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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 289 records · Page 16

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NASA NTRS1981

Transient nonlinear pitch angle scattering of energetic electrons by coherent VLF wave packets in the magnetosphere

Adiabatic theory is used in studying the transient nonlinear pitch angle scattering experienced by energetic electrons under the influence of coherent VLF wave packets in the magnetosphere. Finite wave packets of both fixed and variable frequency are considered, as are wide ranges of L shell, wave amplitude, and wave frequency. The results indicate that large mean pitch angle changes can be induced in the portion of the energetic population that undergoes a nonlinear cyclotron resonance interaction with the wave packet.

Bell, T. F.↗

NASA NTRS1982

Plasma pitch angle distributions near the substorm injection front

ATS-6 spacecraft hot plasma instrument data obtained during January, 1980 is presented, which provides electron and ion pitch distributions in the vicinity of an earthward-propagating, substorm-associated abrupt plasma change near synchronous orbit. Evidence is found of symmetric atmospheric source cones for few 100-eV electrons after front passage, supporting both (1) concept of atmospheric electron degradation of the hot, high-altitude plasma, and (2) the proposal that the injection front is a moving, precipitation-flow boundary between the hot plasma and the cooler plasma that has become spectrally degraded via interaction with the atmosphere. The enhanced hot plasma electron intensities appearing in association with front passage exhibit a modest, field-aligned anisotropy with minima at pitch angles characteristic of symmetric loss cones, consistent with mirror compression of the electrons on inward-collapsing field lines.

Moore, T. E.↗

NASA NTRS1982

Alleviation of the subsonic pitch-up of delta wings

A 'pylon vortex generator' concept has been proposed for alleviating the subsonic pitch-up instability of highly swept supersonic-cruise wings. Fixed at a part-span location, this leading-edge device utilizes the lateral velocity component in the flow approaching the swept leading edge to generate a streamwise vortex, opposite in sense to the tip vortex. The vortex-induced downwash outboard of the device serves to control the leading-edge stall development in the wing-tip regions. Wind-tunnel results on 60-deg and 74-deg flat-plate delta wings are presented to illustrate the operation of the pylon vortex generator in modifying the spanwise leading-edge separation characteristics resulting in effective alleviation of the pitch-up.

Rao, D. M.↗

NASA NTRS1981

Monte-Carlo model of pitch-angle scattering in solar cosmic ray events

Monte Carlo simulations of the propagation of solar cosmic-rays in interplanetary space are reported, including the effects of pitch-angle scattering and adiabatic focusing. Time intensity profiles agree well with the corresponding spatial diffusion approximation for models close to those used by Gombosi and Owens (1980). Monte Carlo simulations of the same model problem yield results that disagree with those of Gombosi and Owens, and the most likely possible source of error in the Monte Carlo simulation is considered to be in the region near the 90 deg pitch angle where the finite step size introduces certain inconsistencies.

Palmer, I. D.↗

NASA NTRS1980

Selection of some rotor parameters to reduce pitch-roll coupling of helicopter flight dynamics

The results of a study conducted to investigate further a means of choosing primary rotor parameters to reduce the coupling of longitudinal and lateral flapping in hover and in forward flight are presented. The rotor parameters included - flapping hinge offset, flapping hinge restraint, pitch-flap coupling, and blade Lock number - are known to influence the agility, stability, and operational safety of helicopters. Effects of the nonuniform downwash model of White and Blake on the blade flapping motion are examined, and the theoretical calculation is then correlated with experimental test data. The condition for achieving perfect decoupling of the flapping response due to aircraft pitch and roll rates, which was previously obtained for a hovering rotor, is evaluated in forward flight. The results show that negligible coupling is achieved in forward flight; moreover, there is the additional benefit of a slight reduction in the coupling of the roll rate to coning. It is also indicated that the values of the rotor parameters chosen according to the decoupling condition are moderate and that the flapping motion is stable with the parameters chosen.

