Aircraft Rotor Blade Segmentation for Weight Reduction

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Solution Overview

Problem

Bearingless rotors for aircraft, such as helicopters, face challenges in reducing weight and complexity while maintaining structural efficiency and control over blade displacement in multiple directions, leading to geometric constraints that require large blade sizes.

Innovation Solution

A rotor configuration featuring an outer blade shell surrounding an inner structural member, utilizing centering blocks with cylindrical bearings to allow pitch adjustment and load sharing between the structural member and the blade shell, which reduces the size of the blade shell and improves the lift-to-drag ratio.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Weight of moving object

If bearingless rotor designs use a flexbeam for blade retention to reduce weight and complexity, then weight and complexity are reduced, but geometric constraints require a relatively large inboard blade size

Engineering Contradiction:

Improverotor assembly weightVSAvoidinboard blade size

Core Design Contradiction:

Weight of moving objectVSVolume of moving object

Solution Approach 1:

The rotor blade is divided into two distinct components: an outer blade shell and an inner structural member (flexbeam). The flexbeam handles the structural load-bearing functions while the blade shell provides the aerodynamic surface. This segmentation allows the blade to meet structural requirements without requiring excessive size, as the loads are efficiently carried by the specialized inner structural member rather than requiring the entire blade to be oversized.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The inner structural member (flexbeam) is nested within the outer blade shell, creating a compact configuration where the structural support element is contained within the aerodynamic shell. This nesting arrangement allows the blade to achieve the necessary structural strength through the inner member while maintaining a compact overall size, eliminating the need for large inboard blade dimensions.

Inventive Principle:

Principle #7Nested doll (Nesting)

2Strength

If the outer blade shell is made larger to provide sufficient structural support, then structural strength is improved, but rotor weight and size increase

Engineering Contradiction:

Improveblade shell structural supportVSAvoidrotor weight

Core Design Contradiction:

StrengthVSWeight of moving object

Solution Approach 1:

By separating the structural support function (handled by the inner flexbeam) from the aerodynamic function (handled by the outer blade shell), the blade shell does not need to be oversized for structural support. The flexbeam is specifically designed to carry the loads, allowing the blade shell to be optimized for aerodynamics and weight rather than structural strength alone.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The rotor blade combines different material systems: the inner structural member uses fiber reinforced resin matrix materials (composite) optimized for structural strength-to-weight ratio, while the outer blade shell can use different materials optimized for aerodynamic performance. This composite approach allows each component to be optimized for its specific function, achieving necessary strength without excessive weight.

Inventive Principle:

Principle #40Composite materials

3Ease of operation

If metallic ball bearings are used to attach blades to the rotor hub, then blade pitch adjustment is enabled, but rotor assembly weight increases

Engineering Contradiction:

Improveblade pitch adjustmentVSAvoidrotor assembly weight

Core Design Contradiction:

Ease of operationVSWeight of moving object

Solution Approach 1:

The invention replaces the traditional metallic ball bearing mechanical system with a bearingless flexbeam connection system. The flexbeam provides flexible structural support that enables blade pitch adjustment through elastic deformation rather than through rolling element bearings. This substitution eliminates the heavy metallic bearings while maintaining the essential pitch adjustment capability through the flexible structural properties of the composite flexbeam.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentEP2570346B1Rotor with blades including outer blade shell and inner structural member

Publication Date: 2016.05.11 SIKORSKY AIRCRAFT CORP

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AI summary

A rotor for use in an aircraft includes an inner hub; and a plurality of blades arranged around the inner hub, each of the plurality of blades comprising an inner structural member (102); an outer blade shell (103) surrounding the inner structural member; and a centering block located at a base of the inner structural member proximal to the inner hub, wherein the centering block is located between a first lateral portion of the inner structural member and a second lateral portion of the inner structural member, wherein the centering block is further connected to the outer blade shell, and wherein the centering block allows the outer blade shell to rotate about an axis approximately corresponding to the inner structural member.