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Aviation History
1975
1975 - 2119.PDF
522 FLIGHT International. 9 October 1975 DEFENCE AV-8B: first hurdle cleared AN EXECUTIVE BOARD meeting of the Chief of US Naval Operations * (CNO) gave its approval on September 30 to development plans for the AV-8B improved Hawker Sid- deley Harrier. CNO approval was the first hurdle to clear and the way is now open for the first Defence Sys tems Acquisition Review Council (Dsarc) on the programme to be held probably during December. Basic US Marine Corps requirement for the AV-8B is 340 aircraft with first deliveries allowing an initial operational capability by the end of 1982. Two aircraft from the current USMC fleet will be bailed back to McDonnell Douglas, the US licence holder, for modification to demon strate AV-8B aerodynamics, starting in 1978. The AV-J5B is an almost entirely American development of the Harrier/ AV-8A and as such would be built in the USA with McDonnell Douglas as prime airframe contractor, and HSA as a probable 40 per cent subcontrac tor. The position with the Pegasus powerplant is slightly different and no decision has yet been made as to whether Rolls-Royce, the present sole manufacturer, would be prime or whether Pratt & Whitney, the US partner, would take over making the engines for the US aircraft. Improvements planned by McDon nell and the USMC centre on four main areas: lift-augmentation devices; a new wing; new weapon delivery systems; and an improved engine. McDonnell Douglas has built a full-scale AV-8B mock-up. Clearly in evidence are the modified wing with six weapon stations, massive flap (lowered only one side), gun-pack strokes and the flap across the front which forms an air-trap and augments vertical take off lift. Outriggers have been moved inboard to between flaps and ailerons. Guns will probably be American 20mm-calibre instead of British 30mm Adens with increased inlet efficiency. As re gards lift augmentation, the Harrier can hover, unlike a helicopter, at a greater weight than that at which it can take off vertically. With the aid of a powered wind-tunnel model McDon nell has identified the "suck-down" effects on take-off and added strakes on the gun-packs and a flap which lowers across the front of the packs When the AV-8B is flying on other than wirig lift. The new wing is supercritical in section and composite in structure. With about 5ft more span than the current wing, and its new section, it This general-arrangement drawing clearly emphasises the increased area and 10° less sweep of the new AV-8B wing, as well as the otherwise barely changed Harrier charac teristics offers more area, more fuel capacity (total internal now more than 7,0001b) and two additional pylons for no in crease in weight as a result of the extensive use of graphite epoxy in the torque box, ribs, skins and (reposi tioned) outrigger fairings. The vectoring nozzles of the AV-8A entrain a substantial amount of air in forward flight and its relationship with the existing wing and flap is less than ideal. Wind-tunnel tests at St Louis indicated that a glove over the forward nozzle could not stop this entrainment effect but at the same time it was discovered that there was a significantly greater beneficial effect on the wing trailing edge than had been expected. Furthermore the nozzle, when rotated downwards, re duces airflow separation all the way out to the tip of the wing, which partly explains the excellent handling characteristics of the Harrier at very low airspeeds. The improved weapon delivery sys tem planned for the AV-8B is, as reported in Flight for February 13, page 232, the Angle-Rate Bombing System (ARBS) also to be fitted to US Marine Corps Skyhawks. This consists of a dual-mode television and laser spot seeker coupled via an IBM digital computer to a Marconi- Elliott head-up display. The current Harrier system is essentially analogue and employs a Smiths head-up display. The attitude and heading reference system is also to be improved and passive electronic countermeasures will be added. Inlet improvements, as shown on the general-arrangement drawing, in clude a double row of blow-in doors. The current inlet was designed for the Pegasus 6 engine with an airflow of 4181b/sec. The Pegasus 11 takes 4501b/sec. Nozzle losses in the AV-8A are some 7 per cent of the uninstalled engine thrust. With the modifications an improvement of about 1 per cent is expected; any greater improvement would entail a major redesign. The engine for the AV-8B has not
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