Sometimes, however, the task specifics suddenly become unusually severe, requiring a highly aggressive pilot response to exert precise control and regulation of the aircraft. In fact, the pilot may be very experienced with the aircraft and with the task in general.

The oscillations are akin to the benign 'learning experience' variety, but they are not associated with pilot maladaptation. Within this group, PIOs are distinguished from non-oscillatory APC events like divergences. The undesirable APC events that are the subject of this study appear in the right half of Figure 2-1. The pilot's input constitutes an open-loop forcing function, and the pilot's action and the resultant aircraft oscillation frequency are not directly conditioned by the aircraft's response. The outstanding example of this is 'stick pumping,' when the pilot applies an oscillatory input to the aircraft either to 'feel out' its effective dynamics or to counter large control-system nonlinearities (as a kind of 'dithering control'). The next class of favorable and benign interactions includes oscillations deliberately introduced by the pilot to generate a periodic forcing function. They are, at worst, short-term, mild PIOs that do not cause difficulties in controlling the aircraft. The other kind of closed-loop PVS oscillations that can be considered normal is a low-amplitude, damped oscillation, which is often referred to as a 'bobble.' Bobbles are associated with short-duration, excessive pilot gain. Because this is basically a learning experience, the ultimate cure is practice. The usual initial 'cure' is simply for the pilot to get out of the loop by releasing the inceptor and relying on the stability of the effective aircraft dynamics to handle the recovery. For example, 15 oscillation incidents occurred during testing of the SAAB J-35 in 1960 7 of these occurred when a pilot was flying the J-35 for the first time.įrom time to time in this learning process, the pilot's gain is momentarily high enough to create a closed-loop oscillation. These oscillations usually occur when the pilot is adapting to the aircraft dynamics and performing high-gain, precision-control tasks. The first, which arises from incomplete pilot adaptation to the effective aircraft dynamics, is very common and, fortunately, usually benign. Routine piloting includes all well-accomplished piloting tasks as well as two kinds of PVS oscillations. Routine piloting, which is the most prevalent form of aircraft-pilot interaction and which can involve both open-loop and closed-loop operations of the PVS, is shown on the far left of Figure 2-1 as the most benign (and desirable) class. The hierarchical structure shown in Figure 2-1 provides a taxonomy that is useful for classifying, discussing, and analyzing APC phenomena.Īt the highest level, aircraft-pilot interactions are divided into benign and undesirable. Unfavorable responses need to be understood in the context of the all-inclusive set of all PVS operations. The focus here is on unfavorable, closed-loop PVS responses, both oscillatory and divergent. They can result in favorable PVS responses that converge to provide the desired PVS performance, or they can result in undesired responses, either oscillatory or divergent. The interactions may result in motions that are desirable and 'benign' or 'undesirable.' For this study, the interactions of interest are primarily closed-loop in character.

In either case, the PVS operations involve 'aircraft-pilot interactions' that constitute an all-inclusive set. Near the opposite extreme is the 'open-loop' control system, in which the pilot operates as a forcing function, generating commands to the effective aircraft that are not directly related to the pilot's perception of aircraft motion. In this situation, the pilot's commands are more or less continuous and depend, at least partly, upon pilot-perceived 'errors' or differences between desired and actual aircraft responses. In the fully interactive extreme, the pilot is said to be 'in the loop,' and the PVS operates as a closed-loop feedback control system. From the pilot's perspective, aircraft-pilot interactions fall somewhere between two extremes-the pilot may be fully interactive, or the pilot may be effectively detached.

Tunneled air combat maneuvering