Definition
Energy height (ES) is the total mechanical energy of an airplane expressed as an altitude. It combines potential energy (height above a reference) and kinetic energy (energy of motion due to airspeed) into a single value, stated in feet. It is calculated as altitude plus the square of true airspeed divided by twice the acceleration of gravity (ES = h + V²/2g).
Plain English
It is a single number, in feet, that captures both how high you are and how fast you are going. Speed can be 'traded' for altitude and altitude for speed, so combining them shows the total energy the airplane has available.
Context Anchor
Seen in energy management, airplane performance, and maneuvering discussions, especially when comparing altitude and speed as forms of usable aircraft energy.
Derivation
The term combines 'energy' (the capacity to do work) with 'height' because the total energy is expressed as the altitude the airplane could reach if all its speed were converted to climb. 'Specific' means 'per unit of mass,' so the value does not depend on how heavy the airplane is.
Why Pilots Care
Knowing energy height helps a pilot judge whether the airplane has enough total energy to reach a safe landing spot or complete a maneuver without running out of options.
Grounding Statement
If an airplane at 5,000 feet is flying fast enough that its speed alone could carry it another 2,000 feet upward, its energy height is about 7,000 feet.
Intuition Check
Energy height does not mean the airplane’s actual altitude. It means actual altitude plus the airplane’s speed energy expressed as an added height value.
Example Sentence 1
By trading airspeed for altitude in the climb, the pilot kept the airplane's energy height nearly constant.
Example Sentence 2
During the practice forced landing, maintaining the proper energy height allowed a safe touchdown on the chosen field.