The Hornet used "slimline" Merlin engines of types 130 and 131, which had engine ancillaries repositioned to minimise frontal area and drag. It was unusual for a British design in having propellers that rotated in opposite directions; the two engine crankshafts rotated in the same direction but the Merlin 131 added an idler gear to reverse its propeller's rotation (to clockwise, viewed from the front). This cancelled the torque effect of two propellers turning in the same direction that had affected earlier designs (such as the Mosquito). It also reduced adverse yaw caused by aileron trim corrections and generally provided more stable and predictable behaviour in flight. De Havilland tried propellers that rotated outward at the tops of their arcs (as in the P-38 Lightning), but this configuration blanketed the fin and reduced rudder effectiveness at low speeds, compromising ground handling. On production Hornets the conventionally rotating Merlin 130 was on the port wing with the Merlin 131 on the starboard.