.
The bearing matrix formulations proposed by Lim and Singh (1990) are extended to analyze the overall dynamics of a geared rotor system which includes a spur gear pair, shafts, rolling-element bearings, a motor, a load, a casing, and flexible or rigid mounts. For this purpose, discrete vibration models are developed and used to predict vibration transmission through the bearings and to investigate the effects of the bearing, casing, and mount dynamics on the dynamic characteristics of the internal rotating system. Analytical predictions show that the theory is capable of predicting the bearing and mount moment transmissibilities in addition to the force transmissibilities. The predicted flexural vibrations of the casing plate are in good agreement with measurements conducted on an experimental set-up that consisted of a high-precision beam and pinion, and four identical rolling element bearings contained in a flexible casing mounted rigidly on a massive foundation.
Many operational limitations of helicopters and other rotary-wing aircraft are due to nonlinear aerodynamic phenomena incuding unsteady, three-dimensional transonic and separated flow near the surfaces and highly vortical flow in the wakes of rotating blades. Modern computational fluid dynamics (CFD) technology offers new tools to study and simulate these complex flows. However, existing Euler and Navier-Stokes codes have to be modified significantly for rotorcraft applications, and the enormous computational requirements presently limit their use in routine design applications. Nevertheless, the Euler/Navier-Stokes technology is progressing in anticipation of future supercomputers that will enable meaningful calculations to be made for complete rotorcraft configurations.
The paper summarizes the fundamental gravity field constants for Mars and a brief historical review of early determinations and current-day accurate estimates. These include the planetary gravitational constant, global figure, dynamical oblateness, mean density, and rotational period. Topographic results from data acquired from the 1967 opposition to the most recent, 1988, opposition are presented. Both global and selected local topographic variations and features are discussed. The inertia tensor and the nonhydrostatic component of Mars are examined in detail. The dimensionless moment of inertia about the rotational axis is 0.4 for a body of uniform density and 0.37621 if Mars were in hydrostatic equilibrium. By comparing models of both gravity and topography, inferences are made about the degree and depth of compensation in the interior and stresses in the lithosphere.
The paper is an operating manual for the Dynamic Stability Instrumentation System in specific NASA Langley wind tunnels. The instrumentation system performs either a synchronous demodulation or a Fast Fourier Transform on dynamic balance strain gage signals, and ultimately computes aerodynamic coefficients. The dynamic balance converts sting motor rotation into pitch or yaw plane or roll axis oscillation, with timing information provided by a shaft encoder. Additional instruments control model attitude and balance temperature and monitor sting vibrations. Other instruments perform self-calibration and diagnostics. Procedures for conducting calibrations and wind-off and wind-on tests are listed.
Urban Air Mobility vehicle concepts represent a new type of vertical lift machine. From the use of multirotor configurations to the use of variable RPM for thrust control of rigid, propeller-style rotors, many of the UAM concepts observed in industry have departed significantly from traditional VTOL designs. While such novel vehicle types may provide beneficial mission capability and efficiency, they have not been as thoroughly studied as more traditional configurations, and new aeromechanics analysis must be conducted. Operating states such as low-tip-speed rotors in edgewise flight may prove to yield unusual aeroelastic behavior and must be investigated. In the present work, a rotorcraft comprehensive analysis is used to analyze the aeroelastic characteristics of a fixed-pitch, variable RPM rotor in edgewise flight. The rotor model, a three-bladed, fixed pitch propeller, was developed in a previous work. Floquet theory analysis is used to capture the periodic nature of the dynamics. Parameters such as rotor rotational speed, forward flight speed, and blade torsion stiffness are varied and their impact on performance and stability are assessed. A value of torsion stiffness is identified to yield stable flight from 0-100 kts with a wide range of RPM values. The results may be used to provide insight into the aeroelastic characteristics of certain UAM-type rotors.
The paper describes a computerized data distribution capability, IMAT, in place at the NASA Langley Research Center for the multidisciplinary analysis of the dynamics and control of large flexible space structures. The paper includes results obtained in using IMAT to investigate the influence of the structural response of the space station framework on the control of a 300kw class, solar-dynamic-powered, dual-keel space station during an orbital reboost maneuver. The method of control, using an unfiltered proportional-plus-differential control law, led to a stable control system even with local flexible response measured at the control sensor location included as a part of the control error signal. The flexible response at the outboard solar dynamic system sun-line axis was close to the maximum rotation allowed for efficient operation; thus, active local control of each solar dynamic system may be necessary to limit sun-line axis rotations effectively during a reboost maneuver.
The dynamical behavior of fluids, in particular the effect of surface tension on partially-filled rotating fluids (cryogenic liquid helium and helium vapor), in a full-scale Gravity Probe-B Spacecraft propellant tank without probe imposed by various frequencies of gravity jitters have been investigated. Twelve case studies of slosh wave excitation due to various frequencies of gravity jitters under different rotating speeds of propellant tank and different levels of background gravity environment have been numerically simulated. Results disclose the conditions for the excitation of large amplitude slosh waves which shall be avoided in the design of cryogenic liquid propellant system.
Neutral buoyancy has often been used in the past for EVA development activities, but little has been done to provide an analytical understanding of the environment and its correlation with space. This paper covers a set of related research topics at the MIT Space Systems Laboratory, dealing with the modeling of the space and underwater environments, validation of the models through testing in neutral buoyancy, parabolic flight, and space flight experiments, and applications of the models to gain a better design methodology for creating meaningful neutral buoyancy simulations. Examples covered include simulation validation criteria for human body dynamics, and for applied torques in a beam rotation task, which is the pacing crew operation for EVA structural assembly. Extensions of the dynamics models are presented for powered vehicles in the underwater environment, and examples given from the MIT Space Telerobotics Research Program, including the Beam Assembly Teleoperator and the Multimode Proximity Operations Device. Future expansions of the modeling theory are also presented, leading to remote vehicles which behave in neutral buoyancy exactly as the modeled system would in space.
The dynamical behavior of fluids, in particular the effect of surface tension on partially filled rotating fluids in a full-scale prototype Gravity Probe-B Spacecraft propellant tank and various 10 percent subscale containers with identical values of similarity parameters such as Bond number, dynamical capillary number, rotational Reynolds number, and Weber number, as well as imposed gravity jitters have been investigated. It is shown that the Bond number can be used to simulate the wave characteristics of slosh wave excitation, whereas the Weber number can be used to simulate the wave amplitude of slosh-mode excitation. It is shown that a dynamical capillary number can be used to simulate the induced perturbation of the fluid stress distribution exerted on the wall. This distribution is governed by the interaction between surface tension (slosh-wave excitation along the liquid-vapor interface) and viscous (fluid stress exerted on the wall) forces.