Hard "on the right front". Why?

[Brian Gray]

Huck you may have seen it but you clearly don't understand it.

[hpmaster]

I used Bernoulli as a first step in understanding a fluid, air, reacting on one surface as it flows horizontally along one surface. Key here is first principal. The number of know principles that come into play when trying to figure out how to generate "down force" on a car as it travels in changing directions on different surfaces at variable speeds while changing angles attack and then have braking forces, suspension reactions changing the distance of the car to the ground while going thru air is mind boggling. When confronted with a statement that a race car is like a wing or bullet I frankly lose it. This is partly because of my work in the 1980's on developing what are know as VLD bullets. Bullets and wings are completely surrounded by the air they are traveling thru making the predications on the reactions on them infinitely more predictable. Even then it took years of work field testing, development of computer technology and programs to get where we are today. My input was to attempt to get people to make the first step to understanding there are no simple solutions to where down force is generated on a car rolling on the ground. Now lets look at the drag created. Time to start drinking.

[Brian Gray]

I used Bernoulli as a first step in understanding a fluid, air, reacting on one surface as it flows horizontally along one surface. Key here is first principal. The number of know principles that come into play when trying to figure out how to generate "down force" on a car as it travels in changing directions on different surfaces at variable speeds while changing angles attack and then have braking forces, suspension reactions changing the distance of the car to the ground while going thru air is mind boggling. When confronted with a statement that a race car is like a wing or bullet I frankly lose it. This is partly because of my work in the 1980's on developing what are know as VLD bullets. Bullets and wings are completely surrounded by the air they are traveling thru making the predications on the reactions on them infinitely more predictable. Even then it took years of work field testing, development of computer technology and programs to get where we are today. My input was to attempt to get people to make the first step to understanding there are no simple solutions to where down force is generated on a car rolling on the ground. Now lets look at the drag created. Time to start drinking.

Agreed. But even as your thought process develops the basics apply to every variance you encounter. The amount of mis information in racing is astounding. I just wanted to make it clear so as not to be misleading that when you approach an aero issue you remember how it works.

[Ghopper]

My input was to attempt to get people to make the first step to understanding there are no simple solutions to where down force is generated on a car rolling on the ground. Now lets look at the drag created. Time to start drinking.

I agree. Good clarification.

Ground interaction is lost in most persons view of downforce. There is air under car (for brian), just not enough flow to talk about a wing as HP mentions in the above post. Having to bodies (car and ground) with differential velocity is huge for sucking air from under the car.

Testing for aero could be done on a moving road tunnel ($$$$) or with data acquisition ($$) on an open road with load sensors in body or spring mounts. Many papers have be produced to show procedures and comparison of results for other types of racing.....but when it comes down to putting these in practice...we (I) don't have the time or extra money to do this.


Ghopper

[hpmaster]

One of the best mechanical engineers I ever knew, my father, said Yea, BUT Yes, BUT or Agreed, BUT translated is Yes you are right BUT I want to continue to argue.

[Matt49]

Brian,
I don't think this is an argument for the sake of argument. I am disputing your theory that you must have air flowing under the car to create down force. You keep referring to physics but you're ignoring the physics presented that debunk your theory. Wing physics don't apply to race cars on a race track for the reasons already mentioned by others. But to summarize; wings are in complete interaction with the fluid through which they flow. Cars (unless they are flying) are not. The same physics and aerodynamic principals do NOT apply.

Take this example:
Imagine the body was all the way down against the race track and NO air was allowed under the car from the front. For the sake of this hypothetical we'll have to assume that the body is touching the race track but with zero coefficient of friction between the body and the track to eliminate the variable that would be introduced there. The variable I'm isolating is the amount of air allowed under the car from the front and I want it to be ZERO. But there is still a big opening in the back of the car and the rest of the boy has the same general shape (wedge nose, spoiler, etc.).
Down force comes from three places in this example. A high pressure area over the nose, a high pressure area over the spoiler, and a low-pressure area (in this case a vacuum) under the body. This low-pressure area occurs despite the fact the NO air is flowing under the car. Therefore, air flow under the car is not required to create down force. In fact, the less air flow, the better.
Of course there is drag but ALL down force creates drag. It's a trade-off. Identifying how much drag is acceptable for the amount of down force you are producing is an entirely different problem that brings motor and speed into the equation. What most people don't understand is that the force required overcome aerodynamic drag increases exponentially as speed increases. Compared to the force required to overcome other types of drag (like component drag) which increases linearly with increases in speed. But suffice to say in most short-track situations, we'll take all the down force we can get. We spend a lot more time trying to get the car to stick in the corners than we do drag racing.

