Figure 9-6 Specific Energy

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

your adversary.

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