1. Drones take advantage of their multiple rotating wings to generate lift (L), which in a simplified version looks like this:

\[\boxed{L=\dfrac12\rho V^2CA}\]

\(L\) is lift force
\(C\) is the lift coefficient
\(A\) is the blade area
\(\rho\) is the air density
\(V\) is the speed of the blades

2. At the top of Mt. Everest 🏔 (8,900 m), the air density \(\rho\) is 1/3 compared to sea level, so to maintain lift, you need to spin the blades faster (C remains constant as it mostly depends on the angle of attack).

3. Spinning faster means the blades and drone structure need to withstand a bigger centrifugal force (\(\propto\omega^2\)), and in extreme cases, the tip of the blade can get dangerously close to the speed of sound. As the airflow exceeds the speed of sound, the drag rises sharply and the lift drops!

4. Additionally, at that altitude, you have a high risk of ice forming in the rotors/blades + fuel and hydraulics freezing! ❄️