© 2022, American Institute of Aeronautics and Astronautics Inc, AIAA., All rights reserved.Today, survival depends on seconds in air combats. The delay in communication of unmanned aerial vehicles with pilots in the ground station is the most important shortcoming in terms of survivability. One solution to this shortcoming is to develop autonomous operation methods for all possible types of missions that onboard computers will process the information collected by the aircraft’s sensors and to take countermeasures against the threats without human input. With this regard, unmanned combat aerial vehicles (UCAVs) will take a more active role in air combat and contribute to air superiority in the future. In this study, various combat scenarios are generated and trajectory optimization solutions are obtained to perform autonomous evasive maneuvers for UCAVs against air-to-air missiles without human input. To accomplish this objective, an engagement geometry that includes details of a UCAV and a missile is introduced. This geometry is constructed by employing factors such as line-of-sight (LOS), velocity vectors, angle of attack, flight path angle, and heading angle, which expresses the relative positions of the missile and the UCAV in 3-dimensional space. The UCAV and missile are represented as point-mass models using the given geometry. Along with point-mass models, the commonly used Proportional Navigation (PN) method for missiles guidance is implemented. An energy formulation is incorporated into the model to calculate the instantaneous energy consumption of the missile. An optimization algorithm is developed so that the UCAV can automatically command the angle of attack and the bank angle to maximize the instantaneous energy consumption of the missile at every time step using the generated model. Optimal trajectories for different engagement scenarios are automatically generated by the optimization algorithm for variable initial conditions such as the missile's heading angle, altitude, and distance from the UCAV. Finally, the UCAV performed successful evasive maneuvers to evade the missile in all of its medium/long-range engagements and one of the short-range engagements which demonstrates that adaptive maneuvers suitable for real combat situations are produced for different initial condition sets.