Aerodynamic Definitions

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KennyFlys

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I'm trying to develop a better lesson plan on aerodynamics. So, I was digging through some college course notes I found.

I'm reading "dM" and "dL" with regard to static stability. I understand "M" represents Moment but what is "d" representing?

Thanks for the help!

Tony, I looked for ya online... where were ya?!?! :)
 
I'd assume that it's Delta, as in "change in" moment and change in L.
 
Teller1900 said:
I'd assume that it's Delta, as in "change in" moment and change in L.
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Ahhhhhhhhhh..... ok. That makes sense. If they had used "Δ" I would have caught on right away.

I suppose this is one of those... well, in my case the "d" is for "Doh!" :)

Thanks Matt.
 
I think it is short hand for differential. Used in calculus when integrating an equation.

It kinda does mean delta in a way.

The differential of M, or dM, means a unit of M or a piece of M. If it is written dM/dL. It means the change in M with respect to L. Kinda like a velocity.....Miles/hour.
 
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Usually,

dM/dL would mean the derivative of mass with respect to something. I suspect that M is not moment, usually M is used for mass and I is used for moment. I have usually seen delta something spelled out deltaM.

I cannot think of what L is for off the top of my head.

Post some excerpts and I can help you make sense of the gobblydygook.

~ Christopher
 
jwriteclub said:
Usually,

dM/dL would mean the derivative of mass with respect to something. I suspect that M is not moment, usually M is used for mass and I is used for moment. I have usually seen delta something spelled out deltaM.

I cannot think of what L is for off the top of my head.

Post some excerpts and I can help you make sense of the gobblydygook.

~ Christopher
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In this case, M is for moment and L is for life. You are right Christopher, it is the derivative of moment to lift. the little d means for little changes or little deltas. It is a term used in calculus. Derivatives are a way of showing rates of change for one thing related to another in a common function.

In linear math where a line can be described by the equation y=mx+b, m is the first derivative of the function and in this case it is the slope. The slope tells us how steep the line is or in another term how fast the value of one item (y) will change in relation to another value (x)

Here is a very detailed explanation for those that want to know or those that forgot about Calc 1, http://www.hyper-ad.com/tutoring/math/calculus/Derivatives.html
 
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As long as I don't have to deal with the square root of -1!
 
Yay journalism degree! After reading Scott's post, informative as it may have been, I wish we had a smiley of a guy looking confused, then his head blowing up. Cause that'd be a great one for me!
 
Scott has it right -- it's the first deriviative of Moment with respect to change in Lift. It's the slope of a tangent to the M vs L curve at one particular point. And now you know why we required Calc I before taking Aerodynamics at the university.
 
kenny - yea they got it right. not online cause im in the middle of moving half way across the state. keep us updated on how your checkride goes!
 
smigaldi said:
it is i or j depending on your field, easy!
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In my case, it was i and I did not have the least desire to work a calculation where i was anything but resulting in ice cream. :)

My ex-girlfriend's father was a retired HS math teacher. He would try to explain it to me. Key word: "Try!" He was a smart man, though. During WWII, he was a navigator on B-17s out of England. Now, I wish he were around when I'm more capable and desiring to learn.
 
tonycondon said:
kenny - yea they got it right. not online cause im in the middle of moving half way across the state. keep us updated on how your checkride goes!
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It was slated for Tuesday and Wednesday but after a couple days lost to weather and a couple more to equipment problems, today I decided to put it off until after the first. As of now, it's scheduled for January 11 and 12.

Brian had two concerns as did I. One, that I was ready without the slightest question. Even though it's with a DPE, FSDO still rides the school as well as Brian pretty hard about how well prepared candidates are. Two, the less doubt I have and the more confident I feel when making my first appearance, particularly for the FOI, the easier the rest of the exam will go.

Only now am I really doing a decent job of talking through a maneuver and teaching the elements. They aren't perfect but I'm talking which was a huge step for me considering how quiet I am most of the time.

Living alone all these years (talking to a cat) and driving by myself with limited interaction with customers has been somewhat of a detriment. So, I've got to make sure... I'm no longer as quiet. Uh oh, look out! :)
 
Back to the original topic: I stand corrected, but slightly confused.

In physics (my field) we usually use different symbols.

Essentially what slide 9 is saying is what you already know: If there is a little extra lift, this causes a small change in lift (dL) which causes the aircraft to rotate around the CG (dM). To counteract this there must either be a small decrease in lift (unlikely to happen spontaneously) or there must be something "turning" back the other way (dM/dL negative).

~ Christopher
 
KennyFlys said:
Only now am I really doing a decent job of talking through a maneuver and teaching the elements. They aren't perfect but I'm talking which was a huge step for me considering how quiet I am most of the time.
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You? Quiet?!?!

I don't believe it. :no: ;)
 
Okay, so I get a little noisy when I kick my cat out of the way. :)
 
jwriteclub said:
Back to the original topic: I stand corrected, but slightly confused.

In physics (my field) we usually use different symbols.


~ Christopher
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There certainly are some pretty standard symbols, but there just aren't enough roman and greek letters to go around. Consider the virtually infinite number of properties that could be measured and described in an equation. Even in physics there is a lot of doubling up and you need to consider context. It gets much worse when you're working accross disciplines and everybody uses different conventions (like i vs j for root (-1)).
 
Your point is well taken.

Which is why it is important to include the "where x = ..." after an equation.

~ Christopher
 
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