Quote from 510N3D :

Right, are your sure you understood the context in which i made this statement correctly?

Yeah. I figured that was what you were talking about, but the fact that you wrote "I think" made ME think that you weren't 100% positive, so I was simply agreeing with you

Quote from Dark Elite :

I'm now completely stuck between deciding whether air moving more quickly results in a higher pressure or a lower pressure. Air moving more quickly means that air doesn't need to be in the same place for as long, resulting in a lower atmospheric pressure, but also that more air hits the surfaces of the wing, resulting in a higher pressure on that. Which effect is greater?

Better find out before I go any further on this one

Sam

Well, air moving more quickly parallel to the surface would result in a lower pressure, pulling it up. If the air is moving more quickly at an angle less than 180 degrees then you start to get the effect of the air pushing back down on the wing. My guess is that there is a critical angle at which point the air hitting the wing overpowers any effect of negative pressure. Especially since as that angle gets larger, the air isn't really traveling as fast over the wing anymore. Wonder what that angle is...?

Quote from Stang70Fastback :

Yeah. I figured that was what you were talking about, but the fact that you wrote "I think" made ME think that you weren't 100% positive, so I was simply agreeing with you

Ah ok then, my bad, fair enough, guess i missunderstood your reply and the context of it. Nevermind then

Quote from Stang :

Well, air moving more quickly parallel to the surface would result in a lower pressure, pulling it up. If the air is moving more quickly at an angle less than 180 degrees then you start to get the effect of the air pushing back down on the wing. My guess is that there is a critical angle at which point the air hitting the wing overpowers any effect of negative pressure. Especially since as that angle gets larger, the air isn't really traveling as fast over the wing anymore. Wonder what that angle is...?

It wouldn't be a given angle, would it, because it would be changed by the difference in velocity, the velocities themselves (seeing as drag/lift is proportional to the square of the velocity) and then the angle. There's probably a formula for it somewhere in the bowels of Wikipedia, but... Meh. It's not important enough to find it

Right, I've looked into the pressure thing myself now- bit of research never goes amiss! The fact of the matter, it seems, is that the higher the speed of the airflow, the lower the pressure. So what I said in #22 is actually the opposite of what would happen

The tilting and curving of the wing will slow the air down in the areas that are curved or exposed - but seeing as the air will either pass straight underneath the curved area or along it, air going underneath the wing actually won't be affected by the curve very much, will it? So the air underneath remains pretty fast, whilst the air above slows down quite considerably - thus gaining a higher pressure and pushing the wing down. Then you have the effect of the air pushing against the wing as well, but whether this is the same effect, another effect, or just drag, I'm not sure.

Have I finally got this the right way round now?

Sam

Quote from Dark Elite :

The tilting and curving of the wing will slow the air down in the areas that are curved or exposed - but seeing as the air will either pass straight underneath the curved area or along it, air going underneath the wing actually won't be affected by the curve very much, will it? So the air underneath remains pretty fast, whilst the air above slows down quite considerably - thus gaining a higher pressure and pushing the wing down. Then you have the effect of the air pushing against the wing as well, but whether this is the same effect, another effect, or just drag, I'm not sure.

Have I finally got this the right way round now?

Yes that's better. In your Post #22 I was like FASTER AIR IS HIGHER PRESSURE?!?!? NO WAY!!

This is the way I see it:

This pretty much spells it out

The front car does get a substantial gain in speed from a car in behind drafting, but not as much as the back car. This is why drivers will pair up and drive away from the field, the back car is "pushing" them without necessarily touching them. Then you get into bump drafting and you get goin quite fast if you don't crash :P

also, this says its about stock cars, but it applies in this way to pretty much everything.

So was I right about the whole two cars drafting then? That's pretty sweet. I feel smart, lol

Don't try and explain how wings work - scientists have been trying for hundreds of years (well, maybe not hundreds), and so far they've whittled it down to about 10 conflicting arguments, none of which are fully understood, and none of which really work experiementally.

