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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
I originally tried the large Pro-Awe tunnels and just couldn't get the placement I wanted, either too much under the engine cradle or too much on the face of the tire, and too long for my splitter. So, Alessandro was nice enough to let me borrow his tunnels for test fitment while AJ was making my splitter. Unfortunately I wasn't able to get the curved tunnels in there. Although it LOOKS like there's room on the blade, the short and narrow nose of the s197 just wouldn't allow it. As it is I had to hang the tunnels off the back of the splitter to get them in there. I did however get a really good shot of air exiting between the tire and frame rail, straight to the custom fender louvers @302blown made for me over at Race Louvers .
AJ also made me some sweet splitter fences like Ale's. Should be a major improvement over last years configuration.

(Bottom pic shows how much of the splitter is on the outside of the body so, no more room for tunnels)

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Back to aero
Some update on my aero package
New Splitter worked great.
The 2 pairs of AJ tunnels worked great.
I added also his side plates and tire deflectors
And now i just added 2 canards. All works together with hood and fender vents. (Racelouvers)
The splitter has also a leading edge made with 2 Alluminium plates curved about 30deg to facilitate air under the car.
I called it ROMA.


To balance this new front splitter i sold my APR250 wing and added AJ Fulcrum14.
I ran it at 7-8deg at Sonoma where the speeds are not super high.

To compensate the bigger DF load I put stiffer springs using AJ video on how to calculate the increasing spring rate ( roughly).
I lost some low speed grip cause the stiffer springs. Saturday was bad ,sunday better after adjusting compression and rebound. I feel a slightly softer spring would be better. We will see. Cause I'll be testing slicks real soon. So maybe the stiffer springs are necessary for the extra grip of the tire (especially in braking zone)

The car was 5 sec faster than previous laptime.
Of course is not only the aero. But BECAUSE THE AERO you just push harder cause you feel the car "glued"

Hope this help.
Ale
5 second around a track you are familiar and add in that you already had some aero from your previous setup is massive! Glad everything worked out like it was designed.
 
5,122
5,605
Exp. Type
W2W Racing
Exp. Level
20+ Years
Pleasanton: 1/2 way between Sonoma and Laguna Seca
The pro awe tunnels dumped right into the tire with my short s197 nose and extra wide 335’s. No bueno. Just not enough room to pull this off. In this application the AJ hartman large straight tunnels were just the ticket. The rugged carbon fiber construction allowed me to hang them off the back of the splitter and move them more inboard where they needed to be.

Soon to be put to the test….stay tuned.
.

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194
146
Exp. Type
Autocross
Exp. Level
20+ Years
So Cal
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That's a fairly complex little arrangement. What was the evolution path?

And for AJ, it seems that most doing Time Attack have what appears to be a flat splitter significantly wider than the car itself and often for no apparent reason. I suppose if there were enough crap sticking off the outside edge to act as some sort of end-plate, I can see it, but most of the time, there is little to nothing attatched. Have you seen any justification for this extra splitter width? If so, what is it actually accomplishing in terms of flow?
 
5,122
5,605
Exp. Type
W2W Racing
Exp. Level
20+ Years
Pleasanton: 1/2 way between Sonoma and Laguna Seca
View attachment 75708

That's a fairly complex little arrangement. What was the evolution path?

And for AJ, it seems that most doing Time Attack have what appears to be a flat splitter significantly wider than the car itself and often for no apparent reason. I suppose if there were enough crap sticking off the outside edge to act as some sort of end-plate, I can see it, but most of the time, there is little to nothing attatched. Have you seen any justification for this extra splitter width? If so, what is it actually accomplishing in terms of flow?
I have no idea...lol. Aero isn't my specialty. I've been adding stuff a piece at a time over the years.
At this point I may have stuff that interferes with other stuff, but AJ knows what I have and will tell me if I'm doing something stupid. Which is likely.
 
194
146
Exp. Type
Autocross
Exp. Level
20+ Years
So Cal
One way to get a little more nose tunnel area is to start with a wider diffusor and neck it down while increasing depth. I don't know if something like this picture helps, but it's a different way of skinning the cat which might give some ideas. Your fender venting should help exhaust the nose reasonably well, particularly if you put some turning vanes in the wheel well to direct the air appropriately.

