 Its thrust-to-drag ratio was excellent, allowing a maximum speed well in excess of Mach 2.Available thrust was actually limited by the geometry of the inlet scoop and duct; the aircraft was capable even higher Mach numbers if the aluminum skin of the aircraft were able to withstand the heating due to air friction.Furthermore, speeds above Mach 2 quickly overheated the J79 engine beyond its thermal capabilities, which resulted in the F-104 being "placarded" at Mach 2.