Calculating Coefficient of Lift: Angle of Attack of 7°

  • #1
yecko
Gold Member
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1. Homework Statement
https://i.imgur.com/tG9unNs.png
tG9unNs.png


2. Homework Equations
in picture below

3. The Attempt at a Solution
https://i.imgur.com/egZC3Ay.jpg
egZC3Ay.jpg

I calculated the angle of attack is "7", yet the answer is "1", which implies the coefficient of lift is about 0.2 from the answer. I am not sure where of my answer have got mistake...
can anyone help?
thank you very much!
 
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  • #2
I think there is a problem of slugs versus lbs. Standard atmosphere has density 0.000889378 slugs/cubic foot, not lbs/cubic foot. Using your numbers, I get Cl = 7.3, which is way too high. But dividing by 32.2 gives Cl = 0.23
 
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  • #3
Thank you very much!
FactChecker said:
Standard atmosphere has density 0.000889378 slugs/cubic foot, not lbs/cubic foot.

It is because https://i.imgur.com/a43giFt.png is what I have got in my assignment and I misunderstood lb(f) as lb(m) represented by lb in the question.
a43giFt.png

So, I do not need to multiply 32.2 on the right side.

FactChecker said:
But dividing by 32.2 gives Cl = 0.23

Thank you so much for reminding me!
 
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