sentences:  The engine and fan installation incorporates a freely-moving turbine, which necessitates constant-speed control over the fan along with the use of reduction gear to roughly half the 6,000 rpm output of the engine to achieve a fan speed of 3,090 rpm; both of these were designed by British supplier Dowty Group.The constant speed of the five-bladed fan enables the use of a relatively simple blade profile.Various noise reduction measures were implemented, including the use of Hoffmann-sourced plastic-covered wooden blades and the adoption of a re-designed fan that used five blades instead of seven.