Section 5
Page 44
5.3 Windage Forces The windage drag is incorporated into the force balance by adding to the aerodynamic drag a windage drag determined from equation [32]. Each of the (n) windage elements is ascribed its own dynamic head (qn) based on an apparent wind velocity appropriate to its centre of effort height (ZCE), reference area (A) and drag coefficient (Cd). n
DWINDAGE qn AREF Cd n
[32]
1
The windage drag for each element is calculated at apparent wind angles of 0 and 90 degrees and a shape factor is used to calculate the drag coefficient at intermediate angles. The calculation of Centre of Effort Height (ZCE), Drag Coefficient (Cd0) and reference area (AREF) at apparent wind angles of 0 and 90 degrees is shown in the table below, the values for 180 degrees are the same as those for the headwind case.