Under-flap Stiffener Orientation for Bird Strike Energy Absorption
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Solution Overview
Problem
Aircraft fuselage structures are vulnerable to bird impacts during take-off and landing, with existing structural stiffeners often under-dimensioned, risking damage to critical equipment and crew safety, especially when the fuselage angle varies between 20 and 35°, dispersing energy over a small surface.
Innovation Solution
The implementation of a fuselage assembly with longitudinal structural stiffeners positioned below the fuselage surface, where the main plane of bending resistance coincides with the local normal and impact axis, maximizing stress absorption during impacts, and a method for calculating optimal stiffener placement and fiber orientation in composite materials to enhance impact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If traditional structural stiffeners are used with main plane perpendicular to fuselage surface, then manufacturing is simplified, but impact resistance during bird strikes is insufficient
Solution Approach 1:
The stiffener's main plane of bending resistance is oriented to coincide with the reaction plane of potential impactors at each specific location on the fuselage. This local optimization ensures that each stiffener is positioned to maximize its bending resistance against the specific direction of impact expected at that point, rather than using a uniform orientation throughout.
Solution Approach 2:
The orientation parameter of the stiffener's main plane is changed from a fixed perpendicular-to-surface orientation to a variable orientation that coincides with the impact reaction plane. This parameter change allows the stiffener to adapt its resistance direction to match the specific impact scenario at each location.
2Strength
If fuselage angle is increased to disperse impact energy, then impact resistance improves, but the effective protection area decreases
Solution Approach 1:
Instead of uniformly increasing the fuselage angle across the entire surface, the invention applies local optimization by orienting each stiffener's main plane to coincide with the reaction plane at its specific location. This allows energy dispersion to be maximized at each point without requiring a global increase in fuselage angle that would reduce the effective protected area.
3Strength
If stiffener mass is increased to improve impact resistance, then protection capability improves, but overall aircraft weight increases
Solution Approach 1:
The orientation parameter of the stiffener's main plane is changed to coincide with the impact reaction plane, which optimizes the structural efficiency of each stiffener. This parameter change allows the existing stiffener mass to provide maximum possible protection for its weight, reducing the need to increase mass to achieve adequate protection levels.
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 configuration enhances the fuselage's ability to absorb impact energy, minimizing the risk of equipment damage and ensuring crew safety while maintaining a reduced mass of structural stiffeners, effectively dispersing impact forces across the fuselage surface.
Implementation Method 1
the birds' mass, combined with the relative speed of the airplane in relation to these birds, is transformed into considerable kinetic energy on impact, which is transformed into mechanical deformation energy
Implementation Method 2
stiffeners, of the type comprising a main plane of bending resistance substantially perpendicular to the fuselage surface
Data Source
AI summary
An assembly of longitudinal structural stiffeners for an aircraft including, in a front portion of the fuselage, a windscreen that is slightly recessed relative to the airplane nose, and a fuselage portion extending in alignment with the airplane nose up to the base of the windscreen. The stiffeners include a bending-resistance main plane and are arranged under the flap and connected to the fuselage along a force transfer line. For one or more of the stiffeners, the bending resistance main plane substantially coincides, at at least a certain number of points of the fuselage force transfer line, with the plane predetermined by the local normal to the fuselage surface and the longitudinal axis of the airplane. A method is also provided for calculating the shape of the stiffeners.