Ask AJ Hartman - Aero Questions

[navseng]

plenty of room, but the fan shroud has to go. https://racelouvers.com/content/Race-Louvers-Fan-Shroud-Wind-Tunnel-Data.pdf

Interesting, didnt think of that.. I wonder how effective the vent flaps are to the left and right of the fan.. Or I could remove the shroud or simply cut it open some more..

 

[AJ Hartman]

Interesting, didnt think of that.. I wonder how effective the vent flaps are to the left and right of the fan.. Or I could remove the shroud or simply cut it open some more..

I agree with @302blown as well. Any time we had a car in the tunnel with a shroud, even the GT350 which has some of those flaps on it, from a performance standpoint wasn't good and was fairly restrictive at race car speeds.

 

[BluPil]

Thanks a lot Dave and AJ.
The approach I'm having is very similar to what you were mentioning.
1. Stock for baseline.
2. Add 1 piece at the time and not all together
3. Knowing the car better. Recognize when a performance is not there because a bad setup( i. E. A bad tirepressure) or because a car issue/deficency.
4. After a year of experience. I'm upgrading to coilovers. The choice of the spring rate will be also dictate to what time of aereo my car will accept without unbalancing the front.
5. Together with Dan I'm trying to find a good solution between cost and effectiveness.(i wish i could unlimited budget but is not possible )
This will dictate the choice of the wing IMO.
6. My 2018 is doing definetely a great work for the weight she has(3780lbs) and the few "mods" she has. There is an old italian who can be translate :the devil you know is better than the devil you don't.
So I guess I'm. Just worry about the unknown.
Last but not the least.
CAN YOU GUYS PLEASE ANSWER THE QUESTIONS.
1. " Why a splitter generates the DF?" Is it because high pressure pushing down or fast air under sucks it Down?
2. Why a wing generates downforce? Is the low pressure under sucks it down or is the the air above "mechanically pushing it down follow the action/reaction principle or both?(see pic and blu
(Pleass forgive me but this is very hard argument to be treated in my second language)
Thanks again!
Alessandro

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Higher Pressure always pushes.....
if you think about an airplane wing the top of the wing is always 'longer' than the bottom due to its shape, so the air going over the top has to go faster than the air going over the bottom of the wing. the air going faster creates a low pressure area above the wing, so the pressure below the wing pushes up on the wing.... of course we are trying to do the opposite with cars to get down force instead of upforce.... https://www.khanacademy.org/science/physics/fluids/fluid-dynamics/a/what-is-bernoullis-equation

 

[Grant 302]

if you think about an airplane wing the top of the wing is always 'longer' than the bottom due to its shape, so the air going over the top has to go faster than the air going over the bottom of the wing. the air going faster creates a low pressure area above the wing, so the pressure below the wing pushes up on the wing

Incorrect Lift Theory

 

[BluPil]

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Incorrect Lift Theory

https://www.nasa.gov/sites/default/files/atoms/files/bernoulli_principle_k-4.pdf

and a NASA document that contradicts the above slide......

 

[AJ Hartman]

I did this video several years ago but should be helpful with some of the recent comments about Bernoulli's principal.

 

[Kaj]

With all this back and forth, and I'm probably over simplifying here: Our OEM fan shrouds do more harm than good?
Also, I'm comparing AJ's wing and splitter to aero on my other car: you guys are VERY fortunate. It's much, much more expensive to get a tested wing/splitter on my other car. Almost makes me want to keep the Mustang hahaha.
Thanks for all you do AJ.

 

[Ewheels]

Apologies if this has already been discussed, but @AJ Hartman what's your take on the "parachute" oem rear "diffuser" on non-Shelby cars?
Is it worth cutting out to let air flow through from under the car or just leave it?

I remember an old Myth Busters episode where they tested a truck's tailgate position and mpg. They found tailgate up created a circulating air pocket in the bed that actually helped air flow. Curious if the same applies to the oem bumper or if removing it would make less drag.

 

[Fabman]

Apologies if this has already been discussed, but @AJ Hartman what's your take on the "parachute" oem rear "diffuser" on non-Shelby cars?
Is it worth cutting out to let air flow through from under the car or just leave it?

I remember an old Myth Busters episode where they tested a truck's tailgate position and mpg. They found tailgate up created a circulating air pocket in the bed that actually helped air flow. Curious if the same applies to the oem bumper or if removing it would make less drag.

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I think Kyle drives/Kyle engineers has a video about this....I know I saw it somewhere.

 

[Fabman]

 

[Ewheels]

So it would help but it's pretty darn marginal

Thanks for the video link!

 

[RES_22]

Trailer hitch prolly not helping effectiveness of diffuser, sadly.

 

[Ewheels]

Trailer hitch prolly not helping effectiveness of diffuser, sadly.

Definitely not but I pull a tire trailer.
I have yet to see if I can fit 4 wheels + tools in car with roll bar and passenger seat out. If they fit, then I could remove the hitch

 

[Mad Hatter]

that's were the stick axle S197 wins... I fit 5, 315 R7s in the car once... with a full role bar... was it safe.. No! But it worked. no rear seat and no passenger seat.

 

[navseng]

Definitely not but I pull a tire trailer.
I have yet to see if I can fit 4 wheels + tools in car with roll bar and passenger seat out. If they fit, then I could remove the hitch

I bet you could with the passenger seat out. I cant quite fit 4 of my 305s in the car anymore once I made the roll bar but it could be how I have it angled back a bit. Not sure have the other bars are but I cant quite stand a tire up in the back seat area anymore.

 

[Ewheels]

I bet you could with the passenger seat out. I cant quite fit 4 of my 305s in the car anymore once I made the roll bar but it could be how I have it angled back a bit. Not sure have the other bars are but I cant quite stand a tire up in the back seat area anymore.

I've heard a handful of people fitting 4 wheels in with a roll bar + passenger seat out so it's doable; I just need to brush up on my Tetris skills.

 

[flyhalf]

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

 

[Grant 302]

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

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Looks like a good way to keep it somewhat like your OEM ‘tunnels’ that aim to the outsides of the tires…and left a center portion that doesn’t feed the tire quite directly. Seems like a better installation than suggested by others. Do you have a pic of them installed to share and show your alignment relative to the tire?

 

[flyhalf]

Looks like a good way to keep it somewhat like your OEM ‘tunnels’ that aim to the outsides of the tires…and left a center portion that doesn’t feed the tire quite directly. Seems like a better installation than suggested by others. Do you have a pic of them installed to share and show your alignment relative to the tire?

I also have the double fender vents (top and rear .)this should help.even more

 

[Fabman]

I dunno but this pic looked a lot like a package of bacon and now I'm hungry for breakfast.