If helicopters didn't have tail rotors, they would spin in circles because they need a force pushing in the opposite direction as the main rotor.

But helicopter-maker Bell has been flying a new experimental craft with a totally different tail rotor, a system that could be safer in some cases, and is also quieter than a traditional tail rotor.

The images, reportedly captured in April, show a compound helicopter with coaxial main rotors and pusher propeller, which bears similarity to Sikorsky’s ...

Video taken by an eyewitness showed the helicopter plummet into the Hudson River, followed by a detached rotor from the aircraft itself.