Propeller Blade Spar Retention via Compressive Interface

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Solution Overview

Problem

Modern propeller blades face challenges in maintaining bending moment capacity due to lower centrifugal loads, which can lead to insufficient loading at the interface between the spar and outer sleeve, potentially causing tensile stresses and reducing the overall structural integrity.

Innovation Solution

The propeller blade assembly features a segmented inner ring and wedges that expand to ensure compressive stresses at the adhesive interface, providing a secondary load path and preventing tensile stresses, while the outer sleeve is secured to the spar using a convex or concave surface configuration to enhance load transmission and mechanical locking.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If a steel retention member is used to accommodate a bond joint with the spar, then the structural integrity and load-bearing capacity are improved, but the weight of the propeller blade increases significantly (retention member weight can be about 1/3 the total blade weight)

Engineering Contradiction:

Improvestructural integrityVSAvoidblade weight

Core Design Contradiction:

StrengthVSWeight of moving object

Solution Approach 1:

The patent changes the material parameter from steel to aluminum alloy for the retention member, reducing density and weight while maintaining structural integrity through optimized geometric parameters and interface design

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs composite material construction for the spar (carbon fiber reinforced polymer) combined with aluminum alloy retention member, creating a hybrid structure that optimizes both strength and weight characteristics

Inventive Principle:

Principle #40Composite materials

2Strength

If the retention member is made longer to accommodate the bond joint inside the spar, then the bonding surface area and structural connection are improved, but the device complexity and manufacturing difficulty increase

Engineering Contradiction:

Improvebond joint capacityVSAvoidretention member geometry

Core Design Contradiction:

StrengthVSDevice complexity

Solution Approach 1:

The retention member is divided into distinct functional segments: an external portion for bearing integration and an internal portion for bonding to the spar, allowing each segment to be optimized independently for its specific function

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Instead of extending the retention member outward to increase bonding area, the patent inverts the approach by having the retention member extend inward into the spar, utilizing the spar's internal volume for the bond joint

Inventive Principle:

Principle #13The other way round (Inversion)

3Use of energy by moving object

If lower centrifugal loads are present, then energy consumption and operational efficiency are improved, but the loading at the spar-outer sleeve interface becomes insufficient, potentially causing tensile stresses and reducing structural integrity

Engineering Contradiction:

Improveenergy consumptionVSAvoidinterface loading

Core Design Contradiction:

Use of energy by moving objectVSStrength

Solution Approach 1:

The patent applies preliminary compressive stress to the adhesive interface through the expansion of the segmented inner ring, creating a pre-compression state that counteracts potential tensile stresses from operational loads, preventing interface separation

Inventive Principle:

Principle #9Preliminary anti-action

Solution Approach 2:

The segmented inner ring is designed to be expandable, allowing the compression force at the adhesive interface to be dynamically adjusted and optimized based on operational requirements, ensuring adequate preload under varying centrifugal load conditions

Inventive Principle:

Principle #15Dynamics

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This configuration improves the bending moment capacity by maintaining compressive stresses at the adhesive interface, ensuring structural integrity under high loads and preventing collapse of the spar, thereby enhancing the propeller blade's performance.

Implementation Method 1

a segmented inner ring and wedges that expand to ensure compressive stresses at the adhesive interface

Methodology Applied

Scientific EffectMechanical expansion: Mechanical Force

Implementation Method 2

the outer sleeve is secured to the spar using a convex or concave surface configuration to enhance load transmission and mechanical locking

Methodology Applied

Scientific EffectMechanical locking: Mechanical Force

Data Source

PatentEP3069989B1Lightweight propeller blade with improved retention capacity

Publication Date: 2019.02.27 HAMILTON SUNDSTRAND CORP

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AI summary

A propeller blade assembly (12) includes a spar (18) extending along a propeller blade axis (16) and an outer sleeve (20) surrounding the spar (18) at a root end of the rotor blade assembly. The spar (18) is adhesively bonded to the outer sleeve (20) at an interface portion. A spar maximum diameter (38) along the interface portion is larger than an outer sleeve minimum diameter (40) along the interface portion. A method of assembling a propeller blade includes installing an outer sleeve (20) over a spar (18) at a root end of the spar (18), the spar (18) a not fully cured composite component, and urging the spar (18) into compressive conformance with the outer sleeve (20) at an interface portion of the propeller blade assembly. A spar maximum diameter (38) along the interface portion is larger than an outer sleeve minimum diameter (40) along the interface portion. The spar (18) is cured thereby adhesively bonding the spar (15) to the outer sleeve (20) at the interface portion.