ENHANCEMENT OF DRAG OF AIRCRAFT BY BLOWING

Abstract

Performance augmentation of machines is always needed. It is generally required to increase the aircraft efficiency and lift. Spanwise, chordwise and tangential blowing techniques have been used in the past to enhance the performance of aircraft. However, the objective of present technique i.e. upright blowing is quite different from the existing techniques. The objective of this technique is to increase the aircraft drag so that the landing run is reduced. For identifying the suitable location of the blowing ports experimental investigation has been carried out with reference to existing practice of allowable blowing momentum co-efficient. Flow visualization through smoke and tufts have indicated the presence of turbulent flow in the form of vortex at the leading edge. This is true even for small angle of attack. However, the airflow over the inboard region of the wing ( i.e. near the fuselage) has been found to be laminar even for higher angle of attack. Therefore it was decided to keep the blowing ports close to leading edge to make the downstream flow more turbulent to enhance drag. It is found that within 10 percent of root chord length close to the leading edge three blowing ports were effective to enhance the drag as compared to blowing ports at other locations. It has been observed that higher blowing momentum co-efficient provides higher drag. Blowing through two ports side by side at the same root chord length is more effective than blowing through two ports located at different root chord lengths. To get an idea of changes in lift, the lift coefficients have been - also studied for the sake of completion. It is found that there is no significant change in lift with and without blowing. It is concluded that blowing through the port at each wing can significantly increase the drag. Further a single port blowing with blowing momentum co-efficient around CN, = 0.08 provides higher drag than the conventional airbrake. Because of practical limitations the experimental study is restricted corresponding to blowing momentum co-efficient of 0.08. However, this can be increased upto 0.1 as per the existing code of practice. The existing code of practice