Halifax B VI of No. 466 Squadron RAF 1945
By February 1944, the Bristol Hercules 100 engine had finally entered production as a self-contained powerplant, significantly enhancing performance when paired with 100-octane fuel and RAE-Hobson injector carburetors. These carburetors required a high-pressure fuel supply, necessitating a completely redesigned fuel system with seven flexible main tanks in each wing, divided into inboard and outboard groups. Each engine was fed from its respective group, and all fuel cocks were relocated to the flight deck instead of behind the front spar. This configuration provided a permanent fuel capacity of 2,190 gallons, which could be augmented with an additional 690 gallons in three fuselage bomb-cell tanks, totaling a maximum overload tankage of 2,880 gallons. Alongside this fuel system, the Halifax was equipped with larger Gallay oil coolers, the Graveley cabin heating system using four exhaust heaters, and all retrospective modifications, including extended wingtips. Thus, the Halifax evolved into the Mark VI with Hercules 100s and Mark VII with Hercules XVIs. Development engines of the Hercules 100 were installed at Filton in the trial installation of Halifax III, HX234, and in the Mk.VI prototype LV776, which first flew at Radlett on December 19, 1943. It subsequently featured various airscrew blade root cuffs and cooling fans before being sent to Filton for further development in March 1944.
The first production Halifax B.VI, NP715, took its maiden flight on October 10, 1944, and served operationally for several months before becoming a trial installation aircraft at Radlett. In 1946, NP715 conducted flight tests for a new lateral control system using curved spoilers moving in and out of slots in front of the ailerons on the wing’s upper surface. These tests did not yield better control than conventional ailerons, and the goal of significantly reducing the aileron area was not achieved. Consequently, in 1948, NP715 was flown to Filton, where it was grounded and used as a fire test rig during 1949 and 1950. The Halifax VI and VII were the final bomber variants produced, built by both the parent company and English Electric. Additionally, the Halifax VII was manufactured by the Merseyside factories of Fairey and Rootes; 457 Mk.VI and 423 Mk.VII units were delivered, with other units in progress canceled after VJ-Day.