Helicopter Flight Control Yaw Rate Limiting for Tail Rotor Effectiveness
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Solution Overview
Problem
Conventional helicopters face Loss of Tail Rotor Effectiveness (LTE), characterized by uncommanded high yaw rates due to vortex ring state conditions, which can lead to loss of aircraft control, especially during aggressive pedal inputs or strong tail winds, without mechanical failure, and existing flight control systems lack criteria to prevent such yaw rates.
Innovation Solution
Incorporating an algorithm into the helicopter flight control system to set specific yaw rate limits based on vortex ring state avoidance, using a computing device to translate control inputs into actuator commands, and providing alerts or restrictions to prevent exceeding these limits, thereby preventing LTE by managing tail rotor thrust and pilot inputs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the pilot applies aggressive pedal input to achieve directional control, then the responsiveness and maneuverability of the helicopter is improved, but the risk of inducing vortex ring state at the tail rotor increases
Solution Approach 1:
The flight control system performs preliminary assessment of pilot inputs to predict whether they will result in unsafe yaw rates. The system evaluates commanded yaw rates against a database of acceptable rates before execution, preventing vortex ring state conditions before they occur rather than reacting after the problem arises.
Solution Approach 2:
The system continuously monitors pilot control inputs and provides feedback by limiting actuator commands when unsafe conditions are predicted. The flight control computer compares commanded yaw rates with acceptable rates from the database and automatically restricts tail rotor actuator commands to prevent exceeding safe yaw rate thresholds.
2Reliability
If the flight control system implements comprehensive yaw rate monitoring and limiting, then the prevention of loss of tail rotor effectiveness is improved, but the system complexity increases
Solution Approach 1:
The system manages complexity by focusing on a single critical parameter - yaw rate - rather than monitoring all possible flight conditions. A database stores pre-calculated acceptable yaw rates as lookup tables based on flight conditions, allowing the system to make safety decisions through simple parameter comparison rather than complex real-time calculations.
Solution Approach 2:
The patent extracts the safety assessment function into a separate database of acceptable yaw rates that can be independently developed and updated. This separates the safety criteria from the flight control logic, allowing the control system to simply query and compare against pre-determined safe operating parameters without embedding complex vortex ring state prediction algorithms.
3Measurement precision
If real-time assessment of commanded yaw rates is performed against a database of acceptable rates, then the accuracy of vortex ring state prediction is improved, but the computational load increases
Solution Approach 1:
Complex computational work is performed in advance to create comprehensive databases of acceptable yaw rates covering the full range of flight conditions. These pre-calculated lookup tables enable real-time operation to rely on simple data retrieval and comparison rather than intensive mathematical modeling during flight.
Solution Approach 2:
Instead of performing complex vortex ring state physics calculations in real-time, the system uses pre-computed representations (lookup tables) that capture the essential safety criteria. The flight control computer copies and compares commanded yaw rates against stored acceptable rates, achieving accurate safety assessment through data comparison rather than real-time physical modeling.
Data Source
AI summary
Embodiments are directed to a flight control system for a helicopter comprises a pilot interface configured to receive a control input, at least one electronically controlled actuator, and a computing device configured to translate the control input to an actuator command, wherein the computing device is further configured to apply yaw rate limits to the actuator command to avoid loss of tail rotor effectiveness. The yaw rate limits are associated with a vortex ring state (VRS) envelope for a tail rotor of the helicopter. The electronically controlled actuator comprises a tail rotor actuator. The control input is a pedal input.