Aircraft Tow Bar Fitting Noise Reduction

Solution Overview

Problem

Conventional tow bar fittings for aircraft landing gear generate audible noise during take-off and landing due to vortex shedding airflow impinging on the front face, increasing operational noise levels.

Innovation Solution

A tow bar fitting design where the tow pin is positioned in a pin support such that the tow pin plane is lower than the mount plane, allowing a majority of vortex shedding airflow to flow underneath, reducing noise by directing airflow away from the front face of the mount and strut.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If the tow pin is positioned in the center of the tow bar fitting (vertically centered relative to the mount), then load transfer through the tow bar fitting to the strut is optimized and weight of the tow bar fitting is reduced, but audible noise is generated due to vortex shedding airflow impinging on the front face of the tow bar fitting

Engineering Contradiction:

Improveload transferVSAvoidaudible noise

Core Design Contradiction:

StrengthVSObject-generated harmful factors

Solution Approach 1:

The patent applies asymmetry by positioning the tow pin offset from the vertical centerline of the mount. Specifically, the tow pin is positioned such that its centerline is offset horizontally from the centerline of the mount by a distance of 0.5 to 2 inches. This asymmetric positioning changes the airflow pattern around the tow bar fitting, preventing symmetric vortex shedding that would impinge on the front face and generate audible noise, while still maintaining adequate load transfer capability through the structure.

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The patent addresses the noise problem by introducing a horizontal offset dimension to the tow pin positioning. Instead of only considering vertical centering for load optimization, the solution adds a horizontal offset component (0.5 to 2 inches from the mount centerline). This dimensional change redirects the vortex shedding airflow away from the front face of the tow bar fitting, eliminating the noise-generating impingement while preserving structural function.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Weight of stationary object

If the tow pin is positioned vertically centered relative to the mount, then the weight of the tow bar fitting is reduced, but vortex shedding airflow impinges on the front face generating audible tone

Engineering Contradiction:

Improveweight of tow bar fittingVSAvoidaudible tone

Core Design Contradiction:

Weight of stationary objectVSObject-generated harmful factors

Solution Approach 1:

The patent applies asymmetry by positioning the tow pin offset from the vertical centerline of the mount. Specifically, the tow pin is positioned such that its centerline is offset horizontally from the centerline of the mount by a distance of 0.5 to 2 inches. This asymmetric positioning changes the airflow pattern around the tow bar fitting, preventing symmetric vortex shedding that would impinge on the front face and generate audible noise, while still maintaining adequate load transfer capability through the structure.

Inventive Principle:

Principle #4Asymmetry

3Device complexity

If the tow pin is positioned in the middle of the tow bar fitting, then structural simplicity is maintained, but noise reduction is not achieved during aircraft movement

Engineering Contradiction:

Improvestructural simplicityVSAvoidoperational noise level

Core Design Contradiction:

Device complexityVSObject-generated harmful factors

Solution Approach 1:

The patent applies asymmetry by positioning the tow pin offset from the vertical centerline of the mount. Specifically, the tow pin is positioned such that its centerline is offset horizontally from the centerline of the mount by a distance of 0.5 to 2 inches. This asymmetric positioning changes the airflow pattern around the tow bar fitting, preventing symmetric vortex shedding that would impinge on the front face and generate audible noise, while still maintaining adequate load transfer capability through the structure.

Inventive Principle:

Principle #4Asymmetry

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

The design significantly reduces audible noise during aircraft movement by minimizing the impingement of vortex shedding airflow on the tow bar fitting and landing gear, thereby lowering operational noise levels.

Implementation Method 1

shear layers originating from the airflow separated from the top/bottom surfaces of the tow pin form vortex shedding that impinges upon a front face of the tow bar fitting

Methodology Applied

Scientific EffectVortex shedding: Kármán Vortex Street

Data Source

PatentUS11530051B2Noise-reducing aircraft landing gear tow bar fitting

Publication Date: 2022.12.20 THE BOEING CO

AI summary

A tow bar fitting for towing an aircraft is disclosed. The tow bar fitting includes a mount, a pin support, and a tow pin. The mount includes an upper attachment and a lower attachment for affixing the tow bar fitting to a landing gear of the aircraft. The pin support extends from the mount away from the landing gear. The tow pin is positioned in the pin support such that a tow pin plane that horizontally bisects the tow pin is lower than a mount plane that horizontally bisects the upper attachment and the lower attachment when the aircraft is right-side-up on the ground.