|Bell 409 / YAH-63|
In November 1972 the Army solicited design proposals for a new Advanced Attack Helicopter (AAH) intended for the all-weather anti-armor role. The Army's specifications required that the new 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.
Bell's entry in the AAH competition carried the company model number 409 and the military designation YAH-63, and was based largely on the firm's earlier, privately-developed Model 309 King Cobra. Like the Model 309 the YAH-63 seated its two man crew in tandem within a narrow fuselage, though the Bell design teamed reversed the generally accepted seating arrangement by putting 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 by the same 1536shp GE T700-GE-700 engines as those used in the competing Hughes YAH-64 and, also like the Hughes aircraft, 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 Bell AAH entry carried its three-barreled XM-188 30mm cannon in a small chin turret just below the nose, immediately forward of a stabilized TOW sight. The YAH-63 had wheeled tricycle landing gear and a distinctive T-tail, and retained the two-bladed, wide-chord main rotor characteristic of nearly all Bell helicopter designs.
The first prototype YAH-63 (serial 73-22246) made its maiden flight on 1 October 1975, but crashed during a test flight the following June. The aircraft was repaired and, along with the second prototype (73-22247), entered the official Army 'fly-off' against the YAH-64. On 10 December 1976 the Hughes machine was selected as the winning AAH design, and both YAH-63 prototypes were subsequently returned to Bell for disposal.
S.Harding "U.S.Army Aircraft since 1947", 1990
In November 1972, after abandoning the Lockheed AH-56A Cheyenne programme as well as the Sikorsky S-67 and Bell Model 309 replacement proposals, the US Army created an Advanced Attack Helicopter (AAH) Task Force which issued a new set of specifications. The key objectives for the future aircraft were the ability to operate by day or night and in adverse weather, to strike the enemy with great accuracy, to have superior flight performance, to survive battle damage (no single hit by a 12.7mm round was to cause a mission to be aborted and maximum invulnerability to 23mm rounds was required) and to be easily maintained in the field. As far as performance was concerned, the cruising speed at 1200m was to be 270km/h, the vertical rate of climb with eight Hellfire missiles and 320 rounds of 30mm ammunition was to be 135m/min and endurance was to be 1hr 50min.
Submissions were received from Boeing-Vertol, Lockheed, Sikorsky, Hughes and Bell. The Bell Model 409, designated YAH-63, was one of the two designs selected by the US Army in June 1973 for competetive evaluation for selection, its competitor being the Hughes Model 77 (YAH-64). A 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). The Bell YAH-63 embodied a tandem cockpit with flat-plate canopy for reduced glint detection in combat. The pilot was now positioned in the forward cockpit for better visibility while flying nap-of-the-earth. The two-blade tail rotor and drive train were supported and protected by the tail boom and an I tail. This I tail played an important role in stabilty and control; it also prevented inadvertent ground strikes. The YAH-63 also 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. Power was provided by two widely separated 1500shp General Electric YT700-GE-700 turboshafts 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 weapon 'systems consisted of a 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) began its flight-test programme 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 today and is preserved by the US Army Aviation Museum, at Fort Rucker, Alabama.
A.J.Pelletier "Bell Aircraft since 1935", 1992
A competitor in the AAH programme (won by the Hughes AH-64), the Bell 409 (AH-63) was derived from the Model 309 KingCobra. It retained the latter's two-blade main rotor and tail rotor, but had a completely redesigned fuselage, with a large ventral fin, stub wings and a horizontal tail plane on top of the dorsal fin. Two prototypes were built.
G.Apostolo "The Illustrated Encyclopedia of Helicopters", 1984