Composite Aeroengine Blade Leading Edge Metal Strip Stitching
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Solution Overview
Problem
Organic matrix composite (OMC) blades in gas turbine aeroengines face issues with metal strips becoming unstuck during impacts, leading to repair costs and aerodynamic degradation due to inadequate fastening methods.
Innovation Solution
A metal strip is fastened to the OMC blade using stitching threads that extend transversely, with external thread segments positioned to minimize aerodynamic disruption, and optionally embedded in a thermoplastic resin to enhance retention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a metal strip is adhesively bonded to the leading edge of an OMC blade, then the blade gains good protection against impacts, but the strip becomes unstuck during high-energy impacts leading to repair costs and aerodynamic degradation
Solution Approach 1:
The patent replaces the chemical bonding mechanism (adhesive) with a mechanical fastening system (stitching thread passing through the metal strip and OMC blade). This mechanical interlocking provides superior retention during high-energy impacts compared to adhesive bonding, as the stitching thread physically anchors the strip to the blade structure through multiple penetration points along its length.
Solution Approach 2:
The invention changes the fastening mechanism from continuous adhesive bonding to discrete mechanical stitching at specific intervals. This parameter change in the fastening system allows the metal strip to remain securely attached during normal operation while permitting controlled movement or detachment during extreme impact events, thereby maintaining reliability without sacrificing protection.
2Reliability
If stitching threads are used to fasten the metal strip, then the retention during impact is improved, but the aerodynamics may be affected by the presence of external thread segments
Solution Approach 1:
The patent applies local quality by positioning external thread segments specifically in regions where they cause minimal aerodynamic disruption. The stitching thread is arranged so that external segments are located on the pressure side of the blade or in areas of lower flow sensitivity, while maintaining effective retention on the suction side where aerodynamic requirements are more critical.
Solution Approach 2:
The invention converts the potentially harmful effect of external thread segments on aerodynamics into a beneficial configuration where the thread segments are positioned to create minimal flow disturbance. The stitching pattern is designed so that the thread segments align with natural flow patterns or are placed in regions where their aerodynamic impact is negligible, thereby transforming a potential disadvantage into an acceptable or even advantageous feature.
Data Source
AI summary
A blade made of organic matrix composite material for a gas turbine aeroengine, includes an airfoil extending transversely between a leading edge and a trailing edge; and a metal strip positioned on the leading edge of the airfoil, the metal strip having two flanges extending on either side of the leading edge over portions of the side faces of the airfoil forming a pressure side face and a suction side face so that the strip fits closely to the profile of the leading edge, the metal strip being fastened to the leading edge of the airfoil by at least one stitching thread; wherein the stitching thread has at least one external thread segment extending substantially transversely between a hole formed through a flange of the strip and a passage formed in a portion of the airfoil that has at least one face that is not covered by the metal strip.