"Present on-aircraft ground alignment gyro bias methods can basically be categorized as (1) periodic maintenance performed by the ground crew, (2) pre-flight calibration requiring a two-position gyro compass alignment or (3) optimal filter estimation of the north gyro bias error.
This thesis discussion presents an interrupted alignment method that allows adequate level axes gyro bias correction without the restrictions associated with a conventional two-position gyrocompass alignment (i.e., a minimum time for bias calibration on a steady aircraft). The interrupted alignment technique allows the pilot to select the navigate mode at any point during gyrocompass and reselect the align mode at a later point in time (after taxi) to continue gyro bias correction.
A mathematical error model for a north pointing inertial navigation system is derived to demonstrate the principle. Error states for the covariance simulation are 2 platform tilts, azimuth misalignment, level velocity errors, position errors, and north and east gyro bias errors (random and constant). Parameter variations and wind disturbances were introduced to evaluate the filter response under these conditions. Six additional error states are added to obtain gyro bias corrections during a more accurate simulation of the effects of wind gust.
A comparison of the results of the basic and expanded filters is made. The conclusion is that the expanded mathematical error model (although appearing to require longer gyro bias correction times) is a more accurate representation of the adverse effects of wind gust disturbances. Thus the results of the expanded mathematical error model are more realistic. The basic and expanded filter response to typical standard deviations is recorded and presented. Excessive initial errors (10x typical standard deviations) are simulated for the basic error model. These results were recorded and are presented.
Plots of the optimal (Kalman) gains associated with the basic error state corrections are presented.
Also discussed are the additional benefits derived from the implementation of the interrupted alignment technique in a wander azimuth system. Filter alignments and equivalent north gyro biasing at random aircraft headings result in correction of both level gyro bias errors. This results from resolving various equivalent north gyro drifts computed at random aircraft headings through the wander azimuth angle into x and y components.
Storing these biases in permanent memory effectively eliminates long term drift (trending errors) in both level axis gyros"--Abstract, pages ii-iii.
Noack, Thomas L.
Carlson, Gordon E.
Pagano, Sylvester J., 1924-2006
Electrical and Computer Engineering
M.S. in Electrical Engineering
University of Missouri--Rolla
xi, 74 pages
© 1973 Ralph E. Herndon, All rights reserved.
Thesis - Restricted Access
Inertial navigation -- Mathematical models
Electronics in navigation
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Electronic access to the full-text of this document is restricted to Missouri S&T users. Otherwise, request this publication directly from Missouri S&T Library or contact your local library.http://merlin.lib.umsystem.edu/record=b1066696~S5
Herndon, Ralph E., "Inertial navigation performance improvement realized by the technique of interrupted alignment" (1973). Masters Theses. 3499.
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