What is the primary voltage conversion done by a rotary inverter?

The primary function of a rotary inverter is to convert direct current (DC) to alternating current (AC). In the context of aviation and electrical systems, rotary inverters are often used to provide the necessary AC power at specific voltages and frequencies for various aircraft systems. The correct answer indicates that the rotary inverter effectively transforms DC power into 115 volts AC at a frequency of 400 cycles (Hz), which aligns with the operational requirements of many onboard electrical systems.

This capability is essential as aircraft systems typically require AC power to function, particularly at specific voltage and frequency levels for equipment to operate efficiently and safely. By providing 115 volts AC at 400 Hz, the rotary inverter fulfills the essential role of supporting the aircraft's various electrical loads while ensuring compatibility with the standards used in aviation.

In contrast, the other options describe either conversions that are not applicable to the primary function of rotary inverters or involve incorrect voltage levels or power types. The functionality of converting from AC to DC or altering DC voltages not specific to 115 volts at 400 Hz does not align with the intended operation of rotary inverters in aircraft systems.