Rotorcraft Blade Attachment Assembly Using Nested Hollow Shear Pin
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Solution Overview
Problem
Conventional fastener assemblies for coupling rotary blades to rotor assemblies in rotorcraft often protrude, leading to drag and reduced aerodynamic efficiency, especially in high-speed flight.
Innovation Solution
An attachment assembly comprising a hollow shear pin, a nut cap, and a tensioning fastener that are housed within the aerodynamic profile of the rotary blade, using a low-profile design to minimize drag and maintain structural integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional nut and bolt arrangements are used to couple rotor blades to the rotor hub, then the rotor blade can be securely attached, but protruding hardware generates drag and reduces aerodynamic efficiency
Solution Approach 1:
The tensioning fastener is nested within the hollow shear pin, and the entire fastener assembly is contained within the rotor blade profile. The hollow shear pin acts as a housing for the tensioning fastener, allowing the fastening mechanism to be concealed within the aerodynamic contour of the blade rather than protruding outward.
Solution Approach 2:
The invention transitions from a protruding three-dimensional fastener arrangement to a low-profile design where the fastener components are recessed into the blade profile. By utilizing the hollow interior space of the shear pin and recessing the tensioning fastener, the attachment hardware is moved from an external protruding position to an internal concealed position within the blade's aerodynamic envelope.
2Ease of operation
If protruding nut and bolt arrangements are used for maintenance access, then inspection and maintenance are easier, but drag increases and aerodynamic performance decreases
Solution Approach 1:
The tensioning fastener is nested within the hollow shear pin, and the entire fastener assembly is contained within the rotor blade profile. The hollow shear pin acts as a housing for the tensioning fastener, allowing the fastening mechanism to be concealed within the aerodynamic contour of the blade rather than protruding outward.
3Object-generated harmful factors
If a low-profile attachment design is used, then aerodynamic drag is reduced, but the complexity of the fastener assembly increases
Solution Approach 1:
The invention merges the functions of multiple components into a unified low-profile assembly. The hollow shear pin serves both as a structural shear load carrier and as a housing for the tensioning fastener. The nut cap integrates the threading function and the fastening mechanism, combining multiple functions into fewer parts that work together within the constrained profile space.
Solution Approach 2:
The hollow shear pin performs multiple functions: it carries shear loads, houses the tensioning fastener, and provides the outer contour of the attachment assembly. The tensioning fastener both secures the rotor blade and maintains a low profile. This multi-functionality reduces the number of separate components needed, thereby managing complexity while achieving the low-profile goal.
4Object-generated harmful factors
If the tensioning fastener axial length is made smaller than the shear pin axial length, then the fastener can be housed within the blade profile, but the fastener design becomes more constrained
Solution Approach 1:
The tensioning fastener is designed with specific local characteristics: its axial length is deliberately made shorter than the hollow shear pin to enable low-profile housing, while its threading and head geometry are optimized for the specific function of tensioning within the constrained space. This localized dimensional optimization allows the fastener to meet both the aerodynamic profile requirement and the functional requirements.
Data Source
AI summary
An attachment assembly for coupling a rotary blade to a hub includes a hollow shear pin, a nut cap, and a tensioning fastener. The hollow shear pin defines an attachment axis. The nut cap abuts the shear pin along the attachment axis. The tensioning fastener is seated within the shear pin, is threadably engaged to the nut cap, and has an axial length that is smaller than an axial length of the shear pin to fix a rotary blade to a rotor assembly within a profile of the rotary blade.