September 10, 2017 AT 6:00 am


Wired dives into the science and physics of drones to figure out this age old question. The short answer is yes, with enough rotor area a “drone” can generate enough force. For a standard drone size the power requirements to generate enough lift are too great. Please do not attempt.

Let’s focus on the rotor-based drones, though. Their key to lift is their rotors’ thrust: A rotor’s main job is to take air from above the aircraft and push it down at some speed. Let’s imagine that in some short time interval, the rotor takes a cylinder of air above (that was initially at rest) and gives it some final velocity moving down.

Spring 2017 sketches key

In the end, the total rotor area is very important. For a given drone weight, you could either make a larger rotor (or more rotors) and push the air down at a slow speed, or you could make a small rotor and push the air down at a fast speed.

The air starts from rest above the rotors but then has kinetic energy below. This energy depends on the mass and the velocity of the air.

La te xi t 1

Theoretically, a drone could lift any amount no matter what size rotor it has. But on a practical level, there are two limitations. First, the maximum air speed is probably around 40 m/s (based on my calculations for the physics of the S.H.I.E.L.D. Helicarrier). Second, if the drone had a power of something crazy like 1,000 Watts, it wouldn’t be able to fly very long.

I get a rotor radius of 0.188 meters for a total rotor area (6 rotors) of 0.67 m2. Assuming a total drone plus human mass of 70 kg I can first calculate the required thrust speed in order to hover. With these values I get 43 m/s—that seems plausible. Now for the power, I get 14.8 kilowatts (you can see my calculations here. A power of 14.8 kilowatts is sort of crazy high. A normal-sized house could probably get by with less than 3 kilowatts. Just saying.

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