Persisting with the idea of improving the H-6’s performance, on 23rd March 1970 the Chinese government tasked the No. 603 Research Institute with developing a strategic bomber designated Xain H-8. The aircraft was to be capable of delivering conventional and nuclear free-fall weapons or air-to-surface missiles over long range, as well as of operating at night and in adverse weather without the assistance of airborne command posts.
The designers chose a ‘quick fix’ approach, retaining much of the H-5’s airframe structure. The forward and rear fuselage sections were basically unchanged, except that the navigator’s station glazing was tipped by a small radome. The centre fuselage and the wings were new; albeit the basic wing design was the same, the Xian H-8 featured a conventional wing/fuselage joint without the engine housings flanking the fuselage and the inlet ducts passing through the wing torsion box. The centre fuselage section was longer than the progenitor’s, making for a larger bomb bay that was 8.6 m (28 ft 2 in) long, 1.8 m (5 ft 10 in) wide and 2.72 m (8 ft 10 in) deep. The H-6’s landing gear and the tail unit were retained.
The powerplant was completely different. The first project version, designated Xian H-8 I, had four 11,026-kgp (24,308-lbst) WS-6Jia (Type 910) non-afterburning turbofans in pylon- mounted nacelles located outboard of the main landing gear fairings. An alternative version powered by six 8,175-kgp (18,020-lbst) Pratt & Whitney JT-3D-3B non-afterburning turbofans also came into consideration.
The overall dimensions of the machine were increased. The Xian H-8 I was to be 48.5 m (159 ft 4 in) long, with a wing span of 46.47 m (152 ft 1 in). The maximum ordnance load was to reach 18,000 kg (39,680 lb), half of which was to be carried externally on pylons under the inner wings.
An even more ambitious project was the Xian H-8 II – an even larger bomber powered by six WS-6Jia turbofans; the engine nacelles were spaced equally along the span so that the inboard ones were located inboard of the main gear units. The overall length and wing span were even greater. Some drawings show a redesigned flightdeck section with an extended ‘solid’ nose. Very little information is available about this project; anyway the Xian H-8 never materialised.