Abstract: A grille (102) for an acoustic transducer unit for example a tweeter has an arrangement of apertures such that when projected onto a notional flat surface there is a pattern of holes (104) formed by a repeating tessellating cell (106). The repeating cell comprises a hole of a first shape (114) and a hole of a second shape (116). The second shape (116) may have a convex region that faces a concave region (128) of the first shape (114). At least one of the shape, size and orientation of the first shape may be different from that of the second shape. Adjacent holes in the pattern are separated from each other by one or more walls (112), which may extend along a non-linear path between the holes.

Abstract: A computer implemented lean assist function monitors exhaust gas temperature in a plurality of cylinders in an engine along with fuel flow. The lean assist function automatically detects whether the pilot is leaning for best power or best economy and provides an indication to the pilot when the desired fuel mixture has been achieved based on the monitored temperatures.