A Simple Explanation of Inertial Navigation

The equipment and hence the aircraft, knows where it is at all times. It knows this because it knows where it isn't.

By subtracting where it is from where it isn't (or where it isn't from where it is, depending on which is greater), it obtains a difference or deviation. The inertial guidance system uses deviations to generate corrective commands to fly the aircraft from a position where it is to a position where it isn't. The aircraft arrives at the position where it wasn't; consequently, the position where it was, is now the position where it wasn't.

In the event that the position where it is now is not the same as the position where it originally wasn't, the system will acquire a variation. (Variations are caused by external factors and the discussion of these factors is beyond the scope of this simple explanation.) The variation is the difference between where the aircraft is and where the aircraft wasn't.

If the variation is considered to be a significant factor, it too may be corrected by the internal guidance system. The aircraft must now know where it was.

The "Thought Process" of the equipment is as follows: because a variation has modified some of the navigation information which the aircraft required, it is not sure where it is. However, it is sure where it isn't and knows where it was. It now subtracts where it should be from where it wasn't (or vice-versa) and by differentiating this from the algebraic difference between where it should be and where it was, it is able to obtain the difference between it's deviation and it's variation. This difference being called error...

Last updated: 08 April, 2003 13:17