Things are starting to move
Yesterday I got the balloon and crow behavior classes implemented. The crow was fairly simple, but the balloon took more effort to get right than I had expected.
In my first attempt, the balloon would instantly rise when the flame was on, but that wasn't very realistic. The flame heats the air in the balloon, which will increase lift, which in turn will get the balloon going up. It is kind of a slow process and my current implementation simulates it pretty good. It took some fiddling to find the right balance between the correct physical behavior and not causing too much player frustration. :-) I will probably have to do more finetuning once everything is implemented, but this is a good start.
I decided that (as is the case with a real hot air balloon) no directional control will be implemented. Instead, there will be windy layers in the trench, so the player will have to raise and lower the balloon into these layers if the balloon needs to be nudged in a certain direction. These layers will also pose a challenge as they may push the balloon into a wall. Besides the challenges of avoiding crows, limited fuel supply and catching parachuted fuel, having to work with these windy layers will add a puzzle-like aspect to the game that should make it more fun to play.