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Ask AJ Hartman - Aero Questions

5,122
5,605
Exp. Type
W2W Racing
Exp. Level
20+ Years
Pleasanton: 1/2 way between Sonoma and Laguna Seca
The issue I have as you can imagine, is that the front tires stick out so far that any significant coverage of their face render the canards less efficient and opening up the canards leave the tires exposed and inefficient....so its going to be a compromise with something in between all or nothing. Below are a couple options I was initially mocking up starting with the current configuration.

110717670_10158657647298535_2273904944538464757_n.jpg1a.jpg2a.jpg


I'm leaning towards making them narrower at the top and taper out towards the bottom. (about half the width of the current setup) The OCD part of me wants to see everything at 90* but that's just not going to be practical or efficient. I'm doing this tomorrow folks so if you have an opinion, now's the time to say something.
 
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5,122
5,605
Exp. Type
W2W Racing
Exp. Level
20+ Years
Pleasanton: 1/2 way between Sonoma and Laguna Seca
I.feel.this is the best option.
A spat behind and completely.coverimg the width of the canards will create high pressure all around canards .. nulling the canards benefit IMO
Seems to be the consensus, yes.
 
194
146
Exp. Type
Autocross
Exp. Level
20+ Years
So Cal
Here's a different way to do dive planes. I don't know if it's better or worse (that will depend on the specifics), just different. It does not have the leading-edge front wheel opening gurney. 2016 Porsche GT3R.

20220603_183459.jpg
 
70
44
Exp. Type
HPDE
Exp. Level
Under 3 Years
Cantley
I do not mean to break the flow of this interesting thread but I think this is the right place to ask this question:
If I am not constricted by any rules and want to setup a rear wing, am I not always better off getting the biggest, most aggressive one at a lesser angle vs a smaller one at a steeper angle?
Same with race louvers: why not get the most efficient ones and tune down as needed to achieve a balance, unless you are restricted by rules? You know what I mean?
 
194
146
Exp. Type
Autocross
Exp. Level
20+ Years
So Cal
I do not mean to break the flow of this interesting thread but I think this is the right place to ask this question:
If I am not constricted by any rules and want to setup a rear wing, am I not always better off getting the biggest, most aggressive one at a leser angle vs a smaller one at a steeper angle?
Same with race louvers: why not get the most efficient ones and tune down as needed to achieve a balance, unless you are restricted by rules? You know what I mean?

Regardless of the rules involved, you have to maintain a balance. You want your center of pressure (CoP, fore/aft distribution of downforce) to be a bit (a few %) rearward of your static CoG. Sticking a massive rear wing on the car and then running it completely flat may or may not be more efficient than a smaller wing with more AoA, but carrying extra weight at the highest point on the car and outside of the wheelbase is generally not what people want to do, because it has too many negative implications for the mechanical aspects of the car. Those 2 always need to be balanced. It's easy to make a car faster, but don't mistake that for making it more fun to drive. They're not the same.
 

Grant 302

basic and well known psychic
Here's a different way to do dive planes. I don't know if it's better or worse (that will depend on the specifics), just different. It does not have the leading-edge front wheel opening gurney. 2016 Porsche GT3R.

View attachment 76386
Not trying to be snarky, but it looks to me like they swapped the top and bottom elements.
(CoP, fore/aft distribution of downforce) to be a bit (a few %)
I generally agree with your point, but CoP isn’t the same as any particular DF distribution, right? Maybe I’m not getting how your using CoP.
 

Grant 302

basic and well known psychic
I do not mean to break the flow of this interesting thread but I think this is the right place to ask this question:
If I am not constricted by any rules and want to setup a rear wing, am I not always better off getting the biggest, most aggressive one at a lesser angle vs a smaller one at a steeper angle?
Same with race louvers: why not get the most efficient ones and tune down as needed to achieve a balance, unless you are restricted by rules? You know what I mean?
I generally agree, but I have a hard time considering louvers to be an ‘efficient’ solution on our cars, regardless. So trying to define which ones are the ‘most efficient’ would seem a difficult task with most offerings available.
IOW, it’s is one of the items I think most likely that you’d choose the one with most downforce (for you intended budget or whatever) and sort out the balance with your wing adjustment.
 
194
146
Exp. Type
Autocross
Exp. Level
20+ Years
So Cal
Not trying to be snarky, but it looks to me like they swapped the top and bottom elements.

