Boeing and Ford have successfully tested a new hydrogen aircraft engine with a simulated flight that lasted nearly four days.

The project, called the High Altitude Long Endurance (HALE) aircraft, is being run to test the feasibility of having unmanned craft in permanent flight to act as communications systems that can be quickly and cheaply set up where coverage by traditional means isn't available.

"This test could help convince potential customers that hydrogen-powered aircraft are viable in the near-term," said Boeing Advanced Systems president George Muellner.

"This is a substantial step towards providing the persistent intelligence, surveillance and reconnaissance capabilities our customers desire."

The HALE's engine is a modified four cylinder Ford engine that can use hydrogen as a fuel and run for extended period. In a simulation chamber the engine ran for nearly four days, powering the craft up to an equivalent of 65,000 feet.

"This simulated flight allows us to showcase the capabilities of Ford's proprietary hydrogen engine technology and the durability of our four-cylinder engines," said Gerhard Schmidt, vice president of Ford Research and Advanced Engineering.

"We are very pleased with the results. The gasoline version of this same engine can be found in our Ford Fusion and Escape Hybrid vehicles."