A STRAPDOWN INERTIAL NAVIGATION SYSTEM FOR THE FLAT-EARTH MODEL

The development of a strapdown inertial navigation system (SINS) for a erodynamically controlled vehicles, which are limited to altitudes bel ow 30 km (that is, a small distance compared with the Earth's radius o f about 7000 km), or using the so-called flat Earth model (FEM), is th e principal objective of this work. In dealing with the FEM equations, the north, east, down (NED) frame on the surface of the Earth is take n as an inertial reference frame. Although, this name is both accelera ting and rotating, the accelerations associated with the Earth's rotat ion are negligible compared with the acceleration that can be produced by a maneuvering aircraft. Also, in this model, the gravity is taken as constant In developing the SINS for the PEM, the aerodynamic force and moment have dominant roles, depending primarily on such variables as the angle of attack and sideslip, their derivatives, components of the angular velocity of the aircraft, and the control inputs. On the o ther hand, the SINS deals with such variables as the small-angle rotat ion vectors. Thus, it was necessary to link both set of variables as s tate variables of the strapdown FEM, as is done in this work. The deve loped model is relevant for small (less than 20 degrees) angles of att ack and sideslip.