Snow Plane Sound Level Measurements

The purpose of this study of snow plane sound levels is to provide quantitative information on snow plane sound emissions. The sound emissions of snow planes in the national park setting have been controversial and this research may provide decision makers and designers with some objective data for regulating sound levels. A snow plane is an over snow vehicle consisting of a passenger cabin supported on skis and driven by a light aircraft engine and propeller. In this regard, it is similar to the air-boats used on swamps and marshes.

The pass-by sound levels of a variety of snow planes were measured at normal operating speeds. The pass-by testing included eight different snow planes. Two of these were equipped with dual muffler systems with balance tubes, four planes were equipped with dual muffler systems, and two of the snow planes had no muffling of the exhaust. Two of the snow planes were equipped with liquid cooled automotive engines, while the other six had horizontally opposed aircraft engines of four or six cylinders. All testing was conducted on the same day in the same location with the same terrain and background conditions.

The results of sound levels show that the dominant factor influencing sound levels was the speed of the blade tip. The sound level in dB(A) and the blade tip mach number follow a linear trend with an R² value of 0.8724. This trend suggests that snow planes can be made quieter by reducing the diameter of the prop while increasing pitch and/or the number of blades to retain similar thrust characteristics.