I noticed the note:
Warning: If using these modes, be sure your model is initialized on a flat surface, not tilted to any side. Do not tilt the model for more than 5 seconds after initialization. It can be initialized in normal or inverted position.

Does this mean that you would have to hold the tail on a taildragger level during power up? Or just keep the wings level?

Such angle as are present in taildragger models is not a problem, but bigger could be.
So just initialize the model in normal position and fly.

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Spirit System developer