Flight dynamics simulation of formation flight for energy saving using LES-generated wake flow fields

Abstract

Wake vortices are an inevitable result of lift generation and can pose a threat to any aircraft, which accidentally encounters the wake of another aircraft. However, wake vortices can also be used in a beneficial way. Due to its rotational direction, the air flows upwards outside of the vortex pair, giving additional energy to any aircraft located in these regions. This method to save energy is used by migratory birds, resulting in these birds flying in the typical V-formations. This study deals with the question, whether it is possible with a standard autopilot (without a dedicated formation flight mode) to keep the aircraft's position accurately at a desired position in the wake flow field without accidentally encountering those areas of the wake where steady-state-flight is impossible, even in the presence of atmospheric disturbances (e.g. turbulence) and fluctuating vortex core positions. For this purpose, simulations were performed applying threedimensional flowfields generated with large eddy simulations (LES). Here, even with young vortices the target _____________________________________________

Aerodynamic Interactions in Formation Flight for Wake Vortex Surfing

“…As trailing aircraft is the beneficiary, its position in the formation must be determined and maintained during the vortex surfing phase to maximize the gains. Other than the flight test, several numerical simulations research [25][26][27][28] have been conducted over the last few decades to investigate the trailing aircraft position and its aerodynamics implications on vortex surfing. With the available data from SAVE program, Halaas et al [25] used Reynolds-Averaged Navier Stokes (RANS) for the C-17 formation simulation, with consideration on the trim condition of following aircraft.…”

“…Whereas Zhang et al [27] used RANS to determine the optimal lateral spacing, vertical distance and the optimum formation of simplified tailless delta wing UAVs in the close formation flight. Vechtel et al [28] used Large Eddy Simulation (LES) to generate vortex flow fields with small perturbations of the vortex lines, which is a more representative flow field for real flight conditions.…”

A Stochastic Switched Optimal Control Approach to Formation Mission Design for Commercial Aircraft

“…Dynamic flight simulations described in [Vechtel et al, 2018] demonstrate that it is possible to maintain the position of the trailing aircraft in the wake vortex generated by the leader accurately using a regular autopilot.…”

Flight Control Systems for fuel efficient wake surfing

“…In order to reduce the fuel consumption of an aircraft, fuel-saving formation flight has been studied for several decades. An overview about already conducted investigations including flight tests is for example given in [1]. The first manual flight tests have been conducted in 1984 by the Technical University of Braunschweig, Germany [2], the first ones with a modified autopilot in 1987/88 also by the Technical University of Braunschweig [3].…”