Study on visibility in falling and blowing snow of civil aircraft APU inlet system

According to the requirements of CAAC, FAA and EASA on falling and blowing snow of Auxiliary Power Unit inlet system, the environmental conditions of compliance test were sorted out. The relationships among visibility, water content of falling snow and snow mass flux of blowing snow were studied. The research shows that: 1) FAA and EASA have basically the equivalent requirements for snowfall intensity, wet snow temperature and blowing snow conditions. Compared with falling snow requirements, the requirements of blowing snow test is more briefly; 2) Based on the NCEP visibility estimation method, under the same visibility, the water content of different snow types is significantly different, and snowflakes are more like ly to cause visibility reduction. The water content value corresponding to 0.4 km suggested by FAA is basically consistent with the snow water content value estimated by NCEP; 3) The height of typical civil aircraft APU inlet system above ground is about 5.5 m. Combining with the extreme value of snow flux given in MIL-STD-810G and GJB1172.6-91, 4.5 g/(m2·s) can be used as the test mass flux for blowing snow test. The visibility under this mass flux is about 218.8 m, which is equivalent to the intensity of heavy snow.