Aircraft DC motors
DC electric motors are the inverse of the DC generator. They comprise armature field windings and commutator/brushgear and therefore are similarly self excited. The main elements of importance in relation to motors are the speed and torque characteristics, i.e. the variations of speed and torque with load respectively. Motors are categorised by their field winding configuration (as for generators) and typical examples are series-wound electric motors, shunt-wound electric motors and compound-wound (a mixture of series- and shunt-wound). Each of these kinds of motor offers differing performance characteristics that could possibly be matched to the application which is why they are intended.
A specialized type of series motor may be the split-field motor where two groups of series windings of opposite polarity are each used in series while using armature but parallel with each other.