"Axial Fan" in the performance curve impeller speed and blade mounting angle constant measured. Its shape is p-qv characteristic curve appears saddle shape in a small flow rate region, in a large flow area is very steep drop in when qv = 0, p maximum; Pa-qv curve, when qv = 0, Pa maximum with the increase in Pa qv reduced axial fan and therefore is not allowed when the air load start, unless variable pitch; η-qv curve, the high zone is quite narrow, maximum efficiency point near the unstable boundary point c.