Smoke generators show the twisting paths of wingtip vortices behind two NASA Dryden F/A-18 jets used in the Autonomous Formation Flight (AFF) program. A vortex is a spiraling current of air emanating from aircraft wingtips as they fly. By mapping the vortex pattern and using sophisticated software to put the trailing aircraft in the optimum location, the energy of the vortex could result in fuel savings for the follower aircraft of 15 percent or more.