Showing papers on "Aerodynamic force published in 1981"

Optimal trajectories in atmospheric flight

Abstract: Aspects of optimization theory and switching theory are discussed, taking into account the necessary conditions for extrema, a solution subject to constraints, the calculus of variations, the Pontryagin maximum principle, the canonical transformation, Contensou's domain of maneuverability, optimal switching, a junction with singular arc, and linearized singular control. Equations of motion are considered along with aerodynamic and propulsive forces, the general properties of optimal trajectories, flight in a horizontal plane, optimal coasting flight, supersonic cruise, the supersonic turn, supersonic maneuvers in a vertical plane, energy state approximation, a modified Chapman's formulation for optimal reentry trajectories, optimal planar reentry trajectories, and an optimal glide of reentry vehicles. Orbital aerodynamic maneuvers are examined, giving attention to aerodynamic capture, a change in the apogee, a change in the eccentricity, a change in the perigee, an orbital maneuver, an aerodynamic maneuver, and a combined maneuver.

Development of a linear unsteady aerodynamic analysis for finite-deflection subsonic cascades

Abstract: An unsteady potential flow analysis, which accounts for the effects of blade geometry and steady turning, was developed to predict aerodynamic forces and moments associated with free vibration or flutter phenomena in the fan, compressor, or turbine stages of modern jet engines Based on the assumption of small amplitude blade motions, the unsteady flow is governed by linear equations with variable coefficients which depend on the underlying steady low These equations were approximated using difference expressions determined from an implicit least squares development and applicable on arbitrary grids The resulting linear system of algebraic equations is block tridiagonal, which permits an efficient, direct (ie, noniterative) solution The solution procedure was extended to treat blades with rounded or blunt edges at incidence relative to the inlet flow

Measurements of Unsteady Periodic Forces generated by the Blowfly Flying in a Wind Tunnel

Abstract: A technique was developed for the measurement of the instantaneous lift and drag forces generated by the blowfly, Sarcophaga bullata, flying fixed in a wind tunnel Apparatus for the measurement of insect-generated forces was checked in part for mean force accuracy by measurement of the drag on a circular cylinder Our experimental device detects the sum of the aerodynamic forces and wing inertial forces as experienced by the thorax The streamwise and vertical force waveforms show a surprising lack of higher harmonic content Wind speeds in the neighbourhood of the known preferred flying speed were used, without an explicit attempt to nullify the mean vertical and horizontal forces to simulate free flight Several measurements of the phase angle between the force waveform and the wing beating kinematics indicated that vertical forces in the liftward direction achieved a maximum during the downstroke and thrustward forces achieved a maximum during the upstroke

Dynamics of a Flexible Cylinder in Subsonic Axial Flow

Abstract: This paper examines the dynamics of a flexible cylinder with pinned ends immersed in axial subsonic flow, either bounded or unconfined. The problem proves to be surprisingly resistant to exact solution, as compared to the incompressible flow case, because of difficulties in determining precisely the inviscid aerodynamic forces. This paper presents a number of distinct formulations of these forces, involving different approximations: (1) a slender-body approximation; (2) an approximate three-dimensional formulation where, in the determination of the aerodynamic forces, the axial shape is prescribed in advance; and (3) an exact integral formulation of the generalized aerodynamic forces. In each case, Galerkin-type solutions yield the system eigenfrequencies which describe the dynamical behavior of the system. It is found that for sufficiently high flow velocities, divergence and flutter are possible. The different methods yield similar, but not quantitatively identical results. Interestingly, dependence of the dynamical characteristics on Mach number is shown to be weak for slender cylinders; for nonslender ones, it is stronger. Finally, a brief discussion of wave propagation in an unconstrained cylinder indicates the existence of a cutoff flow velocity for backward propagating waves, followed by wave amplification at higher flow, which is closely related to loss of stability inmore » the constrained system.« less

Performance and Loads Data from a Wind Tunnel Test of a Full-Scale, Coaxial, Hingeless Rotor Helicopter.

