Yaw Coefficients Research Articles

Dynamic modelling of parafoil system based on aerodynamic coefficients identification

This study focuses on the identification of aerodynamic coefficients through airdrop data based on a known six-degree-of-freedom (6-DOF) model. Since the precise modelling of the parafoil system is a prerequisite for design of guidance, navigation and control systems, the accurate calculation of aerodynamic coefficients is vital. This paper first presents a rigid 6-DOF nonlinear model and simplifies it by linearizing the equations around the equilibrium point, which facilitates the acquisition of aerodynamic parameters next. Then, the recursive weighted least square method is applied to identify roll and yaw coefficients from airdrop test data. At last, simulations in the wind environment are implemented to analyse the dynamics of gliding and turning. The airdrop experiment also verifies the effectiveness of the dynamic model and the accuracy of identification.

Effect investigation of yaw on wind turbine performance based on SCADA data

Due to the time-varying wind direction, yaw operation of wind turbines is a common state. Under yaw, the aerodynamic behavior of wind turbines is complicated, and also causes complex energy capture performance. To clarify some vague knowledge, a detailed investigation of yaw effect based on SCADA data is carried out. Firstly, a yaw coefficient definition and its specific calculation method are presented. Furthermore, to analyze the energy capture mechanism, the loss factor of energy capture (power coefficient) is subdivided into aerodynamic loss factor and inertia loss factor, which means both the effects of aerodynamic characteristic and mechanical inertia on energy capture are considered. According to this understanding, power coefficient is expanded as a function of four factors. Then, a single-valued processing method is employed to investigate the relationship between wind speed and output power. Subsequently, relationship between yaw coefficient and output power is investigated. Comparative investigations are carried out by two different methods, that is, least square fitting (LSF) method and kernel density estimation (KDE) method. Also, characteristics of power coefficient and rotor torque under yaw are investigated. Effect laws of yaw coefficient on wind turbine power, power coefficient, and rotor torque are obtained. Finally, the relationship between the internal control mechanism and external output of wind turbines is discussed.

Flight Stability and Control of Tailless Lambda Unmanned Aircraft

Marques P. (2013). Flight stability and control of tailless lambda unmanned aircraft. International Journal of Unmanned Systems Engineering. 1(S2): 1-4. This paper illustrates the unique challenges with which Aerospace Engineers are presented in achieving dynamic stability and autonomous flight control in tailless lambda unmanned aircraft. The static margin in lambda configurations is short, making the aircraft unstable. To compensate for the short static margin, a priority in lambda UAV design is to obtain a small linear pitching moment. Negligible pitching moment is implemented using reflex camber airfoils that complement the longitudinal dihedral provided by combined wing sweep back and washout. The reflex airfoil permits a wider choice of wing planform and enhances control authority with minimum elevon deflection. Stability analysis shows that a lambda UCAV is longitudinally unstable in ground effect, in both the flaps extended and flaps retracted configurations. Vortical flow and asymmetrical vortex bursting unsteadiness in a rapidly maneuvering next generation near-lambda 1303 UCAV are responsible for unexpected changes in pitch, roll and yaw coefficients and illustrate the difficulty in maneuvering the UCAV beyond certain critical angles of attack. The primary mechanism of lateral-directional control in a W–shaped flying wing UAV is provided by drag rudders, however lateral-directional control in such aircraft requires a sophisticated on-board flight control system. © Marques Aviation Ltd – Press.

An analytical approach to the uniqueness problem of hot-wire probes to measure simultaneously three velocity components

The uniqueness range of hot-wire probes to simultaneously measure all three velocity components is analysed analytically. Expressions defining the uniqueness cone half-angle are presented for triple as well as for quadruple sensor configurations. Using these expressions the influence of the main probe parameters on the uniqueness cone, i.e. the number of sensors and their orientation, the effective angle and the pitch and yaw coefficients, are analysed. Different types of probes are compared and optimum parameters are proposed. The same analysis is valid for complex vorticity probes configured as combinations of triple and quadruple sensor arrays.

On the directional sensitivity of hot-wires: a new look at an old phenomenon

The directional response of a constant temperature hotwire anemometer to variations in pitch and yaw is reviewed, and a new data reduction technique for obtaining velocity vector data in a steady flow is described. Sequential sampling of the signal as the probe shaft is rotated through 360° provides data to yield a three-dimensional velocity vector. Jorgensen's expression was found to be suitable for the data reduction using independently measured pitch and yaw coefficients. Within the range of velocity and flow direction investigated, the velocity magnitude and direction can be determined to within 2% and 2° respectively if the yaw coefficient is neglected. This measurement method is currently being used to determine velocity distributions on the intake-valve/cylinder boundary for different induction system designs.

Frequency Response of Tires Using the Point Contact Theory

The theoretical frequency response of a rolling tire is obtained here for angular oscillations about a vertical axis through the axle in the wheel plane. The point contact theory, also known as the DeCarbon or Moreland theory, is used to describe the side (cornering) force and the torsional (self-aligning) moment as a function of the oscillating frequency. These results are compared to previously published experimental results and found to show reasonable correlation especially when compared to theoretical results obtained using the von Schlippe or stretched string theory. It is noted, both from experimental and theoretical results, that the frequency response is considerably influenced by rolling speed which is contrary to implications given in previous papers. It is also pointed out that an upper limit of the forcing frequency exists above which the empirical data is not likely to represent natural shimmy oscillations. The results indicate that the point contact theory is adequate for use in shimmy analysis over both the tire yaw and structural-torsion shimmy modes of vibration if appropriate tire parameters are used. Nomenclature b = half width of tire footprint or contact area c = tire yaw coefficient CL = tire lateral damping coefficient ct = tire time constant D = tire diameter Airum = drum diameter d = effective tire width F = magnitude of dimensionless, complex lateral force ampli_ tude