Wind tunnel investigations of potential UAV configuration to meet requirements of TERN mission

Abstract

In the mid 80’s, a wind tunnel study of a 1/6 scale model RPV was performed to determine the influence of the close-coupled canard on the aerodynamic coefficients. Now, more than 20 years after, these tests are repeated for the design of a full scale prototype for TERN mission, where the necessity of minimum Weight Specific Kinetic Energy for operation on Littoral Combat ships is the key feature that makes the close coupled canard a design candidate. To determine the aerodynamic characteristics of the model a wind tunnel study was done. The results are compared with the previous data, and the stability coefficients were determined. The existing wood model of a close coupled canard with a swept delta platform was used. With a gap of 0.27 mean geometric chord of wing (MGCw) and a stagger of 1.01 MGCw, its geometry is near optimal for maximum lift enhancement. Once a new spindle was machined, the pyramidal balance calibrated and the acquisition program modified, tests were performed at Reynolds number of 600,000 in order to reproduce the conditions of the previous experiments. Several configurations were tested: the Wing/Body (W/B) and the Wing/Body/Canard (W/B/C) with different canard deflection (decalage) of 0°,+10°,+20°,-10° and -20°, with angle of attack and sideslip sweeps. The loads were obtained from the balance, transferred to the computer through Labview and later analyzed by MatLab. The results show that the close coupled canard increases lift coefficient and delays stall compared to the Wing/Body configuration. The lift coefficient increases as the canard deflection is increased. The highest CL/CD is for the W/B, as is the smallest drag. The neutral point is shifted from 0.3 MGCw for W/B to 0.1 MGCw for W/B/C. All configurations can be trimmed. In overall, the new results match the ones obtained 20 years ago. The trends in lift, drag and pitching moment are the same. Small differences are appreciated due to the fact that the effect of the tunnel blockage was not corrected. Also, the new results present lower drag due to the absence of grit type boundary trips. It has been demonstrated the influence the canard has on the aerodynamic coefficient. The lift enhancement due to the flow reattachment produced by the canard vortex delays stall and allows level flight at higher angles of attack than the conventional W/B configuration. The results were reliable as they matched the experimental data obtained more than 20 years ago. The gathered data will be used to calibrate a VLM which will be employed for the design of a vehicle for TERN mission