Abstract: A full-scale XH-59A advancing blade concept helicopter was tested in Ames Research Center's 40 by 80 foot wind tunnel. The helicopter was tested with the rotor on and off, rotor hub fairings on and off, interrotor shaft fairing on and off, rotor instrumentation module on and off, and auxiliary propulsion thrust on and off. An advance ratio range of 0.25 and 0.45 with the rotor on and from 60 to 180 knots with the rotor off was investigated. Data on aerodynamic forces and moments, rotor loads, rotor control positions and vibration for the XH-59A as well as the aerodynamic performance of the isolated rotor are presented.

Aeroelastic divergence of unrestrained vehicles

Abstract: T effect of inertial relief on the aeroelastic redistribution of wing lift is discussed in Refs. 1-3. Reference 2 also discusses aeroelastic divergence with a distinction being made between static divergence of a restrained vehicle and dynamic divergence of an unrestrained vehicle. Equation (7-127) of Ref. 2 states the eigenvalue problem for dynamic divergence of a vehicle with a single rigid-body degree of freedom in plunge. We wish to generalize that result to multiple rigid-body degrees of freedom by following the development of Ref. 3 while using the notation of Refs. 4-6. The net force distribution [F] acting on a flexible lifting surface or body is the difference between the aerodynamic forces [Fa} and the inertial forces [F,).

Directionally stabilized wind turbine

Abstract: A downwind rotor wind turbine having a rotor with a horizontal axis carried for operation on the downwind end of a pod or nacelle pivotally mounted on a vertical pivot located upwind of the rotor on the top of an elevated structure. Each blade is provided at its tip with a tip plate. The tip plates have a surface area large enough to provide an aerodynamic force on the rotor when the wind shifts away from the rotational axis of the rotor such that a restoring moment is furnished about the turbine pivot to turn the turbine automatically back into the wind.

Aerodynamic Design Manual for Tactical Weapons

Abstract: : The Naval Surface Weapons Center Aeroprediction Code has been extensively applied to the prediction of static and dynamic aerodynamics of missile configurations. Major extensions have recently been made to the Code, extending its capability to 0 less than or equal to M (infinity) less than or equal to 8 and 0 degrees less than or equal to alpha less than or equal to 180 degrees and improving the transonic and dynamic derivative predictions. The theoretical basis for the Code is reviewed. The Code is evaluated through comparisons of computational examples with experiment for body alone, body-tail, and body-tail-canard configurations. The speed and accuracy of the Code is ideal for use in preliminary design. Representative design charts (generated by the use of the Code) for both the static and dynamic aerodynamic coefficients of a wide variety of configuration components are included. The charts will aid the designer in making preliminary design estimates or for data comparisons.

Dynamic analysis of lightly iced conductor galloping in two degrees of freedom

Abstract: Field observations have been repeatedly reported on the galloping of transmission lines having only a small acretion of ice of the order of 10% of the diameter on the windward side. Aerodynamic force measurements in wind tunnels reveal that significant lift forces are present, having a steep gradient with respect to angle of attack, and which satisfy the Den Hartog negative damping criteria. Drag forces are essentially constant, and aerodynamic moments are zero over the 3600 range of angle of attack. Similarly, no unbalanced inertia forces exist for such light-ice deposits, which precludes the dynamic inertia coupling between galloping and torsion modes. Blow back of the conductor is shown to explain such galloping owing to the angle of attack reaching the critical range, Within a finite range of wind speed. The addition of control devices, identified as the windamper, and the detuner, is shown to modify the distribution of angle of attack along the span, thus altering the angle of attack ‘exposure’ compared with that of an untreated span. Stability analyses in two degrees of freedom (galloping and dynamic twist) are performed for a number of representative cases. Stability is expressed as the root locus of a fourth-degree polynomial (quartic) equation, as a function of wind speed. Perforated cylinder dampers are also considered, and they are found to supply inadequate damping for control, unless the span coverage is unreasonably large. The twisting effect of the Windamper is shown to be its primary stabilising influence. The detuner appears to increase the range of instability in two out of three cases.

