Induced Moment Effects of Formation Flight Using Two F/A-18 Aircraft

b F/A-18 wingspan (37.5 ft)Previous investigations into formation flight haveshown the possibility for significant fuel savings through Cdrag reduction. Using two F/A-18 aircraft, NASADryden Flight Research Center has investigated flying Claircraft in autonomous formation. Positioning the C,ntrailing airplane for best drag reduction requiresinvestigation of the wingtip vortex effects induced by Cnthe leading airplane. A full accounting of the vortex CFeffect on the trailing airplane is desired to validatevortex-effect prediction methods and provide a database gfor the design of a formation flight autopilot. A recent GPSflight phase has mapped the complete wingtip vortexeffects at two flight conditions with the trailing airplane hat varying distances behind the leading one. Force and imoment data at Mach 0.56 and an altitude of 25,000 ftand Mach 0.86 and an altitude of 36,000 ft have been Ix, Ii_ Izobtained with 20, 55, 110, and 190 ft of longitudinaldistance between the aircraft. The moments induced bythe vortex on the trailing airplane were well within thepilot's ability to control. This report discusses the dataanalysis methods and vortex-induced effects onmoments and side force. An assessment of the impact ofthe nonlinear vortex effects on the design of a formationautopilot is offered.