They just work. Very very very vague approximations, like Bernoulli's equations, seem to work, but don't actually hold up to investigation.

Quote from Stang :

I would think that would make more sense...?

Considerably so.
With 'curve' in #28 I really should have been saying 'tilt' - what I meant was the curving effect the wing had on the airflow, but I managed to express it exceptionally badly!

Thanks for that. I was considering it much too much in an aircraft sense, where the tilting angle of the wing is obviously lacking, seeing as that's where my basic (and then butchered) understanding of aerodynamics came from

Sam

Quote from tristancliffe :

Don't try and explain how wings work - scientists have been trying for hundreds of years (well, maybe not hundreds), and so far they've whittled it down to about 10 conflicting arguments, none of which are fully understood, and none of which really work experiementally.

They just work. Very very very vague approximations, like Bernoulli's equations, seem to work, but don't actually hold up to investigation.

That's what happens when humans are trying to push the technological limits.

I'm studying in engineering and there are may questions classmates asks and teachers are often researching about it.

Quote from -DrftMstr- :

That's what happens when humans are trying to push the technological limits.

I'm studying in engineering and there are may questions classmates asks and teachers are often researching about it.

Exactly. Besides, it's FUN trying to explain it. Especially if you're an engineering student.

I guess it shows how little we truely know about aerodynamics when I,
a senior in high school with one semester of physics, know almost as much as
you engineering people.(notice i said almost)
Kinda makes me not want to get on a plane ever again.

I have an easy way toi explain drafting for the un-initiated:

Imagine a clear day with a 0kph wind. No wind at all.
Now, imagine a car moving at 300kph.
One milimiter in front of the car, the wind is 0kph.
As soon as the car passes, in the same exact spot, the wind is now 100kph, in the direction the car was moving.
(You can see this effect when cars are going in roads with leaves on them - the leaves fly away, following the car).

Now, if you put your car right behind the fast-moving car, instead of having wind coming into your windscreen @ 300kph, since the air is moving in the same direction you are @ 100kph, the wind hitting your windscreen (or car) is only coming @ 200kph. So in fact, you are only getting the drag of a car moving @ 200kph.
(so your engine has an easier time to push the car faster, so you go faster).

All the above numbers have been pulled out of my rear end. Plus, there are other things that add complexity to this: The wheels on the ground keep their 300kph drag, among other things.
But the basic idea is this: a fast-moving object pulls air behind it, and thus, another object close to it will have a lower speed in relation to the wind.

Even easier way to explain it:

Imagine your neighbor plowing the snow in his 4x4 while you follow him in your lower V-Tack Civic. You make much less effort and so you go faster.

Quote from EvilVendingMachine :

I guess it shows how little we truely know about aerodynamics when I,
a senior in high school with one semester of physics, know almost as much as
you engineering people.(notice i said almost)
Kinda makes me not want to get on a plane ever again.

I was thinking the same thing. I'm a freshman in college - and haven't had ANY aerodynamics or anything courses yet, and yet here I am explaining things to Aerospace Majors...

WTF?! Lol.

Quote :

Correct. It's a Newton's Third Law type of setup. Air pushed up by the wing pushes the wing and car into the ground.

Incorrect.

Air flow UNDER the wing PULLS the car down.

Best, Maz

Yeah, you're right. I did the research after this discussion but forgot to post the results

Air cannot pull. Air can only push. So the LACK of air under the wing can't push as hard as the air on top, and so the air on top wins.

Rope is great for tension, but rubbish in compression.
Air is rubbish in tension, but rather better in compression (at speed, over aerofoil sections etc etc).

All very simplified as there isn't a human being who has ever lived that understands exactly how and why wings work.

Quote :

All very simplified as there isn't a human being who has ever lived that understands exactly how and why wings work.

Aerodynamics are well understood, wings especially and certainly not a black art in automotive racing terms.

Quote :

Air cannot pull. Air can only push. So the LACK of air under the wing can't push as hard as the air on top, and so the air on top wins.

