Evaluation of Formation Flights with Long Range Aircraft for Different Flight Conditions and Atmospheric Disturbances

Abstract

The aerodynamic formation flight, which is also called air wake surfing for efficiency (AWSE), can lead to a high drag reduction at the trailing aircraft of more than ten percent resulting in a reduced fuel burn. Therefore, this operational strategy represents a promising means to reduce the greenhouse effect of aviation. The following study investigates the flight of two long haul commercial aircraft in an echelon formation in a stationary state, a flight dynamic simulation and finally at trajectory level. Thereby, the effect of different cruise altitudes and speeds, aircraft masses, lateral and vertical separations and different intensities of gusts and turbulence are evaluated. Based on the aircraft data set from the in house preliminary aircraft design tool MICADO a vortex lattice method calculates the induced loads in the trailing wake behind the leader. Subsequently, the results are used in the flight simulation program to analyze the flight behavior of the trailing aircraft in the formation under the influence of atmospheric disturbances. Finally, the results of the vortex lattice method and the flight simulation provide the necessary input data for the evaluation of the benefits achievable during the entire mission based on a detailed trajectory calculation. High altitudes and low Mach numbers during the formation flight lead to the highest drag reductions at the trailing aircraft. Movements of the trailing aircraft away from the optimum location in the vortex of the leading aircraft and additional detours lead to reduced fuel savings of ten percent or less.