Lateral Control Surfaces for Vertical Path Tracking
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Solution Overview
Problem
Conventional aircraft autopilot systems face challenges in maintaining precise vertical path control during automatic landings, particularly in low visibility weather and adverse conditions like shearing winds, due to high feedback gains that can compromise stability and cause excessive pitch activity.
Innovation Solution
The method involves determining vertical path errors and converting them into delta lift commands, which are then limited and filtered before being converted into lateral surface position commands to reduce vertical position errors, using symmetric deflections of lateral control surfaces to augment the existing vertical position feedback control loop.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high feedback gains are used in the elevator feedback control system to achieve desired vertical path tracking accuracy, then vertical path tracking precision is improved, but system stability is compromised and excessive pitch activity occurs
Solution Approach 1:
The patent divides the vertical path control function into two separate control loops: an outer loop that generates pitch attitude commands for glide path control and flare maneuver, and an inner loop that generates elevator commands for vertical path tracking. This segmentation allows each loop to operate with appropriate gain levels, preventing the stability issues caused by excessively high feedback gains in a single loop.
Solution Approach 2:
The patent introduces pitch attitude as an intermediary variable between vertical position error and elevator command. The outer loop converts vertical position errors into pitch attitude commands, which then serve as reference inputs for the inner loop. This intermediary approach distributes the control effort and avoids the need for excessively high gains directly from position error to elevator deflection.
2Measurement precision
If high feedback gains are used in the elevator feedback control system, then vertical path tracking accuracy is improved, but excessive pitch activity is generated that is objectionable to the flight crew
Solution Approach 1:
By segmenting the control system into outer and inner loops with distinct functions, the patent eliminates excessive pitch activity. The outer loop generates smooth pitch attitude commands based on vertical position errors, while the inner loop executes these commands with appropriate damping. This segmentation ensures that pitch activity remains within acceptable limits while maintaining tracking accuracy.
Solution Approach 2:
The patent implements dynamic gain scheduling where the inner loop gain is reduced when the aircraft is near the desired vertical path and increased when further away. This dynamic adjustment of gains allows accurate tracking without generating excessive pitch activity during the approach and landing phases.
Data Source
AI summary
In one embodiment of a method for reducing vertical position errors of an aircraft, the displacement of the aircraft from a commanded vertical path may be determined. A determination may be made as to whether a magnitude of a vertical path error meets criteria. No more steps of the method may be followed if the vertical path error does not meet the criteria, while the vertical path error may be converted into a delta lift command if the vertical path error meets the criteria. The delta lift command may be limited. The delta lift command may be converted into lateral surface position commands for control surfaces. The lateral surface position commands may be communicated to lateral control surface actuators to move the control surfaces according to the lateral surface position commands.