Abstract: The present invention provides a stackable drone and a drone swarm comprising at least two stackable drones. Each drone comprising: a fuselage comprising a first end and a second end; a mating structure arranged in the fuselage and configured to have an opening at the first end of the fuselage, the mating structure forming a mating recess on a first side of the fuselage, the mating recess having an opening at the first side of the fuselage for receiving a mating projection from a further stacking unmanned aerial vehicle. The stackable drones do not require a large area of ground for take-off and landing, require only a small space for storage and transportation. When landing, based on the conical or pyramidal structure, the drone may slide down by gravitational force into the mating recess of another drone thereunder without needs of high precision positioning or alignment system.

Abstract: The present invention provides a navigation controller with real-time visual indication of a specific cardinal direction in relation to a front direction of the navigation controller which allows checking on whether the heading estimation of the UAV is subject to any magnetic interference. The navigation controller comprises a housing comprising a distinctive visual mark for indicating the front direction of the navigation controller; a GNSS satellite signal receiving module and a visual indication module comprising a circular array of visual indicators evenly arranged in a circular ring and configured to generate visual indication of the specific cardinal direction in relation to the front direction of the navigation controller.