The time rate of change of the total energy (kinetic plus potential) per unit weight is referred to as the specific energy and is defined as:
It therefore follows that:
The time derivative of specific energy, dhe/dt, is referred to as the specific excess power of the aircraft (S.E.P.). The above equation can be interpreted to say that, if the S.E.P. of an aircraft is known, its rate of climb, R.C. = dh/dt and its acceleration, dU/dt can be determined.