Showing papers on "Aerodynamic force published in 1976"
TL;DR: In this paper, a wind tunnel technique has been developed to measure the aerodynamic forces acting on golf balls over a wide range of Reynolds number and spin rate, and balls with round and hexagonal dimples have been investigated.
Abstract: A wind tunnel technique has been developed to measure the aerodynamic forces acting on golf balls over a wide range of Reynolds number and spin rate. Balls with round dimples and hexagonal dimples have been investigated. The dimples are found to induce a critical Reynolds number behaviour at a lower value of Reynolds number than that experienced by a smooth sphere and beyond this point, unlike the behaviour of a sand-roughened sphere, there is little dependence of the forces on further increases in Reynolds number. A hexagonally-dimpled ball has a higher lift coefficient and a slightly lower drag coefficient than a conventional round-dimpled ball. Trajectories are calculated using the aerodynamic data and the ranges are compared with data obtained from a driving machine on a golf course.
270 citations
01 Apr 1976
TL;DR: In this paper, the stability of elastic flap bending, lead-lag bending, and torsion of uniform, untwisted, cantilever rotor blades without chordwise offsets between the elastic, mass, tension, and areodynamic center axes is investigated for the hovering flight condition.
Abstract: The stability of elastic flap bending, lead-lag bending, and torsion of uniform, untwisted, cantilever rotor blades without chordwise offsets between the elastic, mass, tension, and areodynamic center axes is investigated for the hovering flight condition. The equations of motion are obtained by simplifying the general, nonlinear, partial differential equations of motion of an elastic rotating cantilever blade. The equations are adapted for a linearized stability analysis in the hovering flight condition by prescribing aerodynamic forces, applying Galerkin's method, and linearizing the resulting ordinary differential equations about the equilibrium operating condition. The aerodynamic forces are obtained from strip theory based on a quasi-steady approximation of two-dimensional unsteady airfoil theory. Six coupled mode shapes, calculated from free vibration about the equilibrium operating condition, are used in the linearized stability analysis. The study emphasizes the effects of two types of structural coupling that strongly influence the stability of hingeless rotor blades. The first structural coupling is the linear coupling between flap and lead-lag bending of the rotor blade. The second structural coupling is a nonlinear coupling between flap bending, lead-lag bending, and torsion deflections. Results are obtained for a wide variety of hingeless rotor configurations and operating conditions in order to provide a reasonably complete picture of hingeless rotor blade stability characteristics.
124 citations
TL;DR: In this article, an experimental investigation was conducted to determine the effect of a uniform pitching motion on a slender axisymmetric body while undergoing large excursions in angle of attack.
Abstract: : An experimental investigation was conducted to determine the effect of a uniform pitching motion on a slender axisymmetric body while undergoing large excursions in angle of attack Force and moment measurements were obtained for a slender tangent-ogive/cylindrical body over a range of Reynolds numbers from 50,000 to 140,000 while varying the angle of attack from zero to 90 degrees and the pitch rate between zero and 281 degrees per second Smoke flow visualization studies were used as an aid in assessing wake vortex transitions
49 citations
01 Jan 1976
TL;DR: In this article, wind-tunnel measurements of side force over the Mach number range of 0.25 to 2 for pointed forebody alone and for ogive-cylinder models of various fineness ratios up to 16, are presented.
Abstract: Wind-tunnel measurements of side force over the Mach number range of 0.25 to 2 for pointed forebody-alone and for ogive-cylinder models of various fineness ratios up to 16, are presented. The angle of attack where side force first occurs (onset), where it returns to zero (upper limit), and its magnitude are examined. The onset angle depends only on body geometry, longer bodies having lower onset angles. The upper limit, which is about 80 deg at M = 0.25, decreases with Mach number. The maximum side forces decrease with increasing Mach number, approaching zero within the Mach number range of 0.8 to 1.2; within this range, the Mach number at which the forces approach zero varies directly with forebody slenderness.
47 citations
TL;DR: In this paper, a theoretical method is derived for predicting trim angle and speed coefficient at the inception of porpoising of prismatic planing hulls, and the effect of surge is small at ordinary operating trim angles.
Abstract: : A theoretical method is derived for predicting trim angle and speed coefficient at the inception of porpoising of prismatic planing hulls. Although equations are derived for the surge, pitch, and heave degrees of freedom, it is seen that the effect of surge is small at ordinary operating trim angles. Comparisons of theoretical predictions with existing experimental data on coupled pitch and heave porpoising show reasonably good agreement for a wide range of speed coefficients, load coefficients, and deadrise angles. The theory may also be used for estimating the natural frequencies and damping characteristics of prismatic hulls in the stable, high-speed planing range.
