Avionics Navigation Systems, 2nd Edition

9 Attitude and Heading References

9.1 INTRODUCTION

A heading reference is required for steering and navigation. It may be as simple as a gravity-leveled magnetic compass or as elaborate as an inertial navigator (Chapter 7). An aircraft also requires some form of attitude reference. In the simplest case, it may be the visible horizon, but, if the aircraft is to be flown in poor weather, then an instrument must substitute for the visible horizon.

An automatic pilot (flight-control system) requires measurements of body rates and attitude. Attitude and rate instruments stabilize other avionic sensors such as Doppler radars (Chapter 10), navigational radars (Chapter 11), and weapon delivery systems.

In the late 1990s the trend was toward obtaining attitude and heading information from inertial navigators including low-cost inertial systems called Attitude and Heading Reference Systems (AHRS). Rate measurements (for crew-display or flight-control computers) were from separate instruments whose bandwidth was wide enough for flight control (high bandwidth increases the apparent bias and raises the sensitivity to vibration, so the unit might not also be suitable for navigation).

Cockpit displays in inexpensive aircraft incorporate self-contained vertical and directional gyroscopes that are viewed directly by the crew. In complex aircraft, the cockpit displays of attitude are driven from remotely located sensors and are displayed on “glass” instruments, Figure 9.1. The vertical situation ...