Correction for deflections of the vertical at the runup site

The effects of unmodeled deflections of the vertical on aircraft inertial navigation system performance are considered. It is argued that, with few exceptions, the work on the area to date has ignored an important aspect, the correlated effects of deflections of the vertical at the runup site interacting with the systems´s self-alignment algorithm. The author reviews statistical analysis and flight test results, examines the effects of self-alignment on navigation errors, and describes a methodology that applies appropriate corrections during self-alignment and static navigation testing, and removes those corrections during flight. An implementation that substantially reduced the resulting errors for navigation time of one or two Schuler cycles was successfully demonstrated during flight test of the Mini-GEANS (Gimbaled Electrostatic Gyro Aircraft Navigation System)