An Influence Function Method for Predicting Store Aerodynamic Characteristics during Weapon Separation

Abstract: : A method has been developed for predicting the forces and moments on a store during weapon separation based on previous wind tunnel data for another store in the same flow field. This new technique uses conventional grid survey store force and moment data and parameter identification analysis to 'identify' the local angle-of-attack distribution in proximity to the parent aircraft. Predicted force and moment characteristics for other stores based on this derived angle-of-attack show excellent correlation with supersonic data. The evidence to date indicates that the method will be applicable to virtually all stores at subsonic-supersonic Mach numbers. (Author)

Computational Parametric Study of the Aerodynamics of Spinning Slender Bodies at Supersonic Speeds

Abstract: : Three dimensional finite-difference flow field computation techniques have been employed to generate a parametric aerodynamic study at supersonic speeds. Computations for viscous turbulent and inviscid flow have been performed for cone-cylinder, secant-ogive-cylinder, and tangent-ogive-cylinder bodies for a Mach number range of 1.75 or = M or = 5. The aerodynamic coefficients computed are pitching moment, normal force, center of pressure, Magnus moment, Magnus force, Magnus center of pressure, form drag, viscous drag, roll damping and pitch damping. All aerodynamic coefficients are computed in a conceptually exact manner. The only empirical input is that required for turbulence modeling. Computed results are compared to experimental data from free flight aerodynamic ranges and wind tunnels in order to validate the computational techniques. parametric comparisons illustrate the effects of body configuration and Mach number for the ten aerodynamic coefficients. The results for Magnus and pitch damping are of particular interest.

Impact of high-alpha aerodynamics on dynamic stability parameters of aircraft and missiles

Abstract: The aerodynamic phenomena associated with high angles of attack and their effects on the dynamic stability characteristics of airplane and missile configurations are examined. Information on dynamic effects is limited. Steady flow phenomena and their effects on the forces and moments are reviewed. The effects of asymmetric vortices and of vortex bursting on the dynamic response of flight vehicles are reviewed with respect to their influence on: (1) nonlinearity of aerodynamic coefficients with attitude, rates, and accelerations; (2) cross coupling between longitudinal and lateral directional models of motion; (3) time dependence and hysteresis effects; (4) configuration dependencey; and (5) mathematical modeling of the aerodynamics.

Flap-lag-torsional dynamic modelling of rotor blades in hover and in forward flight, including the effect of cubic nonlinearities

Abstract: The differential equations of motion, and boundary conditions, describing the flap-lead/lag-torsional motion of a flexible rotor blade with a precone angle and a variable pitch angle, which incorporates a pretwist, are derived via Hamilton's principle. The meaning of inextensionality is discussed. The equations are reduced to a set of three integro partial differential equations by elimination of the extension variable. The generalized aerodynamic forces are modelled using Greenberg's extension of Theodorsen's strip theory. The equations of motion are systematically expanded into polynomial nonlinearities with the objective of retaining all terms up to third degree. The blade is modeled as a long, slender, of isotropic Hookean materials. Offsets from the blade's elastic axis through its shear center and the axes for the mass, area and aerodynamic centers, radial nonuniformaties of the blade's stiffnesses and cross section properties are considered and the effect of warp of the cross section is included in the formulation.

Linear/nonlinear behavior in unsteady transonic aerodynamics

Abstract: The accurate calculation of the aerodynamic forces in unsteady transonic flow requires the solution of the nonlinear flow equations. The aeroelastician, on the other hand, seeks to treat his problems (flutter, for example) by means of linear equations whenever possible. He may do this, even when the underlying flow is nonlinear, if the perturbation forces are linear over some (perhaps small) range of unsteady amplitude of motion. This paper assesses the range of parameters over which linear behavior occurs. In particular calculations are made for an NACA 64A006 airfoil oscillating in pitch over a range of amplitudes, frequencies, and Mach numbers. The primary aerodynamic method used is the well known LTRAN2 code of Ballhaus and Goorjian that provides a finite-difference solution to the low frequency, small disturbance, two-dimensional potential flow equation. Comparisons are made with linear subsonic theory, local linearization, and, for steady flow, with the full potential equation code of Bauer, Garabedian, and Korn.

