Rich Sandor

Here is a scan from one of my aerodynamics textbooks: Race Car Aerodynamics, by Joeseph Katz

944J

there is not such thing as an INTENSITY of a vector. A vector only has a magnitude and direction.

So you are saying that somehow a new force is created magically when the angle of a wing is changed?

I say no, that its the same force (force of the air moving over the wing) that produces drag and lift.

I'm talking about forces, you are inventing different words to describe the same force.

Rich Sandor

You're correct. I used the wrong term... when you change the "angle of attack" a wing, you increase the MAGNITUDE ("intensity" is an incorrect term..) of the Lift Vector, and therefore, you increase the magnitude of the drag vector, (but not it's direction.)

No, I only said that the Magnitude of the Drag vector increases. There is no new force. Refer to my previous diagrams. Thrust acts forwards, horizontally. It is opposed by Drag, which acts opposite to Thrust. Lift acts vertically upward, which is opposed by Weight.

"Air moving over the wing" is NOT a force. Thrust, Weight, Drag, and Lift/Downforce are the only forces acting on an airfoil.

Refer to the previous diagrams I posted.

I'm not sure how old you are, so I don't want to make any assumptions about your experience. What sort of formal eductation do you have in terms of Physics, Engineering, and Aerodynamics?

944J

Very simplified, but we are still saying the SAME THING, your explanation is the 9th grade version of what I am saying.

What do you get when you add the two vectors together? You get a resultant vector that is 45 degrees and in a different magnitude that is the actual force acting on the wing, this means:

the wing cant go up AND back at the same time so it takes the middle path which is up and to the back because there is just one body of air producing the force on the wing, if they are different forces then you would have to have one group of air molecules acting under the wing and one group of air molecules acting in front of the wing, but we all know that this isnt the case, the actual physics treats it as one body of fluid.














sources:

http://en.wikipedia.org/wiki/Bernoulli%27s_principle

http://web.mit.edu/wwmath/vectorc/summary.html

http://www.av8n.com/how/htm/airfoils.html

Rich Sandor

No we are not. You think that Lift and Drag are the same. They aren't. Even the aerodynamics proffessor who drew that diagram is telling you that they are two different forces. Yes, one is a result of the other, but it is still a different force which acts in a different direction.

First of all, why would you add those vectors together? The only time you combine vectors, is when one of them in acting at an angle, and you need to measure the vertical or horiztonal component.

Also, you KNOW that thrust and weight are missing from the diagram, yet you somehow theorise that the lift & drag vectors result in a net "upwards & backwards" force? Why would you even bring that up, it's totally pointless..

My reason for posting that diagram was to PROVE to you that an educated Aerodynamics PROFESSOR says that Lift and Drag are two difference forces acting in two different directions.

If you cannot understand and accept that, then you may as well be argueing that 1 + 1 = 3.

By the way, posting articles from all over the web after 15 min of googling, does not mean that you know anything about the subject.

testarossa_td

Holy flightplan Batman!

luckett

DING! DING! end of round one.

BTW, Rich is correct.


Now for round two, let's discuss efficiency and how you can have equivalent levels of negative lift and different levels of drag.

Rich Sandor

Meh. There's no point in internet debating when everyone has access to google and can pretend to know what they're talking about. Besides, I've got some friends (cute female ones too! . and human to boot!) waiting for me to join them at a local pub. I'm outttta here!

BeerBurner

So, if you had an airplane on a conveyor belt and- <gets shot>

user 8430

Yah it'll flty if you can get a pilot stupid enough to fly it!!!
-Rich

944J

force = mass x acceleration. The only thing accelerating with mass is the car and inversely the air (the fluid) across the car hence creating the force acting on it. This is an equation I learned in HS and in my freshman year when getting my Physics degree at UCLA. The engine creates the force, moves the car, then the air pushes down and back on the car. The air is the last accelerating mass acting on the car, hence the Fa (force of the air) creates drag and downforce. (just change the component of drag and the Fdrag turns into what you call thrust, change the component of Fa and it turns into lift or downforce.)

The only time the forces are referred to as separated vectors are on paper in order to calculate the different vectors (like if you want to know how much heavier the car is due to the force of the air pressing on it), but the actual FORCE is from the movement of the fluid (air) over the surface of the car. That's why a stock 944 spoiler/wing has a force component in the negative x direction (backward) and in the negative y direction (downward). One FORCE (force = mass of the air x acceleration of the air over the car) acting to create a net force that if all things are equal ~ 140deg force (backwards and down at a 45 degree angle) on the stock 944 spoiler/wing. Remove the wing and there is less -x component and less -y component (less downforce and drag) so you loose the benefits of keeping the car on the ground at high speeds where it tends to lift.

Also see my sources where they state that to calculate the speed of air over a wing you don't take the speed of air at any point but right before it comes in contact with the wing. So its kind of crazy to say that the air isn't a force.(it's not unless its accelerating which it is)

You said removing the lower wing creates MORE drag and thats where this started because I feel that removing the wing gives the car less drag and less downforce because the big thing sticking in the way of the air is gone. You don't need to calculate anything to come to this conclusion. Thats why drag speed king cars don't have the spoiler like on a stock 944, because having it slows them down and creates, as you call it, drag (or a negative acceleration in on the x axis):



notice no horizontal rear spoiler/wing

tifosiman

FYI I have been told the 924/944 rubber strip is no longer available as well. For the weight weenies, the 944 euro bumper is lighter than the 951 unit, it is thinner fiberglass and doesn't have the heavier provisions for a tow eye. The thickness difference between the two strips is very small, about 3/4 inch or so. I personally like both for different reasons, but to each their own.

All this bantering back and forth about lift is a real drag.

Guns951

Did someone say downforce? Personally I think this is the best approach after the TRS wing which I think is way to "sleeperish"

Dr.Porsche

Ok, I pretty muched re-logged onto this thread after about post 3...and how the hell did page three happen!

Let me just tell you, that as someone who teaches undergrad Physics (on the side) I am sooooo proud of you guys. All of the other teachers/professors should be grinnin' ear to ear. "When will we use this stuff?" On the internet Baby! Last summer I think there were some posts involving Hook's Law.

ok, i'm done now

944J

Physics is much more fun when you have an interesting application. Kids would really get into it if they knew they could use to make their cars go faster or handle better or to do something that was useful to them or would get them chics.

I've found this interesting software application that will calculate the best parameters for a race car wing on your PC.

http://www.hanleyinnovations.com/racecar1.html

And found a similar discussion on a Physics board:
http://www.physicsforums.com/archive...p/t-12123.html

So removing the stock 944 spoiler will give the car a lower coefficient of drag (better aerodynamics), then adding a big wing will add more downforace (and some drag too), you can't get a wing that doesn't add both drag and downforce since they are just components of the same force, you must have at the least a little of one AND the other (drag AND downforce.)

This whole convo started about this cool car here and whether removing the lower wing increases or decreses drag (Force of air in the negative x direction):