Rotor Blade Tip Clearance Estimation via Strain Harmonics

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Solution Overview

Problem

Existing methods for monitoring tip clearance in coaxial rotorcrafts rely on direct sensing, which lacks predictive capability and cannot provide additional state information, leading to potential blade collisions.

Innovation Solution

A method involving strain sensing on rotor blades to measure deflection, generate harmonic functions, predict tip displacement, and adjust blade positions to maintain minimum tip clearance, using strain gages installed near the rotor hub and a flight computer for feedback loop control.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If direct sensing methods such as proximity sensors are used to monitor tip clearance, then tip clearance measurement is achieved, but predictive capability is lost and additional state information cannot be gathered

Engineering Contradiction:

Improvetip clearance measurementVSAvoidpredictive capability and state information

Core Design Contradiction:

Measurement precisionVSLoss of information

Solution Approach 1:

The patent introduces strain gages as intermediary sensors that measure blade deflection rather than directly measuring tip clearance. This indirect measurement approach allows the system to capture additional state information about blade behavior while still enabling tip clearance estimation through harmonic analysis of the deflection data

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent replaces direct mechanical/proximity sensing with strain measurement and harmonic analysis. By measuring strain in the blade structure and analyzing the harmonic components of blade deflection, the system can predict tip clearance and blade position without requiring direct proximity sensors at the blade tips

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Measurement precision

If proximity sensors are used to measure tip clearance at blade crossings, then tip clearance is monitored, but the measurements lack predictive capability for future blade positions

Engineering Contradiction:

Improvetip clearance measurementVSAvoidpredictive capability

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The patent performs preliminary measurement of blade deflection using strain gages during normal operation. By continuously monitoring strain and establishing harmonic relationships between deflection and blade position, the system prepares predictive models that can forecast future tip clearance conditions before blade crossings occur

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent implements a feedback mechanism where strain measurements are continuously converted to blade deflection, which is then used to update harmonic functions that predict future blade positions and tip clearance. This closed-loop approach enables real-time predictive capability rather than just reactive measurement

Inventive Principle:

Principle #23Feedback

3Reliability

If strain gages are installed on rotor blades to measure deflection, then predictive capability is achieved, but device complexity increases

Engineering Contradiction:

Improvepredictive capabilityVSAvoidsensing and processing system

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent leverages the blade's own structural properties by installing strain gages directly on the blade to measure its natural deflection behavior. The blade essentially serves itself as the sensing element, converting mechanical strain into useful measurement data without requiring external measurement infrastructure

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The patent transforms the measurement parameter from direct tip clearance distance to blade strain and deflection. This parameter change simplifies the sensing approach by using readily available strain measurement technology on the blade structure, with the harmonic analysis serving as a computational transformation rather than additional physical sensors

Inventive Principle:

Principle #35Parameter changes

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

Enables predictive maintenance of minimum tip clearance between rotor blades, preventing collisions and enhancing operational safety by providing continuous estimation and adjustment of blade positions.

Implementation Method 1

sensors disposed in or on respective rotor blades of the coaxial rotors to sense strain therein

Methodology Applied

Scientific EffectStrain sensing: Piezoresistive Effect

Data Source

PatentUS10752341B2Tip clearance harmonic estimation

Publication Date: 2020.08.25 SIKORSKY AIRCRAFT CORP

AI summary

A method of tip clearance estimation for a rotor blade is provided. The method includes measuring blade deflection of the rotor blade, generating a harmonic function for the rotor blade from the measured blade deflection, predicting tip displacement of the rotor blade using the generated harmonic function and adjusting a position of the rotor blade according to the predicted tip displacement.