I've managed to make the Hawk more stable by changing quite a few things, such as the wings and tail. The wings were moved toward the rear and their design has been changed. The tail should have less drag than the old one, and I also moved the horizontal stabilizers to the tips of the vertical ones in order to keep them out of the exhaust of the engines and to hopefully keep them in less turbulent air. The inlets have been made smaller and more aerodynamic. This way the aircraft's speed is more consistent across all altitudes, as it makes up for engine performance with aerodynamics at high altitude and vice versa at low altitude.