Inertial Navigation – Aircraft Axes Definition The three axes of the aircraft are: 1. The roll axis which is roughly parallel to the line joining the nose and the tail Positive angle: right wing down 2. The pitch axis which is roughly parallel to the line joining the wingtips Positive angle: nose up 3. The yaw axis is vertical Positive angle: nose to the right
Inertial Navigation – Aircraft Axes Definition ROLL PITCH Y A W
Inertial Navigation – Platform Isolation The platform is isolated from the aircraft rotation by means of a gimbal system • The platform is connected to the first (inner) gimbal by two pivots along the vertical (yaw) axis. This isolates it in the yaw axis • The inner gimbal is the connected to the second gimbal by means of two pivots along the roll axis. This isolates the platform in the roll axis. • The second gimbal is connected to the INU (Inertial Navigation Unit) chassis by means of two pivots along the pitch axis. This isolates it in the pitch axis.
Inertial Navigation – Platform Isolation Now the platform can be completely isolated from the aircraft rotations
Inertial Navigation – Gyroscopes To keep the platform level we must be able to: • Sense platform rotation and • Correct for it To do this we mount gyroscopes on the stable platform and install small motors at each of the gimbal pivots. The gyroscopes sense platform rotation in any of the three axes and then send a correction signal to the pivot motors which then rotates the relevant gimbal to maintain the platform at the correct attitude
Inertial Navigation – Alignment Before the INS can navigate it must do two things: • Orient the platform perpendicular to the gravity vector • Determine the direction of True North Also it must be given: • Initial Position: Input by the Pilot (or navigation computer) • Velocity: This is always zero for commercial systems
Inertial Navigation – Orientation
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- Summer '18