(3)D与B成0角 Dy ucos0 v,=osin0 R= mo, no sinθ qB qB i 2元R 2元m T= 01 9B 螺距h:h=D,T=Dcos0,T 2πmDc0s0 9B RqB m h T T    ==  =    2 cos cos / / 与B成  角   ( 3 ) //  ⊥   B •  qR //  ⊥   B // = cos   ⊥ = sin  qB m R  ⊥ = qB m   = sin qB R m T  =  = ⊥ 2 2 螺距 h ： h