Airbus Helicopters' Racer demonstrator is back in flight testing after a six-month lay-up to install new parts to boost the high-speed rotorcraft's aerodynamic performance.

In general, airspace is mixed-use by default. Certain restrictions apply to military corridors and takeoff and landing paths around major airports, but broadly, the skies above the U.S. are open. But ...

Military experts speculate that this was done to prevent anyone from getting their hands on the helicopter parts and technology and selling them to foreign countries, such as China, which is ...