concept

Specific excess power

The power left over after the drag bill is paid, per unit of weight - what a flyer can spend on climbing, on accelerating, or on holding a hard turn without bleeding speed. This number is how John Boyd reframed the whole idea of advantage in air combat: whoever holds more excess power does not need to be faster, only to keep more options than the other side. A close-quarters hunter can accept a negative value for a few seconds to force a capture; a long-range pursuer has to live near zero.