REDUCING THE COST IMPACT OF HELICOPTER INTERNAL NOISE CONTROL

A new generation of faster, more powerful helicopters is being introduced to meet the demands of a growing commercial market. Increased speed, payload, and range are the measures of increased productivity. For a passenger carrier, low internal noise is an important design feature. However, as the installed power grows, maintaining a low noise cabin environment requires an increasing fraction of aircraft empty weight. This limits payload and range, reducing productivity. A point of diminishing returns is being reached with traditional interior designs, where it is no longer feasible to control cabin noise economically. This paper explores new design strategies that are being used to improve the weight efficiency of soundproofing. In particular, isolation and damping treatments are discussed to show how significant noise reductions can be achieved with a relatively small weight penalty. The economic impact of soundproofing weight growth is analyzed by showing the reduction in payload required at a given gross weight to achieve a design internal noise level. An idealized "rubber" aircraft design with a gross weight range of 10,000 to 50,000 pounds is investigated. By incorporating weight reductions possible with new soundproofing design concepts, the economic benefits are demonstrated in terms of productivity and direct operating cost. It is concluded that as helicopter installed power grows, new noise control measures will be required to achieve acceptable cabin noise levels while maintaining aircraft productivity and economics.