Projeto, construção e verificação de um dinamômetro para o grupo motopropulsor de aeronaves do aerodesign

Abstract

This study aimed at the project, the construction and verification of a bench dynamometer, denominated TracTor, that collects data of torque and traction of the Aerodesign aircraft powertrain, as a function of the wind speed. The powerplant used in the validation consisted of an APC 12.25 '' x 3.75 '' propeller and an O.S 55FX engine. For its development, it was used measuring instruments such as: two 100 N load cells, a Hobbico digital tachometer, a Measurement Specialties MS4525 pitot tube and the UCS wind tunnel. The load cells were calibrated by means of standard masses. The wind speed measured by the MS4525 pitot tube was compared to Kimo MP120 pitot tube values. Three experimental tests were performed, each in 5 different levels of relative wind velocities. For each verified wind speed it was processed, by a 100 arduino mega 2560 platform, 100 values of torque, traction and wind speed were subsequently saved in an Excel spreadsheet. The torque and traction verification process was performed by comparing the results obtained in the experimental tests, considering a 95.45% confidence interval, in relation to the same theoretical data provided by the propeller manufacturer, APC Propellers. However, it was found that the measured torque results were up to six times higher than the theoretical ones. This difference may be related to the vibrations generated by the motor that have resulted in pulsating loads in the load cell. This effect is confirmed by the high standard uncertainty values obtained in the torque measurements. Meanwhile, the traction check showed an average difference of 25.56% between the experimental and theoretical values. The parabolic behavior of the experimental tensile force curve proved to be compatible with the theoretical curves available in the literature. In addition, the low values of standard tensile strength uncertainty indicated that the engine vibration did not influence the results. The differences observed in relation to the theoretical values of the manufacturer may be related to the actual geometric shape of the propeller tested which may differ in theory. Another source of error may be related to the measurement of the rotation speed of the propeller. Finally, the Tractor dynamometer proved to be adequate, especially to make the static and dynamic traction readings of the Aerodesign aircraft powertrain (sic).