Cruise Range in Formation Flight

Abstract

A new set of analytical range equations (a modification of the traditional Bréguet range equation) suitable for formation flight at transonic flight speeds under realistic operating conditions (constant Mach number and altitude) is derived. Formations of two aircraft of the same type are analyzed to determine the effects of 1) weight differences between the aircraft, 2) altitude, and 3) the formation flight range on the potential fuel benefits and the associated optimum Mach number. In the case of a weight difference, the lightest aircraft should lead the formation to realize the largest fuel benefits. Overall, fuel savings of 6 to 12% for the total formation can be realized at the expense of a reduction in cruise Mach number from 0.85 to 0.80. The fuel benefit is much less (2 to 8%) when the formation is flown at the original design cruise Mach number. In terms of fuel benefits and Mach number, it is beneficial to fly in formation at higher altitudes. Formation flight step climb procedures are possible, but the additional fuel savings are minimal compared to a constant-altitude formation flight.