Graham Warwick/WASHINGTON DC
GKN Westland hopes to launch an advanced compound helicopter (ACH) technology demonstration programme by the end of the year. The aircraft, based on a Westland Lynx, will be equipped with wings and modified Rolls-Royce Turboméca RTM322 engines to demonstrate lift and thrust compounding.
A compound helicopter uses a wing to offload the rotor and allow higher forward speeds.
Research into the concept is being supported with UK Ministry of Defence funding. Speaking at the American Helicopter Society convention in Washington DC on 22 May, David Humpherson, head of Westland Helicopters' advanced projects department, said that getting the demonstrator programme launched is "-proving to be far more challenging than originally anticipated. Despite this, we look forward to getting under way by the turn of the year."
Target requirements for the ACH include speeds of around 250kt (460km/h), operating altitudes of over 20,000ft (6,100m), lift-to-drag improvements of 25-50%, propulsive efficiency increases of up to 50%, payload/range improvements of 20% and life-cycle cost reductions of 10-20%.
The demonstrator is expected to be about 50% faster than a standard Lynx, he said.
The helicopter will be fitted with wings equipped with trailing-edge flaps to vary lift compounding. A moving tailplane will trim the pitching moment created by the flaps and a trimming rudder will offload the tail rotor at high speed. The main rotor will use Westland's BERP blade, which complements the compound concept by retaining its efficiency to higher speeds, Humpherson said.
To provide the higher power required, the demonstrator will have its R-R Gem engines replaced with two RTM322 turboshafts driving an uprated gearbox developed for the defunct Westland 30-200 helicopter. Excess power will be converted to jet thrust by variable-area nozzles. Adjusting throttle setting and nozzle area will provide a range of thrust and shaft power combinations to vary thrust compounding, he said.
According to Humpherson, Westland is studying the concept of a family of helicopters, with conventional, lift-compounded and thrust-compounded variants providing expanded capabilities. High speed/low altitude missions favour lift compounding, he said, while roles which combine low speed/hover with high dash speed favour thrust compounding.