Aircraft Stringer Runout Stress Reduction via Raised Area Design
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Solution Overview
Problem
Stringer runouts in aircraft skins experience premature failure due to local stress concentrations, and traditional water drainage configurations, such as U-shaped cutouts, increase stress concentrations and are impractical for reducing premature failures without increasing weight and cost.
Innovation Solution
A stringer configuration with a raised area extending beyond the distal end of the web, featuring a tapered distal edge and inverse tapering on opposite sides, which guides water drainage and redistributes stress loads, reducing peak stresses without significantly increasing component stiffness or weight.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If traditional U-shaped cutouts are used for water drainage, then water drainage is enabled, but stress concentrations increase leading to premature failure
Solution Approach 1:
The patent replaces the sharp-cornered U-shaped cutout with a configuration featuring rounded fillets and curved surfaces at the runout edges. This curvature eliminates stress concentration points while maintaining water drainage capability through the rounded geometry of the runout area.
Solution Approach 2:
The patent modifies the geometric parameters of the runout area by introducing specific radius values (e.g., fillet radii of 0.125 to 0.25 inches) and controlled taper angles (15-45 degrees). These parameter changes optimize both stress distribution and water drainage flow characteristics.
2Strength
If skin and stringer thickness are increased to reduce stress concentrations, then strength improves, but weight and cost increase
Solution Approach 1:
The patent applies local geometric modifications (fillets, tapers, rounded edges) specifically at the high-stress runout regions rather than uniformly increasing thickness throughout the entire skin and stringer structure. This localized approach reduces stress concentrations without adding overall weight.
Solution Approach 2:
The patent changes the geometric parameters (radius, taper angle, runout length) of specific regions to optimize stress distribution, avoiding the need to increase material thickness and thereby avoiding increased weight and cost.
3Reliability
If a larger radius U-shaped cutout is used to reduce stress concentrations, then peak stresses decrease, but the cutout becomes impractical when radius exceeds web height
Solution Approach 1:
The patent segments the runout geometry into distinct features: a tapered distal edge portion, a rounded fillet portion, and an inverse taper portion. This segmentation allows each feature to be optimized independently for both stress reduction and manufacturability, avoiding the impracticality of oversized single-radius cutouts.
Solution Approach 2:
The patent uses controlled curvature through fillets with specific radius values that are optimized to reduce stress concentrations while remaining within practical manufacturing limits and within the available web height of the stringer.
4Duration of action of stationary object
If stringer runouts are configured to reduce stress concentrations, then durability improves, but structural integrity may be compromised
Solution Approach 1:
The patent applies local geometric modifications (fillets, tapers) that redirect stress flow around the runout area while maintaining the overall structural integrity of the stringer. The modifications are designed to reduce peak stresses without creating weak points that would compromise global structural strength.
Solution Approach 2:
The patent optimizes geometric parameters (fillet radius, taper angle, runout length) to achieve the best balance between reducing peak stresses for improved durability and maintaining sufficient structural integrity for load-bearing requirements.
Data Source
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AI summary
A stringer (52) having a runout (66) with a raised area (70) configured to reduces stress while improving drainage across the runout when utilized in a close structural component of a vehicle such as an aileron of an aircraft. In one or more configurations, the raised area (70) of the runout (66) of the stringer (52) includes multiple tapered surfaces (78) adjacent to one another oriented and configured as ramps to collectively guide water up, over and down the raised area of the stringer.