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Canard Airplanes and Biplanes
Published in James DeLaurier, Aircraft Design Concepts, 2022
The pitching-moment coefficient about the wings’ aerodynamic center is the same as that for the 7.5% circular-arc airfoil: CMacw1=CMacw2=Cmacairfoil=παZLL/2=−0.2356,CMacs=0
Introduction to Boundary Layer Theory and Drag Reduction
Published in Ranjan Vepa, Electric Aircraft Dynamics, 2020
In a real flow field, potential flow theories of flow around an airfoil are generally applicable, which generally implies that all viscous forces may be neglected, provided the Kutta–Joukowski condition for a smooth flow at the trailing edge are imposed. The lift of an airfoil is created by a pressure differential between the bottom, or pressure side, and top, or suction side. The drag force developed is assumed to be in the same direction as the relative wind velocity direction. The net lift force is assumed to be normal to the direction of the drag force. Under such circumstances, the lift, drag and pitching moment characteristics of an airfoil can be assumed to be functions of the angle of attack alone. Given the lift force L and the drag force D per unit span and the chord length c, the coefficients of lift and drag may be defined asCscriptl=L12ρV2c,Cd=D12ρV2c.
Unsteady Aerodynamics
Published in Rama B. Bhat, Principles of Aeroelasticity, 2018
Consequently, unsteady-aerodynamic theories need to account for at least three separate physical phenomena, as follows: In view of the airfoil’s unsteady motion relative to the air, the relative wind vector is not fixed in space. The changing direction of the relative wind changes the effective angle of attack and thus changes the lift.The airfoil motion disturbs the flow and causes a vortex to be shed at the trailing edge (Fung 1955). The downwash from this vortex, in turn, changes the flow that impinges on the airfoil. This unsteady downwash changes the effective angle of attack and thus changes the lift.The motion of the airfoil accelerates air particles near the airfoil surface, thus creating the need to account for the resulting inertial forces (although this “apparent-inertia” effect is less significant than that of the shed vorticity). The apparent-inertia effect does not change the angle of attack but it does, in general, affect both lift and pitching moment.
Sampled-data control of underwater gliders: digital redesign approach
Published in International Journal of Control, 2021
To fully make use of the advantages of underwater gliders, one needs to adopt an elaborate control law taking account of the vehicle's feature such as severe nonlinearity and underactuation (Bhatta, 2006). Integrated studies have been conducted about the dynamics analysis and controller design in Bhatta (2006), Zhang, Thon, Thon, and Tan (2014). In Bender, Steinberg, Friedman, and Williams (2008), the dynamics of an underwater glider for buoyancy, pitch, and heading control was analysed in the longitudinal and lateral plane. In Mahmoudian and Woolsey (2008), a proportional-integral-derivative controller was used to control the vertical motion of the glider. The linear quadratic regulation technique was applied to the linearised model about specific operating points of the underwater glider in Isa and Arshad (2012), da Silva Tchilian, Rafikova, Gafurov, and Rafikov (2017). In Yang and Ma (2010), a sliding mode controller was designed for the glider to be robust against disturbances on the ocean environment. In Graver and Leonard (2001), a pitching moment adjustment module was supplemented for attitude control by moving the centre-of-gravity or through an elevator tuning. The reduced-order model of the underwater glider was derived through the singular perturbation technique in Zhang and Tan (2015). Lyapunov-based control design for the stability of steady gliding motions was explored in Bhatta and Leonard (2008). In Bhatta and Leonard (2002), the feedback-linearisation method was applied to the underwater glider for the stability problem. However, since the nonlinear model is partially linearised and the approximation error is ignored, the method does not guarantee global stability.