Conventional wisdom says that you need at least four fixed motor propeller pairs in order to fly, because there are four degrees of freedom to control: roll, pitch, yaw and acceleration.
Herkömmlicherweise braucht man mindestens vier fest angebrachte, angetriebene  Propellerpaare, um zu fliegen, weil es vier Freiheitsgrade gibt: Rollen, Kippen, Gieren und Beschleunigung.