The US Army is extending the Boeing Sikorsky RAH-66 Comanche's operational range and endurance with further refinements to the scout helicopter's design weight and main rotor.
"We're making changes to the aircraft to increase the fuel load, really because the army wants more range than they said eight years ago," says Arthur Linden, director of the Boeing Sikorsky joint programme office. The net result is a 25% increase in the helicopter's endurance, to a maximum of 2.6h.
RAH-66 internal fuel tank capacity is unchanged, but mission fuel weight has been increased by 180kg (400lb) to 870kg. "The mission never required that we fully fill up the tank and we designed it with a little bit of growth," says Linden.
To accommodate the additional fuel, maximum take of weight (MTOW) has been increased to 5,850kg, a growth of 370kg. According to the US Army, on internal fuel the Comanche has an operational radius of 275km (150nm).
"The aircraft could always take that weight," says Daryl Harrison, US Army deputy programme manager, noting that the first prototype is operating at over 5,900kg MTOW. He adds that the need for more fuel has been driven by changes in the RAH-66's primary mission which calls for longer cruise distances and hover times.
Boeing Sikorsky is also working on a preliminary design to install up to two auxiliary 425 litre (112 USgal) fuel tanks in the RAH-66's twin internal weapon bays. One extra tank would extend the helicopter's radius to 380km and with two this increases to 480km. There is provision in the design to externally carry two 870 litre or 1,700 litre self-deployment tanks.
The US Army at the same time has increased the RAH-66's design target empty weight to 4,060kg and raised its threshold not-to-exceed weight to 4,220kg. This has mainly been to accommodate "minor changes" in components and reinforcement of the helicopter's five-blade main rotor, says Harrison.
Design changes have centred on a 0.3m (1ft) increase to the 12.2m diameter main rotor and 0.15m blade extension. The blade chord is unchanged. The larger blades will be fitted with anhedral tips to reduce acoustics and are to be incorporated into the third prototype, scheduled to fly in 2003.
Source: Flight International