Experimental and computational investigation of stacked rotor performance in hover

Hover Performance Analyses of Coaxial Co-Rotating Rotors for eVTOL Aircraft

“…In addition, it was concluded that the thickness noise could decrease at a specific index angle region [13]. Considering the advantages of the coaxial co-rotating rotor, simulation and experimental studies on the hover performance were conducted [1,[14][15][16][17][18][19][20][21].…”

“…Previous studies [14][15][16][17][18][19][20][21] were conducted on the hover performance of a coaxial corotating rotor, with the index angles and axial spacings based on the Rotorcraft Comprehensive Analysis System (RCAS [22]), computational fluid dynamics (CFD), and experimental measurements. Unlike the coaxial counter-rotating rotor that satisfies the balance of the entire rotor torque, the coaxial co-rotating rotor does not achieve a torque balance The coaxial co-rotating rotor can improve the hover performance efficiency and reduce acoustic noise during operation using the two key design parameters [1,7,8].…”

“…The AH-64A Apache helicopter's tail rotor uses a coaxial corotating rotor with an index angle of 55 • to reduce the acoustic noise for comparison with conventional rotor configurations [11]. The previous analysis [12] showed that the sound pressure level of the coaxial co-rotating rotor decreased by 5 dB when the index angle increased from 0 • to 90 • . In addition, it was concluded that the thickness noise could decrease at a specific index angle region [13].…”

“…The trim of the coaxial co-rotating rotor was not considered in the hover performance analyses using RCAS with the viscous vortex particle method (VVPM), CFD, and experimental studies [20,21]. When the collective pitch angle of both the upper and lower rotors was fixed, it was found that the hover efficiency for a large axial spacing was approximately 10% higher compared with the case of a small axial spacing [20]. Moreover, it was shown that the hover efficiency improved by approximately 2% to 4% close to an index angle of 0 • [20].…”

“…When the collective pitch angle of both the upper and lower rotors was fixed, it was found that the hover efficiency for a large axial spacing was approximately 10% higher compared with the case of a small axial spacing [20]. Moreover, it was shown that the hover efficiency improved by approximately 2% to 4% close to an index angle of 0 • [20]. Further investigations were conducted in [21] based on [20].…”