Aircraft Mode Suppression During Landing Braking
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Uneven deceleration of an aircraft during braking on landing excites structural modes, leading to undesirable fatigue and passenger discomfort due to variations in braking force, coefficient of friction, and oscillations between stable and unstable braking behaviors.
Innovation Solution
An aircraft control system comprising sensors and a controller that provide control signals to reduce mode excitation and vertical load variations by measuring and filtering signals from accelerometers, strain-measuring devices, and inertial reference systems to adjust control surfaces and steering angles during braking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If wheel brakes are used to provide braking force during landing, then the aircraft can decelerate effectively, but uneven vertical load on wheels causes variation in braking force that excites aircraft modes
Solution Approach 1:
The system uses sensors (accelerometers, strain-measuring devices, inertial reference systems) to detect aircraft modes and vertical load variations, then feeds this information back to the controller which adjusts control surfaces and steering angles to counteract the excitations and maintain uniform braking force
Solution Approach 2:
Control surfaces and steering angles act as intermediary elements between the braking system and aircraft modes. By adjusting these intermediaries, the system indirectly controls the vertical load distribution on wheels, thereby stabilizing braking force without directly modifying the brake system
2Reliability
If the coefficient of friction varies along the runway, then braking force becomes unpredictable, but increasing brake pressure to compensate causes mode excitation
Solution Approach 1:
The real-time monitoring of aircraft modes through sensors provides feedback that allows the control system to detect and compensate for braking force variations caused by friction changes, maintaining reliable braking performance while preventing structural excitation
Solution Approach 2:
The system dynamically changes control parameters (control surface deflections, steering angles) in response to detected mode excitations, adapting the braking behavior to maintain both reliability and structural stability under varying friction conditions
3Reliability
If brake control system prevents skids by switching between stable and unstable behavior, then wheel skidding is reduced, but the switching causes attitude oscillations that excite aircraft modes
Solution Approach 1:
The system continuously monitors aircraft attitude and mode excitations, providing feedback to smooth the brake control switching process and reduce attitude oscillations while maintaining effective skid prevention
Solution Approach 2:
The control system applies periodic adjustments to control surfaces and steering angles that counteract the oscillatory effects of brake switching, transforming the harmful periodic attitude oscillations into controlled, damped motions
4Stability of the object's composition
If aircraft modes are excited during braking, then uneven deceleration occurs, but adding control surfaces and sensors to suppress modes increases system complexity
Solution Approach 1:
The control system integrates multiple functions into existing aircraft components: control surfaces serve both their primary flight control function and mode suppression function; sensors serve both navigation/flight management and mode detection purposes, reducing overall system complexity
Solution Approach 2:
The system uses the aircraft's own existing structures and components (control surfaces, steering mechanisms, sensors) to suppress modes, rather than adding dedicated suppression hardware, allowing the system to serve itself in multiple functions
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
Effectively suppresses aircraft modes such as shimmy, pitch, roll, and yaw, reducing fatigue and discomfort by stabilizing braking forces and minimizing vertical load variations, thereby improving the landing experience.
Implementation Method 1
the one or more sensors is, or includes, an accelerometer
Implementation Method 2
the one or more sensors is, or includes, a strain-measuring device mounted on the aircraft so as to measure the vertical load on a landing gear or landing wheel
Implementation Method 3
the control signals provided by the controller being such that they reduce the excitation of the said one or more of the modes of the aircraft
Data Source
AI summary
An aircraft control system operates during landing to suppress normal modes of flexing of the aircraft or modes of rigid rotation. The excitation of the modes are measured using accelerometers attached to the aircraft or strain-measuring devices attached to the landing gears. To suppress the modes, the controller operates the flight control surfaces, e.g., elevators, ailerons, rudders and spoilers and/or the steering angle of the nose wheel. This reduces vibration, which reduces wear and makes braking more even because the variation in load on the ground wheels caused by the excitation of the modes is reduced.