Boyd: The Fighter Pilot Who Changed the Art of War

by Robert Coram

The fuel fraction is derived by considering the weight of the fuel relative to the combat weight of the aircraft. The crucial thing about understanding fuel fraction is that it is the relative fuel and not the absolute fuel that is important in determining how far an airplane flies. That is, the percentage of fuel relative to the weight of the aircraft is more important than the absolute gallons of fuel carried. Boyd was adamant that the fuel fraction for the lightweight fighter not go below 30 percent. That was the sacred number, not to be violated, doubtless because the fuel fraction of the F-15 was 25 percent and Boyd wanted the lightweight fighter to be better. The new fighter would have about six thousand five hundred pounds of fuel, for a fuel fraction of 31.5 percent. As mind-boggling as it sounds, the Air Force looked at the total amount of fuel carried and never considered the fuel fraction. The school of Bigger-Higher-Faster-Farther was so firmly ingrained that it was almost genetic: big airplanes have more range than small airplanes. The MiG-21 was a small aircraft and notoriously short-legged. So was the F-5, another small fighter. If the Blue Suiters had considered birds, rather than airplanes, they might have found a better example. There is a hummingbird that can fly across the Gulf of Mexico, while birds many times its size can fly only a few miles. The hummingbird has a high fuel fraction.