Lab4_PBevis
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School
University of Colorado, Boulder *
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Course
1070
Subject
Aerospace Engineering
Date
Apr 3, 2024
Type
Pages
7
Uploaded by PresidentFireSquirrel30
Lab 4 Report
Name: Peyton____________________ Partners: _Drew Noah_______________ , _______________ Please paste your Excel data and graph below this line. Highlight everything you need in Excel, copy, and then use ‘Paste Special’ to paste as an image (e.g., PNG, PDF, etc.). You can take a screenshot as well and paste it here, but please make sure it is easily viewable by your TA. Please remove the example image below before pasting your own.
Question 1 (10 points): a.
Is your experimental value of n
greater or less than the expected value of 2? Our value is greater at 2.1038 b. Choose 1 condition (A-D from lab manual) that you think makes the most sense here for your experiment’s physical shortcomings. Which one did you choose? Condition B c. For the condition you chose, what problems with the setup or experimental procedures could have caused this specific measurement to be higher/lower than expected? It is possible that the pressure gauge in the wind tunnel causes abnormal wind flow. Question 2 (10 points): a. What kind of vehicle was your model car? (often written on the bottom of the vehicle) Hot wheels monster truck (not written) b. What was the wind speed (m/sec) you measured when the model blew out of the tunnel? 10.1 m/s c. Based on your experiment, what wind speed in miles per hour (multiply m/sec by 2.3 to get mph) would move or turn over a full-size vehicle (remember to also use the scaling factor of 4 here)? 92.92 miles per hour
d. Does your predicted wind speed (for the full-size vehicle) seem high enough to blow your type of vehicle off a real road? Justify your answer. Yes, because it takes 60mph+ winds to move a normal car. e. Give two differences between the model sitting in the wind tunnel and a real car in a real windstorm on a real road (Besides the aforementioned differences of scale). The car does not have enough weight relative to the scale of the car. Also there is far less friction with the plastic wheels on a plastic surface compared to real roads and vehicles. Question 3 (10 points): a. What was your measured wind speed (m/sec) for this part of the experiment? 6.45 m/sec b. Multiply your wind speed in m/sec by 2.3 to obtain the speed in m.p.h. 14.84 miles per hour c. In order to scale your measurements, multiply the speed in m.p.h. by 10
. What do you get? 148.40 miles per hour d. What was the lowest negative pressure (i.e., which negative value was the most negative) measured on the hut? -0.055 kPa
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e. Multiply your answer in Question 3d by 2100
*
to arrive at scaled pressure units of pounds per square foot (lbs/ft
2
).
*The 2100 number converts pressure from kPa to lbs/ft
2 and scales the P value by 10
2
since we scaled V by 10 (remember dynamic pressure equation). -0.055 x 2100= -115.5 lbs/ft
2 Question 4 (10 points): Consider a 100 square foot section of roof (10 feet by 10 feet, or 100 ft
2
) a. Using the pressure from Question 3e, what is the magnitude of the upward force [pressure (lbs/ft
2
) times area (ft
2
)] exerted on this section of roof by the winds? Show work and units! -115
.5 lbs/ft
2
x 100ft
2
= -11550 lbs b. A 10 by 10 foot section of an average asphalt roof (with underlying wood) puts roughly 800 lbs of downward force on the roof. Divide the magnitude of the upward force due to the wind (your answer to 4a) with this 800 lb downward force due to gravity. This is now a ratio of upward to downward forces. How many times larger or smaller is the magnitude of the upward force when compared with the downward force (your ratio should give you this directly)? Show your work! -115.5 lbs/ 800 lbs=-14.44lbs c. Based on your calculation, what do you think your wind force would do to this average roof?
Based on our calculation I believe the average roof will come off relatively easily. This is because the ratio of upwards forces is 14 times the downward force. Conclusion Question 1 (10 points): Identify 1 potential physical or experimental source of error for Experiment 1 and explain how it may have affected the final graph of dynamic pressure vs. wind speed. A physical source of error in the experiment is that the instrument that measured the wind flow was not stable and instead was being held. Also, the chamber has a lot of spaces and places air can flow besides the pressure gauge and the wind speed instrument. This could cause inaccurate data. Conclusion Question 2 (10 points): Identify 1 potential physical or experimental source of error for Experiment 3 and explain how it may have affected the final graph of dynamic pressure vs. angular position on the Quonset hut. One potential physical or experimental source of error for Experiment 3 could be that in the experiment there was likely not uniform airflow through the whole chamber. This could easily give wrong data without consistent flow.
Conclusion Question 3 (5 points): Sum up all pressures for all angles around the Quonset hut. Does this value come out as negative or positive? Does this mean that the air has an overall lower or higher pressure than ambient pressure? The overall sum of pressures around the Quonset hut is likely to be negative. This negative value indicates that the air pressure around the Quonset hut is lower than the ambient pressure. Conclusion Question 4 (5 points): Some airfoils show some resemblance to the shape of the Quonset hut. The wind across the foil moves from left to right. Assume that the air flowing underneath the foil has a pressure about equal to ambient pressure, while the the air flowing over the top has a pressure like the one you deduced in Conclusion Question 3. Would this vertical pressure gradient (change in pressure with height) create lift or not? Explain your answer. The vertical pressure gradient would cause lift. As the airflow moves over the curved upper surface of the airfoil, it accelerates, and the pressure decreases. This creates a pressure gradient between the upper and lower surfaces of the airfoil, with higher pressure underneath and lower pressure on top.
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