The US Army is seeking to reduce the Boeing-Sikorsky RAH-66 Comanche's empty weight as full-scale engineering and manufacturing development (EMD) progresses, and structural design continues to be refined.


Detailed design is underway for the 13 pre-production helicopters planned for EMD. The first is scheduled to fly in April 2004. But army RAH-66 deputy programme manager Darrell Harrison says "Each IPT [integrated product team] has made its submission and come up with a total weight that's not going to work."

The empty weight is fluctuating at just under 4,300kg (9,500lb). The target is around 4,220kg. There is a 4,274kg not-to-exceed threshold weight for the machine to meet a 152.5m (500ft) a minute vertical climb rate at 1,220m and 35°C (95°F). "We want to be below that because history says weight will grow," adds Harrison.

An Army team has been established to work with the IPTs to identify potential weight reductions. "We would like to get a couple of hundred pounds out of the aircraft. Some material changes have been proposed," Harrison reveals.

The weight growth is the result of the heavier than expected forward structure, which is needed to accommodate mission equipment and changes to the rotor and drive system. The latter includes a 0.3m anhedral tip extension to the main rotor and 25mm added to the chord to bolster performance.

Boeing Sikorsky plans to start test flying a modified tail configuration on one of the two pre-EMD prototypes by the end of this year. The vertical stabiliser has been reduced in size to eliminate buffeting and two endplates are being added to the horizontal tail.

Other planned changes to the prototype include fitting the first improved LHTEC T800-801turboshaft, which offers 17% more installed power. The RAH-66's powerplant has been uprated to accommodate a repackaged version of the Lockheed Martin/ Northrop Grumman Longbow millimetre-wave fire control radar.

Aerodynamic testing of the radar's new mast-mounted housing has started, using the second prototype Comanche. The army has decided to abandon the doughnut shaped-dome employed by the Boeing AH-64D Apache Longbow in favour of a stealthier cone-like arrangement.

Source: Flight International