Behind closed doors at the UK headquarters of Rolls-Royce Aerospace, machinery whirs, fans hum and blades screech as some 1,000 people go about the complex task of getting an airplane engine off ...

Cummins is making a hydrogen fuel cell airplane engine, being used in the concept HY4. It offers a unique alternative to traditional fuel options.

In the coming months, the company plans to do more engine testing while the first aircraft, called Quarterhorse, is built. The plan is to roll out the aircraft next year.