The engine, a multistage turbocharged internal-combustion design, ran for four days straight in a controlled chamber. (Gas versions of the same engine are used in Ford’s Fusion and Escape Hybrid vehicles.) For three days of the test, the chamber replicated conditions at 65,000 ft. The engine is said to have demonstrated better than expected fuel economy and showed complete control of torque and airflow across the engine’s operating range.

The Hale aircraft is designed to loiter over an area for extended periods while onboard sensors gather intelligence information. Once fully operational, it will be able to stay aloft for seven days carrying payloads of up to 2,000 lb.