Definition
A system that exchanges energy with its surroundings, allowing energy to flow in and out rather than being sealed off. An airplane in flight is treated as an open energy system because it continuously takes in chemical energy from fuel, converts it through the engine, and exchanges kinetic and potential energy with the surrounding air through thrust, drag, lift, and weight.
Plain English
An airplane is constantly trading energy with the world around it. Fuel adds energy in, drag takes energy out, and the pilot manages how that energy moves between speed and altitude. It is not a closed box — energy is always flowing through it.
Context Anchor
Used in the Airplane Flying Handbook when explaining how pilots manage airspeed, altitude, power, and airplane configuration together.
Derivation
From physics, where systems are described as 'open' if they exchange matter or energy with their surroundings, and 'closed' if they do not. Aviation borrows the term to describe the airplane as a system that is always trading energy with its environment, never isolated from it.
Why Pilots Care
Recognizing the airplane as an open energy system helps pilots understand how power, drag, and altitude changes affect total energy and therefore airspeed and safety margins.
Analogy
It is like a bank account that can receive deposits, make withdrawals, and move money between pockets. Power adds energy, air resistance spends energy, and the pilot can shift energy between speed and altitude.
Grounding Statement
Fuel energy flows in, drag bleeds energy out, and altitude and airspeed are the two main places that energy is stored in between.
Intuition Check
Open does not mean a door, window, or vent is open. Here, open means the airplane can gain energy from outside sources and lose energy to outside effects.
Example Sentence 1
Treating the airplane as an open energy system, the instructor explained that adding power increases the total energy available, while pitch determines whether that energy goes into climbing or accelerating.
Example Sentence 2
During a glide with idle power, the open energy system loses kinetic energy as drag converts it into heat in the surrounding air.