Eli5 why do drones have four blades and helicopters only have one?
In: 2
There are multiple reasons:
* Helicopters like to have the biggest possible rotors because it’s more efficient to push lots of air down slowly compared to a little air down very fast. Quadcopters are small so they can better tolerate the loss of efficiency.
* It’s difficult to make a quadcopter that can tolerate having a rotor or its engine fail. That gives you four single points of failure which is a safety issue. Quadcopters avoid spinning by having their rotors turn two each in opposite directions. Losing one rotor means you have to shut down the opposite rotor to avoid spinning, and staying up on the two remaining rotors requires a large safety margin. I’ve seen a man-size quadcopter use two motors with two separate rotors on all four corners, presumably in an attempt to work around the safety problems.
* It’s the square-cube law. The various properties of things scale up differently so you can’t just scale up a design drastically and expect it to still work. If you scaled up a quadcopter by a factor of 10 then it would weigh 1000 times more (cube law) but only be 100 times as strong (square law). Rotor area would also be only 100 times greater but be expected to generate 1000 times more lift.
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