Guy Norris/LOS ANGELES
McDONNELL DOUGLAS Helicopter Systems (MDHS) is to phase out production of the MD900 Explorer in 1997 and replace it with a more advanced version, the MD902.
The US company is upgrading the Explorer largely in response to competition from Bell, with its 427, and Eurocopter, with its EC135. "We're making sure that the 900 stays ahead competitively," says MDHS. The eight-seater 902, will have a slightly, more powerful engine and design improvements, giving better range, payload and endurance.
The 902 will achieve air speeds of "up to 137kt [253km/h] at sea level", a range of 580km (310nm), or 7% further, and an endurance of 3.34h - or roughly an additional 10min. The helicopter will also have a maximum take-off weight of almost 2,840kg, including 110kg extra payload capability.
The helicopter will be certificated to the same US FAR 27 rules as the original MD 900, despite the even higher operating weight capabilities of the 902. "We got an exemption for the Explorer and the Federal Aviation Administration has also agreed to that this time," says MDHS. Operationally, the MD902 will be certified as Category A, which governs tighter operational restrictions such as one-engine-inoperative take-off, and landings at sites such as city-centre roof top helipads.
The helicopter will be fitted with two Pratt & Whitney Canada PW206Es in place of the 470kW (630shp) PW206Bs. Although normally rated at roughly the same power, the 206E has a one-engine- inoperative maximum rating, of almost 500kW compared with 460kW at present. "That means you can fly pretty well on one engine," says the company. The optional Turbom‚ca TM319-2 Arrius engine will also be available.
The engine air inlets will be enlarged to provide more airflow to the turbo-shafts. The inlet screen for the NOTAR (no-tail rotor anti-torque control system) is also being redesigned to create a more uniform flow pattern into the NOTAR fan. "The current design made one part of the fan work harder," says MDHS. The shape of the fan shroud is being redesigned to improve efficiency.
Another change reflecting the increased power to the rotor includes a more powerful stabiliser control system. A stronger actuator will be built in to give the stabiliser fin a larger degree of travel. "The fins will take over more of the anti-torque loads in forward flight at higher speeds, and will therefore off-load the NOTAR and improve handling," says the company.
Source: Flight International
