Experimental Determination of Lift and Lift Distributions for Wings In Formation Flight

Methods to experimentally determine trailing vortex strengths and spanwise circulation distributions for two wings in formation flight using a flow measurement probe are presented. With these experiments we model compound aircraft flight either docked tip-totip, or flying in formation. Data were collected for the case of a full wing trailing a larger wing. The absence of fixed walls on either end of the wing permits the development of asymmetric shedding of vortices, and the determination of the asymmetric circulation distribution induced by the proximity of the leading wing. The pair consisted of a swept NACA 0012 non-cambered wing simulating one half of a leading aircraft and a rectangular cambered NACA 63-420 wing simulating the trailing aircraft. Velocity and vorticity distributions obtained along a near-field plane were processed to calculate wingtip vortex strengths. Vortex position instabilities and the shedding of vorticity inboard of the wingtips were observed. Circulation distributions for the trailing wing are measured. Comparisons are made to directly measured loads and to results reported earlier. Directly measured lift and drag coefficients were found to agree with existing literature.