[FlatTire]

http://aprperformance.com/index.php?option=com_content&task=view&id=174&Itemid=44

Check out the diagram showing the high pressure/slower velocity air flowing over the top of the car and the low pressure higher velocity air flowing beneath and the effect the splitter has.
We essentially have a splitter on all the modern day late model noses but I don't get the feeling it was put there based on engineering data. Maybe Bentley from Dominator can tell us? Or Brian Gray can you shed some light on the splitter you are talking about? got any pics?

I've often thought about designing my own splitter and testing to determine size/placement. A lot of the roadcourse guys use simple manometers to measure pressure differential/determine effectiveness and seem to have a better handle on this stuff than we do. There is no reason that couldn't be done on a late model.

Another question I have is when you begin to add front down force and make these cars more "aero balanced", are you not taking away from rear down force? What effect does a front splitter have on the rear spoiler? Does it not act like a teeter-totter? Will adding more downforce to the front end decrease downforce at the rear spoiler in effect reducing forward bite?

On a side note, has anybody ever thought about installing hinged flaps on the deck to let out any high pressure that might be underneath?

[Ghopper]

On a side note, has anybody ever thought about installing hinged flaps on the deck to let out any high pressure that might be underneath?

We put strings around the deck with a camera mainly to look at turbulence and flow direction. All the strings near the opening, like oil cooler, go straight down into the hole. i would say that there the pressure is clearly lower there. Which is why I think scopes are overkill for oil coolers.


Ghopper

[keeks]

Correct me if I am wrong, but don't F1 cars create a combination of high pressure areas and low pressure areas producing enough downforce to overcome the entire weight of the car? Thereby in theory allowing said car to actually drive upside down at speed? Sure doesn't seem to be a drag issue negatively affecting performance. (that being said I know it's a huge balancing act).

[hpmaster]

F1 cars use a drag reduction system, DRS, the box like wing system on the rear of the car. There are rules to when, where, how and how far from a competitor it can currently be used. Frankly if you have an hour or three read the official F1 rules, not the short version, you will soon realize an F1 car is closer to an F16 flying on 4 tires than a LM dirt car.

[EAMShater]

Not trying to get in the thick of things here, but I think what Brian is mainly trying to say is there has to be air under the car in the first place to be sucked out to create the downforce/vacuum. Not necessarily air flowing under from the front.

[Brian Gray]

You would be correct.

I can clearly see there is no point to further discuss this topic some people can't think past their old philosophy s

[Ghopper]

Brian stepped in it the moment he said "wing" and used it as an example.

We will not be able to stop air from entering the car from the front. Air is present as we are not working in a vacuum. No body is arguing against that. However, you shouldn't think that increasing air flow under the nose helps with down force on a latemodel. Seal that nose to the ground best you can and still be able to cool the car.


Ghopper

[Brian Gray]

Where did I imply you should try to increase air under the car?

Im pretty sure I said you cannot have down force without air under.

[FlatTire]

In order to generate an aero force, there has to be a pressure differential betwen the air above the car and air under the car. When the pressure above is higher you have down force. The other way around and you have lift.

But the idea is not to flow more air beneath the car which would cause higher pressure resulting in more lift. The idea is to speed up the airflow that already exists under the car, reducing its pressure(Mr. Bernoulli's Law) to help aid in downforce. Its the whole reason they use diffusers on F1 cars & redirected exhauast gas flow to help evacuate air under the car, and they've even used fans.