Characteristic Lateral-Directional Transients

This chapter discusses the natural transient motions of the aircraft, which are the unforced motions starting from initial conditions. The chapter describes the factors influencing their character and variety. The classical lateral-directional dynamics of conventional subsonic airplanes and some of the peculiar problems of the super-performance aircraft of the day are also discussed in the chapter. The rolling mode characterizes the way the roll rate builds up to a balance between applied rolling moments and roll damping. The buildup is usually very rapid, corresponding to the large negative root. The Dutch roll mode corresponds to a coupled banking, side slipping, and yawing motion. It is often noticeably oscillatory, and when lightly damped, it is annoying for pilots and uncomfortable for passengers. The spiral mode can be seen as the tendency of the airplane to recover slowly, or diverge slowly, from an initial bank. If the characteristic is divergence, an ever-steepening spiral occurs.