Prediction of Forces and Moments on Finned Missiles at High Angle of Attack in Transonic Flow

Abstract: This report describes a theoretical method for the prediction of fin forces and moments on bodies at high angle of attack in subsonic and transonic flow The body is assumed to be a circular cylinder with cruciform fins (or wings) of arbitrary planform The body can have an arbitrary roll (or bank) angle, and each fin can have individual control deflection The method combines a body vortex flow model and lifting surface theory to predict the normal force distribution over each fin surface Extensive comparisons are made between theory and experiment for various planform fins A description of the use of the computer program that implements the method is given

An experimental investigation of gapwise periodicity and unsteady aerodynamic response in an oscillating cascade. Volume 2: Data report. Part 2: Mode 2 data

Abstract: Computer data are provided for tests conducted on a linear cascade of airfoils oscillating in pitch to measure the unsteady pressure response on selected blades along the leading edge plane of the cascade, over the chord of the center blade, and on the sidewall in the plane of the leading edge

Improved surface velocity method for transonic finite-volume solutions

Abstract: A new surface velocity metho was developed which provides an improved prediction of the flow field near the surface and the aerodynamic forces on the body. The original surface velocity method produces strong flow normal to the wing and the fuselage. This leads to pronounced error in the leading edge region, and low prediction of drag and overprediction of the lift-to-drag ratio. Application of the method to two heavily used transonic potential flow finite-volume programs, FLO27 and FLO28, are presented to illustrate the improvement.

An Investigation of F-16 Nozzle-Afterbody Forces at Transonic Mach Numbers with Emphasis on Model Scale Effects

Abstract: : An experimental program was conducted to provide nozzle-afterbody data with a minimum interference support system on a 0.25-scale F-16 model and to determine the interference induced on then nozzle-afterbody region by sting and strut model support systems. Data obtained on the 0.25-scale model are compared with data from a 0.11-scale model for evaluation of model scale effects. The investigation was conducted over the Mach number range from 0.6 to 1.5. Data are presented in terms of coefficients and increments in coefficients of nozzle-afterbody axial and normal forces obtained from integrating pressure data. High-pressure air at ambient temperature was utilized for exhaust plume simulation. The results indicate close agreement in axial-force coefficient between configurations having full and annular nozzles at design pressure ratio. Very little effect of Reynolds number was found on the nozzle-afterbody axial force. Wave interference adversely affected axial-force data from the 0.25-scale model at Mach numbers between 1.0 and 1.1, producing lower axial force on the model afterbody. Large differences were determined in both the magnitude and the sign of strut interference from the two model installations.

Nonlinear aerodynamic modeling of flap oscillations in transonic flow - A numerical validation

Abstract: The regime of validity of a nonlinear aerodynamic force and moment formulation, based on concepts from nonlinear functional analysis and applicable to a transonic airfoil with a deflecting flap, is investigated. A time-dependent finite difference technique is used to evaluate the aerodynamic data of the formulation in terms of specified, characteristic motions. Flap-motion histories are generated from the flap inertial equations of motion, with aerodynamic reactions specified by the moment formulation. The motion histories depicting the cases of decaying and growing flap oscillations are compared with histories generated through simultaneous, coupled solution of the fluid-dynamic equations and flap inertial equations of motion. The range of applicability of the formulation is discussed.

Submissile Aerodynamics during Dispensing

Abstract: : A combined analytical and experimental study was conducted to determine the aerodynamic interference effects of a submissile in the presence of a dispenser missile. The analytical predictions are made using NEAR codes modified for applications to missile systems. A wind tunnel test was conducted to measure the static aerodynamic coefficients of a submissile in the flow field of a dispenser missile at Mach numbers 0.8 and 1.2. The parameters observed to have the greatest effect on the interference aerodynamics are the addition of fins on the submissile, the removal of the dispenser bay covers, the dispenser angle of attack and the submissile pitch angle. (Author)

Nuclear Blast Response Computer Program. Volume III. Program Listing.

