Could the reader be credited with the intelligence to keep in mind that there are several different definitions of Angle of Attack, and to use the one that's appropriate for the work that they're doing at that time?dr.aero wrote: Back to angle of attack: so essentially what you're doing is coming up with a different definition for angle of attack, one that makes sense to you under the conditions of a specific subject, but will fall apart when you start going into different subjects.
I did whatever I had to do to keep the Cl line in the same place on the graph, yes.You had, by keeping the chord line relative to the shape of the airfoil, kept the CL line in the same position (roughly).
You draw a correct conclusion, but from something I didn't say. I didn't say the Cl was the same. I said the Cl curve was the same. Cl is a function of angle of attack. Change the angle of attack - and keep the same Cl curve - and you get a different Cl. That's what gives you the different lift. I hoped that was reasonably clear from the graph I sketched (remember Angle A and Angle B, and the two different values of Cl noted on the graph? Maybe it wasn't clear.)Look at the lift equation --> L = 0.5 rho V^2 S Cl -- you claim that the angle of attack had increased, resulting in more lift, and the Cl had stayed essentially the same. But in the lift equation you have no place to account for AoA separately. AoA and the coefficient line determines what coefficient of lift you're at and the Cl is what determines the lift! So if you make the Cl stay the same, by saying the angle of attack changes, you really haven't changed the lift at all. Does that make sense?
Alright. I understand now, that when you say zero lift angle you mean "relative to the zero lift line of the clean wing". When I say "zero-lift angle" I mean, relative to the zero lift of the wing section as it is, at that second. I will take your word for it that's not how the term is used by professional aerodynamicists. It's how I think Denker uses it (I'll email him to check), but, regardless, there does exist at every moment a physical quantity that is "the angle of the airflow relative to the zero lift line of the actual airfoil section as it exists at this precise second, clean or otherwise". That's the one I want to use. It's a quantity of interest to me, I'm allowed to use it, and I will use it - it's my explanation, after all. I'm much less interested in what name we give it. We can call it something else if the name clashes with a different physical quantity used in any given textbook. But - if you're going to critique my explanation, I'd like you to do it accepting that terms are used to mean what they're defined to mean in that explanation - not in an unrelated academic text. it's out of order to say "that's not the right definition of zero-lift angle". It's my explanation, and my definition. Let's pick a different name for it, if we need to.Back to your quote I have at the top - you say "zero lift angle". That essentially means zero lift angle of attack (geometric). I explained that in detail in my last post (stating that it was the chord line of the clean wing) and you said you understood it. Knowing that, does that clear it up?
If you want to give me a slap on the wrist for using "standard" terms in a non-standard way without explaining them clearly, then I'll accept it. I've learned from numerous discussions on the Internet and elsewhere to make sure that you all use terms in the same way otherwise, yes, you're going to be arguing two sides of two different arguments.
Thank you by the way - I appreciate your consideration, and particularly, your engagement with the technical details.
Are you going to answer my question about providing proof for you? Or have you decided that you won't want any proof now?
Geez! I'm done with this crap. 
