Figure 9-6 Specific Energy

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BASIC FIGHTER MANEUVERING (BFM) THEORY
CHAPTER NINE
The aircrew that best manages its energy package often gains the tactical advantage. Although
determining the total energy advantage for a tactical scenario is difficult because of possible
speed differences between aircraft, total energy remains a vital factor for determining relative
advantage. As you gain experience in BFM, you will soon learn to judge the energy package of
Specific Energy
Using total energy to compare the relative energy states between fighter aircraft, tends to portray
larger, heavier aircraft as having the energy advantage. However, this is not the sole factor used
in comparisons. Maintaining a large total energy package does not necessarily produce the
margin of victory all by itself, or we would be strapping missiles on C-5s and 727s. Therefore,
another expression of energy is necessary. Energy per pound of gross weight is more appropriate
for comparative analysis. This is referred to as Specific Energy. Curves representing equal lines
of specific energy can be plotted on a graph of altitude vs. mach number as shown in Figure 9-6.
Figure 9-6 Specific Energy
From this graph we can see that an arbitrary object at point A at 5000 feet and .9 IMN has the
same specific energy after being at point B at 20,000 feet at .1 IMN. If the total specific energy
is being maintained, then as the potential energy is increased, the kinetic energy is decreased by
an equal amount.
The bottom line: A fighter crew has the ability to trade airspeed for altitude and still preserve
the energy state of the aircraft.
9-11
BASIC FIGHTER MANEUVERING (BFM) THEORY

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