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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Experimental pitch-, yaw-, and roll-damping characteristics of a shuttle orbiter at Mach number 8

Wind tunnel tests were conducted to measure the pitch-, yaw-, and roll-damping characteristics of a modified 089B shuttle orbiter. These tests were conducted for NASA-Langley at the von Karman Gas Dynamics Facility of the Arnold Engineering Development Center. Data were obtained utilizing the small amplitude forced-oscillation technique at angles of attack of -4.9 to 26.5 deg at Reynolds numbers, based on model length, of 1,180,000 to 4,820,000. The orbiter was dynamically stable in pitch, yaw, and roll, and the pitch derivatives were dependent on Reynolds number, while the roll derivatives were independent of Reynolds number.

Uselton, B. L.↗
NASA NTRS1975

The pitch-heave dynamics of transportation vehicles

The analysis and design of suspensions for vehicles of finite length using pitch-heave models is presented. Dynamic models for the finite length vehicle include the spatial distribution of the guideway input disturbance over the vehicle length, as well as both pitch and heave degrees-of-freedom. Analytical results relate the vehicle front and rear accelerations to the pitch and heave natural frequencies, which are functions of vehicle suspension geometry and mass distribution. The effects of vehicle asymmetry and suspension contact area are evaluated. Design guidelines are presented for the modification of vehicle and suspension parameters to meet alternative ride quality criteria.

Sweet, L. M.↗
NASA NTRS1976

Aerodynamic Performance of Two Variable-Pitch Fan Stages

The NASA-Lewis Research Center is investigating a variety of fan stages applicable for short haul aircraft. These low-pressure-ratio low-speed fan stages may require variable-pitch rotor blades to provide optimum performance for the varied flight demands and for thrust reversal on landing. A number of the aerodynamic and structural compromises relating to the variable-pitch rotor blades are discussed. The aerodynamic performance of two variable-pitch fan stages operated at several rotor blade setting angles for both forward and reverse flow application are presented. Detailed radial surveys are presented for both forward and reverse flow.

Moore, R. D.↗
NASA NTRS1975

Hamilton Standard Q-fan demonstrator dynamic pitch change test program, volume 1

Tests of a full scale variable pitch fan engine to obtain data on the structural characteristics, response times, and fan/core engine compatibility during transient changes in blade angle, fan rpm, and engine power is reported. Steady state reverse thrust tests with a take off nozzle configuration were also conducted. The 1.4 meter diameter, 13 bladed controllable pitch fan was driven by a T55 L 11A engine with power and blade angle coordinated by a digital computer. The tests demonstrated an ability to change from full forward thrust to reverse thrust in less than one (1) second. Reverse thrust was effected through feather and through flat pitch; structural characteristics and engine/fan compatibility were within satisfactory limits.

Demers, W. J.↗
NASA NTRS1976

Evidence that pitch angle scattering is an important loss mechanism for energetic electrons in the inner radiation belt of Jupiter

Analysis of data from the Pioneer 10 flyby discloses that pitch angle scattering plays an important part in determining the distribution of energetic electrons in the inner magnetosphere of Jupiter. Angular distributions measured by a Cerenkov detector reveal that redistribution takes place in pitch angle. Additionally, the radial profile of phase space density along the equator demands simultaneous particle losses. The loss rates are too high to be accounted for by synchrotron radiation loss, but are reasonably attributed to pitch angle scattering into the planetary loss cone.

Fillius, W.↗
NASA NTRS1976

A nonlinear theory of cosmic-ray pitch-angle diffusion in homogeneous magnetostatic turbulence

A plasma strong turbulence, weak coupling, theory is applied to the problem of cosmic-ray pitch-angle scattering in magnetostatic turbulence. The theory used is a rigorous generalization of Weinstock's 'resonance broadening' theory and contains no ad hoc approximations. A detailed calculation is presented for a model of 'slab' turbulence with an exponential correlation function. The results agree well with numerical simulations. The rigidity dependence of the pitch-angle scattering coefficient differs from that found by previous researchers. The differences result from an inadequate treatment of particle trajectories near 90 deg pitch angle in earlier work.

