The H.P.42 was powered by an arrangement of four Bristol Jupiter XIFs, each capable of producing up to , while the H.P.45 variant instead used four Jupiter XFBM supercharged engines, which could generate a maximum of each. Both models placed their engines in the same positions: two engines on the upper wing and one on each side of the fuselage on the lower wing; while this arrangement was uncommon, it was not an original innovation, having been previously used on aircraft produced by Blériot. The upper engines are placed as close together as permissible by the diameter of their propellers. The engines are mounted on rigid duralumin plates that are attached to rear wing spar via welded steel tubing; fuel for the engines is housed within the upper wing and is gravity-fed to all four engines. The throttle controls for the engine includes a 'lost motion' mechanism, which uses the first degrees of movement from the idle position to turn on the fuel.