Evaluation of the Potential Radar Cross-Section & Experimental Aero-Acoustic Noise Merits of the GA-ASI MQ-9 Reaper by Applying Flap Morphing

Abstract

Defence institutions and military aircraft manufacturers are increasingly exploring the ways to im- prove stealth in new aircraft designs. Design for low observability, more specifically for low Radar Cross-Section is the fundamental design aspect during design of a new military aerial vehicle. Acoustic stealth is also an important characteristic of an aerial vehicle and is one of the main objectives during the design of a stealth aircraft to avoid being heard by the enemy troops below.

Although there has been some work done in the past on flap morphing of wings, there are still some engineering aspects of flap morphing which are still left unexplored. Previous research focused more on aerodynamic and structural aspects of flap morphing. Couple of these unexplored aspects are the Aero-Acoustic Noise and Radar Cross-Section assessment of flap morphing. Flap gaps, kinematics and side-edges are a source of generating noise and radar signature and through flap morphing potential merits of these two aspects can be assessed.

Flap morphing technology is most likely to be used on unmanned military aerial vehicles. Therefore, the GA-ASI MQ-9 Reaper was used for achieving the research objectives in this thesis work. The study focuses on the Aero-Acoustic noise and Radar Cross-Section merits through flap morphing of the GA- ASI MQ-9 Reaper. Aero-Acoustic noise analysis were performed experimentally as well as analytically whereas Radar Cross-Section merits were obtained by performing simulations.

From the Aero-Acoustic noise experiments on the scaled 3D printed morphing and conventional wings of GA-ASI MQ-9 Reaper, noise reduction in the morphing wing have been observed in all configurations and operational settings. From the 35m/s noise experiments, Overall Sound Pressure Level reduction is observed between 4.7% and 38.2% for dierent angles of attack whereas reduction in the overall Sound Pressure Level between 20.66% and 32.2% have been observed with 50m/s. Similarly, with the Werner Dobrzynski’s noise prediction technique, together with Karl-Stephane Rossignol’s flap side-edge noise prediction model, benefits in the noise generation are observed for the morphing wings. For similar geometrical configurations as experiments, noise reduction variation in the predicted Overall Sound Pressure Level lies between 37% and 46% for dierent angles of attack at 50 m/s.

For the mono-static Radar Cross-Section with trailing edge and flap deflection of 0°, a significant reduction in the radar signature is observed for the morphing wing, whereas for 25°trailing edge and flap deflection it turns out that the radar signature for the morphing wing is very similar or slightly higher than the conventional wing. For the mono-static radar signature with 0° trailing edge and flap deflection, after summation of total RCS in all 360 directions, a maximum and minimum decrease of 10.52dBsm and 9.95dBsm have been observed by flap morphing whereas for 25° trailing edge and flap deflection an increase in radar signature between 1.54 and 2 dBsm was noticed. Bi-static RCS analysis were also performed on the 0° trailing edge and flap deflection of where the decrease in radar signature between 4 and 18 dBsm was observed.