Aircraft specific energy
Encyclopedia
Aircraft specific energy is a form of specific energy
applied to aircraft and missile trajectory
analysis. It represents the combined kinetic
and potential
energy of the vehicle at any given time. It is the total energy of the vehicle (relative to the Earth's surface) per unit weight of the vehicle and being independent of the mass of the vehicle provides a powerful tool for the design of optimal trajectories. Being flying vehicles aircraft specific energy is very similar to specific orbital energy
except that it is expressed as a positive quantity. A zero value of aircraft specific energy is at the Earth's surface and increases as speed and altitude increases. Orbital specific energy is zero at infinite altitude and decreases as one approaches the surface of the earth. As with other forms of specific energy, aircraft specific energy is an intensive property and is represented in units of length since it is independent of the mass of the vehicle.
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 apogee that the rocket would obtain. It is used extensively in Energy-Maneuverability theory
that is used to determine the optimal paths for aircraft in dogfights.
Specific energy
Specific energy is defined as the energy per unit mass. Common metric units are J/kg. It is an intensive property. Contrast this with energy, which is an extensive property. There are two main types of specific energy: potential energy and specific kinetic energy. Others are the gray and sievert,...
applied to aircraft and missile trajectory
Trajectory
A trajectory is the path that a moving object follows through space as a function of time. The object might be a projectile or a satellite, for example. It thus includes the meaning of orbit—the path of a planet, an asteroid or a comet as it travels around a central mass...
analysis. It represents the combined kinetic
Kinetic energy
The kinetic energy of an object is the energy which it possesses due to its motion.It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes...
and potential
Potential
*In linguistics, the potential mood*The mathematical study of potentials is known as potential theory; it is the study of harmonic functions on manifolds...
energy of the vehicle at any given time. It is the total energy of the vehicle (relative to the Earth's surface) per unit weight of the vehicle and being independent of the mass of the vehicle provides a powerful tool for the design of optimal trajectories. Being flying vehicles aircraft specific energy is very similar to specific orbital energy
Specific orbital energy
In the gravitational two-body problem, the specific orbital energy \epsilon\,\! of two orbiting bodies is the constant sum of their mutual potential energy and their total kinetic energy , divided by the reduced mass...
except that it is expressed as a positive quantity. A zero value of aircraft specific energy is at the Earth's surface and increases as speed and altitude increases. Orbital specific energy is zero at infinite altitude and decreases as one approaches the surface of the earth. As with other forms of specific energy, aircraft specific energy is an intensive property and is represented in units of length since it is independent of the mass of the vehicle.
Applications
The field of trajectory optimizationTrajectory optimization
Trajectory optimization is the process of designing a trajectory that minimizes or maximizes some measure of performance within prescribed constraint boundaries...
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
Altitude
Altitude or height is defined based on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The reference datum also often varies according to the context...
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
Vacuum
In everyday usage, vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty". A perfect vacuum would be one with no particles in it at all, which is impossible to achieve in...
), it is the apogee that the rocket would obtain. It is used extensively in Energy-Maneuverability theory
Energy-Maneuverability theory
Energy Maneuverability theory is a model of aircraft performance. It was promulgated by Col. John Boyd, and is useful in describing an aircraft's performance as the total of kinetic and potential energies or aircraft specific energy. It relates the thrust, weight, drag, wing area, and other flight...
that is used to determine the optimal paths for aircraft in dogfights.