I generally agree with your point, but CoP isn’t the same as any particular DF distribution, right? Maybe I’m not getting how your using CoP.
You can contact these guys to tell them they did the dive planes wrong, if you want. https://porschemotorsportna.com/ I doubt if you get very far, it's ancient to them.

CoP is "Center of Pressure", which is technically a linear dimension, is expressed as in reference to the wheelbase/axle. If we have a 100" wheelbase & the CoP is 60 inches from the front axle centerline, then you'll have 40% of the downforce distributed on the front axle.

In practice, "CoP" and "% Front Aero" are used interchangeably. If I were to tell my driver that we were "putting some CoP into the car" or "putting some front aero into the car", it conveys the same message (even if not a technically correct way to speak about what you've done). I probably let some of my speech bleed over into my writing, which would make it a little confusing.

The important part is that you always want the CoP to be further longitudinally from the front axle centerline than the CoG (center of gravity). This is how make certain that the car will maintain an aerodynamic understeer, which should be your goal. Once this is established, you can adjust aero balance 2 ways, by moving the CoP *or* CoG. Obviously, changing wing angles or rake will influence balance, but fewer realize that, if you carry ballast, the placement of that ballast is as vital aerodynamically as it is mechanically to the handling balance of the car.
 
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194
146
Exp. Type
Autocross
Exp. Level
20+ Years
So Cal
I just looked at those dive planes some more. They might be swapped. I'll have to check that out further. There's been a couple versions.
 

Grant 302

basic and well known psychic
I just looked at those dive planes some more. They might be swapped. I'll have to check that out further. There's been a couple versions.

I think the angle of your pic just made it look like the top element was over-hanging the lower element. To me at least, and that seemed odd for many reasons. Looking at some other frontal pics make me think this isn’t the case.

——

I get how you’re using CoP now. Referencing it in the singular seemed odd to me…because it moves with changes in speed, yaw, and pitch, etc. Thanks for the clarification.
 
I do not mean to break the flow of this interesting thread but I think this is the right place to ask this question:
If I am not constricted by any rules and want to setup a rear wing, am I not always better off getting the biggest, most aggressive one at a lesser angle vs a smaller one at a steeper angle?
Same with race louvers: why not get the most efficient ones and tune down as needed to achieve a balance, unless you are restricted by rules? You know what I mean?
Well there are two ways to look at it. You used the word "aggressive" which would steer towards the profile of the wing. A shorter cord wing could make more Df than a larger cord wing if the smaller one was a more aggressive profile vs. the larger one. Plus how much more or less cord are we talking? But the smaller one with a more aggressive profile would almost always be at a lower efficiency, despite making more Df. Now if we are talking the same exact profile, just scaled up or down, the larger profile at a lower angle would be more efficient. This is a test we've done many times in the wind tunnel and a wing is always more efficient at a lower angle, than a steeper angle. So generally, you should pick the largest wing your rules allow, or a wing that will allow a good balance for whatever the front aero rules allow. Which brings me to the point below.
Regardless of the rules involved, you have to maintain a balance. You want your center of pressure (CoP, fore/aft distribution of downforce) to be a bit (a few %) rearward of your static CoG. Sticking a massive rear wing on the car and then running it completely flat may or may not be more efficient than a smaller wing with more AoA, but carrying extra weight at the highest point on the car and outside of the wheelbase is generally not what people want to do, because it has too many negative implications for the mechanical aspects of the car. Those 2 always need to be balanced. It's easy to make a car faster, but don't mistake that for making it more fun to drive. They're not the same.
There is a CoP of individual parts, and a CoP of the total car with everything on it. Yes, balance is extremely important. Like when I took my race car to the wind tunnel, with everything on the front, and we were running a host of wings across the rear, we still had lift on the rear. The car would be undrivable. We also do "no wing runs" to figure out how much lift the smaller wings cancel out cause they obviously don't make lift. So the opposite could be true where a huge wing on the rear could actually cause lift on the front. But like TeeLew said, you want to aim for a total CoP close to the weight distribution of the car, with maybe a few percent more in the rear. This means that as the car goes faster, it will get a little more understeer. As opposed to if the car was front aero heavy a few percent, as you go faster, the rear would get looser and oversteer.
 

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