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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Sample data effects of high-pass filters

Four mathematical models of linear first and second order high pass washout filters were analyzed. These models were Euler's Integration, Zero-Order Hold, Bilinear Transformation, and Second-Order Adams-Bashforth Integration. Bode responses for each model at various sample rates were compared to the continuous filter response. Higher sample rates produced Bode responses approaching the continuous response and the Bilinear Transformation model produced the best responses over the frequency spectrum and sample rates. Pole location analysis of each model in the z-plane showed the Bilinear Transformation and Zero-Order Hold models gave stable poles regardless of time step size, whereas the other models did not display stable poles. A near constant gain error over the entire frequency spectrum was discovered in the Zero-Order Hold cases and a correction gain was calculated for the first-order high-pass filter case.

Chin, D. O.↗
NASA NTRS1980

Conceptual design study of a visual system for a rotorcraft simulator and some advances in platform motion utilization

A conceptual design of a visual system for a rotorcraft flight simulator is presented. Also, drive logic elements for a coupled motion base for such a simulator are given. The design is the result of an assessment of many potential arrangements of electro-optical elements and is a concept considered feasible for the application. The motion drive elements represent an example logic for a coupled motion base and is essentially an appeal to the designers of such logic to combine their washout and braking functions.

Sinacori, J. B.↗
NASA NTRS1982

Non-isothermal effects on SO2 absorption by water droplets. I - Model development. II - Results and discussion

An analytic model of SO2 absorption in a falling water droplet is developed and a simulation of SO2 washout is performed. Nonisothermic effects on drop growth, droplet physical parameters, reaction rates, and multicomponent diffusion are treated in the model. The gas-liquid interface is assumed to be at equilibrium, and interfacial resistance is negligible. Raindrops are simulated as falling from a 2 km height through an atmospheric region containing SO2. The droplets decrease in size from evaporation and cooling, and their slightly basic pH aids SO2 absorption. The simulation indicates higher SO2 absorption at higher altitudes, and desorption may occur at ground level. Isothermal effects are concluded to be significant, and quantification of effects will depend on further modelling.

Reda, M.↗
NASA NTRS1982

H2O2 levels in rainwater collected in south Florida and the Bahama Islands

Measurements of H2O2 in rainwater collected in Miami, Florida, and the Bahama Islands area indicate the presence of H2O2 concentration levels ranging from 100,000 to 700,000 M. No systematic trends in H2O2 concentration were observed during an individual storm, in marked contrast to the behavior of other anions for example, NO3(-), SO4(-2), and Cl(-). The data suggest that a substantial fraction of the H2O2 found in precipitation is generated by aqueous-phase reactions within the cloudwater rather than via rainout and washout of gaseous H2O2.

Zika, R.↗
NASA NTRS1982

Measurement of cardiopulmonary performance during acute exposure to a 2440-m equivalent atmosphere

Each of 20 subjects (ranging in age from 18 to 38 years, 15 being male, five female) was given two Bruce Protocol symptom-limited maximum treadmill stress tests, breathing sea-level compressed air (20.9% O2) for one test and a 2440-m equivalent (15.5% O2) for the other. A significant difference was found to exist between measured VO2 max (p less than 0.0002) and exercise time (p less than 0.0004) for the two conditions. No significant differences were observed in heart rate or the recovery time to a respiratory quotient of less than 1. Hemoglobin saturation, as measured by an ear oximeter, averaged 95% for sea-level and 91% for the 2440-m equivalent gases. These results support a 2440-m equivalent contingency atmosphere in the Space Shuttle prior to donning a low-pressure suit for the purpose reducing nitrogen washout times.

Levitan, B. M.↗
NASA NTRS1982

An optimal control approach to the design of moving flight simulators

An abstract flight simulator design problem is formulated in the form of an optimal control problem, which is solved for the linear-quadratic-Gaussian special case using a mathematical model of the vestibular organs. The optimization criterion used is the mean-square difference between the physiological outputs of the vestibular organs of the pilot in the aircraft and the pilot in the simulator. The dynamical equations are linearized, and the output signal is modeled as a random process with rational power spectral density. The method described yields the optimal structure of the simulator's motion generator, or 'washout filter'. A two-degree-of-freedom flight simulator design, including single output simulations, is presented.

