Pitching moment

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

Actuator-Work Concepts Applied to Unconventional Aerodynamic Control Devices

Abstract: This paper investigates the resistance to a change in wing shape due to the aerodynamic forces. In particular, the work required by an airfoil to overcome the aerodynamic forces and produce a change in lift is examined. The relationship between this work and the total aerodynamic energy balance is shown to have significant consequences for transient changes in airfoil shape. Specification of the placement of the actuators and the actuator energetics is shown to be required for the determination of the airfoil shape change, requiring minimum energy input. A general simplified actuator model is adopted in this study, which assigns different values of actuator efficiency for negative and positive power output. Unsteady thin airfoil theory is used to analytically determine the pressure distribution and aerodynamic coefficients as a function of time for a ramp input of control deflection. This allows the required power and work to overcome the aerodynamic forces to be determined for a prescribed change in the airfoil camberline. The energy required for a pitching flat plate, conventional flap, conformal flap, and two variable camber configurations is investigated. For the pitching flat plate, the minimum energy pitching axis is shown to be dependent on the pitch rate and the initial angle of attack. The conformal flap is shown to require less actuator energy than the conventional flap to overcome the aerodynamic forces for a prescribed change in lift. The energy requirements of a variable camber configuration are shown to be sensitive to the layout of the variable camber device. The present analysis shows that the unsteady aerodynamic influence is important only for τ* values less than five. For τ* values larger than this, the present analysis reduces to the steady airfoil results of past studies.

Experimental and predicted aerodynamic characteristics of a proposed Assured Crew Return Vehicle (ACRV) lifting-body configuration at Mach 6 and 10

Abstract: The effects of Mach number, Reynolds number, and ratio of specific heats on the aerodynamic characteristics of a proposed Assured Crew Return Vehicle (ACRV) lifting-body configuration were examined for a range of angles of attack from -5 deg to 50 deg. Predictions made with a Langley-developed, three-dimensional Navier Stokes solver known as LAURA, which was exercised as an Euler solver for the present study, are compared with the experimental results. Unlike the Shuttle Orbiter, which experienced a significant nose-up increment in pitching moment with decreasing specific heat ratio (i.e., real gas effects), the aerodynamic characteristics of this lifting-body configuration are insensitive to changes in specific heat ratio. The maximum trimmed lift-to-drag ratio achieved was about 1.5. Predicted inviscid values of aerodynamic coefficients were generally in good agreement with measurement.

Numerical study of a variable camber plunge airfoil under wind gust condition

Abstract: Variable camber deformation is observed during the flight of some insects and bird species; however, the effect of this special airfoil shape motion on the aerodynamic characteristics of the airfoil is not well understood, especially for the airfoil under gust wind. We did a numerical study to investigate the aerodynamic characteristics of a variable camber plunge airfoil under wind gusts. A weak coupling program was developed to simulate the interaction between the variable camber plunge airfoil and fluid, and the flow field, aerodynamic force and energy efficiency of different camber airfoils under different wind gust conditions are investigated. It was found that camber deformation influences the aerodynamic characteristics of the airfoil greatly. If the airfoil has an appropriate camber deformation, the deformation can increase the mean thrust and the propulsive efficiency of the airfoil. Moreover, the aerodynamic characteristics of the appropriate camber airfoils are not significantly affected by the gust frequency, and there exists a range of gust amplitude where the aerodynamic characteristics of the airfoils are also not significantly affected by the gust amplitude, which may be beneficial for aerodynamic stability of the airfoil. The results also show that appropriate camber deformation can suppress leading edge vortex separation, which improves the aerodynamic characteristics of the airfoil.

Numerical method for design of minimum-drag supersonic wing camber with constraints on pitching moment and surface deformation

Abstract: A numerical method, based on linearized theory, for designing minimum-drag supersonic wing camber surfaces of arbitrary planform for a given lift, with options for constraining the pitching moment and/or the surface deformation at the trailing edge of the root chord and for selecting any desired combination of eight specified wing-loading distributions to be employed in the optimization procedure is presented. Two examples are given to illustrate applications of the method. The results indicate that relatively small drag penalties are incurred in designing wings to be self-trimming and to have a reasonable camber surface.