47 citations
TL;DR: In this article, various flow regimes and theoretical models were described for out-of-ground and in-ground effect, where multijet interactions with the ground plane cause significantly increased entrainment and fountain forces.
Abstract: Successful design and development of V/STOL aircraft requires an understanding and accurate prediction of aircraft forces and moments caused by jet-induced phenomena. Several computerized analytic procedures have been developed using potential flow theoretical solutions to model the entrainment and displacement effects of a propulsion system efflux. The various flow regimes and theoretical models will be described for out-of-ground effect and in-ground effect, where multijet interactions with the ground plane cause significantly increased entrainment and fountain forces. These jet models are coupled with a panel method for calculating the aerodynamic forces and moments. Excellent agreement between calculated and model test data is displayed.
38 citations
TL;DR: In this paper, the self-excited oscillation of a flexible, square section, slender, cantilever beam in a uniform, smooth wind stream was examined experimentally and theoretically.
25 citations
TL;DR: In this paper, the authors examined some of these effects analytically and obtains a two-dimensionala l body shape which has a maximum lift under a specific set of constraints.
Abstract: The lift developed by a body moving in close ground proximity can be affected significantly by the shape of the body and its height above the ground. The research described examines some of these effects analytically and obtains a two-dimensiona l body shape which has a maximum lift under a specific set of constraints. Experimental work which gives confirmation of the analytical technique and provides some insight into the lift developed by a three-dimensional body of small aspect ratio is described. It is shown that, for low heights and proper vehicle geometry, the two-dimensional analytical technique can be used to give an estimate of the threedimensional pressure distribution. The effects of end plates and of venting around the bottom of the vehicle also are examined, and the importance of minimizing such venting is emphasized.
19 citations
01 Aug 1976
TL;DR: An integrated system of computer programs was developed for the design and analysis of supersonic configurations that uses linearized theory methods for the calculation of surface pressures and su personic area rule concepts in combination withlinearized theory for calculation of aerodynamic force coefficients.
Abstract: An integrated system of computer programs was developed for the design and analysis of supersonic configurations. The system uses linearized theory methods for the calculation of surface pressures and supersonic area rule concepts in combination with linearized theory for calculation of aerodynamic force coefficients. Interactive graphics are optional at the user's request. This user's manual contains a description of the system, an explanation of its usage, the input definition, and example output.
16 citations
01 Jul 1976
TL;DR: In this article, a baseline wing and a version of the same wing fitted with winglets were tested at the same angle-of-attack range at fixed sideslip angles of 2.5 deg and 5 deg.
Abstract: A baseline wing and a version of the same wing fitted with winglets were tested. The longitudinal aerodynamic characteristics were determined through an angle-of-attack range from -1 deg to 10 deg at an angle of sideslip of 0 deg for Mach numbers of 0.750, 0.800, and 0.825. The lateral aerodynamic characteristics were determined through the same angle-of-attack range at fixed sideslip angles of 2.5 deg and 5 deg. Both configurations were investigated at Reynolds numbers of 13,000,000, per meter (4,000,000 per foot) and approximately 20,000,000 per meter (6,000,000 per foot). The winglet configuration showed slight increases over the baseline wing in static longitudinal and lateral aerodynamic stability throughout the test Mach number range for a model design lift coefficient of 0.53. Reynolds number variation had very little effect on stability.
15 citations
TL;DR: In this paper, a numerical integrated velocity potential method for the determination of unsteady aerodynamic forces on arbitrary interacting wings and tails in supersonic flow has been developed, where the constant Mach number has been assumed throughout the flow field.
Abstract: A numerical integrated velocity potential method for the determination of unsteady aerodynamic forces on arbitrary interacting wings and tails in supersonic flow has been developed. Constant Mach number has been assumed throughout the flow field. Normalwash and sidewash integrals have been derived. The upwash integral remains to be derived. Singular integrals in the expressions for the velocity components have been evaluated in closed form. Lifting surfaces are represented by triangular elements defined by arbitrarily spaced characteristic lines and the true surface edges. The wake field is represented by rectangular strip elements. Velocity potential distributions and generalized aerodynamic coefficients have been compared.
