A solid state attitude heading reference system for general aviation

An Attitude Heading Reference System (AHRS) is presented which has been developed for use in general aviation aircraft. The AHRS is contained in a 4.5"/spl times/4.0"/spl times/4.5" aluminum box, weighing 2.2 lb., with integral mounting flanges. Two connectors are provided, one for power and data out and another for a remote flux gate compass input. The AHRS is being marketed as part of an Electronic Flight Instrument System (EFIS) for use in experimental aircraft. Work is underway to certify the AHRS to enable its use in any aircraft as part of an Electronic Horizontal Situation Indicator (EHSI) and Electronic Air Data Indicator (EADI). The advantages of this system are low power usage, ease of interfacing the device to other aircraft systems and the durability and longevity of the solid state components. The internal architecture of the AHRS is presented along with the considerations used in the design process. The use of relatively inexpensive solid state piezo-electric rate gyros to determine instantaneous rotations about the three axes of the plane present unique problems due to the inherent drift characteristics of the rate gyros. Solid state G-cell accelerometers, with integral self-testing, are used as long term inertial reference devices to stabilize the gyros.