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At least 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Extended flight evaluation of a near-term pitch active control system

Fuel savings can be achieved by moving the center of gravity of an aircraft aft which reduces the static stability margin and consequently the trim drag. However, flying qualities of an aircraft with relaxed static stability can be significantly degraded. The flying qualities can be restored by using a pitch active control system (PACS). This report documents the work accomplished during a follow-on program (see NASA CR-165951 for initial program report) to perform extended flight tests of a near-term PACS. The program included flying qualities analyses, piloted flight simulation tests, aircraft preparation and flight tests to demonstrate that the near-term PACS provided good flying qualities within the linear static stability envelope to a negative 3% static stability margin.

Guinn, Wiley A.↗
NASA NTRS1987

Stability of bromine, iodine monochloride, copper (II) chloride, and nickel (II) chloride intercalated pitch-based graphite fibers

Four different grades of pitch-based graphite fibers (Amoco P-55, P-75, P-100. and P-120) were intercalated with each of four different intercalates: bromine (Br2), iodine monochloride (ICl), copper (II) chloride (CuCl2), and nickel (II) chloride (NiCl2). The P-55 fibers did not react with Br2 or NiCl2, and the P-75 did not react with NiCl2. The stability of the electrical resistance of the intercalated fibers was monitored over long periods of time in ambient, high humidity (100 percent at 60 C), vacuum (10 to the -6 torr), and high temperature (up to 400 C) conditions. Fibers with lower graphitization form graphite intercalation compounds (GIC's) which are more stable than those with higher graphitization (i.e., P-55 (most stable) greater than P-75 greater than P-100 greater than P-120 (least stable). Br2 formed the most stable GIC's followed in order of decreasing stability by ICl, CuCl2, and NiCl2. While Br2 GIC's had the most stability, ICl had the advantages of forming GIC's with slightly greater reduction in resistance (by about 10%) than Br2, and the ability to intercalate P-55 fiber. Transition metal chlorides are susceptible to water vapor and high temperature. The stability of fibers in composites differs.

Gaier, James R.↗
NASA NTRS1986

Anticorrelation of Shubnikov-deHaas amplitudes and negative magnetoresistance magnitudes in intercalated pitch based graphite fibers

In pitch based carbon fibers at low temperatures, simultaneous presence of a negative magnetoresistance and the Shubnikov-deHaas effect are found. The strengths of these effects correlate inversely. These results can be understood in terms of the amount of order vs disorder in the fiber, as described by Guigon and Oberlin from structural studies.

Woollam, John A.↗
NASA NTRS1986

Steady and unsteady transonic pressure measurements on a clipped delta wing for pitching and control-surface oscillations

Steady and unsteady pressures were measured on a clipped delta wing with a 6-percent circular-arc airfoil section and a leading-edge sweep angle of 50.40 deg. The model was oscillated in pitch and had an oscillating trailing-edge control surface. Measurements were concentrated over a Mach number range from 0.88 to 0.94; less extensive measurements were made at Mach numbers of 0.40, 0.96, and 1.12. The Reynolds number based on mean chord was approximately 10 x 10 to the 6th power. The interaction of wing or control-surface deflection with the formation of shock waves and with a leading-edge vortex generated complex pressure distributions that were sensitive to frequency and to small changes in Mach number at transonic speeds.

Hess, Robert W.↗
NASA NTRS1988

Energy dependent pitch angle distributions of auroral primary electrons

Double-layer/parallel-electric field accelerations and the subsequent electron-beam plasma interactions involving Cerenkov and anomalous cyclotron resonances are considered. It is found that these phenomena yield pitch angle distributions as noted from rocket and satellite studies. Although the electron acceleration by weak parallel electric fields forming a runaway electron tail is limited to a critical parallel energy determined by the anomalous cyclotron resonance, such a limitation does not occur with acceleration by a localized parallel electric field such as that in a double layer.

Singh, N.↗
NASA NTRS1988

A static investigation of a simultaneous pitch and yaw thrust vectoring 2-D C-D nozzle

An investigation has been conducted in the static test facility of the Langley 16-Foot Transonic Tunnel to determine the internal performance and flow-turning capability of a two-dimensional convergent-divergent nozzle. Thrust vectoring in the pitch plane was provided by rotation of the divergent flaps. The exhaust stream was turned in the yaw direction by deflection of yaw flaps hinged at the end of the nozzle sidewalls. The yaw flap hinge location was varied along the divergent region of the nozzle at four locations including the exit plane and the throat plane. The three hinge locations upstream of the nozzle exit plane required the downstream corners of both upper and lower divergent flaps to be cut off to eliminate interference when the yaw flaps were deflected. Three different lengths of yaw flaps were tested at several angles of deflection. The nozzle simulated a dry power setting with an expansion ratio typical of subsonic cruise and was tested at nozzle pressure ratios from 2.0 to 7.0.

