Propeller Blade Segmented Spar Design for Thermal Stress Reduction
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Solution Overview
Problem
Modern propeller blades experience significant thermal stresses during manufacturing and service life due to aerodynamic and inertial loads, which can lead to undesirable structural consequences, as the spar foam is not considered a significant structural component and primarily serves as a mandrel for over-braiding the carbon spar.
Innovation Solution
The propeller blade design incorporates an inner spar structure with an inner spar foam core, leading and trailing edge foam structures, and an outer spar structure, along with a blade shell, where the inner spar provides torsional stiffness and shear load transfer, and the outer spar enhances bending stiffness, reducing thermal stresses by segmenting the spar structure into multiple volumes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single foam core is used as a mandrel for over-braiding the carbon spar, then the manufacturing process is simple, but thermal stresses during manufacturing and service life cause undesirable structural consequences
Solution Approach 1:
The single foam core is divided into multiple separate foam cores (inner spar foam core, leading edge foam core, trailing edge foam core) that are positioned at different locations within the blade structure. This segmentation reduces thermal stresses by creating smaller, distributed volume elements rather than one large continuous foam structure, thereby improving reliability while maintaining manufacturing feasibility through modular assembly
2Weight of moving object
If the spar foam is used only as a non-structural mandrel, then the blade structure is lighter, but thermal stresses combined with aerodynamic and inertial loads result in undesirable structural consequences
Solution Approach 1:
The patent combines foam cores with braided carbon fiber spar structures to create a composite construction. The carbon fiber provides the primary structural strength and stiffness, while the segmented foam cores provide shear transfer and thermal stress management. This composite approach maintains light weight while significantly improving structural integrity and reliability under combined thermal, aerodynamic, and inertial loads
3Reliability
If thermal stresses are reduced by segmenting the spar structure into multiple volumes, then structural integrity is improved, but the device complexity increases
Solution Approach 1:
The spar structure is segmented into multiple foam cores positioned at critical locations (inner spar, leading edge, trailing edge) rather than uniformly throughout. This targeted segmentation reduces thermal stresses in high-stress areas while minimizing the overall increase in structural complexity. The braided carbon fiber construction provides a unifying framework that integrates these segmented foam elements into a cohesive structure
Data Source
AI summary
A propeller blade includes an inner spar structure surrounding an inner spar foam core. Also included is a leading edge foam structure disposed proximate a leading edge of the inner spar structure. Further included is a trailing edge foam structure disposed proximate a trailing edge of the inner spar structure. Yet further included is an outer spar structure surrounding the inner spar structure, the leading edge foam structure and the trailing edge foam structure. Also included is a blade shell, a leading edge foam core located between the outer spar structure and the blade shell, and a trailing edge foam core located between the outer spar structure and the blade shell.