Lockheed Martin

Lockheed Martin

Eaton’s New Ground Maintenance Motorpump Optimizes Safety, Weight Savings and Power Management for F-35 Joint Strike Fighter


The Lockheed Martin F-35 Joint Strike Fighter aircraft comes in variants customized for three branches of the United States Armed Forces: F-35A for the Air Force, F-35B for the Marines and F-35C for the Navy. All versions are fifth-generation stealth fighters that have introduced profound capability improvements over existing multi-role fighters.

Lockheed Martin selected Eaton's hydraulic systems division to provide the primary fluid power system for this revolutionary aircraft. Eaton was responsible for the total design, development and integration of the 4,000-psi hydraulic power generation system, utility actuation and control valve sub-systems.

At the heart of the F-35’s original hydraulic power generation system were two engine-driven pumps and two ground maintenance motorpumps (GMMPs). The design and development phase of the F-35 program included many changes in governing requirements as the overall aircraft evolved into its present configuration. One of the most challenging involved the GMMPs and their role in the hydraulic power generation system.


To meet Lockheed Martin’s new expectations for nextgeneration F-35 fighters, Eaton’s project team was directed to comply with two major changes in requirements affecting the GMMP. The first was the need for a design that could reduce overall aircraft weight while continuing to provide enough power to drive two hydraulic pumps.

The second change, which presented a more daunting challenge to the team, was designing the GMMP to function as an inflight backup hydraulic power source.

This introduced a number of new and more complex considerations into the design process, including much stricter safety requirements, additional required qualification testing and a broader range of input voltages for the electric motor to handle.


Eaton’s hydraulic systems division resolved both challenges through teamwork and collaboration among engineers from facilities in Jackson, Miss., Fort Worth, Texas, and Bedhampton, U.K.

The GMMP was originally two electric motor-driven hydraulic pumps, one for each main hydraulic system. To address the requirement for reduced aircraft weight, Eaton engineers streamlined the new design into a single electric motor that could drive two identical hydraulic pumps. The inventive design allows the electric motor to spin in one direction to drive the system A pump and in the opposite direction to drive the system B pump. This concept was possible because there was no need to operate both pumps simultaneously.

The original GMMP also was designed to be used as a ground maintenance hydraulic power source to allow maintenance crews to open and close hydraulically actuated doors and to charge brake accumulators for towmodetowmode braking. The aircraft architecture safety studies highlighted an urgent need for an inflight backup hydraulic power source in case of lossof-engine scenarios.

The Eaton project team designed a GMMP that could function as an inflight emergency backup pump capable of providing enough hydraulic power to lower the landing gear and provide brake capability in the event of an engine-out landing.


Eaton’s new GMMP design completed all qualification testing and was granted full certification for use on all three variants of the F-35 as the ground maintenance and inflight emergency backup motor pump.

The GMMP is now actively being used for ground maintenance operations in a flight test fleet of more than 15 aircraft at various military test sites across the United States, including Naval Air Station Patuxent River and Edwards Air Force Base.

Fortunately, the inflight emergency capabilities of the new GMMP have not been required. But thanks to the successful design, test and verification efforts of Eaton’s design team, future F-35 pilots can fly safely with the knowledge that if an emergency occurs, Eaton’s GMMPs will be ready for action.