Incorrect. If you hold you hand out of the window of a car, angled upwards front to back like the rear wing of a formula single seater, it is not the air pushing your hand down.

The air underneath your hand travels faster than the air above your hand, pulling your hand down. When you increase the steepness of your rear wing the distance the air has to travel underneath increases and this gains more downforce, or negative lift.

Best, Maz

Quote from Mazar :

Incorrect. If you hold you hand out of the window of a car, angled upwards front to back like the rear wing of a formula single seater, it is not the air pushing your hand down.

The air underneath your hand travels faster than the air above your hand, pulling your hand down. When you increase the steepness of your rear wing the distance the air has to travel underneath increases and this gains more downforce, or negative lift.

No. That is wrong. In that case, the force that pushes your hand down IS the air. If you were to look at your hand in a wind tunnel angled like you state, you would clearly see this. That is because your hand is not curved like a wing, it is flat, and round at both ends. So the air travels just as far under your hand as it does on top, meaning there is equal pressure in that regard. In this case, the force pushing your hand down comes solely from the fact that your hand is deflecting the air above, upwards, which in turn pushes your hand down. If anything, the air under your hand is most likely extremely turbulent as your hand does not have the proper aerodynamics to channel the air neatly underneath.

Quote from Mazar :

Aerodynamics are well understood, wings especially and certainly not a black art in automotive racing terms.



Incorrect. If you hold you hand out of the window of a car, angled upwards front to back like the rear wing of a formula single seater, it is not the air pushing your hand down.

The air underneath your hand travels faster than the air above your hand, pulling your hand down. When you increase the steepness of your rear wing the distance the air has to travel underneath increases and this gains more downforce, or negative lift.

Best, Maz

Aero isn't understood at all. I believe there are about 6 different theories as to why wings work, but none of them are the same. This is especially true on cars, which work close to the ground and in 'dirty' air, causing some very odd behaviour.

In very simplified terms the air under a wing (on a car) or over a wing (on a plane) travels faster, lowering it's pressure, so the pressure differential causes the air on the other side to push. There is no such thing as suction - the higher pressure side is the cause of the force and pushes, and this applies to vacuum cleaners, aerodynamic surfaces or drinking straws.

Quote :

No. That is wrong.

Hehe, sure could be..depending on the exact shape, angle of hand etc, lol

It is a very complicated series of laws to explain easily and I thought that might fit, the point being the air on the racing wing is most certainly pulling down not pushing down.

Best, Maz

Alright, I see what Mazar is saying here. I think Mazar and Tristan are saying the same thing, but Tristan is getting caught up in the definition of what it what. Tristan is technically right - the higher pressure air pushes down on the lower pressure air. I think Mazar understands this, and is not debating that fact. What he's saying is that it is NOT a result of air deflection on top (e.g. Newton's Third Law) that the wing generates downforce, and in order to eliminate confusion, he's using the word pull not push to emphasize this. Is this correct? That way we're all on the same page.

This might help clarify some things, btw.

Quote :

think Mazar understands this, and is not debating that fact. What he's saying is that it is NOT a result of air deflection on top (e.g. Newton's Third Law) that the wing generates downforce, and in order to eliminate confusion, he's using the word pull not push to emphasize this. Is this correct? That way we're all on the same page.

Best, Maz

If that is indeed the case, and we were both stating the same thing in different ways, then I'm terribly sorry for the misunderstanding. It demonstrates well the difficulties of communicating via text alone, even with fairly small language differences.

Yeah you were both right.

But the air "pushes" a bit the wing at first, then the difference of pressure does its jobs.
For example, most race wings have a very small "flat" (or less angled) zone before going up to their standard angle. Thus, the air will go either above or below, and get in contact with the wing when the curve takes angle, pushing it down.
But this is a very small effect of launching the high pressure up/low pressure down pattern indeed, and mostly a unwanted one because it create a very little drag, which is perceptible at very high speeds.