Abstract: : The VIBRA-6 computer program is a digital computer program developed to determine the response of aircraft to nuclear explosions when flying at subsonic speeds. It is similar to the VIBRA-4 program but uses the latest Doublet-Lattice Method for obtaining subsonic aerodynamic forces for arbitrary lifting surface-body configurations. The Doublet-Lattice procedure has been extended to account for the moving blast wave by considering it as a traveling gust. The nuclear blast representation remains the same as that used in the VIBRA-4 program but the method of solution of the equations of motion has been changed from that of numerical integration of quasi-steady equations of motion to a Fourier transform procedure to move from frequency domain solutions to time history solutions. This report is divided into three volumes: Volume I contains the overall program descriptions and method of analysis, the input and output data descriptions, the program operation and a sample problem. Volume II details the unsteady aerodynamic procedure and Volume III contains the program listings.

Wind tunnel force and pressure tests

Abstract: Force and surface pressure distributions were measured for a 13% medium speed (NASA MS(1)-0313) airfoil fitted with 20% aileron, 25% slotted flap and 10% slot lip spoiler. All tests were conducted in the Walter Beech Memorial Wind Tunnel at a Reynolds number of 2.2 million and a Mach number of 0.13. Results include lift, drag, pitching moments, control surface normal force and hinge moments, and surface pressure distributions. The basic airfoil exhibits low speed characteristics similar to the GA(W)-2 airfoil. Incremental aileron and spoiler performance are quite comparable to that obtained on the GA(W)-2 airfoil. Slotted flap performance on this section is reduced compared to the GA(W)-2, resulting in a highest c sub l max of 3.00 compared to 3.35 for the GA(W)-2.

The Application of Subsonic Theoretical Aerodynamics to Active Controls

Abstract: : Analytical and numerical studies are made of aerodynamic forces for wing and control-surface motion with general time-dependence in linearized subsonic flow. Alternative formulations are discussed, with particular attention to one in the time domain where quasi-steady displacement and rate terms are combined with a residual history term. An accurate calculation procedure is devised, and results are illustrated for a high-aspect-ratio wing at Mach number 0.8 with trailing-edge, leading-edge and all-moving tip controls. Emphasis is placed on asymptotic behaviour at small and large times. Individual control characteristics are compared over a wide range of control rate. The usefulness of the quasi-steady approximation is established for hinge moments and is analysed for lift, where the rate and history terms become important together. The rapid lift response to the leading-edge control and the sluggish lift response to the trailing-edge control are explained. These forces in the time domain are confirmed by Fourier transform calculations in the frequency domain, which show the extent to which the range of frequency can be truncated. The control-surface motion to produce a known time-dependent force is determined. It is remarkable how rapidly the controls can neutralize the growth of lift as the wing enters a step gust.

Measurements of Aerodynamic Damping in the MIT Transonic Rotor

Abstract: A method was developed and demonstrated for the direct measurement of aerodynamic forcing and aerodynamic damping of a transonic compressor. The method is based on the inverse solution of the structural dynamic equations of motion of the blade disk system in order to determine the forces acting on the system. The disturbing and damping forces acting on a given blade are determined if the equations of motion are expressed in individual blade coordinates. If the structural dynamic equations are transformed to multiblade coordinates, the damping can be measured for blade disk modes, and related to a reduced frequency and interblade phase angle. In order to measure the aerodynamic damping in this way, the free response to a known excitation is studied.

Nuclear Blast Response Computer Program. Volume II. Doublet-Lattice and Piston Theory Aerodynamics.

Abstract: : The VIBRA-6 computer program is a digital computer program developed to deter the response of aircraft to nuclear explosions when flying at subsonic speeds. It is similar to the VIBRA-4 program but uses the latest Doublet-Lattice Method for obtaining subsonic aerodynamic forces for arbitrary lifting surface-body configurations. The Doublet-Lattice procedure has been extended to account for the moving blast wave by considering it as a traveling gust. The nuclear blast representation remains the same as that used in the VIBRA-4 program but the method of solution of the equations of motion has been changed from that of numerical integration of quasi-steady equations of motion to a Fourier transform procedure to move from frequency domain solutions to time history solutions. The concept of dynamic core has been introduced to the program thus removing any restrictions on the size of the aircraft idealization which can be analyzed. (Author)