Safety Analysis of an Airship Which Loses Lifting Gas from the Hull

This study investigates the physical phenomena that affect a high-altitude airship in the presence of lifting gas losses from the hull. General atmospheric thermodynamics and basic physical principles are adopted to describe the behavior of an airship with envelope failures that generate buoyant gas dispersion or depressurisation phenomena. Overpressure that could grant to maintain some controllability during a large part of the descent is assessed by mean of the thermodynamic model of the envelope in the presence of gas losses. Optimisation of the inflation parameters is provided and the conditions for avoiding dangerous crashes on the ground and the potential recovery of a damaged vehicle, people and its payload. In particular, the requirements for a slow depressurisation is computed by the equilibrium with the atmosphere and then how can it be possible to sustain controlled navigation are determined. A key factor for security relates directly to the capability of preserving some airship balloon overpressure for the longest time possible. This condition can extend much the range of control. Complete forfeit conditions will be determined to demonstrate that airship cannot be anymore controllable below 20% of the initial altitude at which the failure has started.

In some cases, specific manoeuvres could allow configuring the deflated balloon as a parachute, if coupled with adequate safety systems. This research about safety conditions will also be useful for designing safety systems. A general guideline for safety systems has been defined showing that airship if well created and well governed in emergency conditions will be much safer than any other aerial vehicle.