The aerial application using unmanned aerial vehicles has become a new paradigm in farming. The technology would reduce the possibility of pesticide exposure to farm workers. Previous studies in Korea showed that an insufficient lift deteriorates the performance and efficiency of unmanned rotorcraft operation. These studies suggested that lift could not be improved by increasing the engine power and lift only can be enhanced by increasing the performance of rotor.
A wind tunnel experiment was conducted for 400 mm blade sections of V1505A and V2008B airfoils, selected for agricultural unmanned helicopters.
The characteristics of lift and drag were measured and analyzed. The Laminar model was employed to simulate lift at a region of Re=0.32x10^6 corresponding the wind velocity of 36 m/s, which represents the wind speed at inner grip area of the rotor. The CFD simulation model was verified by the experiment results.
For the range of Re>0.32x10^6 , the Spalart?Allmaras (S-A) model, known to be able to capture the abrupt changes of lift and drag forces, was used to extend the simulation to the outer region of blade. Subsequently, the required power for a couple of rotating blades was determined to predict a proper range of lift for unmanned helicopters at a limited power source.
Generally, V2008B shows better lift performance than that of V1505A. The V1505A stably performs at the high angle of attack. Contrarily, V2008B shows a high lift and low drag at the range of low angle of attack. The V2008B exhibits higher induced power and lower profile power than V1505A.
The rotor blade mounted on the agricultural rotor craft currently has one simple airfoil through out entire span. Therefore, it would be possible to increase the lift by improving the airfoil by apply of transitional airfoils. The airfoil V1505A shows stable characteristics at high angles. Consequently, it would be suitable for the inner grip area of a rotor, which requires stable aerodynamic characteristics. The airfoil V2008B revealed higher power efficiency than the airfoil V1505A. However, it abruptly lost the lift after losing speed at the high angle of attack.
Therefore, it is considered that airfoil V2008B would be suitable for the outer tip area of a rotor, where a negative twist angle is applied