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Big Week For Drones: Dubai Permits Passenger-Carrying Drone; Kenya Finally Approves Commercial Use (apnews.com)
It's shaping up to be a major week for drone enthusiasts. A pilot-less drone designed to carry one passenger at a time is set to start making regular trips in Dubai later this year. In some other news, Kenya has joined the neighbor Rwanda in opening up its skies for commercial drone use. From an AP report: Up, up and away: Dubai hopes to have a passenger-carrying drone regularly buzzing through the skyline of this futuristic city-state in July. The arrival of the Chinese-made EHang 184 -- which already has had its flying debut over Dubai's iconic, sail-shaped Burj al-Arab skyscraper hotel -- comes as the Emirati city also has partnered with other cutting-edge technology companies, including Hyperloop One. The question is whether the egg-shaped, four-legged craft will really take off as a transportation alternative in this car-clogged city already home to the world's longest driverless metro line. From a Quartz report: Flying a drone will soon be legal in Kenya, which has effectively banned the use of unmanned aerial vehicles for anyone outside of the military for the past two years. A spokesperson for the Kenya Civil Aviation Authority (KCAA) said that draft regulations for the commercial use of drones had been approved by security officials. The agency said details of the law would be released soon. The approval comes as regulators elsewhere in Africa have tightened restrictions on UAVs. In Ghana, flying an unregistered drone is punishable by up to 30 years in jail. In Nigeria, operators require permits from the aviation authority as well as the office of the National Security Adviser (the process of getting a permit costs up to $4,000).
Because of the physics of propellers, quads are workable in small scale (toys) but the efficiency is horrendous in large scale. Experimental helicopters have been built with two and four propellers for many, many years, but never commercially because they are horribly inefficient.
The thrust of a prop is proportional to SQUARE of blade length. In other words, it's proportional to the swept disk area. A 10 foot prop makes over ten times as much thrust as a 3 foot prop, so having four props of 3 feet each is very inefficient compared to a single 10 foot prop.
On a toy sized example, you can live with the inefficiency to get lower mechanical complexity due to another issue with scaling. Basically, for each dimenaion to scale linearly, weight is cubed. Consider a boom that is 1cm X 1cm x 10cm on the small craft. We want to scale it by a factor of ten. It becomes ten times as long, 10cm X 10cm x 100cm. Not only is is ten times as long, it's also ten times as thick and ten times as wide - a thousand times as much total mass, a thousand times as heavy.
Because of that cube calculation as you scale up and down, very small (toy size) craft can have phenomenal power-to-weight ratios and get away with stuff that's not possible in full-sized craft. For a full-sized craft, power-to-weight is a very significant issue. You can't have tiny, inefficient props on a full-size craft, you need a long prop which cubes the thrust.