Aircraft specific energy

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Aircraft-specific energy is a form of

and is represented in units of length since it is independent of the mass of the vehicle.

Applications

The field of trajectory optimization has made use of the concept since the 1950s in the form of energy analysis. In this approach, the specific energy is defined as one of the dynamic states of the problem and is the slowest varying state. All other states such as altitude and flight path angle are approximated as infinitely fast compared to the specific energy dynamics. This assumption allow the solution of optimal trajectories in a relatively simple form.

The specific energy is computed by the total energy (as defined above relative the Earth's surface) divided by the mass of the vehicle. It is a key element in performance of aircraft and rockets. For a rocket flying vertically (in a vacuum), it is the

that the rocket would obtain.

Aircraft-specific energy is used extensively in the energy–maneuverability theory governing modern aircraft dogfighting tactics. The primary goal of ACM (Air Combat Maneuvering) is to maintain an optimal aircraft-specific energy. Speed allows an aircraft the ability to potentially outmaneuver adversaries, and altitude can be converted into speed, while also providing extended range for guided munitions (due to lower air density and therefore lower drag at any given velocity). Aircraft such as the F-16 Fighting Falcon were designed to be optimized in accordance to the energy-maneuverability theory, allowing for an aircraft to quickly gain aircraft-specific energy as fast as possible.