Metallic Dimpled Doubler for Rotor Blade Tip Cap
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Solution Overview
Problem
Existing methods for installing tip caps on aircraft rotor blades, such as using protruding fasteners or countersunk screws, are problematic as they can wear into composite tip caps during cyclic loading, leading to structural issues and reduced durability.
Innovation Solution
A metallic dimpled doubler is introduced, which forms a flush surface and prevents countersunk screws from damaging the tip cap by using a design with plural dimpled portions, staggered fasteners, and a sealant to secure the tip cap and doubler, ensuring a secure and durable attachment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If protruding fasteners or countersunk screws are used to attach tip caps to rotor blades, then the tip cap can be securely attached, but the fasteners wear into the composite tip cap during cyclic loading, reducing durability
Solution Approach 1:
The metallic doubler acts as an intermediary component between the tip cap and the rotor blade. It provides a hardened metal surface for fastener attachment, preventing the fasteners from directly contacting and wearing into the composite tip cap material. The doubler absorbs the mechanical stress and wear, preserving the tip cap's integrity throughout its service life.
2Shape
If countersunk screws are used to create a flush surface, then the aerodynamic profile is improved, but the screws wear into the composite tip cap during cyclic loading
Solution Approach 1:
The metallic doubler serves as a mediator that enables the use of countersunk screws to achieve a flush aerodynamic profile while preventing direct contact between the screws and the composite tip cap. The doubler's metallic surface withstands the cyclic loading and fastener wear, maintaining both the aerodynamic shape and fastener stability.
3Shape
If the doubler includes a tapered section, then the aerodynamic profile is enhanced, but the manufacturing complexity increases
Solution Approach 1:
The doubler incorporates a tapered section that transitions from a thicker first planar section to a thinner second planar section. This parameter change in thickness creates the desired aerodynamic profile while maintaining structural integrity. The taper angle and dimensions are optimized to balance aerodynamic performance with manufacturability.
Data Source
Figure 1A
Figure 1B~2
Figure 3
AI summary
A rotor blade is provided. The rotor blade includes a blade portion, a tip cap formed to define a dimple, a fastener and a doubler. The fastener includes a flat-headed shaft and is disposable such that the flat-headed shaft extends through the blade portion and the tip cap at the dimple. The fastener is configured to urge the blade portion toward the tip cap. The doubler includes a dimpled portion disposable between the tip cap and a portion of the flat-headed shaft at the dimple and an exterior portion. The exterior portion is disposable flush with respective exterior surfaces of the blade portion and the flat-headed shaft.