TL;DR: In this article, an optimization procedure based on the Aerodynamic Energy concept is applied to the problem of flutter suppression using trailing edge (T.E.) and tab control surfaces, which allows the T.E.-Tab system to be driven by both linear and rotational sensors.
Abstract: An optimization procedure, based on the Aerodynamic Energy concept, is applied to the problem of flutter suppression using trailing-edge (T.E.) and tab control surfaces. A control law is assumed which allows the T.E.-Tab system to be driven by both linear and rotational sensors, and the optimum control law parameters are determined. Results are presented which indicate the capability of the T.E.-Tab control system to suppress flutter. A comparison is also made between the T.E.-Tab and the leading edge (L.E.)-T.E. control systems which shows their relative effectiveness together with some aspects connected to the realization of the control law.
01 Jul 1976
TL;DR: An integrated system of computer programs was developed for the design and analysis of supersonic configurations that uses linearized theory methods for the calculation of surface pressures and su personic area rule concepts in combination withlinearized theory for calculation of aerodynamic force coefficients.
Abstract: An integrated system of computer programs was developed for the design and analysis of supersonic configurations. The system uses linearized theory methods for the calculation of surface pressures and supersonic area rule concepts in combination with linearized theory for calculation of aerodynamic force coefficients. Interactive graphics are optional at the user's request. Schematics of the program structure and the individual overlays and subroutines are described.
01 Mar 1976
TL;DR: In this paper, the exact equations of motion for three-dimensional, aerodynamically affected flight are derived and the equations are transformed into a set suitable for analytic integration using asymptotic expansions.
Abstract: The problem of determining the trajectories, partially or wholly contained in the atmosphere of a spherical, nonrotating planet, is considered. The exact equations of motion for three-dimensional, aerodynamically affected flight are derived. Modified Chapman variables are introduced and the equations are transformed into a set suitable for analytic integration using asymptotic expansions. The trajectory is solved in two regions: the outer region, where the force may be considered a gravitational field with aerodynamic perturbations, and the inner region, where the force is predominantly aerodynamic, with gravity as a perturbation. The two solutions are matched directly. A composite solution, valid everywhere, is constructed by additive composition. This approach of directly matched asymptotic expansions applied to the exact equations of motion couched in terms of modified Chapman variables yields an analytical solution which should prove to be a powerful tool for aerodynamic orbit calculations.
TL;DR: In this article, a shock-capturing, finite-difference computational procedure has been used to predict the body flow fields over a wide range of initial conditions, and these results have been compared with wind tunnel data.
Abstract: A shock-capturing, finite-difference computational procedure has been used to predict the body flowfields over a wide range of initial conditions, and these results have been compared with wind tunnel data. Two different studies have been performed. In the first, details of the shock layer surrounding space shuttle orbiter configurations have been calculated. In the second, the aerodynamic forces and moments on a parametrically varied set of blunt biconic bodies of revolution have been evaluated for angles of attack up to 20 degrees and Mach numbers from 5 to 20.
01 Jan 1976
TL;DR: In this paper, an aeroelastic analysis of the dynamics and aerodynamics of fully coupled helicopter main or tail rotor/airframe/control systems is presented to study stability characteristics in conditions of pure axial flow or in forward flight.
Abstract: : This report describes an aeroelastic analysis that provides a complete description of the dynamics and aerodynamics of fully coupled helicopter main or tail rotor/airframe/control systems. The analysis is designed to study stability characteristics in conditions of pure axial flow or in forward flight, for which it computes the systems eigenvalues and eigenvectors. For hover studies, the aerodynamic derivatives include stall and compressibility effects, and circulatory and noncirculatory unsteady effects are accounted for through use of Theodorsen and Loewy type lift deficiency functions. The forward- flight aerodynamic derivatives are obtained from any appropriate linear or nonlinear time history analysis. The approximations made in the forward-flight analysis limit such applications to an advance ratio of about 0.5.
01 Apr 1976
TL;DR: The highlights of a recent discussion by representatives of the fluid dynamics and structures and materials panels are reported with emphasis on the fundamental aspects of unsteady fluid mechanics as mentioned in this paper, which includes linearized potential flow theory, transonic flow calculations, unstable boundary layers, dynamic stall and transonic buffet.
