Ideally, it is assumed that a sinusoidal distribution of magnetic flux in the air-gap. The resultant radial distribution of air-gap flux density B versus θa is ai shown inFig.14-2(a),where θa is the spatial angle around the rotor periphery. In practice, the air-gap flux-density of practical salient-pole generator can be made to approximate a sinusoidal distribution by properly shaping the pole faces.