Pitching moment

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

Synthesis of a Variable Geometry Trailing Edge Control Surface

Abstract: This paper describes the synthesis of a twodimensional airfoil with a chordwise variable geometry trailing edge control surface. Sequential unconstrained minimization techniques are applied to the control surface camberline representation to determine the optimal deflected shape. In addition to a continuous fourth order equation, a series of segments are used to describe the change in camber of the control surface, and viability of the two models is considered. Design variables consist of parameters which change the camberline including the control surface “hinge” location. The typical aeroelastic airfoil section is modelled with vertical and torsional springs to account for the flexibility of the system. Thin airfoil theory is used to model the pressure differential along the complete airfoil section, and determine aeroelastic performance parameters. The lift, moment imparted by the aerodynamic pressures on the control surface about its effective “hinge” point, and the energy necessary for the variable geometry control surface to overcome the aerodynamic forces as it changes positions are utilized as behavior functions. These behavior functions can be used in combination to provide objectives and constraints to the design process. Preand post-roll reversal cases are studied. 1 American Institute of Aero *Member AIAA †Associate Fellow AIAA ‡Professor, Fellow AIAA s declared a work of the U.S. Government and is not subject to copyright prote Nomenclature = , where is an integer = , where is an integer Aerodynamic Parameters = Density of Air = Freestream Velocity of Air = Dynamic Pressure = Initial Angle of Attack (AoA) = Change in AoA due to flexibility = Pressure Differential = Lift of Airfoil = Change in Energy at TECS = Aerodynamic Moment about Shear Center = “Hinge” Moment at Location = Lift Coefficient of 2-D Section = Slope of the Coefficient of Lift w.r.t. AoA = Moment Coefficient about Shear Center = Pressure Coefficient Differential

Transient Aerodynamic Characteristics of a Two-Dimensional Airfoil During Stepwise Incidence Variation

Abstract: The present paper discusses the transient aerodynamic characteristics of a two-dimensional low-speed airfoil whose angle of attack is varied impulsively. The study is mainly an experimental one with observations made of the three dynamic loads, the static pressure distribution, and flow on the airfoil surface, following the airfoil motion. The changes in the characteristics and their aerodynamic causes are investigated in terms of the ultimate angle of attack and the rise time. foil other than the two-dimensional motion to be discussed in this paper. For instance, Refs. 7-10 deal with the effects of variations in the flow velocity and in the angle of attack. There are other studies11'12 that have analytically pursued the rela- tionship between dynamic stall and the ambient flowfield. Furthermore, little is known about the effects of Reynolds number, Mach number, airfoil profile, and airfoil motion.13 At this stage of information it is natural that the technology should be based on experimentation. In the present paper, in- stead of a conventional study of an oscillating airfoil, which has been often undertaken, the relations between the transient aerodynamic characteristics of an airfoil with stepwise varied angle of attack and the state of the ambient airflow are ex- perimentally investigated as a basic study leading to applica- tion. Another reason for adopting a stepwise varied input is the desirability of obtaining a simple motion for understand- ing the phenomena in a flow with prominent nonlinearity and hysteresis.

Determination of the Pitching Characteristics of Tumbling Bodies by the Free-Rotation Method

Abstract: A method to determine the pitching moment of slender bodies with less support interference was developed by simulating a pitching motion of 1-DOF angular motion in wind tunnels. The pitching moment acting on the bodies was determined to be a one-valued function of the angle of attack a and its time derivative a'. A phase plane concept proved to be useful in the analysis of the pitching motion. It was possible to calculate the pitching motion for an arbitrary initial condition by using the mathematical expression of the moment. The variation of energy in the pitching motion showed the energy exchange between the models and the air flow. The visualization of the wake flowfield revealed the hysteresis of the separated flow about the model which caused the amplification of the pitching motion. The effects of the shapes of models, freestream velocity, and the center of gravity on the pitching moment coefficients were investigated.

The effect of Reynolds number on the stalling characteristics and pressure distributions of four moderately thin airfoil sections

Abstract: Report presenting low-speed measurements of the lift, drag, pitching moment, and pressure distribution of 4 airfoil sections over a range of Reynolds numbers. Results indicated that the nature of the stalls depends on the Reynolds number. Low Reynolds numbers tend to be favorable to the thin-airfoil type of stall while high Reynolds numbers are favorable to to the leading-edge type of stall.