Aircraft Engine Bracket Fastening for Vibration Load Isolation
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Solution Overview
Problem
Existing methods for attaching a mounting bracket to aircraft engine cases are inefficient and do not adequately address the challenges of transmitting large vibrational loads, particularly during events like a fan blade out, which can lead to over-fatigue of aircraft components.
Innovation Solution
A fastener assembly system comprising bolts, nuts, and retainers is used to clamp and preload the mounting bracket to the engine case flanges, with retainers retaining the nuts to prevent loosening under large vibrational loads, allowing for a loose connection that maintains attachment and reduces stiffness changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a rigid fastening system is used to securely attach the mounting bracket to the engine case, then connection strength and reliability are improved, but the system transmits excessive vibrational loads to the airframe causing over-fatigue
Solution Approach 1:
The fastener assembly incorporates a retainer that allows the nut to move axially relative to the bolt shank, transforming the rigid fastening system into a dynamic one. The retainer includes a body portion engaged with the bolt shank and a tail portion that engages the nut, permitting controlled movement that isolates vibrational loads while maintaining connection integrity during normal operation and abnormal events like fan blade out
Solution Approach 2:
The system changes the mechanical parameter of connection stiffness by introducing controlled compliance through the retainer-nut interface. This allows the connection to remain intact while changing from a rigid load-transmitting joint to a compliant joint that absorbs vibrational energy, reducing fatigue on airframe components
2Reliability
If the mounting bracket is firmly clamped to the engine case flange, then attachment reliability is improved, but stiffness changes lead to increased engine installation modes and frequency-related forces
Solution Approach 1:
The retainer-nut assembly creates a dynamically compliant connection that adapts its stiffness characteristics. During normal operation, the connection remains reliable with adequate stiffness, but under vibrational loading, the retainer allows nut movement that reduces stiffness and mitigates frequency-related forces and engine installation modes
Data Source
AI summary
An assembly for an aircraft includes a first engine case, a bracket and fastener assemblies. The first engine case includes a first sidewall and a first flange projecting radially out from the first sidewall. The bracket is abutted axially against the first flange. The fastener assemblies attach the bracket to the first flange. The fastener assemblies include a first fastener assembly with a first bolt, a first nut and a retainer. The first bolt includes a first bolt head and a first bolt shank that projects axially out from the first bolt head and axially through the first flange and the bracket. The first nut is threaded onto the first bolt shank with the first flange and the bracket is axially between the first bolt head and the first nut. The retainer is attached to the first bolt shank with the first nut axially between the retainer and the bracket.