A simplified method to determine gravity vector through aerodynamic coefficients and its applications in attitude determination

Abstract

Position and attitude determine the accuracy on the navigation and control of any airship. The possibility of determining the rotation of a body is provided by the measurements of two different vectors in a couple of independent reference triads, in the case depicted on this paper, North-East-Down (NED) and body reference axes. The first involved vector is velocity, which can be directly measured by Global Navigation Satellite Systems (GNSS) in NED axes and from an integration of a set of at least three accelerometers in the body reference frame. Gravity vector is an known magnitude in NED triad, depending of longitude and latitude. For its estimation in body reference frame, a novel approach is presented, which is based on the aircraft aerodynamics. Combining both vectors enables determination of body rotation. The use of a nonlinear flight dynamics model previously developed for a military rocket, show that, utilizing GNSS sensors, strap-down accelerometers and the proposed approach, aircraft attitude determination is accurate. Application of these concepts is especially interesting in order to substitute high-precision attitude determination devices, which are usually expensive and they are forced to bear high G forces in some military applications.