The vertical take off landing makes for a much larger operating enevelope for a vehicle. The challenge is how to efficiently hover with out burning to much ener

The vertical take off landing makes for a much larger operating enevelope for a vehicle. The challenge is how to efficiently hover with out burning to much energy. Larger rotors can out perform jets for efficinecy, ie rotors move a large volume of air at a slower velocity which is fundamentally more efficient then moving a small volume of air at a high velocity. You can also squeeze some more efficiency out of the system if you put a duct around the rotors, a duct can in itself produce ~40% of the total lift. The Hiller flying platform which was built and test flown in the 1960's is a good model for something that could fly for 30-60 minutes with todays technology. You can search Youtube to find videos of its test flights... https://www.youtube.com/watch?v=GgNlumaVPDw https://www.youtube.com/watch?v=GgNlumaVPDw