Taylor, John G.↗
NASA NTRS1987

A statistical study of ion pitch-angle distributions

Preliminary results of a statistical study of energetic (34-50 keV) ion pitch-angle distributions (PADs) within 9 Re of earth provide evidence for an orderly pattern consistent with both drift-shell splitting and magnetopause shadowing. Normal ion PADs dominate the dayside and inner magnetosphere. Butterfly PADs typically occur in a narrow belt stretching from dusk to dawn through midnight, where they approach within 6 Re of earth. While those ion butterfly PADs that typically occur on closed drift paths are mainly caused by drift-shell splitting, there is also evidence for magnetopause shadowing in observations of more frequent butterfly PAD occurrence in the outer magnetosphere near dawn than dusk. Isotropic and gradient boundary PADs terminate the tailward extent of the butterfly ion PAD belt.

Sibeck, D. G.↗
NASA NTRS1988

Effect of large amplitude pitching motions on the unsteady aerodynamic characteristics of flat-plate wings

Large-amplitude unsteady motion effects on the aerodynamic force and stability characteristics of flat-plate wings were investigated in a wind tunnel for the cases of two delta wings with respective leading edge sweeps of 70 and 45 deg, and a rectangular wing whose aspect ratio was equal to that of the 70-deg delta wing. Attention was given to the effects of reduced frequency and mean angle of attack. It is found that lags in vortex burst location and separation/reattachment of flow on the upper surface of the wing produced large overshoots and hysteresis loops in normal force and pitching moment coefficients that were a strong function of mean oscillation angle and reduced frequency.

Brandon, Jay M.↗
NASA NTRS1988

In-flight simulation investigation of rotorcraft pitch-roll cross coupling

An in-flight simulation experiment investigating the handling qualities effects of the pitch-roll cross-coupling characteristic of single-main-rotor helicopters is described. The experiment was conducted using the NASA/Army CH-47B variable stability helicopter with an explicit-model-following control system. The research is an extension of an earlier ground-based investigation conducted on the NASA Ames Research Center's Vertical Motion Simulator. The model developed for the experiment is for an unaugmented helicopter with cross-coupling implemented using physical rotor parameters. The details of converting the model from the simulation to use in flight are described. A frequency-domain comparison of the model and actual aircraft responses showing the fidelity of the in-flight simulation is described. The evaluation task was representative of nap-of-the-Earth maneuvering flight. The results indicate that task demands are important in determining allowable levels of coupling. In addition, on-axis damping characteristics influence the frequency-dependent characteristics of coupling and affect the handling qualities. Pilot technique, in terms of learned control crossfeeds, can improve performance and lower workload for particular types of coupling. The results obtained in flight corroborated the simulation results.

Watson, Douglas C.↗
NASA NTRS1987

Predicted pitching moment characteristics of X-29A aircraft

The predicted pitching moment characteristics of the X-29A aircraft are presented for angles of attack from 0 to 20 deg. and Mach numbers of 0.2, 0.6, 0.9, 1.2, and 1.5 for altitudes of sea level, 4572 m (15,000 ft), 9144 m (30,000 ft), and 12,192 m (40,000 ft). These data are for both rigid and flexible aircraft and for the full range of control-surface positions. The characteristics were extracted from a nonlinear, symmetric, flexibilized wind tunnel data base.

Budd, Gerald D.↗
NASA NTRS1988

Synthesis and stability of Br2, ICl and IBr intercalated pitch-based graphite fibers

The intercalation of halogens in pitch-based fiber is studied as well as the stability of the resultant intercalation compounds. It is found that IBr intercalates P-100 to yield a high-sigma GIC with attractive stability properties. During ICl intercalation, the presence of O2 interferes with the reaction and necessitates a higher threshold pressure for intercalation.

Wessbecher, Dorothy E.↗
NASA NTRS1990

Development of a preliminary high-angle-of-attack nose-down pitch control requirement for high-performance aircraft

The requirements for high-angle-of-attack nose-down pitch control for advanced high-performance aircraft are discussed. Background information on fundamental factors that influence and, to a large extent, determine the high angle-of-attack nose-down control requirement is briefly reviewed. Guidelines currently proposed by other sources which attempt to define these requirements are discussed. A requirement based on NASA analysis of the characteristics of existing relaxed static stability (RSS) aircraft is presented. This analysis could provide the basis for a preliminary design guide.

