Bell 409 / YAH-63
In November 1972 the Army called for design proposals for a new Advanced Attack Helicopter (AAH) intended for the all-weather anti-armor role. The Army's specifications required that the aircraft be powered by twin General Electric T700 turboshaft engines and armed with up to sixteen Hellfire or TOW anti-tank missiles in addition to a single 30mm cannon. Preliminary design proposals were submitted by Boeing-Vertol, Bell, Hughes, Lockheed, and Sikorsky, and in June 1973 Bell and Hughes were selected as finalists and were each awarded contracts for the construction of two prototype aircraft. The contract was awarded to Bell on 22 June, 1973, for design, construction and qualification (Phase 1) of two flying prototypes (YAH-63A-BF) and a ground test vehicle (GTV).
Bell's 409, military designation YAH-63, was based largely on the earlier 309 King Cobra. The YAH-63 seated its two man crew in tandem within a narrow fuselage, though Bell put the pilot in front in order to improve the aircraft's low-level 'nap-of-the-earth' (NOE) flight capabilities.
In accordance with the Army's specifications the YAH-63 was powered two widely separated 1536shp GE T700-GE-700 engines and was intended to carry its anti-tank ordnance load on short stub wings fixed to either side of the fuselage below the engine air intakes. The engines driving wide-chord, two-bladed semi-rigid main and tail rotors. Main rotor blade chord was 1.08m and an FX-69-H-083 aerofoil was used. The wide-chord had been selected mainly because it met performance requirements, permitted the spar separation required for 23mm survivability and was less complex by a factor of two. The 'flat-pack' transmission had large slow turning herringbone gears for increased survivability, reduced noise and a 30-minute fly-dry capability. The main rotor mast quickly retracted into the transmission for air transport. The YAH-63 had wheeled tricycle landing gear and a distinctive T-tail. The YAH-63 had a high flotation tricycle wheeled undercarriage with oleo struts equipped with 'strut cutter' crash energy absorber to meet the design impact velocity of 12.8m/sec.
The weapon 'systems consisted of a chin turret-mounted triple-barrel 30mm XM-188 rotary cannon (fire rate 600 to 1800rpm) mounted ahead of the stabilised sight to minimize damaging muzzle blast effects, and up to sixteen Rockwell AGM-114A Hellfire air-to-ground missiles or seventy-six 70mm FFAR rockets could be carried on the four wing stores.
The first proroype YAH-63 (s/n 73-22246) first flew on 1 October, 1975, and the second prototype (s/n 73-22247) followed it into the air two months later. On 4 June, 1976, the first prototype experienced a heavy emergency landing and suffered minor damage. It was repaired in time to take part in the evaluation of the two contenders which was made at the Army Engineering Flight Activity (AEFA) from June to September 1976. The comparative tests between YAH-63 and YAH-64 led eventually to the selection of the Hughes design on 10 December, 1976. All flight testing with the YAH-63 then ceased and plans were made to continue work with the T700 powerplant.
One Bell YAH-63 (s/n 73-22247) survives and is preserved by the US Army Aviation Museum, at Fort Rucker, Alabama.
Engine: 2 x General Electric T700-GE-700 turboshaft, 1145kW
Main rotor diameter: 15.54m
Length with rotors turning: 18.51m
Take-off weight: 7237kg
Max speed: 325km/h
Hovering ceiling: 1980m