Abstract: The highlights of a recent discussion by representatives of the fluid dynamics and structures and materials panels are reported with emphasis on the fundamental aspects of unsteady fluid mechanics. Topics include linearized potential flow theory, transonic flow calculations, unsteady boundary layers, dynamic stall, transonic buffet, and techniques for measuring unsteady pressures.
Patent•
10 Jun 1976
TL;DR: Granular bulk material (sugar) is classified into size ranges by adding it to a wide and narrow horizontal air stream from a nozzle Gravitational and aerodynamic forces classify the material into fractions of various size ranges and it drops into consecutive hoppers arranged at a lower level than the nozzle as discussed by the authors.
Abstract: Granular bulk material (sugar) is classified into size ranges by adding it to a wide and narrow horizontal air stream from a nozzle Gravitational and aerodynamic forces classify the material into fractions of various size ranges and it drops into consecutive hoppers arranged at a lower level than the nozzle This is a rapid, clean and non-destructive method of sizing The clogging and the noise of vibrating screens are eliminated, the dust make is reduced and the working conditions for the operators are improved
TL;DR: In this paper, a tensor analysis is employed to derive two simple conditions for vanishing aerodynamic derivatives of arbitrary order, taken with respect to linear and angular velocities, linear accelerations, and control surface deflections.
Abstract: A technique is developed thai takes advantage of the inherent configurational symmetries of aircraft and guided missiles to eliminate some force and moment derivatives. Starting with the Principle of Material Indifference, tensor analysis is employed to derive two simple conditions for vanishing aerodynamic derivatives. The results apply to derivatives of arbitrary order, taken with respect to linear and angular velocities, linear accelerations, and control surface deflections. Two charts are presented that sift out the vanishing derivatives up to second order for missiles with tetragonal symmetry, and up to third order for aircraft with reflectional symmetry.
01 Jun 1976
TL;DR: Aerodynamic side forces on forebodies are considered that are produced by two types of flow: asymmetric vortices on bodies of revolution and nonuniform flow separation on square bodies with rounded corners under spinning conditions.
Abstract: Aerodynamic side forces on forebodies are considered that are produced by two types of flow: asymmetric vortices on bodies of revolution and nonuniform flow separation on square bodies with rounded corners under spinning conditions. Steady side forces that can be as large as the normal force are produced by asymmetric vortices on pointed forebodies. This side force has a large variation with Reynolds number, decreases rapidly with Mach number, and can be nearly eliminated with small nose bluntness or strakes. The angle of attack where the side force first occurs depends primarily on body geometry. The theoretical techniques to predict these side forces are necessarily semi-empirical because the basic phenomenon is not well understood. The side forces produced by nonuniform flow separation under spinning conditions depend extensively on spin rate, angle of attack, and Reynolds number. The application of simple crossflow theory to predict this side force is inadequate much below angles of attack of 90 deg.
TL;DR: In this paper, the magnitude and phase angle of aerodynamic derivatives generated on a fixed airfoil by small oscillations of a jet flap at the trailing edge have been measured in incompressible flow.
Abstract: The experiments described, in conjunction with an earlier study by the author, comprise a set which enables the prediction of aerodynamic forces and moments on a two-dimensional airfoil undergoing general motions involving small displacements. The magnitude and phase angle of aerodynamic derivatives generated on a fixed airfoil by small oscillations of a jet flap at the trailing edge have been measured in incompressible flow. Results are presented for a range of frequency of oscillation and strength of the jet and Reynolds number. The apparatus and techniques used to obtain oscillatory surface pressure distributions are described. The measurements reported agree well with the majority of other experimental data. The trends are predicted by the theory of Potter, but not by the theory of Spence which should be applied only for much higher dimensionless frequencies than those used in the experiments.
01 May 1976
TL;DR: In this article, a recently developed procedure for analysis of free-flight motion to determine the aerodynamic coefficients of a vehicle having appreciable aerodynamic and inertia asymmetries is presented.
Abstract: : The report discusses a recently developed procedure for analysis of free-flight motion to determine the aerodynamic coefficients of a vehicle having appreciable aerodynamic and inertia asymmetries Aerodynamic data obtained by using this procedure in aeroballistic range tests of elliptic cross-section bodies indicate the potential usefulness of the developed procedure
01 Dec 1976
Patent•
22 Jan 1976
TL;DR: In this article, the buoyancy surface is suspended in a trapezoidal bearing in four hinge points, so that the resulting aerodynamic force may be directed into a selected direction.
