Definition
Specific Excess Power is the rate at which an airplane can gain energy at a given flight condition, expressed as the power available beyond what is needed to maintain steady level flight, divided by the airplane's weight. It is measured in feet per second and represents how quickly the airplane can climb, accelerate, or both, at the current airspeed, altitude, weight, and configuration. A positive P_S means the airplane has energy to spare; zero P_S means it can only sustain its current state; negative P_S means it is losing energy.
Plain English
It is a number that tells you how much extra performance the airplane has right now -- how fast it can climb or speed up beyond just holding altitude. If the number is positive, you have room to climb or accelerate. If it is zero, you are flying at the limit of what the airplane can sustain. If it is negative, you are running out of energy.
Context Anchor
Seen in airplane performance and maneuvering discussions, especially when comparing climb ability, acceleration, and energy available during a maneuver.
Derivation
Specific' here means 'per unit of weight' -- the same sense used in 'specific fuel consumption.' 'Excess power' means power left over after holding level flight. So P_S literally means 'leftover power per pound of airplane,' which is why it works out to a speed (feet per second) -- it tells you how fast the airplane's energy state can change.
Why Pilots Care
Higher specific excess power means steeper climbs, faster acceleration, and more options during maneuvering or emergencies.
Grounding Statement
Think of P_S as the airplane's 'spare performance' at this exact moment -- positive means you can climb or speed up, zero means you are right at the edge, negative means something has to give.
Intuition Check
Specific does not mean “particular” here; it means “per unit of airplane weight.” Excess power does not mean unused throttle; it means power available beyond what is needed to overcome drag at that flight condition.
Example Sentence 1
At high altitude in a steep turn, the airplane's specific excess power can drop to zero, meaning it can no longer climb or accelerate without losing altitude or airspeed.
Example Sentence 2
At higher altitudes the specific excess power dropped because engine thrust decreased, limiting the rate of climb.