Design
The balloon should fly in a naturally dynamic fashion, responding to burner & vent control inputs and wind. Terrain objects should be rendered at various levels of detail so that polygons may be efficiently spent on nearby objects. Balloon behavior while in contact with the ground will be treated minimally in this project.

modeling forces

lift

We suppose that as a result of various control inputs, the balloon system as a whole has some potential energy. This determines the altitude at which it stable, and the balloon seeks that altitude. Complexity of lifting behavior is removed to modelling influences on the potential energy.

drag

Drag is modeled as proportional with the square of velocity relative to the wind. The x, y, and z components are decoupled.

dynamic flight

Given models of the forces acting on the ballon, the resulting motion of the balloon is derived by simple mechanics. The force models are used to calculate accelerations in x, y, and z, directions, using the proportional relationship of force and acceleration for constant mass.

Current vector position and vector velocity are maintained as properties of the balloon group node. The last wall-clock time is a property of the node and is compared with the current time to determine the elapsed time for each iteration of the script. The last time is updated on each iteration. The passage of time is measured by the clock so that the flight, if not the rendering, is protected from changes in system load.

Modeled accelerations are integrated once to calculate the change in flight velocity, and the velocity property is updated.

Modeled accelerations are integrated twice to calculate the change in balloon position. The position property is updated, effecting balloon movement in the universe.

Control inputs

Generally, the burner and vent controls are modeled as to their influence on the balloon's potential energy. This is where we add complexity to the balloon flight model.

In the current model the burner produces constant power when on, the vent dumps constant power when open, and there is continuous constant loss to the atmosphere.

As limiting conditions, the vent is set closed when the balloon's potential energy decreases to a level below it's ground level potential energy, and when the balloon is in contact with terrain.

The most needed improvements to promote realistic control are in modeling limiting conditions on the input by way of limiting the magnitude of control inputs, or simulating instability for large inputs.


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Last update: October 14, 1996 by DS