DSC_0222.JPG

DSC_0225.JPG
 
And for AJ, it seems that most doing Time Attack have what appears to be a flat splitter significantly wider than the car itself and often for no apparent reason. I suppose if there were enough crap sticking off the outside edge to act as some sort of end-plate, I can see it, but most of the time, there is little to nothing attatched. Have you seen any justification for this extra splitter width? If so, what is it actually accomplishing in terms of flow?
I think you are thinking a little to much 2D. If I'm thinking of what you are describing correctly, while the extra wide splitters on some top level TT cars don't have a lot going on from the surface or on top, they almost always have some sort of aggressively profiled, wing like shape on the underside. The extra surface area, and sticking out to be in free stream air, and being in ground effect allow them to produce plenty of front downforce. Downsides are they are just huge which wouldn't work in any wheel to wheel racing, hard to produce or manufacture, has to be removed to get on and off teh trailer, or there are much more constrictive class rules, etc. But if you talking about literally just a flat flat splitter much wider than the car, they are leaving a lot to be desired.
 
194
146
Exp. Type
Autocross
Exp. Level
20+ Years
So Cal
I think you are thinking a little to much 2D. If I'm thinking of what you are describing correctly, while the extra wide splitters on some top level TT cars don't have a lot going on from the surface or on top, they almost always have some sort of aggressively profiled, wing like shape on the underside. The extra surface area, and sticking out to be in free stream air, and being in ground effect allow them to produce plenty of front downforce. Downsides are they are just huge which wouldn't work in any wheel to wheel racing, hard to produce or manufacture, has to be removed to get on and off teh trailer, or there are much more constrictive class rules, etc. But if you talking about literally just a flat flat splitter much wider than the car, they are leaving a lot to be desired.

I'm definitely thinking about limiting the airflow to 2 dimensions and wondering how an extended flat plate with nothing on the end would accomplish that. I was in Atlanta last weekend and got a chance to look at some Time Attack cars. What you're saying makes sense if it was an actual airfoil. I'm going to guess that a few of the top level cars have actual airfoils under the extended portion of their splitters. The rest are playing monkey see/monkey do and don't.
 
I'm definitely thinking about limiting the airflow to 2 dimensions and wondering how an extended flat plate with nothing on the end would accomplish that. I was in Atlanta last weekend and got a chance to look at some Time Attack cars. What you're saying makes sense if it was an actual airfoil. I'm going to guess that a few of the top level cars have actual airfoils under the extended portion of their splitters. The rest are playing monkey see/monkey do and don't.
Yeah, I mean I'd have to see specific examples but a lot of "monkey see, monkey do" goes on for sure.
 
5,122
5,605
Exp. Type
W2W Racing
Exp. Level
20+ Years
Pleasanton: 1/2 way between Sonoma and Laguna Seca
I'm definitely thinking about limiting the airflow to 2 dimensions and wondering how an extended flat plate with nothing on the end would accomplish that. I was in Atlanta last weekend and got a chance to look at some Time Attack cars. What you're saying makes sense if it was an actual airfoil. I'm going to guess that a few of the top level cars have actual airfoils under the extended portion of their splitters. The rest are playing monkey see/monkey do and don't.
One thing maybe to consider is that the side part of the splitter is
Still separating the higher pressure air coming from above the splitter and running around the front fascia and the free flow air beneath (lower pressure). Of course without any tire spat , tire deflector or flap/side plate the amount of pressure differential is way less but i think still present.

Screenshot_20220510-153637.png
 

Grant 302

basic and well known psychic
One thing maybe to consider is that the side part of the splitter is
Still separating the higher pressure air coming from above the splitter and running around the front fascia and the free flow air beneath (lower pressure). Of course without any tire spat , tire deflector or flap/side plate the amount of pressure differential is way less but i think still present.

View attachment 75781
Absent a fence or spat, the side/outer and trailing ends of a flat splitter don’t have measurable pressure difference. Just saying.
 
194
146
Exp. Type
Autocross
Exp. Level
20+ Years
So Cal
1652227511240.png
I've played with versions of these and always found a gain, because it helped to evacuate the wheelwell, which makes the underside of the nose work better (at least, that was the logic). I think the biggest ones I've played with were maybe 1/2", but it was definitely noticeable. I think that lower dive plane might be along for the ride, but you only know by testing. I had one car that we'd run double dive-planes which had no real effect, but if you knocked the top one off, then the bottom one would be better than nothing.
 

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