Error Correction in Orbital Flight
Orden, Alexander

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Date
1950-06-13Abstract
As part of an investigation of possible future
forms of air traffic control, an analysis is made of orbital motion around an Omni-Range DME
station. It is assumed that each aircraft would be assigned an azimuth-vs-time schedule, and that
maintenance of the schedule would be by path variation: reduction of radius when behind schedule
and increase of radius when ahead of schedule. In order to estimate the precision of the proposed
type of orbital guidance an autopilot control system is formulated. Aircraft motion is assumed to
be governed by the equations of a "coordinated turn". Feedback of azimuth and heading and their
first derivatives are shown to be needed for stabilization. Linear approximation procedures are
shown to be fairly satisfactory for estimating the control system behavior. For appraisal of
azimuth deviation characteristics, computations are made using reasonable assumptions for various
parameters. Results are: (1) Assuming no wind and constant aircraft speed, an initial error in
azimuth of up to 20° could be reduced about 30% in 1 minute and 80% in 2 minutes. (2)
Assuming 1 mile per minute per minute deceleration, an aircraft on schedule at the beginning of
deceleration would be 10° behind schedule after 2 minutes. (3) Maximum azimuth errors
caused by wind are of the order of 0.1 [w over V] where w = wind speed and V = aircraft speed.
Deviations due to wind might be reduced by means of heading compensation.