How does it fly ?

Let's try to keep it simple :

Lift

Four fixed pitch propellers on four motors provide the lift. (fixed pitch = propeller's hub/blade angle is fixed)
So that it won't spin around, one pair of props (front & rear) must rotate clockwise and the other one (right & left) must rotate counter-clockwise.
Thus, rotation torques cancel each other out but counter rotating propellers are needed.

operation_lift

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