The formula to calculate Pitch Angle (α) is:

\[ \alpha = \sin^{-1} \left( \frac{350 \cdot Q}{\phi \cdot N \cdot D^3} \right) \]

Where:

• \(\alpha\) is the pitch angle (degrees).
• \(Q\) is the airflow (cfm).
• \(N\) is the speed of the impeller (rpm).
• \(D\) is the diameter of the impeller (in.).
• \(\phi\) is the flow coefficient (0.01 to 0.80).