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30 Figure 1. Remote test unit. Figure 2. Snow catch pan. testing and described in SAE ARP 5485. Because it was neces- when the long axes of the collection plates are facing into the sary to acquire data with limited errors, a far more comprehen- wind direction. Wind direction was constantly monitored sive and stringent methodology was applied to the procedure and adjustments were made, but not, however, during any for this testing. The method establishes a rate of icing intensity 10-minute collection period. by catching the precipitation with a known-dimension pan over a specified period of time. This allows for a subsequent calcula- Precipitation Measurement Balance tion of the rate usually represented in g/dm2/h. The following sections describe in detail the test equipment A Sartorius EA series balance was employed for all testing. used in this snow-catching methodology. With a resolution of 0.2 g, this balance allowed for an accu- rate reading of precipitation accumulation. Figure 5 depicts Snow-Catch Pan the balance. A snow-catch pan, placed at a 10° inclination on the test stand, was used to collect and weigh precipitation. The posi- Methodology for Snow-Catch Collection tioning of the snow-catch pan on the test stand was such that Four snow-catch pans were used, numbered from one to the longer dimension axis of the pan is parallel with the four. Each pan was coated with 450 ml of standard Type IV longer dimension axis of the test plate. fluid. The wetted pans were weighed to the nearest 0.2 g. A typical serving pan commonly found in the restaurant All four pans were placed under precipitation for a period industry proved to be an adequate snow-catching pan. A of 10 minutes. The snow-catch pans were turned 180° at in- matching lid allowed full control of precipitation collection. tervals of two minutes to ensure that no snow build-up would Four snow-catch pans were employed at each site. occur at either end of the pan. Past research has proven that Figure 2 shows the pans that were used in testing. Figure 3 pan rotation ensures no loss of accumulation and hence gives is an accurate depiction of the dimensions of each pan. the true precipitation accumulation. At the end of a 10-minute period, all four pans were re- Test Stand weighed. The difference in weight before and after exposure to precipitation was used to compute the precipitation rate. Specially designed test stands were fabricated to form-fit the snow-catch pans and ensure that the pans would sit at a 10° inclination. This 10° inclination is representative of the Other Equipment leading edge of an aircraft wing. In testing locations where Other support equipment used in the field are described in ground surfaces were uneven, the test stands were manually Appendix A. leveled. There were no flanges or obstructions close to the edges of the plates that could interfere with the airflow over Sequence of Events the collection pans. Figure 4 depicts the test stand. The test stand was oriented facing into the predominant The following sections describe the timing and communi- wind direction. A test stand is defined as facing into the wind cation protocols as well as the sequence of testing protocols
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31 X1 = 450 Y = 293 Y1 = 245 mm X = 498 TOP 24 24 55 mm SIDE Figure 3. Dimensions of snow-catch pan. that were followed during the precipitation events at each Sequence of Testing airport. All testing followed the same sequence. This allowed for the collection of three measurements per hour. This sequence Timing and Communication was identical for both testing locations at each airport. The typical sequence for the first collection period is de- Timepieces were synchronized before testing commenced. tailed in Table 19. A detailed schedule of events was distributed before testing Ten minutes elapsed between the end of the first collection and an agreed upon start time established. and the start of the second collection. In order to achieve simultaneous collection of precipita- The typical sequence for the second collection period is de- tion, a well-organized system of communication was incor- tailed in Table 20. porated into all testing. Standard Motorola VHF radios were employed and used frequently in testing; sometimes cell phones were employed. Figure 4. Test stand. Figure 5. Precipitation measurement balance.