Engineers and research pilots involved in NASA Dryden's Autonomous Formation Flight Project explored wingtip vortex energy with a pair of F/A-18s. The airflow from the wingtips of an aircraft can provide energy to another aircraft flying in an optimum position behind the leader. The goal of this project was to demonstrate 10 percent fuel savings of the trailing aircraft. The project extended the symbiotic relationship of migrating formations of birds. In December 2001, an F/A-18 flying in the wingtip vortex behind another F/A-18 exhibited a 14-percent fuel savings. The project ended in late 2001.