Sivan, R.↗
NASA NTRS1982

Importance of heterogeneous processes to tropospheric chemistry - Studies with a one-dimensional model

A one-dimensional, time-dependent model of tropospheric air composition is developed which incorporates several heterogeneous physical and chemical processes. The model includes the interaction of gases, aerosols, and hydrometeors through the physical mechanisms of nucleation, condensation, evaporation, coagulation, coalescence, and deliquescence. Precipitation, sedimentation, and dry deposition act to remove material from the atmosphere, while chemical transformations occur both in the vapor and the condensed phases. The model also incorporates the sources and vertical diffusion of gases and particles, as well as changes in the solar intensity caused by light-scattering from aerosols and clouds. Preliminary simulations made using this model indicate that rainout and washout processes strongly influence the distributions of tropospheric gases and aerosols under certain conditions.

Turco, R. P.↗
NASA NTRS1984

An in flight investigation of pitch rate flight control systems and application of frequency domain and time domain predictive criteria

The degree of attitude control provided by current integral-proportional pitch rate command-type control systems, while a prerequisite for flared landing, is insufficient for 'Level 1' performance. The pilot requires 'surrogate' feedback cues to precisely control flight path in the landing flare. Monotonic stick forces and pilot station vertical acceleration are important cues which can be provided by means of angle-of-attack and pitch rate feedback in order to achieve conventional short period and phugoid characteristics. Integral-proportional pitch rate flight control systems can be upgraded to Level 1 flared landing performance by means of lead/lag and washout prefilters in the command path. Strong pilot station vertical acceleration cues can provide Level 1 flared landing performance even in the absence of monotonic stick forces.

Berthe, C. J.↗
NASA NTRS1984

Water and the photochemistry of the troposphere

A discussion is presented concerning the role of water in its liquid and gaseous states in the chemistry and photochemistry of the earth's troposphere, with attention to the formation of the hydroxyl radical, oxidation chains involving the gases methane, carbon monoxide and ammonia, the atmospheric chemistry of the sulfur, hydrogen, halogen and nitrogen species, and the function of lightning as a source of tropospheric species. The phenomena of 'rainout', 'washout', and the aqueous chemistry of cloud an rain droplets and of water-covered aerosols, are noted. A section is devoted to the past and anticipated impact of anthropogenic activities on the chemistry and composition of the earth's atmosphere.

Levine, J. S.↗
NASA NTRS1985

Visual and motion cueing in helicopter simulation

Early experience in fixed-cockpit simulators, with limited field of view, demonstrated the basic difficulties of simulating helicopter flight at the level of subjective fidelity required for confident evaluation of vehicle characteristics. More recent programs, utilizing large-amplitude cockpit motion and a multiwindow visual-simulation system have received a much higher degree of pilot acceptance. However, none of these simulations has presented critical visual-flight tasks that have been accepted by the pilots as the full equivalent of flight. In this paper, the visual cues presented in the simulator are compared with those of flight in an attempt to identify deficiencies that contribute significantly to these assessments. For the low-amplitude maneuvering tasks normally associated with the hover mode, the unique motion capabilities of the Vertical Motion Simulator (VMS) at Ames Research Center permit nearly a full representation of vehicle motion. Especially appreciated in these tasks are the vertical-acceleration responses to collective control. For larger-amplitude maneuvering, motion fidelity must suffer diminution through direct attenuation through high-pass filtering washout of the computer cockpit accelerations or both. Experiments were conducted in an attempt to determine the effects of these distortions on pilot performance of height-control tasks.

