"Morgans" wrote in message ...

Some aerobatic rag and tub aircraft have a air fill valve, and a pressure gauge where it can be checked at every
pre-flight. It is then filled with some gas, like nitrogen or argon. If the pressure is lower, or at atmospheric
pressure, there is a crack somewhere, meaning that it might not be structurally sound, especially for high G loads.



Some helicopters also pressurize the rotor blades and monitor real time for pressure drop...