Lab_Report_Sample (1)

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Mechanical Engineering

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Feb 20, 2024

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MECH 261/262 Measurement Lab Lab 0: Aircraft Wind-Tunnel Testing GROUP 1 Dimitri CALOMIRIS 123456788 Raphael LIMBOURG 123456789 January 25 th , 2021 Abstract The main purpose of this lab was to determine the aerodynamic forces acting on an aircraft, and experimentally confirm that the lift and drag forces were within reasonable theoretical expectations. The model aircraft in question was conceptually designed as a capstone project, scaled down in size and 3D printed. After conducting several tests, the experiment concluded that the aircraft would indeed have sufficient lift for takeoff and landing, however did not closely match the predicted efficiency for cruising flight – with an error of about 36%.

Introduction The main objective of the lab experiment is to verify that the actual forces acting on a scaled-down aircraft match those predicted by the theoretical equations. This will be accomplished by testing the model in a wind- tunnel, for three configurations: takeoff, cruise and landing. The wind-tunnel uses an analog force-balance to measure the aerodynamic forces, lift and drag. These values will then be used to determine the aerodynamic efficiency and compared with the theory. The following will introduce the reader to some basic aerodynamics for the purposes of this report. The driving force behind aircraft flight is the lift force, and is often calculated using equation (1). One simple way of describing lift force is by pressure. Underneath the wings, typically exists a high pressure region, whereas above is usually low pressure. This difference is often created by rotating the fluid around a particular geometry, such as an airfoil. L = 1 2 ρU 2 SC L (1) A frictional force that opposes the flow motion is referred to the drag force. In aeronautics, the usual goal is to minimize the drag such that the vehicle can perform more efficiently. Having less drag results in longer flight and can save up to millions of dollars of fuel over an entire fleet [1]. Similarly to lift, the drag can be calculated using equation (2). D = 1 2 ρU 2 SC D (2) Another important concept in aerodynamics is how efficient the vehicle can be. Often this value is used to calculate the extended range, and optimal performance of an aircraft. The aerodynamic efficiency, also labeled the lift-to-drag ratio, is described in equation (3). Aerospace engineers often use the maximum lift-to-drag ratio to select their airfoils based on the flight regime and Reynolds number; see MECH 331,533, and other aerodynamic courses to learn more. η = L D (3) The following section will detail the experimental procedure and apparatus used to acquire the data necessary to complete the lab objectives. The data will then be post-processed, analyzed and discussed. NOTE: Any additional background information relevant to the lab, experiment or analysis that is not common knowledge should be described in this section. Treat a lab report audience as someone who is familiar in your field, however is not directly in your class and may require a reminder on how an apparatus functions or how an important parameter is calculated. If you take any information from the Lab Manual, make sure to properly cite it. Experimental Apparatus and Methodology In order to properly conduct the experiment, the equipment listed below was required . After ensuring all the equipment was functioning properly, the 3D printed aircraft was mounted in the wind-tunnel using a support rod apparatus. Several measurements were taken, at velocity increments of 1 m/s, starting at 10 m/s until 22 m/s was reached. It was recommended not to exceed 22 m/s because of equipment limitations. Due to the configuration of the wind tunnel scales for lift and drag forces, the jet had to be mounted on its side. At each step, the force and drag forces were recorded. Once the experiment was conducted, it was also important to measure the effects of the mounting rod, to properly estimate the aerodynamics of the aircraft alone. To do this, force and drag measurements were taken for this external piece, and then respectively subtracted from the initial ones. One Lab 0 Group 1 Page 1

additional requirement that was not listed in the lab handout [2] , necessary to successfully complete the lab, was to zero the force balance before taking any measurements because of a vibrational issue with the apparatus. The experimental methodology used to accomplish the objectives of this lab takes the actual force measurements, and with proper scaling techniques, estimates the full-scale aircraft aerodynamics. These final results will then be analyzed, and compared to the theoretical predictions – highlighting the major advantages of scale down modelling techniques, or perhaps the limitations of the equipment. NOTES: Please, DO NOT write one line stating: “A full experimental procedure and equipment list can be found in the handout [1]”. Briefly explain the main methodology of the experiment required to accomplish the lab objectives, list the important equipment and provide any additional details necessary for the reader to comprehend. Results and Discussion The final results of the experiment have been summarized in Table 1 . By observation, it is clear that there are several differences between the measured and theoretical values for lift, drag and aerodynamic efficiency. These values have also been plotted to better witness the effects of velocity on the aerodynamic forces; which can be found in Figure 1. The trend from this chart depicts increasing lift and drag force with increasing velocity . At a quick glance, this trend demonstrates the proportionality between the forces and velocity given by the theoretical equations, (1) and (2). However, the percent difference between the measurements and mathematical solutions are as high as 150%. Several reasons could explain these discrepancies, and will be discussed thoroughly shortly. Table 1: Summary Table of Final Results at 22 m/s Type Lift [N] Drag [N] Aerodynamic Efficiency [ ] Takeoff Configuration Actual Experiment 1.40 0.50 3.0 Theoretical Prediction 1.50 0.20 7.5 % Difference 6.67 % 150.0 % 60.00 % Cruise Configuration Actual Experiment 0.38 0.10 7.6 Theoretical Prediction 0.60 0.05 12.0 % Difference 36.67 % 100.0 % 36.67 % Lab 0 Group 1 Page 2

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Figure 1: Chart depicting the effects of velocity on lift and drag force Answer Discussion Questions Here. Each lab report will have unique questions, and are considered to be the most important part of the lab. Try to separate each question in a paragraph but make sure they are incorporated into your text. Point form is not acceptable. Conclusion In this lab, we measured the aerodynamic forces exerted on a scaled down aircraft; accomplished by mounting the model in a wind tunnel and using an analog force balance to measure lift and drag. The actual measurements and the theoretical calculations were then compared, as per the main goal of the experiment. In conclusion, the objectives of the lab were mostly successful. The final results demonstrated the aircraft was capable of producing sufficient lift force for takeoff and cruise. The final values during takeoff, for a velocity of 22 m/s, were found to be 1.4 [N] of lift, 0.5 [N] of drag and an aerodynamic efficiency of 3, which is actually quite lower than expected. In fact, there were several discrepancies between the actual values, and the predicted ones; some of which were as high as 150%. Although several sources of error were listed, the main concern was the intense vibrations coming from the wind tunnel and thus inconsistency of the analog force measurements. Nevertheless, the overall trends predicted the theory presented in the introduction, and the team is satisfied with the results. If another iteration were to be conducted, the experiment should attempt to minimize the vibrations of the wind-tunnel and take the measurements once again. Furthermore, a smoother model would be used than the one in the experiment, which had many chips and ridges along the wings; can be seen in the appendix figures. References [1] Wheeler, A. J., & Ganji, A. R. (1996). Introduction to engineering experimentation . Pearson Education. Lab 0 Group 1 Page 3