Bray, R. S.↗
NASA NTRS1986

Visual and motion cueing in helicopter simulation

The visual cues presented in the simulator are compared with those of flight in an attempt to identify deficiencies. For the low-amplitude maneuvering tasks normally associated with the hover mode, the unique motion capabilities of the Vertical Motion Simulator (VMS) at Ames Research Center permit nearly a full representation of vehicle motion. Especially appreciated in these tasks are the vertical-acceleration responses to collective control. For larger-amplitude maneuvering, motion fidelity must suffer diminution through direct attenuation through high-pass filtering washout of the computer cockpit accelerations or both. Experiments were conducted in an attempt to determine the effects of these distortions on pilot performance of height-control tasks.

Bray, Richard S.↗
NASA NTRS1987

The effects of aeroelastic deformation on the unaugmented stopped-rotor dynamics of an X-Wing aircraft

A new design concept in the development of VTOL aircraft with high forward flight speed capability is that of the X-Wing, a stiff, bearingless helicopter rotor system which can be stopped in flight and the blades used as two forward-swept and two aft-swept wings. Because of the usual configuration in the fixed-wing mode, there is a high potential for aeroelastic divergence or flutter and coupling of blade vibration modes with rigid-body modes. An aeroelastic stability analysis of an X-Wing configuration aircraft was undertaken to determine if these problems could exist. This paper reports on the results of dynamic stability analyses in the lateral and longitudinal directions including the vehicle rigid-body and flexible modes. A static aeroelastic analysis using the normal vibration mode equations of motion was performed to determine the cause of a loss of longitudinal static margin with increasing airspeed. This loss of static margin was found to be due to aeroelastic washin of the forward-swept blades and washout of the aft-swept blades moving the aircraft aerodynamic center forward of the center of gravity. This phenomenon is likely to be generic to X-Wing aircraft.

Gilbert, Michael G.↗
NASA NTRS1987

The effects of aeroelastic deformation on the unaugmented stopped-rotor dynamics of an X-Wing aircraft

A new design concept in the development of vertical takeoff and landing aircraft with high forward flight speed capability is that of the X-Wing. The X-Wing is a stiff, bearingless helicopter rotor system which can be stopped in flight and the blades used as two forward-swept wings and two aft-swept wings. Because of the unusual configuration in the fixed-wing mode, there is a high potential for aeroelastic divergence or flutter and coupling of blade vibration modes with rigid-body modes. An aeroelastic stability analysis of an X-Wing configuration aircraft was undertaken to determine if these problems could exist. This paper reports on the results of dynamic stability analyses in the lateral and longitudinal directions including the vehicle rigid-body and flexible modes. A static aeroelastic analysis using the normal vibration mode equations of motion was performed to determine the cause of a loss of longitudinal static margin with increasing airspeed. This loss of static margin was found to be due to aeroelastic 'washin' of the forward-swept blades and 'washout' of the aft-swept blades moving the aircraft aerodynamic center forward of the center of gravity. This phenomenon is likely to be generic to X-Wing aircraft.

Gilbert, Michael G.↗
NASA NTRS1989

The use of vestibular models for design and evaluation of flight simulator motion

Quantitative models for the dynamics of the human vestibular system are applied to the design and evaluation of flight simulator platform motion. An optimal simulator motion control algorithm is generated to minimize the vector difference between perceived spatial orientation estimated in flight and in simulation. The motion controller has been implemented on the Vertical Motion Simulator at NASA Ames Research Center and evaluated experimentally through measurement of pilot performance and subjective rating during VTOL aircraft simulation. In general, pilot performance in a longitudinal tracking task (formation flight) did not appear to be sensitive to variations in platform motion condition as long as motion was present. However, pilot assessment of motion fidelity by means of a rating scale designed for this purpose, were sensitive to motion controller design. Platform motion generated with the optimal motion controller was found to be generally equivalent to that generated by conventional linear crossfeed washout. The vestibular models are used to evaluate the motion fidelity of transport category aircraft (Boeing 727) simulation in a pilot performance and simulator acceptability study at the Man-Vehicle Systems Research Facility at NASA Ames Research Center. Eighteen airline pilots, currently flying B-727, were given a series of flight scenarios in the simulator under various conditions of simulator motion. The scenarios were chosen to reflect the flight maneuvers that these pilots might expect to be given during a routine pilot proficiency check. Pilot performance and subjective rating of simulator fidelity was relatively insensitive to the motion condition, despite large differences in the amplitude of motion provided. This lack of sensitivity may be explained by means of the vestibular models, which predict little difference in the modeled motion sensations of the pilots when different motion conditions are imposed.

