I love airships. I often like to do research on the old designs from the 20s and 30s. Trying to figure out how they work and how they're built etc.
Lately I've been working on trying to calculate how much ballast would have to be dropped to change the altitude by a defined amount. Let me give an example.
I have an airship that is floating happily along at a steady 500ft altitude. The airship, and everything on it weighs exactly 10,000lbs. There's mountains or something ahead so they decided to climb to 7,000ft. To do that they need to become lighter which means dropping ballast. How would I go about calculating the amount of weight I need to loose to become neutrally buoyant at 7,000ft.
I get pretty confused because obviously the air pressure will only be about 79kPa at the new altitude. Which means my helium will expand. But how will that affect the amount of lift it generates? As 1 cubic meter of helium will create less lift, but its expanded so I have more cubic meters. Also I know that the temperature of the air will be different at the new altitude and that would affect things.
I hope my question is clear. And thanks in advance for the help!