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At least 181 records · Page 10

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NASA NTRS1976

Nonlinear Curvature Expressions for Combined Flapwise Bending, Chordwise Bending, Torsion and Extension of Twisted Rotor Blades

The nonlinear curvature expressions for a twisted rotor blade or a beam undergoing transverse bending in two planes, torsion, and extension were developed. The curvature expressions were obtained using simple geometric considerations. The expressions were first developed in a general manner using the geometrical nonlinear theory of elasticity. These general nonlinear expressions were then systematically reduced to four levels of approximation by imposing various simplifying assumptions, and in each of these levels the second degree nonlinear expressions were given. The assumptions were carefully stated and their implications with respect to the nonlinear theory of elasticity as applied to beams were pointed out. The transformation matrices between the deformed and undeformed blade-fixed coordinates, which were needed in the development of the curvature expressions, were also given for three of the levels of approximation. The present curvature expressions and transformation matrices were compared with corresponding expressions existing in the literature.

Kvaternik, R. G.↗

NASA NTRS1977

Subsonic and supersonic aerodynamic characteristics of a supersonic cruise fighter model with a twisted and cambered wing with 74 deg sweep

A wind tunnel investigation has been conducted to determine the longitudinal and lateral aerodynamic characteristics of a model of a supersonic cruise fighter configuration with a design Mach number of 2.60. The configuration is characterized by a highly swept arrow wing twisted and cambered to minimize supersonic drag due to lift, twin wing mounted vertical tails, and an aft mounted integral underslung duel-engine pod. The investigation also included tests of the configuration with larger outboard vertical tails and with small nose strakes.

Morris, O. A.↗

NASA NTRS1977

Lateral equilibrium of asymmetrical swept wings - Aileron control vs geometric twist

A static aeroelastic phenomenon unique to an aircraft with asymmetrically swept wings is discussed. A simple formula is derived from the analysis of a highly idealized model. The validity of this formula is examined through the use of a more sophisticated numerical analysis. Among the results of this analysis are the following: aileron settings of a few degrees are sufficient to trim such aircraft in roll-for-g-flight; the use of built-in twist in the form of initial negative dihedral provides an efficient alternative to aileron trim; if the wing is elastically tailored in a proper fashion, it may be possible to design a wing whose elastic deformation under airloads provides a form of self-trim in roll at the cruise q of the aircraft.

Weisshaar, T. A.↗

NASA NTRS1977

Dynamical theory of stability for elastic rods with nonlinear curvature and twist

Considering non-linear terms in the curvature as well as in the twist, the governing boundary value problem for lateral bending of elastic, transverse loaded rods is formulated by means of Hamilton's principle. Using the method of small vibrations, the associated linearized equations of stability are derived, which complete the currently accepted relations. The example of the simplest lateral bending problem illustrates the improved effect of the proposed equations.

Wauer, J.↗

NASA NTRS1978

Wind-tunnel test results of a full-scale multicyclic controllable twist rotor

Results of wind tunnel testing of a multicyclic controllable twist rotor at several flight conditions and advance ratios of 0.22 and 0.33 are evaluated. It is found that blade flatwise bending moments and root control actuator loads (fixed system) can be reduced with multicyclic control. Flatwise bending moment reductions of 22-30% with concurrent 83% reductions in control loads were predicted. Analysis of profile power changes indicates a decrease in profile power coefficient of 0.00016, corresponding to a loss of 0.12 sq m of equivalent drag area.

Mccloud, J. L., III↗

NASA NTRS1980

Theory of twisted nonuniformly heated bars

Nonlineary distributed stresses in twisted nonuniformly heated bars of arbitrary cross section are calculated taking into account various elasticity parameters. The approximate theory is shown to be sufficiently general and accurate by comparison with experimental data.

