Definition
A measure of an aircraft's performance capability, expressed as the power available beyond what is required to maintain steady level flight, divided by the aircraft's weight. It indicates how much energy the aircraft has available to climb, accelerate, or maneuver at a given flight condition. Specific excess power is typically expressed in feet per second and is calculated as the difference between thrust and drag, multiplied by velocity, divided by weight.
Plain English
How much spare performance an aircraft has at a given moment to climb faster, go faster, or turn harder. If specific excess power is high, the aircraft can still do more. If it's zero, the aircraft is already doing everything it can at that speed and altitude.
Context Anchor
Seen in aircraft performance discussions, especially when comparing climb ability, acceleration, and maneuvering capability.
Derivation
Specific' here means 'per unit of weight' — a common engineering convention used to compare aircraft of different sizes fairly. 'Excess power' means the power left over after maintaining steady flight. Together: leftover performance, normalized by weight.
Why Pilots Care
It determines how quickly an aircraft can climb, accelerate, or sustain a turn without losing energy, directly affecting obstacle clearance, go-around performance, and maneuvering safety margins.
Analogy
It is like money left after paying the required bill. The engine’s power is the income, drag is the bill, and specific excess power is what is left to spend on climbing, speeding up, or maneuvering.
Grounding Statement
At any moment, specific excess power is the airplane’s leftover performance after air resistance has taken its share.
Intuition Check
Do not read “specific” as meaning “particular” or “exact” here. In this term, it means the excess power is measured relative to the airplane’s weight.
Example Sentence 1
At high altitude and heavy weight, the aircraft's specific excess power dropped to nearly zero, leaving no margin to climb.
Example Sentence 2
During the turn, positive specific excess power allowed the aircraft to hold altitude while maintaining bank angle.