Goldstein, M. L.↗
NASA NTRS1976

Aerodynamic performance of two variable-pitch fan stages

NASA-Lewis Research Center is investigating a variety of fan stages applicable for short-haul aircraft. These low-pressure-ratio low-speed fan stages may require variable-pitch rotor blades to provide optimum performance for the varied flight demands and for thrust reversal on landing. A number of the aerodynamic and structural compromises relating to variable-pitch rotor blades are discussed. The aerodynamic performance of two variable-pitch fan stages operated at several rotor-blade setting angles is evaluated for both forward- and reverse-flow application. Detailed radial surveys are presented for both forward and reverse flow.

Moore, R. D.↗
NASA NTRS1977

Acoustic and aerodynamic performance of a variable-pitch 1.83-meter-(6-ft) diameter 1.20-pressure-ratio fan stage (QF-9)

Far field noise data and related aerodynamic performance are presented for a variable pitch fan stage having characteristics suitable for low noise, STOL engine application. However, no acoustic suppression material was used in the flow passages. The fan was externally driven by an electric motor. Tests were made at several forward thrust rotor blade pitch angles and one for reverse thrust. Fan speed was varied from 60 to 120 percent of takeoff (design) speed, and exhaust nozzles having areas 92 to 105 percent of design were tested. The fan noise level was at a minimum at the design rotor blade pitch angles of 64 deg for takeoff thrust and at 57 deg for approach (50 percent takeoff thrust). Perceived noise along a 152.4-m sideline reached 100.1 PNdb for the takeoff (design) configuration for a stage pressure ratio of 1.17 and thrust of 57,600 N. For reverse thrust the PNL values were 4 to 5 PNdb above the takeoff values at comparable fan speeds.

Glaser, F. W.↗
NASA NTRS1977

Adiabatic evolution of trapped particle pitch angle distributions during a storm main phase

Equatorial pitch angle distributions of over 200-keV ions obtained near L = 4 by Explorer 45 during a storm main phase show the development of marked minima at 90 deg pitch angle in direct association with a greater-than-a-factor-of-2 reduction in the equatorial magnetic field magnitude. The evolution of these pitch angle distributions can be quantitatively explained as a result of conservation of the first two adiabatic invariants provided the magnitude of the magnetic field decrease was approximately constant along field lines.

Lyons, L. R.↗
NASA NTRS1976

Ring current loss mechanisms and composition as inferred from equatorial pitch angle distributions observed during a storm recovery phase

Explorer 45 measurements of pitch angle distributions (PAD's) of ring current ions were examined for evidence of charge exchange or pitch-angle diffusion as loss mechanisms for the ring current during a storm recovery phase. The observed rounding of the PAD's above a minimum parallel energy is seen as resulting from pitch angle diffusion driven by resonant interactions with ion cyclotron waves. Calculations of growth rates using observed ion fluxes and PAD's have shown that ion cyclotron waves can be significantly amplified by the ring current plasma. However, wave growth off the equator must be taken into account in order to understand the time evolution of the observed PAD's. Isotropic distributions at lower energies remain isotropic at L-values between 3 and 4 despite the presence of charge exchange losses. An explanation for this apparent inconsistency may be that ring current is dominated by some ion species other than protons during recovery phase.

Lyons, L. R.↗
NASA NTRS1978

Adiabatic modulation of equatorial pitch angle anisotropy

Particle measurements from the geostationary ATS 6 satellite reveal striking equatorial pitch-angle anisotropies. A study of seven days of data shows a diurnal variation in anisotropy with the particle flux at a pitch angle of 40 deg greater than that at 90 deg during times of low magnetic-field intensity on the nightside and vice versa during times of high magnetic-field intensity on the dayside. Six representative anisotropy events are studied in finer detail. The 32- to 51-keV electron anisotropies increase and decrease with the total magnetic-field intensity. The proton and higher-energy electron anisotropies do not show as much variation. The particle anisotropies are studied in light of adiabatic and cyclotron resonance theory; the results indicate that adiabatic effects are the dominant modulation mechanism of particle pitch-angle distributions in the outer radiation belt

Kaye, S. M.↗
NASA NTRS1978

Nonlinear pitch angle scattering of energetic electrons by coherent VLF waves in the magnetosphere

A study is made of nonlinear cyclotron resonance wave-particle interaction in the magnetosphere with attention to the pitch angle scattering of energetic electrons by coherent VLF whistler mode signals. A computer simulation of the full nonlinear equations of motions for energetic particles interacting with a longitudinal whistler mode wave in an inhomogeneous magnetosphere are used. The results are compared to those of a linear theory. Test electrons distributed in energy and pitch angle are used to simulate the full distribution of particles. The scattering of the test particles and their integration over energy and pitch angle yield the precipitated flux. The results suggest that coherent VLF waves significantly influence the dynamics and lifetimes of energetic electrons trapped in the magnetosphere and magnetic shells illuminated by the waves.