Chen, R. T. N.↗

NASA NTRS1982

Pitch angle distributions of geomagnetically trapped MeV helium ions during quiet times

It is noted that during geomagnetically quiet conditions, energetic radiation belt helium ion fluxes at MeV energies have been found to exhibit characteristic radial profiles and large pitch angle anisotropies. Compiling data from many experiments, a systematic dependence of this anisotropy with helium ion energy is deduced. Provided a certain approximation holds for the observed pitch angle distributions, an empirical relation is deduced involving the helium ion energy. The range of the total ion energy here is 0.59-9 MeV (148-2250 keV per nucleon). These values are obtained for L shells in the range where L is approximately 2 to 5. The results are compared with theoretical expectations, and a qualitative explanation for the observed trend is suggested.

Fritz, T. A.↗

NASA NTRS1974

Dynamic stability characteristics in pitch, yaw, and roll of a supercritical-wing research airplane model

The aerodynamic damping in pitch, yaw, and roll and the oscillatory stability in pitch and yaw of a supercritical-wing research airplane model were determined for Mach numbers of 0.25 to 1.20 by using the small-amplitude forced-oscillation technique. The angle-of-attack range was from -2 deg to 20 deg. The effects of the underwing leading-edge vortex generators and the contributions of the wing, vertical tail, and horizontal tail to the appropriate damping and stability were measured.

Boyden, R. P.↗

NASA NTRS1982

Fixed pitch rotor performance of large horizontal axis wind turbines

Experimental fixed pitch wind turbine performance data is presented for both the DOE/NASA Mod-0 and the Danish Gedser wind turbines. Furthermore, a method for calculating the output power from large fixed pitch wind turbines is presented. Modifications to classical blade element momentum theory are given that improve correlation with measured data. Improvement is particularly evident in high winds (low tip speed ratios) where aerodynamic stall occurs as the blade experiences high angles of attack.

Viterna, L. A.↗

NASA NTRS1983

Application of Calspan pitch rate control system to the Space Shuttle for approach and landing

A pitch rate control system designed for use in the shuttle during approach and landing was analyzed and compared with a revised control system developed by NASA and the existing OFT control system. The design concept control system uses filtered pitch rate feedback with proportional plus integral paths in the forward loop. Control system parameters were designed as a function of flight configuration. Analysis included time and frequency domain techniques. Results indicate that both the Calspan and NASA systems significantly improve the flying qualities of the shuttle over the OFT. Better attitude and flight path control and less time delay are the primary reasons. The Calspan system is preferred because of reduced time delay and simpler mechanization. Further testing of the improved flight control systems in an in-flight simulator is recommended.

Weingarten, N. C.↗

NASA NTRS1984

Bifurcation analysis of aircraft pitching motions near the stability boundary

Bifuraction theory is used to analyze the nonlinear dynamic stability characteristics of an aircraft subject to single degree of freedom pitching-motion perturbations about a large mean angle of attack. The requisite aerodynamic information in the equations of motion is represented in a form equivalent to the response to finite-amplitude pitching oscillations about the mean angle of attack. This information is deduced from the case of infinitesimal-amplitude oscillations. The bifurcation theory analysis reveals that when the mean angle of attack is increased beyond a critical value at which the aerodynamic damping vanishes, new solutions representing finite-amplitude periodic motions bifurcate from the previously stable steady motion. The sign of a simple criterion, cast in terms of aerodynamic properties, determines whether the bifurcating solutions are stable (supercritical) or unstable (subcritical). For flat-plate airfoils flying at supersonic/hypersonic speed, the bifurcation is subcritical, implying either that exchanges of stability between steady and periodic motion are accompanied by hysteresis phenomena, or that potentially large aperiodic departures from steady motion may develop.

Hui, W. H.↗

NASA NTRS1984

Pitch angle diffusion in the Jovian magnetodisc

Using a linear approximation to the field variation and a mathematical technique for distorting the orbit integration into the complex gyrophase plane, a formula is derived for the nonadiabatic change in magnetic moment. This change varies as the cosine of the particle gyrophase at the equator, so that if a particle traverses the equator several times with different values of this gyrophase, it suffers randomly correlated values for the nonadiabatic change in magnetic moment. The algebraic formula for this nonadiabatic change is found to be in excellent agreement with previous numerical computations. The phase space density, averaged over several bounce periods, is found to satisfy a diffusion equation in pitch angle. The diffusion coefficient is dependent on particle energy, pitch angle, and the field line along which the particles are moving.

