Eaton validates X-47’s pressure pulsations on iron bird hydraulic system

Background

On February 4, 2011, Northrop Grumman and the U.S. Navy conducted the successful first flight of the X-47B, the first carrier-capable unmanned aircraft developed for the Navy’s Unmanned Combat Air System Carrier Demonstration (UCAS-D) program.  

Eaton is a key system supplier to Northrop Grumman, the Navy’s UCAS-D prime contractor. Eaton contributions include the X-47B fuel system, engine-driven hydraulic pumps, reservoir, selec-tor valves, hoses, Rynglok™ tube-fitting technology, swivels, flanges, couplings and straps. 

During initial aircraft development stages, Eaton worked closely with Northrop Grumman on the X-47B test rig or “iron bird,” located at Northrop Grumman’s Unmanned Systems Center in San Diego, California, to validate test results and provide solutions to improve hydraulic system performance. Eaton’s contributions helped Northrop Grumman identify and resolve performance issues in early stages, which paved the way for the project’s advancement from testing to production to the successful first flight. 

Challenge

Eaton supplies three engine-driven hydraulic pumps for the X-47B. The Model PV3-115-45A pump had been qualified for 4,000 psi operation on the Lockheed-Martin F-22 fighter jet with an 8,000-hour design life. 

Results from the X-47B test rig revealed high-pressure pulsations in an outlet line that were found to originate from an engine-driven pump. Pulsations are pressure disturbances that travel through the fluid in a piping system at the speed of sound. Typically, these pulsations are not large enough to cause serious problems on their own. However, they are capable of producing adverse interactions, or resonances, within the hydraulic system that can cause problems with downstream components. 

Eaton’s challenge was to devise a solution to control pump resonances and ensure that pump installation in the X-47B hydraulic system was correctly configured to eliminate adverse interactions. 

Solution

Eaton engineers entered X-47B test rig data into the Hydraulic System Frequency Resonance program, which Eaton developed to simulate the response of a hydraulic system to pressure pulsations originating from typical in-line hydraulic pumps. 

“It’s basically a high-fidelity check we can perform to ensure that installation of the pump is done correctly to support optimal hydraulic system performance,” said Anil Bhansali, lead engineer in Eaton’s hydraulic systems division. “If problems are detected, the program provides the data we need to pinpoint the source and develop a solution.” 

Pressure pulsations can be controlled using commercially available devices that can be installed in the outlet circuit. The most commonly used device in high-pressure hydraulic applications is an attenuator, which can modify overall system compliance with the addition of volume. An attenuator also has the capability to absorb peaks of flow pulsations and return flow to the main line during valleys or low points in outlet pressure. 

“We had successfully employed the hydraulic resonance analysis tool on several projects to predict pump speeds at which resonance occurs,” Bhansali said. “The tool has the capability to add attenuator volume to increase or reduce circuit ‘springiness’ to tune the line to avoid destructive resonances at normal dwell speeds of the pump.”

Results

Using hydraulic resonance analysis, Eaton helped Northrop Grumman size and place an attenuator to reduce pressure pulsations on the X-47B iron bird test rig. It was a critical step in the validation process that supported Northrop Grumman’s milestone schedule for the X-47B, including the aircraft’s first flight.

“We were able to tune the system so the resolution frequencies were not in areas where they were going to dwell for long periods of time,” said Bhansali. “Our capability to predict the pump speeds at which resonances were going to occur gave Northrop Grumman more confidence in the X-47B’s operational readiness during the buildup to first flight.”