|Budget Amount *help
¥2,800,000 (Direct Cost: ¥2,800,000)
Fiscal Year 2001: ¥1,100,000 (Direct Cost: ¥1,100,000)
Fiscal Year 2000: ¥1,700,000 (Direct Cost: ¥1,700,000)
Hovercrafts of middle or small sizes are going to be used for general purposes including first-aid transportation in a disaster area. Noise is one of serious problems to be solved. Especially, a craft operated for patrol of rivers and lakes causes relatively big noise in a calm circumstance. From the point of view of working environment of operators noise reduction is one of necessary items.
Noise measurements were carried out in open field using a sound level meter of high performance for two different hovercrafts. A measuring desk was made for speedy data processing in field. Video and digital cameras were used to record situations of measurements of high-speed runs of hovercrafts on water surface. Main result thus obtained is as follows. First, maximum noise level is over 110 dB. Second, the noise is composed of that of propeller, lift fun, engines, exhausts, vibration of skirt and other. Third, among them noise from the propeller is the most serious by the reason of its high level, its numbers of higher harmonics and complicated mechanism of noise source.
As a basic research the main effort of work was concentrated to analyze noise from propeller. Test propellers were 6 propellers for large airplane model of 5 different sizes. A propeller stand was made to measure thrust for different rpm. Main result is as follows. First, thrust is proportional to the propeller disk itself instead of its square. Second, noise level is nearly proportional to the disk loading. Third, a combination of propellers of large and small diameters can reduce noise at a constant thrust. Fourth, thrust and noise do not show significant difference for different angle of combination. The authors are now preparing publication of the result.