Pitching moment

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

Modelling and sensitivity analysis of a variable geometry trailing edge control surface

Abstract: This paper describes the development of a design model for the study of a two-dimensional airfoil with a chordwise variable geometry trailing edge control surface. A fourth order equation is used to describe the change in camber of the control surface allowing for discontinuity in the slope but not displacement at the control surface “hinge”. The equation coefficients and the control surface “hinge” location represent the design variables. 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. Relations for the aerodynamic lift and moment about the shear center are established so that the aeroelastic equilibrium equations can be solved. A relationship for the moment imparted by the aerodynamic pressures on the control surface about its effective “hinge” point is determined. Further, a relationship describing the energy necessary for the variable geometry control surface to overcome the aerodynamic forces as it changes position is established. These represent the behavior functions of the model, and thus can be considered as objectives and constraints in the design process. Studies are conducted to establish trends of behavior to aid in future synthesis. Nomenclature

Navier-Stokes Predictions of Pitch-Damping for a Family of Flared Projectiles

Abstract: : A parabolized Navier-Stokes approach has been applied to predict the pitch-damping force and moment coefficients for a family of flared projectiles. This family of flared projectiles, which has been tested in the Army Research Laboratory's (ARL) Aerodynamic Range, consists of a common forebody with various flared afterbodies including straight flares, biconic flares, straked flares, and flares with finlets. The predicted pitch-damping force and moment coefficients are determined from the aerodynamic side force and moment acting on the projectiles due to steady coning motion. The predictions of the flow field about the projectiles undergoing steady coning motion are accomplished using a rotating coordinate frame which rotates at the coning rate of the projectile. The governing equations have been modified to include the centrifugal and Coriolis force terms due to the rotating coordinate frame. The predictions of the pitch-damping moment coefficient are compared with pitch-damping coefficient determined from the inflight motion of the projectile. The predictions of the pitch-damping moment coefficients are in good agreement with the range data.

Global Aerodynamic Modeling with Multivariate Splines

Abstract: A new method for global aerodynamic modeling using multivariate spline functions is presented. The multivariate spline functions are used to phenomenologically model the pitching moment coefficient ( Cm) of a five dimensional NASA F-16 wind tunnel model with an accuracy better than 99.9% over its entire flight envelope. The resulting multivariate spline functions were incorporated in a dynamic model of the F-16 effectively replacing the original lookup table based aerodynamic model for the pitching moment coefficient. Time based simulations were performed with the spline based F-16 model and compared to results obtained with the lookup table based F-16 model. It is argued that the new method would be an attractive alternative for classical approaches to aircraft parameter identification.

Thick Airfoil Deep Dynamic Stall

Abstract: Recent interest in vertical axis wind turbines (VAWTs) has surged due to their appearance in the built environment and their potential for deep water offshore applications. Their well-known advantages include insensitivity to the wind direction, proximity of the generator to the ground and relatively low noise levels. Furthermore, blade profile uniformity along the span can significantly reduce manufacturing costs, particularly for large scale utility machines. A drawback of VAWTs is the tendency of their blades to stall dynamically when they are pitched beyond their static stall angle. Dynamic stall is characterized by a strong vortex, the dynamic stall vortex (DSV), which forms near the leading-edge. When the DSV is convected downstream, a rapid drop in lift and severe pitching moment fluctuations result [1]. On VAWTs operating at low tip-speed ratios, dynamic stall occurs periodically throughout the rotation of the blades [2]. This situation is unique in that the blades experience pitch oscillations about zero angle of attack and the flow separates alternately on both sides. This results in a number of undesired effects: On the one hand, the full separation on the suction surface produces a sharp drop in cl and thus rotor torque. On the other hand, the unsteady aerodynamic loads cause fatigue damage to the generator and drive train [3].

Maximum Likelihood Estimation of Translational Acceleration Derivatives from Flight Data

Abstract: This paper shows that translational acceleration derivatives, such as pitching moment due to rate of change of angle of attack, can be estimated from flight data with the use of appropriately designed maneuvers. No new development of estimation methodology is necessary to analyze these maneuvers. Flight data from a T-37B airplane were used to verify that rate of change of angle of attack could be estimated from rolling maneuvers.