Thrust Measurements of NACA Airfoils in a Small Dual-Rotor Helicopter

Performance measurements are essential for helicopter design and are typically obtained by measuring thrust. We hypothesize that in dual-rotor helicopters, thrust generation is influenced by blade shape and rotor separation. Thrust stands are commonly used to measure thrust under various operating conditions; however, commercial thrust stands are often expensive and complex. To address these challenges, a simple thrust stand was designed and developed. A small dual-rotor helicopter (SREJNGL-31.5"×3.5"×9.4") was mounted on an S-Type 20kg load cell, connected to an HX711 load amplifier for signal processing. A tachometer measured rotational speeds, and a calibration curve was established using known weights. To analyze the effect of airfoil shape on thrust, NACA airfoils (0018, 0021, 2416, 2421, 4418, 4421) with thicknesses of 18-21% of the chord and maximum camber ranging from 0-4% were 3D-printed. Results show that thrust increases with camber but decreases with blade thickness. The maximum thrust values for 0% camber and 4% camber, with thickness held constant at 18% was shown to be 0.14 N and 0.33 N respectively, a 135% increase in the thrust. The maximum thrust values for 18% thickness and 21% thickness, with camber held constant at 4% was shown to be 0.33 N and 0.11 N respectively, showing a 67% decrease in thrust. In addition, the impact of rotors separation on thrust measurements at a fixed operating condition was investigated. It was found that the thrust was maximized at 40 mm separation between rotors.