Inertial Sensors and Attitude Derivation

Abstract

Gyroscopes (gyros) and accelerometers are known as inertial sensors. They are fundamental to the control and guidance of aircraft. This chapter covers gyros and accelerometers and attitude derivation from strap-down gyros and accelerometers. It provides the basic background to inertial navigation and AHRS systems, which are covered in Chap. 6.

Gyros: This chapter covers stable platform gyros, solid state body mounted gyros, Micro Electro-Mechanical Systems (MEMS) gyros, ring laser gyros (RLG) and interferometer fibre optic gyros (IFOG). For each type, a description of its physical operation and mathematical theory is provided along with a summary of its advantages.

Accelerometers: The principles and mathematics behind the measurement of acceleration are explained. The operation and theory behind simple spring restrained pendulous accelerometers and closed-loop torque balance (including ‘solid state’) accelerometers is set out.

The derivation of attitude from inertial information is described. The two types of system are illustrated: the stable platform system from which the Euler angles are output directly, and the strap-down systems in which they are computed. Mathematical derivation of the Euler angles is provided and the computation of aircraft heading is also explained. An introduction to complementary filtering is provided where the data from two independent sources are combined to improve accuracy.