Gearing up for the revolution

Technical director, David Worthington, provides Aerospace Manufacturing with the latest update on Gibbs Gears’ custom gearing interface solution for the revolutionary WheelTug project.

A brand new onboard all-electric drive system capable of allowing aircraft to taxi both backwards and forwards without the use of tugs or engines has set the wheels in motion for an exciting new development in the aviation industry.

WheelTug was founded in 2005 to develop and commercialise a new technology called the Electric Taxi. The ground-breaking technology used patented, high power electric motors integrated inside the wheels to drive full-size commercial aircraft on the ground and in doing so, eliminate the need for engine thrust during taxi and return aircraft control during pushback to the pilot. The system claims to offer huge savings per aircraft, per year, and help airlines lead the industry in environmental responsibility through substantial reductions in CO2 and other greenhouse gas emissions.

Identifying the Boeing 737NG as the most suitable aircraft for the first production systems, WheelTug appointed several technology partners to help bring the product to market, with each partner focusing on the key areas of software, electronics, wiring harnesses, landing gear/wheel integration, motors and custom gearing.

Off and running

For a custom gearing solution, WheelTug announced that Gibbs Gears would become a project partner during the 2010 Farnborough International Airshow. Since then, Gibbs Gears has been busy working on the design and manufacture of the custom gearing interface that links WheelTug’s twin Chorus motors to the nose landing gear wheels.

After several years of development and on-aircraft tests, WheelTug was ready in 2011 to go live with our first drive motor built into the aircraft wheel envelope. However, installing high-power electric motors inside the wheels of a Boeing 737 is no trivial task. Our analysis determined that gearing, as opposed to direct drive, would give us an optimal power solution.

WheelTug needed a partner that could create and manufacture a unique, one-off gear design for the debut of a wholly-new application. WheelTug also needed someone with both aerospace experience and who also understood the demanding environment inside the aircraft. As the full system needed to be tightly integrated, WheelTug wanted its gearing partner to be a full member of the design team; working with it every step of the way to build a solution that met rigorous performance standards.

WheelTug evaluated a number of candidates, and decided that Gibbs Gears had the expertise, the personnel and the drive to make the demonstration ‘M1’ programme a success.

Down to earth

As everyone knows, an aircraft wheel can be a tough place! Pavement condition, precipitation, shocks, temperature, and speed can all vary widely. Through all of that, WheelTug needs to maintain an impressive performance envelope that aircraft operators can rely on. In order to cope with some of the major environment demands, WheelTug needed a gear solution that could sustain a significant amount of power transfer in an environment with frequent shocks, bouncing, and jarring, in addition to significant heating from the drive motors. Even though the M1 motors themselves are a one-off, WheelTug needed a resilient gear solution that would see it through a full testing and development regime.

To overcome some of the technological in producing WheelTug’s components, our brief for the M1 prototype development was to design and manufacture a gearbox in conjunction with the other team members that would be working with in the wheel space envelope. The M1 models we have developed are not ‘flight ready’ variants and will only be used for further testing and development. However, aviation grade materials have been used to manufacture the gearing elements throughout.

Gibbs Gears has always maintained a high level of reinvestment within the business updating our plant regularly for key projects. For the M1 development programme, we based our design within our production capability and plant, although we did have the benefit of installing a Gleason Pfauter P90G and a DuraMaxTM coordinate measuring machine, from Carl Zeiss during the development programme. Ongoing investments will see a Doosan Puma 2600SY Turning Centre installed before the end of March, and additional inspection equipment in the form of a visual data checking, both of which have been purchased for another aerospace manufacturing project.

WheelTug’s design and manufacturing team itself comprises several companies, spread across the globe, all collaborating together. We needed to ensure that each stage of the M1 design work was efficiently coordinated among the partners, so that each stakeholder in the M1 system knew when design changes were being made and understood why.

A poorly coordinated subcomponent update can lead to an avalanche of follow-on changes, or untold lost time in reversions. It was important to avoid surprises, so good communication was the key to taking the system from an innovative concept through design to built product.

The wheel of fortune

We have long been thinking of expanding our horizons by offering a full design service. It is still early days yet, but being involved in this project has certainly shown that we are able to work at this level. We have started discussions with a number of design engineers with gear and transmission experience and will be looking to add design and development services to our existing approvals. We have the necessary office space available and the IT infrastructure is in place. Our involvement in the development of the WheelTug project has resulted in a number of new transmissions related enquiries.

Gibbs Gears has just completed and delivered the first four prototype gearbox assemblies and is eager to watch them perform during the M1 on-aircraft demonstrations this Spring. We’ve been proud to work with WheelTug, and to help them reach this milestone in the commercialisation of an exciting new technology. We have gained a great deal of experience which we are keen to develop as the project moves closer to market.


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