Which type of DC generator is NOT typically used as an airplane generator?

The type of DC generator that is not typically used as an airplane generator is the series wound generator. This is primarily due to the operational characteristics and limitations of a series wound configuration. In a series wound generator, the field winding is connected in series with the armature winding. This means that the field current, and thus the magnetic field strength, varies directly with the load current.

In aviation applications, the electrical load can fluctuate significantly, which could lead to instability in output voltage and make it challenging to maintain a consistent power supply. Since the series wound generator's output is strongly dependent on load, it becomes difficult to control, making it less reliable for the critical power needs of an aircraft.

In contrast, shunt wound and compound wound generators provide better voltage regulation and stability under varying load conditions, which is essential for aviation standards. Permanent magnet generators also excel in reliability and efficiency for the smaller power requirements typically used in aircraft systems. Thus, the operational characteristics of series wound generators make them unsuitable for airplane applications.