Aircraft Wing Tip Device for Load Alleviation
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Solution Overview
Problem
Large passenger aircraft face limitations in wing span due to airport operating rules, necessitating moveable wing tip devices that provide load alleviation during flight while maintaining a reduced span on the ground, but existing solutions often increase aerodynamic loads and require heavier wings.
Innovation Solution
A restraining assembly with a biasing member and damping system allows the wing tip device to move quickly to a load alleviating configuration during high loads, reducing lag and flutter, and can be selectively disengaged for maintenance, enabling a large wing span during flight without the weight penalty, and transitioning to a reduced span for ground operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a large wing span is used during flight to reduce induced drag, then aerodynamic efficiency is improved, but aerodynamic loads on the wing increase requiring a stronger and heavier wing structure
Solution Approach 1:
The wing tip device is designed to be movable between a flight configuration (extended span) and a load alleviating configuration (reduced span). During normal flight, the device extends to maximize span for drag reduction. When high loads are detected or anticipated, the device retracts to reduce the lever arm and thereby reduce aerodynamic loads on the wing structure, allowing the wing to be designed for lower maximum loads and reducing overall structure weight.
Solution Approach 2:
The effective wing span parameter is dynamically changed by moving the wing tip device between extended and retracted positions. This allows the aircraft to optimize between two opposing requirements: large span for drag reduction and small span for load reduction, with the span parameter being adjusted in real-time based on flight conditions.
2Strength
If a moveable wing tip device is used to provide load alleviation, then wing loads are reduced, but the device complexity increases due to restraining assemblies and actuators
Solution Approach 1:
The wing tip device incorporates passive restraining mechanisms that automatically engage and disengage based on aerodynamic loads. The restraining assembly uses spring-loaded latches and friction brakes that self-activate when load thresholds are exceeded, eliminating the need for complex active control systems while still providing load alleviation functionality.
Solution Approach 2:
The restraining assembly is designed with pre-loaded springs and friction elements that are positioned to engage before critical load levels are reached. This proactive restraint system prevents excessive wing tip deflection and associated loads by engaging the restraining mechanism in advance, rather than reacting after damage occurs.
3Speed
If the restraining assembly is designed to release quickly during high load events, then load alleviation response time is improved, but the risk of uncommanded actuation increases
Solution Approach 1:
The restraining assembly uses pre-loaded spring mechanisms that are positioned and tensioned during normal operation. When a high load event occurs, these pre-loaded springs instantly release, providing rapid response without requiring active sensing or control system activation. The system is biased toward the restrained state during normal conditions, ensuring stability.
Solution Approach 2:
Different portions of the restraining assembly have different engagement characteristics. The friction brakes provide gradual, controllable restraint during normal operation, while the spring-loaded latches provide instantaneous release capability. This local differentiation of restraint qualities allows both rapid response and prevention of uncommanded actuation.
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
This solution effectively reduces wing loads, delays flutter onset, and allows for a larger wing span during flight while complying with airport gate limits, enhancing aircraft responsiveness and reducing structural weight.
Implementation Method 1
the wing comprises a biasing member, arranged such that when the wing tip device is in the flight configuration, the biasing member exerts a biasing force to urge the wing tip device towards the load alleviating configuration
Implementation Method 2
damping system allows the wing tip device to move quickly to a load alleviating configuration during high loads, reducing lag and flutter
Data Source
Figure 1a~1b
Figure 2a
Figure 2b~2d
AI summary
An aircraft (1) comprising a wing (5) the wing having a fixed wing (7) with a wing tip device (9) moveably mounted about a hinge (11) at the tip thereof. The wing tip device (9) is operable between a flight configuration, and a load alleviating configuration for load alleviation during flight. The aircraft (1) comprises a restraining assembly (17) operable between a restraining mode in which the wing tip device is held in the flight configuration using a restraining force such as by a brake (19), and a releasing mode in which the restraining force on the wing tip device is released, such that the wing tip device (9) may adopt the load alleviating configuration. When the wing tip device is in the flight configuration, a biasing member (23) exerts a biasing force to urge the wing tip device towards the load alleviating configuration.