A new UCAV concept being developed may very well visually resemble and have similar flight characteristics of the "black triangles" so prevalent in UFO-lore.
The VTOL concept is called the "Unmanned Combat Hybrid Armed Vehicle" and will utilize an oil-less Rolls Royce turbofan engine system that propels the craft horizontally and powers hybrid-electric VTOL lift fans as well as powering sensor arrays and directed-energy weapons (ie solid state lasers).
