Modem large cargo planes have long wings, and their engines are barely above the ground. If the gradient is too big, the ground may scrape the engines and wings.
现代大型运输机机翼翼展长，发动机离地面较低，如果低高度坡度过大，可能擦翼尖或发动机。
2
The magnetism gradient test is a highly effective and high accuracy method which used to detect the depth of ferromagnetic obstacle under ground, and it is very suitable to detect the length of pile.