Pitching moment

About: Pitching moment is a research topic. Over the lifetime, 3213 publications have been published within this topic receiving 38721 citations.

Tests in the variable-density wind tunnel of related airfoils having the maximum camber unusually far forward

Abstract: A family of related airfoils having the position of maximum camber unusually far forward was investigated in the variable-density tunnel as an extension of the study recently completed of a large number of related airfoils. The new airfoils gave improved characteristics over those previously investigated, especially in regard to the pitching moment. Some of the new sections are markedly superior to well-known and commonly used sections and should replace them in applications requiring a slightly cambered section of moderate thickness having a small pitching-moment coefficient.

Numerical Calculation of Effect of Elastic Deformation on Aerodynamic Characteristics of a Rocket

Abstract: The application and workflow of Computational Fluid Dynamics (CFD)/Computational Structure Dynamics (CSD) on solving the static aeroelastic problem of a slender rocket are introduced. To predict static aeroelastic behavior accurately, two-way coupling and inertia relief methods are used to calculate the static deformations and aerodynamic characteristics of the deformed rocket. The aerodynamic coefficients of rigid rocket are computed firstly and compared with the experimental data, which verified the accuracy of CFD output. The results of the analysis for elastic rocket in the nonspinning and spinning states are compared with the rigid ones. The results highlight that the rocket deformation aspects are decided by the normal force distribution along the rocket length. Rocket deformation becomes larger with increasing the flight angle of attack. Drag and lift force coefficients decrease and pitching moment coefficients increase due to rocket deformations, center of pressure location forwards, and stability of the rockets decreases. Accordingly, the flight trajectory may be affected by the change of these aerodynamic coefficients and stability.

Asymptotic theory of an oscillating wing section in weak ground effect

Abstract: This study addresses unsteady aerodynamic forces acting on a wing section oscillating in a steady incompressible (and inviscid) uniform flow in presence of a distant flat ground. Three fundamental dimensionless parameters characterize the magnitude of those forces: the ratio δ of the wing transversal displacement to its chord, the ratio e of the wing chord to its average distance from the ground, and the ratio k of the wing chord to the distance traveled by the flow during one oscillation period. With the first two serving as small parameters, asymptotic series of the form δ f 0 ( k ) + δ e 2 f 1 ( k ) + δ e 2 g ( k / e ) f 2 ( k ) + ⋯ have been constructed for the wing lift and pitching moment. In the case of heave oscillations, three-terms-series for the lift fits nicely the available numerical data for wide range of δ , e and k values.

A generalized dynamic aerodynamic coefficient model for flight dynamics applications

Abstract: A generalized dynamic aerodynamic coefficient model to represent the effect of unsteady aerodynamics for aircraft is presented in this paper. The model is of the nonlinear algebraic form with the coefficients being functions of frequency and determined from a set of large amplitude oscillatory experimental data by using least-squares fitting. In applications, a general dynamic motion at any instant is modelled by an equivalent harmonic motion with an appropriate frequency. The resulting model is a generalization of the conventional dynamic derivatives with the values of the latter being now dependent on the motion. To verify this model, expressions for lift, drag and pitching moment coefficients of an F-18 HARV configuration are generated with one set of large-amplitu de harmonic oscillatory data. The computed results from these models are compared with good agreement to other sets of data in harmonic oscillation with a smaller amplitude and in constant pitch-rate motions. These models are also used in bifurcation analysis and control study for the same F-18 HARV configuration. The results show significant differences in the equilibrium surfaces and dynamic stability. It is also shown that control gains developed with the conventional quasi-steady aerodynamic data may not be adequate when the effect of unsteady aerodynamics is significant.

Unsteady Surface Pressure Measurements on a Pitching Airfoil

Abstract: : Surface pressure measurements were taken in an experimental investigation of energetic dynamic stall vortices. The associated unsteady flowfield was generated by a 6-in. NACA 0015 airfoil pitching at high rates to large angles of attack. The airfoil pitch rates varied from 230 deg/sec to 1380 deg/sec and angles of attack varied from zero degrees to 60 degrees. Pitching occurred about its quarter-chord axis. Pitch rate, Reynolds number, and the non- dimensional pitch rate, alpha plus, were varied to determine the effects on pressure and lift coefficients. It was found that increases in pitch rate and Reynolds number has inverse effects on the flowfield in the immediate vicinity of the airfoil. Maintenance of a constant non-dimensional pitch rate produced very similar flowfields and pressure coefficients.