Inan, U. S.↗
NASA NTRS1979

Effect of forward velocity and crosswind on the reverse-thrust performance of a variable-pitch fan engine

Variable-pitch-fan engines may be attractive for future short-haul aircraft if sufficient reverse thrust is available for aircraft deceleration after touchdown. Thrust reversal is obtained in these engines by changing fan blade pitch about 90 deg, which causes the fan airflow to enter the fan duct nozzle and exhaust through the fan inlet. This capability would eliminate the heavy and costly thrust reverser system required for current fixed-pitch turbofan engines. NASA has, therefore, supported the development of advanced technology for a quiet, clean, high-bypass-ratio turbofan engine for future short-haul aircraft. In connection with this program, tests were conducted to determine the effect of forward velocity and angle of attack on steady-state reverse-thrust performance. Other objectives of the tests were related to the determination of the effect of forward velocity on forward-to-reverse thrust transient performance and the determination of the effectiveness of an overshoot blade angle technique to establish reverse thrust during a transient. The results of the tests are discussed.

Reemsnyder, D. C.↗
NASA NTRS1977

Quiet Clean Short-haul Experimental Engine (QCSEE). Aerodynamic and aeromechanical performance of a 50.8 cm (20 inch) diameter 1.34 PR variable pitch fan with core flow

The fan aerodynamic and aeromechanical performance tests of the quiet clean short haul experimental engine under the wing fan and inlet with a simulated core flow are described. Overall forward mode fan performance is presented at each rotor pitch angle setting with conventional flow pressure ratio efficiency fan maps, distinguishing the performance characteristics of the fan bypass and fan core regions. Effects of off design bypass ratio, hybrid inlet geometry, and tip radial inlet distortion on fan performance are determined. The nonaxisymmetric bypass OGV and pylon configuration is assessed relative to both total pressure loss and induced circumferential flow distortion. Reverse mode performance, obtained by resetting the rotor blades through both the stall pitch and flat pitch directions, is discussed in terms of the conventional flow pressure ratio relationship and its implications upon achievable reverse thrust. Core performance in reverse mode operation is presented in terms of overall recovery levels and radial profiles existing at the simulated core inlet plane. Observations of the starting phenomena associated with the initiation of stable rotor flow during acceleration in the reverse mode are briefly discussed. Aeromechanical response characteristics of the fan blades are presented as a separate appendix, along with a description of the vehicle instrumentation and method of data reduction.

Giffin, R. G.↗
NASA NTRS1981

Passive cyclic pitch control for horizontal axis wind turbines

A flexible rotor concept, called the balanced pitch rotor, is described. The system provides passive adjustment of cyclic pitch in response to unbalanced pitching moments across the rotor disk. Various applications are described and performance predictions are made for wind shear and cross wind operating conditions. Comparisons with the teetered hub are made and significant cost savings are predicted.

Bottrell, G. W.↗
NASA NTRS1983

Aeroacoutic characteristics of a large, variable-pitch, variable-speed fan system

The acoustic and aerodynamic performance of the new drive fans for the NASA Ames 40- by 80-/80- by 120-foot wind tunnel was investigated. Results show that a fan system with variable-speed and variable-pitch rotor blades allows the operator to control noise and energy consumption, at a given mass flow rate, through the choice of blade speed and pitch. A low speed and high blade pitch will generally create the least noise at the least energy cost. An empirical method is described which predicts the sound power of this fan system reasonably well.

Soderman, P. T.↗
NASA NTRS1984

An advanced pitch change mechanism incorporating a hybrid traction drive

A design of a propeller pitch control mechanism is described that meets the demanding requirements of a high-power, advanced turboprop. In this application, blade twisting moment torque can be comparable to that of the main reduction gearbox output: precise pitch control, reliability and compactness are all at a premium. A key element in the design is a compact, high-ratio hybrid traction drive which offers low torque ripple and high torsional stiffness. The traction drive couples a high speed electric motor/alternator unit to a ball screw that actuates the blade control links. The technical merits of this arrangement and the performance characteristics of the traction drive are discussed. Comparisons are made to the more conventional pitch control mechanisms.

Steinetz, B. M.↗