## Friday, February 29, 2008

### Calculus + The Cat in the Hat = Drag Coefficient

So, I’m taking one of the hardest classes in the ME curriculum – Aero-Thermal-Fluids lab. Essentially, each week we work on a new experiment. These past two weeks we’ve been using the wind tunnel to calculate lift and drag coefficients for an airfoil, specifically for the NACA0012 - first with pressure taps on the wing and the second (only the drag) by measuring the momentum thickness of the wake.

I need some help with the error propagation calculation and naturally I go to the prof (Dr. Andreopoulos) for a bit of insight. It’s usually pretty simple: get the equation in standard form, do partial differentiation on the key terms, finally solve based on the error amount. I don’t expect everyone to understand that but know that there is a process. After talking to him for a while, I can not get our variables into the standard form but he goes on and on talking out his butt about the next few steps which are easier but make no sense because step one is not completed and that is essential so as to move on.

I don’t like to waste anyone’s time so I left to work on it myself. Granted through it all, I did get a few bits to gnaw on and with some work I got the standard form. I come back to discuss the manner he did the partial differentiation. There are lots of ways of doing it, in this case only a few, but I’m not getting what he did.

So, I’m back in his office and trying to get what he did, he won’t even listen to my question, which pisses me off a freak of a lot because it is like a disease among profs at my school. Once they get tenure, they flush the listening skills. He goes on and on about simple bs in the partial differentiation which like I said is the easy bit. Finally, I abruptly and poignantly say, “Can I finish my question?” A friend in the room braces himself for what’s next. I ask my question; he explains he is using a substitution but he didn’t write it down. “Oh, now I get it.” I say. (I could have had 20 more minutes of life instead of that meeting had he listened from the beginning. It also would have spared me 2 hours of second guessing myself.)

The worst part was as he was going on and on he kept saying, “It’s partial differentiation. It’s partial differentiation.” I’m thinking “No shit, I wouldn’t be in a 400 level engineering class if I didn’t know how to do it.” I will give him that we do have quite of few people who graduate with many mercy C grades.

Anyway, I go back to the drawing board and solve the bloody equation. I compare to what he did and his work is wrong! It is dirty stinkin’ wrong! (For you math gurus, he used a substitution in the chain rule but squared the sub-elements when he should have only squared the entire element after reverting back from the substitution.)

I’m pissed! Hours wasted! I tell my buddy Jake, I am dedicating this semester to being the Dr Seuss of pronouncing that prof’s name. This week he is Prof. Andrepreposterous.

Tune in next week for the story of the Greek family during Nazi Germany who hired a nun to take of the kids. While she sprightly sings about her favorite things, the Van Tropoulos children chuck plates at her feet – shattering and augmenting the gaiety. The father of the house is elated she brought music back in to the home. Eventually the family escapes the Nazis but where do they end up? Tune in next week!

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