Bussolari, Steven R.↗
NASA NTRS1990

AX-5 space suit bearing torque investigation

The symptoms and eventual resolution of a torque increase problem occurring with ball bearings in the joints of the AX-5 space suit are described. Starting torques that rose 5 to 10 times initial levels were observed in crew evaluation tests of the suit in a zero-g water tank. This bearing problem was identified as a blocking torque anomaly, observed previously in oscillatory gimbal bearings. A large matrix of lubricants, ball separator designs and materials were evaluated. None of these combinations showed sufficient tolerance to lubricant washout when repeatedly cycled in water. The problem was resolved by retrofitting a pressure compensated, water exclusion seal to the outboard side of the bearing cavity. The symptoms and possible remedies to blocking are discussed.

Loewenthal, Stuart↗
NASA NTRS1989

Performance evaluation of advanced space suit concepts for Space Station

The requirements for an advanced space suit for Space Station EVA and the methods used to evaluate candidate suit concepts are examined. Two candidate Space Station suits, the AX-5 and the Mk. III, are described and illustrated. The methods to test these suits are discussed, including, tests at the NASA/Johnson Space Center Weightless Environment Training Facility, tests in the microgravity environment of the KC-135 aircraft, CO2 washout evaluations, component torque measurements, environmental hazards protection evaluations, and component cycle life verification.

Klaus, David M.↗
NASA NTRS1991

Doppler indices of gas phase formation in hypobaric environments: Time-intensity analysis

A semi-quantitative method to analyze decompression data is described. It possesses the advantage that it allows a graded response to decompression rather than the dichotomous response generally employed. A generalized critical volume (C-V), or stoichiometric time-dependent equilibrium model is examined that relates the constant of the equation P sub i equals m P sub f plus b to variable tissue supersaturation and gas washout terms. The effects of the tissue ratio on gas phase formation indicate that a decreased ratio yields fewer individuals with Doppler detectable gas bubbles, but those individuals still present with Spencer Grade 3 or 4. This might indicate a local collapse of tissue saturation. The individuals with Grade 3 or 4 could be at risk for type 2 decompression sickness by transpulmonic arterialization. The primary regulator of the problems of decompression sickness is the reduction of local supersaturation, presumably governed by the presence and number of gas micronuclei. It is postulated that a reduction in these nuclei will favor a low incidence of decompression sickness in microgravity secondary to hypokinesia and adynamia.

Powell, Michael R.↗
NASA NTRS1951

Empirical relation between induced velocity, thrust, and rate of descent of a helicopter rotor as determined by wind-tunnel tests on four model rotors

The empirical relation between the induced velocity, thrust, and rate of vertical descent of a helicopter rotor was calculated from wind tunnel force tests on four model rotors by the application of blade-element theory to the measured values of the thrust, torque, blade angle, and equivalent free-stream rate of descent. The model tests covered the useful range of C(sub t)/sigma(sub e) (where C(sub t) is the thrust coefficient and sigma(sub e) is the effective solidity) and the range of vertical descent from hovering to descent velocities slightly greater than those for autorotation. The three bladed models, each of which had an effective solidity of 0.05 and NACA 0015 blade airfoil sections, were as follows: (1) constant-chord, untwisted blades of 3-ft radius; (2) untwisted blades of 3-ft radius having a 3/1 taper; (3) constant-chord blades of 3-ft radius having a linear twist of 12 degrees (washout) from axis of rotation to tip; and (4) constant-chord, untwisted blades of 2-ft radius. Because of the incorporation of a correction for blade dynamic twist and the use of a method of measuring the approximate equivalent free-stream velocity, it is believed that the data obtained from this program are more applicable to free-flight calculations than the data from previous model tests.

Castles, Walter, Jr.↗