Hot Air Balloon Flight Control Panel: PID Altitude Autopilot (2D)

This 2D companion turns the 3D hot-air-balloon scene's implicit "flight control panel" into an actual one: a real PID controller reads altitude error and drives a single burner/vent actuator against ideal-gas buoyancy physics — heated internal air displacing cooler ambient air, opposed by weight and quadratic drag — while you retune proportional, integral and derivative gains on a live strip chart and watch the classic control-theory failure modes (steady-state offset with Kp alone, slow oscillation from too much Ki, sluggish response from too much Kd) appear for real, not as a canned animation.