Can you please tell me where the collective pitch angle is measured? Is it at the root, at 75% blade span, at the tip, or somewhere else? I looked for this in the FAST manual, but was unable to find it.
In FAST, the blade-pitch angle is defined relative to zero twist. So, for an undeflected blade, the angle between the rotor plane and the local chord is simply equal to the blade pitch plus the local twist.
I hope that helps.