A comparison of time-optimal interception trajectories for the F-8 and F-15: final report

Original publisher: Atlanta, GA : Georgia Institute of Technology, School of Aerospace Engineering, [1990] OCLC Number: (OCoLC)67614090 Excerpt: ... analysis.It canalsobeseenthattheF-15completestheinterceptin nearlyhalfthetimeit takesthe F-8. Thelift andbankangleprofiles areshownin Figs. 13and 14. Notethat bothaircraft bank 180degreesin orderto initiatedescent.In theF-15 simulation, thesuddendecreasein lift at 115 secondsis due to the approachingoptimal cruisevelocity, wherethe throttle control in ( 45 ) is initiated. Thischangestheenergyratetermin ( 40 ), andconsequentlytheverticallift calculatedin ( 42 ). In Figs. 15and16thethrusthistoriesfor eachaircraftaregiven. Thetimeconstant'cE here was set to 6 seconds. Descent initiation is evident by the sharp decrease in thrust at 150 and 350 seconds for the F-15 and F-8 respectively. In the F-15 simulation, at 115 seconds the proportional thrust controller throttles back the engines just prior to the aircraft obtaining its pseudo-cruise energy level. The ground tracks for Case 4 are given in Figs. 17 and 18. This case is a close in intercept which has the target moving at constant altitude, velocity and heading 180 degrees in the opposite direction. This case illustrates a combined initial hard turn and climb ( yo-yo maneuver ) followed by a descent under near tail chase conditions. The pursuer's initial altitude is identical to that of the target and the velocity is above the corner velocity for that altitude. Note that the downrange intercept distance is considerably less for the F-15 aircraft. Figures 19 and 20 give the altitude and commanded altitude time histories. Both aircraft perform a high speed yo-yo maneuver in order to trade speed for increased turning performance. It is interesting to note that the time to complete the hard turn is nearly identical for both aircraft, 10 seconds. The reason for the large altitude command is due to the large initial heading errors. The jump in commanded altitude is at th...