Experimental investigation of aerodynamics of pitching wings in tandem

The aerodynamic interaction of two wings in tandem undergoing pitching motion was experimentally investigated at a Reynolds number of 100,000. Rectangular wings of the NACA 0012 airfoil section with a 4-inch chord and fixed aspect ratio of 5 were utilized. Longitudinal spacing between the wings varied from 0.5 to 2.5 chord lengths. The wings were pitched at constant pitch rates in the quasi-static range from -30 to 90 degrees and back. The direct force and moment measurements were recorded for three cases; (a) front wing fixed, rear wing pitching, (b) front wing pitching, rear wing fixed and (c) both the wings pitching at different rates and phases. The wings proximity had a significant influence on the aerodynamic characteristics. The aerodynamic coefficients were changed considerably for wings in tandem even for a wing at a fixed angle of attack when the other wing was pitching and resulted in better aerodynamic efficiency in some instances. The effects of interaction remained similar but started to diminish with increasing spacing, however, changed considerably by the vertical offset (transverse spacing). Results revealed that at low pitch rates i.e., in the quasi-static range, the aerodynamic coefficients depended only on the geometric angles of attack of two wings at any instant.