Good. Nearly there. More help needed.
Thought that the ballonets were Helium filled. Air explains a lot.
Still a bit stuck though. When you say 'valve Helium' do you mean dump it or allow more into the balloon/tank (what do you call the bag containing Helium as opposed to the bag containing air - the ballonet?).
Whichever, I still think that I'm missing something about Helium or expansion of gases with reducing pressure.
Carbon structures? Yes, nastily conductive with a glue that quite likes to burn. Carbon yachts are a special interest of mine. One had an internal fire caused by a 12V battery lead shorting. On the other hand, I thought that Boeing had developed a (Copper-based) 'Faraday cage' for the 787 wings etc?
Moved off the Guinness on to a rather nice red.