It basically does this. If you are in level flight or a dive, you increase speed up to a certain max (level flight max is less than dive max). If you climb, you bleed off speed. To reach high balloons, you often need to build up more speed before you can climb high enough.

There's probably room for improvement, but it's already enough fun that I can play it for several minutes at a time.

Now I'm trying to decide if there's anything else of value to add - without making it too much of anything. I think I'm about finished now.