What happens when air meets the blades of a UAV quadcopter? That's what NASA went to work to visualize, and the results are not only visually stunning, they could pave the way to more efficient, even quieter drones.
What's actually going on in this video? The blue represents low pressure, while the red represents high pressure. The grey swirls underneath is the disturbed air. It is the pressure differential that creates thrust for the drone.
“When the rotors pass over the arms, the fuselage creates a large download (downward force), which in turn reduces the total thrust,” NASA aerospace engineer Seokkwan Yoon told WIRED magazine. Not only that, but when the rotors and fuselage interact, it can make the drone unsteady if it doesn't have automatic flight control. That system takes a lot of juice out of the battery.
The pressure maps also show why drones are so noisy. Check out this gif:
The blue circles of low pressure air created at the tip of the rotor are still there by the time the other side of the blade comes around. The resulting disturbance is what makes the drone so loud.
If this can be avoided, drones would be a lot quieter.