Off topic: Everybody thinks that states like Kansas or Nebraska are so bad and scary because they get huge tornadoes, but what you don't realize is that Arizona is even worse. When I lived in Arizona on a random day in the summer time the winds would start increasing randomly to speeds of 30+mph and then down the street you would see a giant dust devil coming towards you(I have saw a dust devil pick up a metal lunchbox before). These will come straight at you and are very scary.
At least a couple times a week I would see a dust devil. One day I was hanging out with my best friend and a dust storm blew in randomly and the wing speeds increased and everyone knew what that meant. Dust devils where coming down the street and they were powerful. There was 1 dust devil per 15 seconds coming down the street and where large and 1 dust devil that day was so powerful that it hit my friend and pushed him down to the ground.
weird note -- apparently it may be possible now to fly with only a WAAS GPS for IFR navigation, depending on where you are in the country (RNAV (GPS) approaches are being case-by-case evaluated/authorized for use as alternates)
Dust storms are very common in Arizona and people are always saying that seeing that wall of dust looks like the worlds going to end. I have never seen one of these walls before, but I have seen lots of dust devils during these storms and where very scary( way worse than Kansas). Also monsoons where common in Arizona and during my time living there we had 2 supercells form and produce golf ball size hail and that's bigger hail than in Colorado who has a supercell a week.
So if there is any of you who think Kansas is so scary then try living in Phoenix and there's a huge difference.
Also we have had hurricane force winds before that blew my basketball hoop over and caused severe damage to my backyard. I believe on that day it was an actual hurricane or a supercell.
@casey Hmmm, for some reason that "spin" visualization is causing problems in my head because it reminds of how turbulent air looks going over the top of the wing... But I can see what you mean. Are there formulas for figuring out spin and splat on a wing? (I assume the answer is yes... What are they?)
@JayCarr you can't have the low pressure on top without the high pressure below, I feel it confusing to separate the two things, they should be treated as two parts of a single fenomen.
Seeing as to that we are in principle in the green on the Area 51 statistics (I know these are not exact) and have been for some time.
I feel we have what is a solid community represented by a fairly distributed group. These have varying areas and levels of expertise that should ensure that the...
@falstro put a hand in a bowl of water (or a pool) and try to push the water to one side, you will have "high pressure" (wave forming) on the side you push towards and "low pressure" (if you push hard enough you will see a lack of water) on the other side
I'm just saying that your statement a "wing can't have high pressure below without low pressure above" is false, or at the very least lacking some conditions. Just increase the air pressure below and you've got it. The wing can't "produce" high pressure below without "producing" low pressure above should suffice.
@Federico just to be clear, you're saying that bernoulli's principle cannot actually create a pressure differential where one side is ambient pressure and the other is not?
(not trying to call you on it, I'm asking because I don't know)
no, I am saying that you cannot push a fluid with a finite solid object and not have a high pressure side while at the same time not having a low pressure side (or viceversa)
Bernoulli, like Venturi, needs a change in cross section available. Even if you would consider the atmosphere bounded rigidly both below and on top, the cross section of a wing hardly makes a difference.
In the classical depiction of Bernoulli you have a fluid inside a tube, you have no interaction between what's inside the tube and what's outside, it all relies on the tube to be infinitely rigid
@Ethan I'm pretty sure the answer will be a resounding "no" all around. I guess it depends on your definition of ghost for some (for me it's still no though)
@JayCarr in that case do the stirring cup visualization. Fill the cup mostly full. The pressure at the bottom of the cup is the weight of the atmosphere and the water above it, and the water being much more dense we can focus on that. Stir the water and note that the fluid in the center of the cup dips low. The faster you stir, the lower the fluid level dips. If less fluid is over the center of the cup than the edges, there is less force down on the middle of the cup (m*g)
and so the pressure is lower
you can see it in drains as well when a vortex forms and the water level inside the vortex drops dramatically. that is also spin
@Federico That's more or less what I said in my example. The wing creates both phenomena by moving through the air.
@casey Ah, got it. Can you maybe point me at some formulas for all of this (for people who might possibly suck at math and need really good descriptions of all of the variables?)
yeah, but then you insert remark like this: "The air being pulled down is what makes the downwash." while you cannot isolate the air "pulled down" (above the wing) from the one being "pushed down" (below the wing). They both are part of the downwash and I feel that focusing only on one and mentioning the other with a sentence there almost "by chance" ("But yes, the pressure on the bottom of the wing also matters.") can be misleading.
@JayCarr the simplest is a very generalized "perturbation pressure is proportional to dynamic pressure perturbation - buoyancy pressure perturbation" and "dynamic pressure perturbation = splat - spin"
and "perturbation pressure" is just the pressure anomoly
and this is true for well-behaved pressure fields where $\nabla^2 p' \propto -p'$
@JayCarr "If a group of angry students push Dr. Brack off the roof of the building, assuming a partially elastic collision {insert parameters I don't remember here} and neglecting air resistance, how high will he bounce?"
@casey The best calculus textbook I own (and I happen to own several because apparently you can't escape calculus by taking Computer Science!) is from the 1960s or 70s - it's pea-soup green clothbound with some kind of torroidal solid on the cover, and the title is "Calculus".
I took my differential equations class with the textbook 5 editions old I got used on amazon for $2. I think I found two or three assigned homework problems that differed and no actual content changes aside from those problems...
@casey The joke in my college math department about the Anton calculus books is that each new edition just corrected some error in the solutions manual (or replaced an unsolvable problem with one that actually works).
I remember in my Calc3 class we were working on one of the problems for an entire 2 hour class period, and about 15 minutes from the end the professor got this funny look and we all started muttering to ourselves - I think we all reached the same conclusion of "This doesn't converge" at around the same time
@voretaq7 my vector cal (probably the same as cal3) instructor did this a lot. He'd work for 90% of the class on a problem, realize it can't be solved with the methods we learned in class, then he'd pull some masters level math out just to prove it could be solved.
@voretaq7 I have a pretty good text book on fourier analysis somewhere. To date the only maths textbook I've opened after the final... I liked that class. For once maths turned out to be actually useful for something. ;)
@JayCarr Being a teenager you get so mad at something and then tears come out of your eyes. I get mad and if I'm mad for long enough I will start crying its so weird.
The wifi is not working is when I get really ticked off.
Seeing as to that we are in principle in the green on the Area 51 statistics (I know these are not exact) and have been for some time.
I feel we have what is a solid community represented by a fairly distributed group. These have varying areas and levels of expertise that should ensure that the...
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