What are the two types of oxygen systems commonly found in unpressurized aircraft?

The two types of oxygen systems commonly found in unpressurized aircraft are continuous-flow and pressure-demand types.

Continuous-flow systems deliver a constant flow of oxygen to the user, typically through a mask or nasal cannula. This type is effective at lower altitudes where the need for supplemental oxygen is less critical, and it is simple in design and operation. It operates by releasing oxygen continuously as long as the system is activated, making it readily available for the user.

Pressure-demand systems, on the other hand, are designed to provide oxygen only under certain conditions, such as when the aircraft is at higher altitudes where the atmosphere becomes thinner. This system senses the user's inhalation and delivers oxygen on demand, which helps conserve the supply and ensures that the user receives adequate oxygen even under low-pressure conditions.

Understanding these two types of oxygen systems is crucial for aircraft operation and safety, especially in unpressurized environments where pilots and passengers may be exposed to oxygen deprivation at higher altitudes. The other options do not align with the requirements of aircraft oxygen systems and thus are not applicable in this context.