. Horizontal engagement

Let us put this simulation to work and build two test cases. The first scenario is a coaltitude engagement at 10 km altitude. Both target and shooter fly at constant speed. The initial situation is given in Fig. 9.48. We study the sensitivity of the engagement to the navigation gain N using the values 2,3, and 4 and comparing the flight time, Mach number, and miss distance at intercept.

Figure 9.49 depicts the engagement for the three cases. We conclude that the higher the navigation gain the tighter the engagement and the smaller the miss

distance. The missile with N— 2 fails completely to make the intercept. The details of the simulation can be found on the CAD AC CD. The INPUT. ASC file contains the parameters of the AIM5 missile like launch mass, reference area, autopilot parameters, initial conditions, etc., and aerodynamic tables and thrust character­istics are given in Modules A1 and A2.

Table 9.1 summarizes the engagement conditions. Based on this study we would select N = 4, wondering if we should not have increased the gain even further. How­ever, we must realize that the simulation is an idealized model of the engagement and does not include any noise sources. The effect of these real-world conditions requires a compromise between accuracy and stability. Higher gains lead to tighter but also less stable intercepts. The navigation gain of four is a good compromise.

To investigate further the reason for the failed run with N — 2, we plot the sideslip angle and the lateral acceleration for the three cases in Fig. 9.50. Note that higher navigation gains demand more lateral acceleration earlier, making the intercept more benign. With N — 2 the missile is so sluggish that it misses the target com­pletely and saturates its lateral channel after flyby.