Effect of wing fins on lift-generated wakes

A theoretical and experimental study has been made of the effect of wing-mounted fins on the vortex wakes of subsonic aircraft. The lateral lift on the fins injects vortices into the wake and redistributes the lift on the wing. The revised wake vorticity then interacts convectively to form a new configuration with low rotational velocities. The theory is used 1) to gain an understanding of wake alleviation by vortex injection and 2) to guide the experimental investigation. Wind-tunnel tests were used to evaluate the alleviation achievable and to find the optimum values for the various fin parameters. It was found that vertical fins mounted on the upper surface of a wing could lower the wake-induced rolling moments on an encountering wing by a factor of 3 or more. The most promising fin configuration found for the Boeing 747 model is a fin positioned 48% outboard from the centerline to the wingtip with a height equal to 0.014 wingspan, a chord equal to 0.085 wingspan, and an 18-deg angle of attack. This fin configuration caused a 10% increase in drag but no lift penalty.