Why can a helicopter fly? Part 4

This is the fourth part. If you want to read them in order, here are the previous parts: Part 1: Introduction Part 2: Bernoulli, pressures, lift in detail Part 3: Reaction principle and conservation of momentum Part 4: Completely Airborne: The Vertical Takeoff Before an airplane can take off, it must reach a required minimum speed. Only then will the [...]