Unique Turbofan-Ramjet Design.

The Zephyr utilizes a unique dual engine design that takes advantage of the fuel efficient high bypass turbofan engines without incurring substantial drag penalties at supersonic cruise speed. During subsonic speeds, the Zephyr’s high bypass turbofans operate just as they would on a current aircraft. At supersonic speeds a system of diverter doors open and direct the airflow into a ramjet shielding the high bypass fan from the supersonic airflow. The ramjet then produces over ninety percent of the thrust required during cruise flight.