Shorr, B. F.↗

NASA NTRS1980

Nonlinear Aeroelastic Equations of Motion of Twisted, Nonuniform, Flexible Horizontal-Axis Wind Turbine Blades

The second-degree nonlinear equations of motion for a flexible, twisted, nonuniform, horizontal axis wind turbine blade were developed using Hamilton's principle. A mathematical ordering scheme which was consistent with the assumption of a slender beam was used to discard some higher-order elastic and inertial terms in the second-degree nonlinear equations. The blade aerodynamic loading which was employed accounted for both wind shear and tower shadow and was obtained from strip theory based on a quasi-steady approximation of two-dimensional, incompressible, unsteady, airfoil theory. The resulting equations had periodic coefficients and were suitable for determining the aeroelastic stability and response of large horizontal-axis wind turbine blades.

Kaza, K. R. V.↗

NASA NTRS1981

The influence of leading-edge thrust on twisted and cambered wing design for supersonic cruise

A study of leading-edge thrust phenomena at supersonic speeds has shown that although these forces are not large, they can be a significant factor in the design of wings for supersonic cruise. It is seen that the rather severe twisted and cambered wing surfaces resulting from the application of present design methods, which ignore leading-edge thrust, can be replaced by more moderate surfaces with little or no loss in aerodynamic efficiency if realistic possibilities for the attainment of some fraction of the theoretical thrust are taken into account.

Carlson, H. W.↗

NASA NTRS1982

Solid particle dynamic behavior through twisted blade rows

The particle trajectory calculations provide the essential information which is required for predicting the pattern and intensity of turbomachinery erosion. Consequently, the evaluation of the machine performance deterioration due to erosion is extremely sensitive to the accuracy of the flow field and blade geometry representation in the trajectory computational model. A model is presented that is simple and efficient yet versatile and general to be applicable to axial, radial and mixed flow machines, and to inlets, nozzles, return passages and separators. The results of the computations are presented for the particle trajectories through a row of twisted vanes in the inlet flow field. The effect of the particle size on their trajectories, blade impacts, and on their redistribution and separation are discussed.

Hamed, A.↗

NASA NTRS1985

Twist-Free Wire Stranding

Device for wire-stranding operations provides uniform tension and twist-free conditions for 30 gage or smaller high strand density flexible cable assemblies.

Hines, R. W.↗

NASA NTRS1984

Helical twisting on an adiabatically expanding jet. I Propagation and temporal growth

The local linearized dispersion relation for perturbations to the surface of a constantly adiabatic jet, which is assumed to be in static pressure balance with an isothermal confining medium, is derived in an investigation of the effect of adiabatic expansion on the propagation and temporal growth of helical twisting in a supersonic jet. Cooling of the jet material along such a flow increases Mach number and relative density relative to the confining medium, as distance from the origin increases; this leads to a rather rapid decrease in the maximum rate of growth and an increase in the maximally unstable wavelength, relative to the jet's radius, as the distance along such a jet increases. Attention is given to the consequences of assuming that a change in the phase velocity of a propagating helical wave along a jet causes the wavelength of a helical wave to change.

Hardee, P. E.↗

NASA NTRS1985

The distant magnetotail's response to a strong interplanetary magnetic field By - Twisting, flattening, and field line bending

During an interval of strong interplanetary magnetic field (IMF) By, while ISEE 3 was in the distant magnetotail, the north lobe was observed south of the ecliptic plane. Lobe field lines were strongly bent in the direction of the IMF, and a dense boundary layer plasma was observed. During the interval, magnetopause normals pointed in the z direction, although ISEE 3 was near the dawnside ecliptic plane. The observations are interpreted in terms of field line bending within a twisted and flattened magnetotail.

Sibeck, D. G.↗

NASA NTRS1985

Vibrations of twisted cantilever plates - A comparison of theoretical results

As a result of significant differences in the published results for various methods of analysis involving the use of finite element techniques, there are now some questions regarding the adequacy of these methods to predict accurately the vibratory characteristics of highly twisted cantilever plates. In an attempt to help in a resolution of the arising problems, a joint government/industry/university research effort was initiated. The primary objective of the present paper is to summarize the theoretical methods used in the study and show samples of the obtained results. The study provided 19 sets of theoretical results which are derived from beam theory, shell theory, and finite element methods.

