What is the definition of pressure height in relation to airships?

Pressure height refers to the specific altitude in relation to the atmosphere's pressure where certain conditions related to airship operation are reached. In this context, it is defined as the height at which the lift gas within the airship's ballonets is reduced such that they become empty or nearly so. This condition creates a specific pressure differential that is essential for managing the airship's ascent and maintaining control.

When pressure height is achieved, the airship may become more sensitive to changes in weight and buoyancy, making it critical for operators to understand this parameter in managing flight safety and performance. It's crucial to monitor the state of the ballonets during flight, as ensuring they are empty can help the airship ascend effectively, while being too full may affect buoyancy and stability.

Thus, achieving pressure height involves a careful balance of atmospheric conditions, the airship's internal pressures, and the state of the ballonets, allowing for safe ascent and maneuvering within the desired operational envelope.