Birmingham, T. J.↗

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.

Steinetz, B. M.↗

NASA NTRS1984

Synthesized speech rate and pitch effects on intelligibility of warning messages for pilots

In civilian and military operations, a future threat-warning system with a voice display could warn pilots of other traffic, obstacles in the flight path, and/or terrain during low-altitude helicopter flights. The present study was conducted to learn whether speech rate and voice pitch of phoneme-synthesized speech affects pilot accuracy and response time to typical threat-warning messages. Helicopter pilots engaged in an attention-demanding flying task and listened for voice threat warnings presented in a background of simulated helicopter cockpit noise. Performance was measured by flying-task performance, threat-warning intelligibility, and response time. Pilot ratings were elicited for the different voice pitches and speech rates. Significant effects were obtained only for response time and for pilot ratings, both as a function of speech rate. For the few cases when pilots forgot to respond to a voice message, they remembered 90 percent of the messages accurately when queried for their response 8 to 10 sec later.

Simpson, C. A.↗

NASA NTRS1986

Circulation-Control Variable-Pitch Propeller

Circulation-control variable-pitch propeller has large lift value at moderate blowing coefficients. Based on circulation-control airfoil concept, has no moving parts other than needed for propeller rotation. Substituted for conventional variable-pitch propeller airfoil, lowers manufacturing costs, reduces maintenance, and improves reliability.

Garner, H. D.↗

NASA NTRS1986

Effects of graphitization on the environmental stability of brominated pitch-based fibers

The residual bromine graphite intercalation compounds of high modulus pitch-based fibers (Amoco P-55, P-75, P-100, and P-120) were formed and their resistances were monitored under a variety of environmental conditions. A threshold graphitization was observed below which the bromination reaction does not occur to an appreciable extent. The graphitization of the P-55 fibers falls below that threshold, precluding an extensive reaction. The P-75, P-100, and P-120 fibers all form bromination compounds which are stable at ambient conditions, under vacuum, and under high humidity (100 percent humidity at 60 C). The thermal stability of the resistivity increased with decreasing graphitization, with the stable temperature for P-120 being 100 C; for P-100, 200 C; and for P-75, 250 C. When cost is a consideration, bromination of pitch-based fibers is an economical way to achieve low resistivities.

Gaier, J. R.↗

NASA NTRS1986

Vestibular-visual conflict in pitch and yaw planes in the squirrel monkey

Direction conflicting vestibular and visual (optokinetic) stimuli either in the pitch or yaw plane were given to squirrel monkey subjects. The conflict sickness symptom score in the pitch plane was significantly higher than that in the yaw plane for the initial exposure session (p less than 0.01). A significant score difference was also encountered when the exposure sessions were repeated (p less than 0.05).

Igarashi, Makoto↗

NASA NTRS1988

Pitch-Learning Algorithm For Speech Encoders

Adaptive algorithm detects and corrects errors in sequence of estimates of pitch period of speech. Algorithm operates in conjunction with techniques used to estimate pitch period. Used in such parametric and hybrid speech coders as linear predictive coders and adaptive predictive coders.

Bhaskar, B. R. Udaya↗

NASA NTRS1987

Measurement of velocity and vorticity fields in the wake of an airfoil in periodic pitching motion

The velocity field created by the wake of an airfoil undergoing a prescribed pitching motion was sampled using hot wire anemometry. Data analysis methods concerning resolution of velocity components from cross wire data, computation of vorticity from velocity time history data, and calculation of vortex circulation from vorticity field data are discussed. These data analysis methods are applied to a flow field relevant to a two dimensional blade-vortex interaction study. Velocity time history data were differentiated to yield vorticity field data which are used to characterize the wake of the pitching airfoil. Measurement of vortex strength in sinusoidal and nonsinusoidal wakes show vortices in the sinusoidal wake have stronger circulation and more concentrated vorticity distributions than the tailored nonsinusoidal wake.

Booth, Earl R., Jr.↗