Experimental investigation on aerodynamic coefficients of a flying wing aircraft with different leading edge sweep angle

The aerodynamic coefficients characteristics over a lambda-shaped flying wing aircraft with 55°-30° leading edge sweep angles have been investigated in a closed circuit low speed wind tunnel. The experiments were conducted at tunnel velocity of 90 m/s, the angles of attack of -6 to 17 and the side-slip angles of -8 to 8 degrees. All forces and moments were measured using an external six-component force balance located below the wind tunnel. The wall corrections were also performed for all test conditions. To improve the aircraft longitudinal stability characteristics, a new model with an increased leading edge sweep angle of 2 degrees were also tested and compared with the original model. A “pitch-up” phenomenon identified to occur at a rather low angle of attack of α=7.7 degrees, although it occurred at the higher angle of attack of α=8.7 degrees for the increased swept angle model which means an increase in useable lift of the aircraft. Moreover, off-surface pressure measurement over the wing surface was conducted to examine the onset and development of the flow separation over the wing surface. The results showed that the flow separation started at the trailing edge crank location and extended to the other parts of the wing, especially the outer wing.