The future operation of aircraft will need to meet ever-demanding emission and efficiency targets and therefore, innovative solutions are required to support both new and in-service aircraft fleets. WheelTug is a company that has developed a pioneering concept to meet these challenges. They are developing a taxiing system, which consists of a nose wheel mounted motor and drive, powered by the aircraft’s Auxiliary Power Unit. The ultimate goal of the system is to save time, engine life and fuel use, resulting in reduced emissions and significant cost savings.
WheelTug approached Stirling to assess the system feasibility due to our unique landing gear systems capability. An added challenge for Stirling on this project is the lack of OEM information, which necessitates a reverse engineering approach to develop representative aircraft and landing gear to support the design process. As this is such a novel system, we have had to assess the FAA certification requirements to determine what is applicable and to provide a suitable means of compliance.
Stirling developed a process to achieve the FAA-certified STC for the system. After successfully completing the system feasibility work, our team were also asked to conduct a preliminary loads analysis and generate the certification plan for submission to the FAA. In early 2017, the Federal Aviation Administration (FAA) approved the Project Specific Certification Plans (PSCP) for the installation of the WheelTug® electric drive system for the Boeing 737NG aircraft. This approval was a key milestone for WheelTug and a major step forward in achieving certification for the system. This news was especially meaningful to Stirling as the landing gear and airframe PSCP was issued by Stirling’s engineering team. This PSCP describes the activities required to achieve certification of the Boeing 737NG for use with the WheelTug system.
At the end of 2017, Stirling was awarded a new contract with WheelTug to design and achieve certification for a brand-new landing gear nose wheel, where our engineering team were required to draw on the company’s core capabilities in reverse engineering, wheel analysis, landing gear analysis, safety analysis and structural stress analysis to deliver on this exciting project. In 2019, Stirling’s wheel design specification was issued, development wheels were manufactured in accordance with Stirling’s design and production forgings were manufactured, which have been qualified in accordance with Stirling defined requirements. Work is currently progressing on the Technical Standard Order (TSO) test plan and qualification test plans and procedures.
In early 2020, the nose landing gear rig test and aircraft flight test plans were issued. As a result, both the flight test and landing rig test programmes started in August 2020, in the US and Germany, respectively. Stirling’s test planning has been vital in defining the aircraft and landing gear testing required to acquire capture the data necessary for the to validate the Boeing 737NG models. These models will support certification and the installation of the WheelTug system. Safety documentation for the first design baseline has also been completed by the Stirling Dynamics team.
Our engineers continue to support WheelTug’s design team on a variety of other associated modifications. Isaiah Cox of WheelTug says:
The team at Stirling Dynamics has consistently delivered superb product on very tight deadlines. Their reports and analyses have been impressive: professional in rationale and appearance, complete, and technically accurate. When we send work to Stirling, we are always confident that it is in the very best of hands - they continue to exceed our most demanding expectations.