Abstract: Unmanned aerial vehicles (1), and methods of flying such, comprising at least four rotors (2) arranged such that the plane of rotation of each rotor (2) is co-planar with a face of a notional polyhedron, and wherein each face of the notional polyhedron is co-planar with the plane of rotation of at least one rotor (2). Such methods comprise: a first step of flying the vehicle (1) using a first rotor set (2a-c) to provide lift; and, a second step using a second rotor set (2d-f) to provide lift; wherein, the second rotor set (2d-f) includes at least one rotor (2) that is not used to provide lift in the first step or that operates so that airflow through the rotor (2) is in the opposite direction to that through the rotor (2) during the first step; and, wherein at least one of the first and second sets (2a-c, 2d-f) comprises a plurality of rotors (2).

Abstract: Unmanned aerial vehicles (1), and methods of flying such, comprising at least four rotors (2) arranged such that the plane of rotation of each rotor (2) is co-planar with a face of a notional polyhedron, and wherein each face of the notional polyhedron is co-planar with the plane of rotation of at least one rotor (2). Such methods comprise: a first step of flying the vehicle (1) using a first rotor set (2a-c) to provide lift; and, a second step using a second rotor set (2d-f) to provide lift; wherein, the second rotor set (2d-f) includes at least one rotor (2) that is not used to provide lift in the first step or that operates so that airflow through the rotor (2) is in the opposite direction to that through the rotor (2) during the first step; and, wherein at least one of the first and second sets (2a-c, 2d-f) comprises a plurality of rotors (2).

Abstract: A filter for exhaust gases produced by an internal combustion engine, and a method of using such a mat on a vehicle. The filter is a mat of fibers enclosed within a metal gauze. Preferably, the mats are corrugated and spaced apart within a housing such that exhaust gases will pass through the mats sequentially. The fibers are wettable, and in use are preferably located a sufficient distance from the engine such that the mat is wetted by condensing water or other liquid in the exhaust gas. Preferably also, the filter is adapted for coupling to an existing exhaust pipe opening.