Definition of parameters

Wind & Water Structural Analysis
5

Dear Kumara,

FAST uses the following definitions:

  • The structural twist is the angle (about minus z) from the blade coordinate system to the local principal elastic axes of bending at a given cross section for the undeflected blade.
  • The aerodynamic twist is the angle (about minus z) from the blade coordinate system to the chord at a given cross section for the undeflected blade.
  • The blade-pitch angle is the angle (about minus z) from the hub to the blade coordinate system and is constant along the blade.

So, the sum of pitch plus twist is the angle (about minus z) from the rotor plane to the appropriate local axis (principle or chord) for the undeflected blade.

I hope that helps.