Aircraft Torsion Box With Conical Stringers
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Solution Overview
Problem
Aircraft torsion box skins stiffened with parallel stringers face structural integrity issues due to stringer interruptions and increased weight requirements in regions without stringer support, leading to potential fractures and weight penalties.
Innovation Solution
A torsion box design featuring a 'conical' distribution of stringers with decreasing cross sections towards the skin's outer edge, optimizing the number and geometry of stringers to minimize weight and eliminate interruptions, using composite materials like CFRP for the skins and stringers, such as omega-shaped, T-shaped, I-shaped, or J-shaped configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If parallel stringers are used to stiffen the skin, then the stringers can be oriented along the maximum load direction, but the stringers closest to the front spar have smaller length and are interrupted by the spar
Solution Approach 1:
The patent changes the geometric parameters of the stringers by adopting a conical distribution where stringers have varying cross-sections along their length, with larger cross-sections near the front spar and smaller cross-sections toward the rear. This parameter variation allows stringers to maintain adequate length while accommodating the spar interruption, thereby preserving structural integrity without sacrificing load bearing capacity.
Solution Approach 2:
The patent introduces asymmetry in the stringer configuration by using a conical distribution pattern rather than a uniform parallel arrangement. The stringers are positioned at different chord-wise distances from the front spar, creating an asymmetric layout that optimizes both structural performance and avoids critical end conditions near the spar intersection.
2Strength
If the number of stringers is increased in regions with greatest structural responsibility, then the skin strength is improved, but the weight of the structure increases
Solution Approach 1:
The patent applies local quality by varying the stringer cross-sectional dimensions according to their position along the skin span. Stringers near the front spar (where structural responsibility is greatest) have larger cross-sections, while stringers toward the rear have progressively smaller cross-sections. This localized differentiation optimizes strength where needed while minimizing weight in less critical regions.
Solution Approach 2:
The patent utilizes parameter changes by systematically varying the cross-sectional area of stringers along the span direction. The conical distribution creates a continuous gradient in stringer parameters, allowing the structure to achieve adequate buckling resistance with minimized material usage throughout the skin.
3Ease of manufacture
If stringers are interrupted by the front spar, then the parallel configuration is maintained, but the load transfer to skin becomes problematic and may trigger fracture
Solution Approach 1:
The patent resolves the load transfer problem by changing the cross-sectional parameters of stringers near the spar intersection. The gradually varying cross-section allows for smoother stress distribution and more effective load transfer to the skin, avoiding the abrupt terminations that cause fracture in conventional parallel configurations.
Solution Approach 2:
Instead of maintaining constant cross-sections and accepting the problems at stringer ends, the patent inverts the approach by varying the cross-sections to eliminate the problematic end conditions. The conical distribution ensures that stringer ends are optimized for their specific locations, transforming the weakness of interrupted stringers into a strength through progressive geometry changes.
Data Source
Figure 1~3
Figure 4~6
AI summary
Torsion box of an aircraft stabilizing surface comprising a front spar (15), a rear spar (17), ribs (21) and upper and lower stiffened skins, in which at least one of said skins (31) is stiffened with a plurality of stringers (33, 43), preferably omega-shaped stringers, extending all of them along the full skin span, preferably in a "conical" distribution, and having a decreasing cross section towards the skin outer edge.