# How to approximate the drag for rectangular vertical flat panel placed along the wind and inclined?

So on the top is the view from the top, below it is the side view.

If the angle is zero it is similar to simple flat airfoil. So I calculated the Cl and Cd in xfoil and got the Cl = 0 and Cd = 0.02398 :

It is for 30 cm length in 5 m/s stream

Cl will be directed to the viewer, perpendicular to the panel.

Was it a correct application of xfoil ?

How to approximate the Cd also for non-zero angles like 1 ~ 15 ?

Will it be "almost the same" so the difference can be ignored ?

At non zero angle the plane of the plate will continue to be parallel to the wind but its geometry becomes more complex, similar to swept wing.

• I'd simply decompose $V_{wind}$ in its two components parallel and perpendicular to the plate and calculate the two relevant $C_d$s Mar 25, 2023 at 15:06
• @sophit Do you know some book or article describing this decomposition approach ? Mar 25, 2023 at 22:29
• ? This is basic phisics/trigonometry: your velocity can be decomposed as the sum of two mutually perpendicular velocities, one parallel to the length of the plate and with a value $V_{wind}cos(\alpha)$ and one perpendicular to it with value $V_{wind}sin(\alpha)$. Each one of these two speed generates a relevant drag term, one parallel and one perpendicular, which you can afterward combine in one single term. Mar 26, 2023 at 7:15
• Related question and answers here. Mar 27, 2023 at 4:15
• @sophit I use V when I calculate the Re to get the Cd and when I calculate the q ( dynamic pressure ). Should I decompose V in both cases ? Apr 4, 2023 at 22:26