What does the term "free turbine" mean in the context of the aircraft's engine?

The term "free turbine" refers to a specific configuration in gas turbine engines, particularly where the power turbine is not directly connected to the compressor. In this context, air flow from the compressor does drive the power turbine, but they are not physically linked as they are in some other engine designs, such as a traditional geared turbine engine. This allows the power turbine to operate independently of the compressor's rotational speed, leading to several operational advantages.

This design enables the engine to produce power more efficiently across a range of speeds and conditions, as the power turbine can optimize its performance without being constrained by the compressor speed. The independent operation allows for greater flexibility in engine management, particularly during different flight regimes or when the aircraft requires varying amounts of thrust.

The other options do not accurately describe the characteristics and function of a free turbine system. For example, claiming that air flow from the compressor drives the power turbine while they are physically connected contradicts the definition of a free turbine. Additionally, options suggesting measurements of free air temperature or airflow from the lower air inlet cowling do not pertain to the mechanical and operational principles of the free turbine concept.