Abstract: The aerodynamic drive-and buoyancy surface automatically turns into an optimum air flow direction. The resultant of the occuring air forces extends through the centre of gravity or any other chosen point of the craft. The horizontal air force component of the buoyancy surface, borne about the Z-axis, simultaneously causes its optimum adjustment to the air flow. This is due to the point of impact of the air, in direction of flow, being positioned at a distance behind the Z-axis. The buoyancy surface is suspended in a trapezoidal bearing in four hinge points, so that the resulting aerodynamic force may be directed into a selected direction.
Abstract: The paper considers a rigid pointed body of revolution in a steady uniform subsonic flow. The body performs harmonic small-amplitude pitching oscillations around its zero angle of attack position. The body is assumed to be smooth and sufficiently slender so that the small perturbation concept can be applied. The basis of the method used, following Revell (1960), is the relation of a body-fixed perturbation potential to the general velocity potential. Normal force distributions as well as total force and moment coefficients are calculated for parabolic spindles and the numerical results show good agreement between Revell's second-order slender body theory and the present theory for the static stability derivatives of the parabolic spindles.
01 Jan 1976
TL;DR: In this paper, an analytical method for predicting the longitudinal aerodynamic characteristics of externally blown flap configurations is described, and two potential flow models make up the prediction method: a wing and flap lifting-surface model and a turbofan engine wake model.
Abstract: An analytical method for predicting the longitudinal aerodynamic characteristics of externally blown flap configurations is described. Two potential flow models make up the prediction method: a wing and flap lifting-surface model and a turbofan engine wake model. A vortex-lattice lifting-surface method is used to represent the wing and multiple-slotted trailing-edge flaps. The jet wake is represented by a series of closely spaced vortex rings normal to a centerline which is free to move to conform to the local flow field. The two potential models are combined in an iterative fashion to predict the jet wake interference effects on a typical EBF configuration. Comparisons of measured and predicted span-load distributions, individual surface forces, forces and moments on the complete configuration, and flow fields are included.
TL;DR: In this article, the integral aerodynamic force of a fluidizing agent flowing around a sphere is calculated for a fluidized bed and a method for calculating the integral force is presented.
Abstract: Pressure coefficients have been determined for a fluidizing agent flowing around a sphere. A method is presented for calculating the integral aerodynamic force; formulas are given for the variation in the apparent aerodynamic density and effective density for a fluidized bed.
01 Jun 1976
TL;DR: In this paper, the turbulent wake behind a propeller-driven body was studied in a low speed wind tunnel at nominal conditions of Re sub D 440, 000, and two models, both with the same nose and middle body, were tested.
Abstract: : Studies of the turbulent wake behind a slender, propeller-driven body were conducted in a low speed wind tunnel at nominal conditions of Re sub D 440, 000. Two models, both with the same nose and middle-body, were tested. Wake surveys at Z/D = 2, 10, and 40 were made with a single propeller model at pitch angles of 0 and -2 deg and with a model with dual, side-by-side propellers at zero pitch angle. The variations of mean axial velocity, velocity vector orientation, static pressure and axial turbulence intensity were documented. Force and moment data for both models at pitch angles from -6 deg to +6 deg were obtained. Profiles of the boundary layer on the body ahead of the propeller were also measured. The data obtained, taken as a whole, provide a detailed picture of the development of these complicated flowfields.
01 Feb 1976
TL;DR: In this paper, the interference force and pressure data were obtained on a representative wing-body-nacelle combination at Mach numbers of 0.9 to 1.4, and the primary variables examined included Mach number, angle of attack, nacelle position, and naceelle mass-flow ratio.
Abstract: Detailed interference force and pressure data were obtained on a representative wing-body-nacelle combination at Mach numbers of 0.9 to 1.4. The model consisted of a delta wing-body aerodynamic force model with four independently supported nacelles located beneath the wing-body combination. The model was mounted on a six-component force balance, and the left-hand wing was pressure-instrumented. Each of the two right-hand nacelles was mounted on a six-component force balance housed in the thickness of the nacelle, while each of the left-hand nacelles was pressure-instrumented. The primary variables examined included Mach number, angle of attack, nacelle position, and nacelle mass-flow ratio. Four different configurations were tested to identify various interference forces and pressures on each component; these included tests of the isolated nacelle, the isolated wing-body combination, the four nacelles as a unit, and the total wing-body-nacelle combination. Nacelle axial location, relative to both the wing-body combination and to each other, was the most important variable in determining the net interference among the components.