Aerodynamic Data Generation and Design Support for Solar UAV – Wind Tunnel Testing
The Solar Unmanned Aerial Vehicle (Solar UAV) project aims to design and fabricate a medium altitude long endurance (MALE) UAV with 24-hour continuous flight mission using solar energy as the sole power source. The aircraft has a high wing and T-tail configuration, with a wing span of 17.7m and chord length of 1.26m. Having a target weight of 85kg, the aircraft is targeted to fly at 8000m altitude with flight speed of 14m/s. To have a better understanding of the flight characteristic for further design evaluation of the UAV, a 1:9 scale wind tunnel model was designed to generate aerodynamic data of the aircraft. The wing and horizontal tail were made out of carbon fibre reinforced plastic (CFRP) and foam core structure. The other major components of the model were made out of aluminium and stainless steel. 3D-printed components like control surfaces, wing tips etc were also incorporated in the model. The model weighs only 5.96kg and is well within the desirable weight category for the balance chosen, meeting measuring accuracy. The model also meets the safety requirement set by NASA “Wind Tunnel System Criteria” and low speed wind tunnel practice of limiting the model span to 80% of tunnel width and flow blockage below 3-5%. The wind tunnel test was carried out in the 3m x 2.25m low speed wind tunnel of National Wind Tunnel Facility at Indian Institute of Technology Kanpur to generate aerodynamic force and moment data at test speed of 63.4m/s matching the flight Reynolds number of 610000. The aircraft was found to have good lateral and directional stability and better lifting characteristics than the empirical estimation. However, the aircraft exhibits longitudinal instability and this requires second tunnel entry for test results verification and further aircraft design improvements to enhance the stability of the aircraft.