Variable Diameter Downstream Propeller for CROF Noise Reduction

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Solution Overview

Problem

Current contra-rotation open fan (CROF) propeller systems face challenges in reducing takeoff noise due to Blade Vortex Interaction (BVI) noise, which requires blade cropping, leading to decreased thrust, increased fuel consumption, and aerodynamic inefficiency, while attempts to alter aircraft configuration to mitigate noise result in unacceptable penalties such as increased operating costs and reduced performance.

Innovation Solution

A method and apparatus that uses an electric motor to adjust the diameter of the downstream propeller of a CROF engine, setting it to a reduced diameter during takeoff and climb to minimize noise and increasing it to match the upstream propeller diameter during cruising for optimal efficiency and performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If the downstream propeller diameter is reduced (cropped) to reduce takeoff noise, then noise levels decrease, but thrust and aerodynamic efficiency deteriorate

Engineering Contradiction:

Improvetakeoff noiseVSAvoidthrust

Core Design Contradiction:

Object-affected harmful factorsVSPower

Solution Approach 1:

The patent applies variable geometry by making the downstream propeller diameter adjustable rather than fixed. The propeller can be cropped during takeoff to reduce noise, then extended during cruise to restore thrust and efficiency. This dynamic adjustment resolves the contradiction by allowing the system to optimize for noise when needed and for power when needed.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes the physical parameter of propeller diameter from a fixed value to a variable value. By adjusting the diameter parameter across different flight regimes, the system can reduce noise during takeoff (smaller diameter) and maintain thrust during cruise (larger diameter), resolving the trade-off between noise reduction and power maintenance.

Inventive Principle:

Principle #35Parameter changes

2Object-affected harmful factors

If the downstream propeller diameter is reduced (cropped) to reduce takeoff noise, then noise levels decrease, but fuel consumption increases

Engineering Contradiction:

Improvetakeoff noiseVSAvoidfuel consumption

Core Design Contradiction:

Object-affected harmful factorsVSUse of energy by moving object

Solution Approach 1:

The variable diameter propeller allows the aircraft to operate efficiently across different flight regimes. During takeoff, the cropped configuration reduces noise, and during cruise, the extended configuration restores aerodynamic efficiency, minimizing the overall fuel penalty associated with noise reduction measures.

Inventive Principle:

Principle #15Dynamics

3Power

If the pitch is increased to recover lost thrust from cropping, then thrust is recovered, but drag increases and off-design performance degrades

Engineering Contradiction:

ImprovethrustVSAvoiddrag

Core Design Contradiction:

PowerVSObject-generated harmful factors

Solution Approach 1:

Instead of increasing pitch to compensate for cropping, the patent dynamically adjusts the propeller diameter. This approach recovers thrust by restoring the propeller span rather than increasing pitch, thereby avoiding the associated increase in drag and degradation of off-design performance.

Inventive Principle:

Principle #15Dynamics

4Object-affected harmful factors

If the downstream propeller diameter is reduced (cropped) to reduce takeoff noise, then noise levels decrease, but aerodynamic efficiency decreases

Engineering Contradiction:

Improvetakeoff noiseVSAvoidaerodynamic efficiency

Core Design Contradiction:

Object-affected harmful factorsVSProductivity

Solution Approach 1:

The variable geometry propeller system allows the aircraft to optimize aerodynamic efficiency during cruise by extending the propeller to its full diameter, while still achieving noise reduction during takeoff by cropping it. This dynamic adjustment minimizes the overall penalty to aerodynamic efficiency while maintaining noise compliance.

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 approach effectively reduces noise during takeoff and climb while maintaining aircraft efficiency at cruising speed, thereby addressing the noise and performance penalties associated with blade cropping and alternative configuration changes.

Implementation Method 1

A method and apparatus for controlling a propeller of a contra-rotation open fan (CROF) engine of an aircraft includes setting a diameter of the propeller to be at a first diameter during at least a portion of a first flight condition of the aircraft and setting the diameter of the propeller to be at a second diameter, different from the first diameter, during at least a portion of a second flight condition of the aircraft, wherein setting is performed using at least one electric motor

Methodology Applied

Scientific EffectElectromagnetic conversion: Electromagnetic Induction

Data Source

PatentUS9637221B2Optimization of downstream open fan propeller position and placement of acoustic sensors

Publication Date: 2017.05.02 THE BOEING CO

AI summary

A method and apparatus for controlling a propeller of a contra-rotation open fan (CROF) engine of an aircraft is provided. A diameter of the propeller is set to be at a first diameter during at least a portion of a first flight condition of the aircraft. The diameter of the propeller is set to be at a second diameter, different from the first diameter, during at least a portion of a second flight condition of the aircraft.