Definition
Specific Excess Power (PS) is the rate at which an airplane can gain energy — either by climbing, accelerating, or both — beyond what is needed to maintain its current flight condition. It is expressed as power per unit weight, typically in feet per second, and represents the energy available after the thrust required to overcome drag at the current speed and altitude has been satisfied.
Plain English
It is the spare energy the airplane has left over once it is already holding its current speed and altitude. That extra energy is what lets it climb, speed up, or do both at the same time.
Context Anchor
Seen in energy management discussions, especially when comparing climb, acceleration, drag, and aircraft performance.
Derivation
‘Specific’ here means ‘per unit of weight’ — the same sense used in ‘specific fuel consumption.’ ‘Excess’ means what is left over after a requirement is met. So Specific Excess Power is literally ‘leftover power, measured per pound of airplane.’ Knowing this makes the term feel less abstract: it is just spare energy, scaled to the size of the airplane.
Why Pilots Care
Higher Ps directly improves climb rate, zoom capability, and sustained turn performance while lower Ps limits options during energy-critical phases such as takeoff, go-around, or combat maneuvering.
Analogy
It is like having money left after paying bills. If there is money left over, you can save or spend it. If there is none left, you can only maintain. If you are short, something has to be given up.
Grounding Statement
If the throttle is already wide open and the airplane is holding altitude and speed steadily, PS is essentially zero — there is nothing left to give. Pull the nose up and you will trade speed for altitude, because no spare energy is available.
Intuition Check
“Specific” does not mean detailed here. It means measured relative to the airplane’s weight, so different airplanes can be compared more fairly.
Example Sentence 1
At full throttle in level flight at cruise speed, the airplane had almost no specific excess power left, so the pilot knew a climb would require giving up airspeed.
Example Sentence 2
The instructor pointed out that at high altitude the trainer's specific excess power drops quickly, limiting how steeply the student could climb without losing speed.