Nguyen, Luat T.↗
NASA NTRS1990

Integral solution of unsteady full-potential equation for a transonic pitching airfoil

The unsteady full-potential equation formulation in a moving frame of reference has been has been developed and used to solve unsteady transonic flow problems. An unsteady integral-equation shock-capturing (IE-SC) scheme has been developed. The resulting unsteady IE-SC scheme is applied to a NACA 0012 airfoil undergoing a pitching oscillation. The numerical results are compared with those of an implicit, approximately factored, finite-volume Euler scheme. The present scheme is efficient in terms of the number of iterations as compared to the other existing schemes, which use finite-difference or finite-volume methods.

Kandil, Osama A.↗
NASA NTRS1990

Subsonic and transonic low-Reynolds-number airfoils with reduced pitching moments

A subsonic and a transonic airfoil are presented for application in a high-altitude long-endurance aircraft and a very-high-altitude aircraft, respectively. The subsonic airfoil is designed for a lift coefficient c(l) = 1.4 at a chord Reynolds number Re = 700,000 and a very low Mach number. The transonic airfoil is designed for c(l) = 1.0 at Re = 500,000 and a transonic Mach number M = 0.7. Both airfoils are developed to perform as well or better than previously designed airfoils. However, the present airfoils are developed for a constrained pitching moment to reduce aircraft trim drag and to relieve, to some extent, the torsional loads in the typically high-aspect-ratio wings. The beneficial effects of a cruise flap and of boundary-layer transition control on the off-design performance characteristics are illustrated.

Van Dam, C. P.↗
NASA NTRS1990

Computation of vortex-dominated flow for a delta wing undergoing pitching oscillation

The conservative, unsteady Euler equations for the flow relative to a moving frame of reference are used to solve for the three-dimensional steady and unsteady flows around a sharp-edged delta wing. The resulting equations are solved by using an implicit, approximately factored, finite-volume scheme. Implicit second-order and explicit second- and fourth-order dissipations are added to the scheme. The boundary conditions are explicitly satisfied. The grid is generated by locally using a modified Joukowski transformation in crossflow planes at the grid-chord stations. The computational applications cover a steady flow around a delta wing, whose results serve as the initial conditions for the unsteady flow around a pitching delta wing at a large mean angle of attack. The steady results are compared with the experimental data, and the unsteady results are compared with results of a flux-difference splitting scheme.

Kandil, Osama A.↗
NASA NTRS1990

Pitch angle diffusion of newborn ions due to intrinsic turbulence in the solar wind

The objective of the present study is to understand the interaction of the solar wind with newborn ions in far upstream regions of a comet where the level of intrinsic turbulence is moderately low. Based on the assumption that quasi-linear theory is adequate and applicable, the pitch angle diffusion process and the time evolution of the newborn ion distribution function are investigated. Numerical solutions to the quasi-linear diffusion equation, including the effect of resonance broadening and that of continuous creation of newborn ions due to the ionization process, are obtained under several assumptions and approximations. It is found that theoretical results are consistent with the Giotto observations recently reported by Neugebauer et al. (1989).

Ziebell, L. F.↗
NASA NTRS1990

Pitch angle and velocity diffusions of newborn ions by turbulence in the solar wind

The temporal evolution of the distribution function of newborn ions under the influence of intrinsic low-frequency solar wind turbulences is studied. In particular, an initial ring-beam distribution of newborn ions under the influence of hydromagnetic waves is considered. A simplified treatment of the resonance broadening effect is given, and its role in the pickup process is discussed. Two different configurations of wave polarization amd direction of propagation are considered. The conditions that lead either to the formation of anisotropic shells as a long-duration transient state or to rapid isotropization of the ion pitch angle distribution are discussed, as are the conditions which lead to significant acceleration of the ions.

Ziebell, L. F.↗
NASA NTRS1991

Pitch angle scattering of energetic particles by oblique whistler waves

First order cyclotron or Landau resonant pitch angle scattering of electrons by oblique whistler waves propagating at large angles to the ambient field are found to be at least as large as that due to parallel propagating waves. Commonly observed precipitation of more than 40 keV electrons in association with ducted whistlers may thus be accompanied by substantial fluxes of lower energy (10 eV-40 keV) electrons precipitated by the nonducted components.

Inan, U. S.↗