Engine-Out Roll Rate Limiting for Aircraft Directional Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Multi-engine aircraft face challenges in maintaining directional control during roll maneuvers due to engine thrust asymmetry, where the rudder is fully deflected to control yaw, leaving no additional deflection for sideslip control, especially at low airspeeds, leading to undesirable sideslip angles and reduced roll rates.
Innovation Solution
A system that varies the maximum roll rate command using a primary flight control computer to limit roll rates during engine-out conditions with high thrust asymmetry, ensuring directional control margins are preserved by reducing the commanded roll rate when additional rudder deflection is not available, thereby preventing excessive sideslip angles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the rudder is fully deflected to control thrust asymmetry, then directional control of yaw is improved, but the ability to control sideslip during roll maneuvers deteriorates
Solution Approach 1:
The patent implements a dynamic roll rate limitation system that automatically adjusts the maximum commandable roll rate based on real-time assessment of available rudder deflection margin. When thrust asymmetry is detected and rudder is fully deflected for yaw control, the system dynamically reduces the roll rate limit to prevent excessive sideslip, thereby adapting the roll control capability to the current directional control situation
Solution Approach 2:
The system continuously monitors thrust asymmetry conditions and rudder deflection status, using this feedback to automatically adjust the roll rate command limits. The flight control computer calculates the available rudder deflection margin and feeds this information back to modify the maximum commandable roll rate, creating a closed-loop control system that maintains directional control margins
2Reliability
If a constant roll rate limiter is used, then directional control during roll maneuvers is improved, but roll rate is reduced in all situations including those where large roll rates are controllable
Solution Approach 1:
The patent replaces constant roll rate limitation with a dynamic limitation system that adjusts the maximum commandable roll rate based on actual flight conditions. The system calculates available rudder deflection margin in real-time and adjusts the roll rate limit accordingly, allowing full roll rates when sufficient rudder margin exists and reducing roll rates only when thrust asymmetry consumes the rudder margin
Solution Approach 2:
The system changes the roll rate parameter dynamically based on thrust asymmetry conditions and available rudder deflection margin. Instead of using a fixed roll rate limit, the flight control computer continuously adjusts the maximum commandable roll rate parameter according to the current directional control situation, optimizing both directional control and roll performance
3Adaptability or versatility
If thrust reduction is applied to reduce rudder required for thrust asymmetry control, then rudder deflection available for roll control is improved, but takeoff distance increases and payload is reduced
Solution Approach 1:
The patent extracts the roll rate control limitation function from the thrust management system and implements it independently in the flight control computer. By separating the directional control margin assessment from thrust reduction logic, the system maintains full thrust for takeoff performance while providing adequate roll control through dynamic roll rate limiting based on available rudder deflection margin
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A system and a method for varying a maximum roll rate command for ensuring sufficient directional control during an engine-out rolling maneuver of a multi-engine aircraft. For a multi-engine airplane with a roll rate command flight control system, the primary flight control computer is used to vary the maximum commandable roll rate to preserve the desired control margins during roll maneuvers where the rudder is fully deflected to control a thrust asymmetry. When the engine-out yawing moment exceeds a specified value, the system sets a reduced limit on the amount of roll rate the pilot can command.