The q Derivatives (CZq, CmJ
These derivatives represent the aerodynamic effects that accompany rotation of the airplane about a spanwise axis through the CG while ax remains zero. An example of this kind of motion was treated in Sec. 3.1 (i. e., the steady pull-up). Figure 5.2b shows the general case in which the flight path is arbitrary. This should be contrasted with the situation illustrated in Fig. 5.2a, where q = 0 while ax is changing.
Both the wing and the tail are affected by the rotation, although, when the airplane has a tail, the wing contribution to CZq and Cmq is often negligible in comparison with that of the tail. In such cases it is common practice to increase the tail effect by an arbitrary amount, of the order of 10%, to allow for the wing and body.