What is the primary action required to make an airship rise?

The primary action required to make an airship rise is to release air from the ballonets. The airship is designed to be buoyant due to the lighter-than-air gas, typically helium or hydrogen, that it contains. The ballonets are internal bags within the envelope of the airship that help maintain its shape and control the pressure within the envelope.

When air is released from the ballonets, it decreases the overall weight of the airship by reducing the amount of heavy, denser air contained within these compartments. This change in buoyancy enables the airship to ascend into the atmosphere, as the lifting gas becomes more effective at raising the total weight of the airship compared to the weight of the air it displaces.

The other options do not directly lead to the rising of an airship. Pumping air into the ballonets would actually increase the weight of the airship and potentially decrease its buoyancy, making it more difficult to rise. Increasing the weight of the airship would counteract any rising action, leading to descent instead. Reducing the temperature of the gas could affect buoyancy, but it is not a primary action related to achieving ascent in standard operational scenarios. Thus, releasing air from the ballonets is the correct and