Fly-by-wire Control Surface Failure Detection via Frequency Sweep
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Solution Overview
Problem
Fly-by-wire aircraft face difficulties in controlling rotary-wing aircraft after failures such as loss of tail rotor due to discrepancies between flight control system models and actual aircraft dynamics, as existing systems lack effective detection and response mechanisms.
Innovation Solution
A flight control system that performs a frequency sweep of flight control surfaces to detect failures by computing cross-correlation between acceleration and rate responses, and takes actions such as disabling cross-axis mixing terms to mitigate the effects of detected failures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the flight control system uses conventional control mixing algorithms to compensate for canted tail rotor, then the aircraft maintains stable control during normal operation, but the system produces large pitch and roll motions when tail rotor failure occurs
Solution Approach 1:
The system performs a frequency sweep of the tail rotor before failure occurs to establish baseline correlation values between acceleration and rate responses. This preliminary characterization allows the control system to recognize failure conditions and switch to appropriate control laws, preventing the harmful pitch and roll motions that would otherwise occur during tail rotor failure
Solution Approach 2:
The control mixing algorithm dynamically adjusts based on the detected failure condition. When tail rotor failure is detected through frequency sweep analysis, the system transitions from conventional control mixing that compensates for canted tail rotor to an alternative control law that prevents compounding disturbances, thereby maintaining stability during the failure state
2Reliability
If the flight control system performs frequent frequency sweeps to detect failures early, then detection reliability improves, but system complexity and computational load increase
Solution Approach 1:
The system performs frequency sweeps at periodic intervals during flight operations. This periodic detection approach balances reliability needs with system complexity by conducting sweeps frequently enough to detect failures early but not so frequently as to create excessive computational burden. The periodic nature allows the system to maintain readiness while managing resource consumption
3Speed
If the system applies full yaw input to counteract spin during tail rotor loss, then immediate yaw control is achieved, but pitch and roll disturbances are compounded due to control mixing algorithm responses
Solution Approach 1:
The frequency sweep and failure detection occur before the aircraft enters an uncontrollable state. By detecting tail rotor failure early through analysis of acceleration and rate response correlations, the system can prepare and transition to appropriate control laws in advance, preventing the sequence of events that leads to compounded pitch and roll disturbances
Solution Approach 2:
The control system dynamically switches between different control mixing algorithms based on the detected failure condition. When tail rotor failure is detected, the system transitions from conventional control mixing to an alternative control law that decouples yaw control from pitch and roll mixing, thereby maintaining attitude stability while still providing effective yaw control authority
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables the fly-by-wire system to detect and respond to tail rotor failures, preventing uncontrollable aircraft behavior by adjusting control inputs and alerting the crew, thereby ensuring survivability during critical events.
Implementation Method 1
performing a frequency sweep of a flight control surface to cause an acceleration response and a rate response of the flight control surface
Implementation Method 2
computing a cross-correlation using at least the acceleration response and the rate response
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
A flight control system which detects a failure of a flight control surface and performs at least one action in response to the detected failure.