Session: 06-01-02: General Aerospace-2

Paper Number: 167140

Characterising NACA Airfoils for Thrust Measurements in a Small Dual-Rotor Helicopter 

Due to their improved commercial, civilian, and military applications, drones and small helicopters are gaining increasing attention. The primary focus is now shifting towards enhancing their performance, which has traditionally been measured by the amount of thrust they generate. Blade design, including factors like camber and thickness, plays a crucial role in optimizing this performance. Measuring thrust as a function of these blade design parameters can help identify the optimal performance conditions.

One major challenge is that thrust measurements require an efficient thrust stand capable of measuring thrust under the desired operating conditions. While commercial thrust stands are available, they tend to be task-specific, complex, expensive, and unsuitable for small-scale flying objects. To address this, a small dual-rotor helicopter (SREJNGL-31.5ʺ×3.5ʺ×9.4ʺ) was mounted on an S-Type 20 kg load cell connected to an HX711 load amplifier for signal processing. A small microprocessor was used to retrieve the thrust data generated by the helicopter. Rotational speeds were measured using a tachometer, and a calibration curve was established with known weights.

To analyze the effect of airfoil shape on thrust, six NACA airfoils (0018, 0021, 2416, 2421, 4418, and 4421) were 3D-printed, with thicknesses ranging from 18% to 21% of the chord and maximum camber ranging from 0% to 4%. Special attention was given to the 3D printing process to ensure that the leading and trailing edges of the blades were well-defined and the blade surfaces were smooth enough to avoid boundary layer separation.

The results indicate that thrust increases with camber but decreases with blade thickness. The maximum thrust values for 0% camber and 4% camber, with the blade thickness held constant at 18%, were found to be 0.14 N and 0.33 N, respectively, showing a 135% increase in thrust. Similarly, for a constant camber of 4%, the maximum thrust values for blade thicknesses of 18% and 21% were 0.33 N and 0.11 N, respectively, reflecting a 67% decrease in thrust.

These preliminary results are promising, and a more detailed study is being launched to verify the trends by further adjusting the blade parameters. Detailed results will be included in the final paper.

Additionally, this work investigates the effect of rotor separation on thrust measurements across multiple operating conditions and airfoils. It was found that thrust is maximized at a rotor separation of 40 mm for most of the operating conditions used in this experiment. Recent work also includes fast imaging of the flow separating from the rotating blades, using smoke and a laser sheet that crosses the flow in a vertical direction. Preliminary imaging has shown turbulent eddy currents leaving the trailing edge of the blades. A parametric study of these images under various operating conditions will provide further insights into the complex flow phenomena surrounding rotating blades and their impact on generated thrust. Full details of the images, along with the thrust results, will be included in the final paper.

 

Presenting Author: Rohit Chadalavada Intelliscience institute

Presenting Author Biography: Presenting author is an intern researcher in the department of Mechanical Engineering department and his research areas include aerodynamics of drones and small scale helicopters.

Authors:

Rohit Chadalavada Intelliscience institute
Ayati Vyas Intelliscience Institute
Sohail Zaidi San Jose State University