A new drone which flies almost silently without wings or propellers has raised questions about how many supposed UFO sightings might actually be man-made craft. The Silent Ventus drone, made by Florida-based start-up Undefined Technologies, uses ion propulsion, with electrodes ionizing the air to generate thrust, and flies incredibly quietly. The hi-tech drones may possibly explain sightings such as the famous'Tic Tac' drone sighting, where pilots spotted a craft resembling the breath mint performing impossible maneuvers during a training mission with the USS Nimitz off the Southern California coast in 2004. Undefined Technologies' claim that its ion-propelled eVTOL drone generates 150% more thrust than rivals (Undefined Technologies) The company hopes to achieve a 15-minute flight this year and believes the drone could be used for'last mile' deliveries (Undefined Technologies) Undefined Technologies' claim that its ion-propelled eVTOL drone generates 150 percent more thrust than rivals. The company hopes to demonstrate a 15-minute flight with noise levels below 70dB this year - ion drives are widely used in satellites and spacecraft, but less common on Earth.