Kielb, R. E.↗

NASA NTRS1987

Pressure measurements on a thick cambered and twisted 58 deg delta wing at high subsonic speeds

A pressure experiment at high subsonic speeds was conducted by a cambered and twisted thick delta wing at the design condition (Mach number 0.80), as well as at nearby Mach numbers (0.75 and 0.83) and over an angle-of-attack range. Effects of twin vertical tails on the wing pressure measurements were also assessed. Comparisons of detailed theoretical and experimental surface pressures and sectional characteristics for the wing alone are presented. The theoretical codes employed are FLO-57, FLO-28, PAN AIR, and the Vortex Lattice Method-Suction Analogy.

Chu, Julio↗

NASA NTRS1986

Full-potential circular wake solution of a twisted rotor blade in hover

A solution for transonic flow past a twisted rotor blade in hover is obtained using a modified version of the full-potential code ROT22 and a circular wake. The flow is also evaluated for a fixed-wing-type straight wake. The solutions for the straight wake and circular wake, and the circular wake and a two-dimensional wake are compared. The data reveal that the circular wake and the general two-dimensional wake solutions have similar characteristics.

Aggarwal, Hans R.↗

NASA NTRS1989

Twisted Pair Of Insulated Wires Senses Moisture

Sensitivity of electronic moisture sensor to low levels of moisture increased by new electrode configuration. Moisture-sensing circuit described in "Low-Cost Humidity Sensor" (NPO-16544). New twisted pair of wires takes place of flat-plate capacitor in circuit. Configuration allows for thermal expansion and contraction of polymer while maintaining nearly constant area of contact between polymer and wires.

Laue, Eric G.↗

NASA NTRS1989

Investigation of a free-tip rotor configuration for research on spanwise life distributions and wake velocity surveys of a semi-span wing with a discontinuous twist

A wind tunnel test was conducted in the NASA Ames 7 x 10 Foot Wind Tunnel to investigate the lift distribution on a semi-span wing with a discontinuous change in spanwise twist. The semi-span wing had a tip with an adjustable pitch angle independent on the inboard section pitch angle simulating the free-tip rotor blade when its free-tip is at a deflected position. The spanwise lift distribution over the wing and the tip were measured and three component velocity surveys behind the wing were obtained with a three dimensional laser Doppler velocimeter (LV) with the wing at one angle of attack and the tip deflected at different pitch angles. A six component internal strain gage balance was also used to measure total forces and moments on the tip. The three dimensional lift was computed from the two dimensional life distributions obtained from the LV and from the strain gage balance. The results from both experimental methods are shown to be in agreement with predictions made by a steady, three dimensional panel code, VSAERO.

Fortin, Paul↗

NASA NTRS1989

Spanwise lift distributions and wake velocity surveys of a semi-span wing with a discontinuous twist

A wind tunnel test was conducted in the NASA-Ames 7 x 10 ft wind tunnel to investigate the lift distribution on a semispan wing with a discontinuous change in spanwise twist. The semispan wing had a tip with an adjustable pitch angle independent on the inboard section pitch angle simulating the free tip rotor blade when its free tip is at a deflected position. The spanwise lift distribution over the wing and the tip were measured and three component velocity surveys behind the wing were obtained with a 3-D laser Doppler velocimeter (LV) with the wing at one angle of attack and the tip deflected at different pitch angles. A six-component internal strain gage balance was also used to measure total forces and moments on the tip. The 3-D lift was computed from the 2-D lift distributions obtained from the LV and from the strain gage balance. The results from both experimental methods are shown to be in agreement with predictions made by a steady, 3-D panel code, VSAERO.

Kumagai, Hiroyuki↗