Ask AJ Hartman - Aero Questions

[AJ Hartman]

Video going over the 2 splitters I've made for my car.

 

[AJ Hartman]

Not a mustang, but principles are pretty much the same.

 

[flyhalf]

Thanks AJ
They have trackspec hoodvents. They extract air but not like expected.
I'm testing now for them wickers for the mustang vents.
I hope to take some videos on it.

Couple of question
1. If reducing the underhood pressure =less lift why tape the hood/windshield area?
2. Splitter side flaps
Do you think you just need GT500style flaps(in red) or would it be better having side flaps also(blue )?

Thanks!

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[JDee]

Try RaceLouvers. Just the addition of their center vent took 1.2 sec a lap off at Mosport and dropped engine temps from 240+ to 215. Very happy with it, prolly biggest bang for the buck I've ever had.

 

[AJ Hartman]

Thanks AJ
They have trackspec hoodvents. They extract air but not like expected.
I'm testing now for them wickers for the mustang vents.
I hope to take some videos on it.

Couple of question
1. If reducing the underhood pressure =less lift why tape the hood/windshield area?
2. Splitter side flaps
Do you think you just need GT500style flaps(in red) or would it be better having side flaps also(blue )?

Thanks!

Sent from my LG-H932 using Tapatalk

Try RaceLouvers.com . Video below of when I went with them. Its geared more toward our wing vs. a competitors wing since I didn't want to put all their stuff out there, but they do sorta a gurney flap setup where the forward more louvers are higher then the rears to help extraction. They definitely out performed the track spec louvers in downforce, efficiency, and the pressure drop across the front and rear of the radiator.
1. Simple. Cause less air is allowed to get under the hood.
2. Both would most likely yield the most Df, but maybe not the most efficiency.

 

[TrackAire]

AJ,
What do you think about the driver and passenger door window being open and how it effects aero? I only do HPDE and have no rules to adhere to but every organization makes us track with the windows down.

I envisioned a canard type attachment running up the A pillar to deflect the air either over the roof or push it away from the window opening and have it attach back onto the rear trunk area.

I'm not sure how bad having the windows open effects aero in a negative way....I'm assuming it creates some sort of lift and or breaks up the flow and how it goes over the rear quarter panels. Any thoughts?

 

[AJ Hartman]

AJ,
What do you think about the driver and passenger door window being open and how it effects aero? I only do HPDE and have no rules to adhere to but every organization makes us track with the windows down.

I envisioned a canard type attachment running up the A pillar to deflect the air either over the roof or push it away from the window opening and have it attach back onto the rear trunk area.

I'm not sure how bad having the windows open effects aero in a negative way....I'm assuming it creates some sort of lift and or breaks up the flow and how it goes over the rear quarter panels. Any thoughts?

Closing them, if the rules allow, is definitely an aero advantage. How much I'm not really sure. That would be a fun easy run to do next time I go to the tunnel.

 

[JAJ]

Closing them, if the rules allow, is definitely an aero advantage. How much I'm not really sure. That would be a fun easy run to do next time I go to the tunnel.

A safety advantage too. More and more Euro manufacturers are requiring windows-up for their factory sponsored driving events. It reduces the chance of injuries, by a lot, apparently.

 

[JDee]

I never run with them down, the buffeting at 145 mph is just wild. No groups I run with require them down.

 

[JeffV8]

SCCA Track Night has windows down. At the drag strip requires them up.

 

[TMSBOSS]

Same experience here. Drags, Windows up. Road course, windows down.

 

[flyhalf]

AJ
thanks for sharing the 2 videos on wind tunnel. it appears from the video#1 that racelouvers vents added ..14lbs of Downforce.
Am I reading well?
A last question.
What is the principle behind ' changing angle of attack of the splitter increase DF?
in other words, why a splitter works ?
Is it because the highpressure on top 'push down the splitter?or because under splitter you have a highspeed flow (=lower pressure) 'sucking down the front?
for my understanding It is not a wing but more a...SPLIT, FORCING THE AIR to PASS under, to increase speed ( and lower the pressure).
Kyle Engineer showed that in theory in we increase the air going under the splitter ( by lifting up the front ) in theory we generate more down force cause the air will increase even more the speed.
So i'm a little confuse here but especccialy I'M WORRY I WILL SEVERE UNBALANCE MY CAR with a rear wing, even If I put a huge splitter in the front.
I mean that car with huge splitter, canards, front diffuser had...lift in the front.
Please let me know!
Alex

 

[Grant 302]

@AJ Hartman - For your use.

 

[ddozier]

So i'm a little confuse here but especccialy I'M WORRY I WILL SEVERE UNBALANCE MY CAR with a rear wing, even If I put a huge splitter in the front.
I mean that car with huge splitter, canards, front diffuser had...lift in the front.
Please let me know!
Alex

I know you are looking for the best result possible, and I can tell you are going about this the right way, thinking through the entire process and asking lots of questions. The truth is without a wind tunnel to collect data and test there are so many variables it will be hard for anyone to know what the balance will be like. In my own setup all by trial and error mind you, I have seen a significant drop in lap times. I view that as progress but it would sure be nice to have a definitive data set to back up the track times and seat of the pants feel. You could also add ride height sensors to the car and with a lot of math you could determine the increase or decrease in effectiveness of any new aero part you would add.

There are a few general guidelines you can follow that should yield positive results. There are many but here are a few I can think of that should help you get started:

1. Aero is not going to fix a bad setup, make sure the cars mechanical grip is balanced first, then you have a neutral place to start and can judge the effect of the changes better. In order to achieve a balanced aero setup you start with a balanced mechanical setup, then the goal is to add aero to increase overall performance. This is also helpful when running in traffic as the effect of the car in front washing away your aero gains still leaves you a car you can drive. Changes in aero will force changes in the mechanical setup, the two feed each other. As you increase downforce that force goes through the springs to the tires. In general you will run a stiffer spring as downforce is increased, this is not always the case as some will try a softer spring setup with a short travel and a stiff bumpstop. This allows the car to have a higher mechanical grip but when the aero has overcome the spring the car is riding on the bump stops, transferring all the aero gains directly to the tires. This is incredibly complex to achieve and can make for a very ill handling car until everything is perfect or on bumpy tracks.

2. Rear downforce is much easier to generate than front downforce, you should keep this in mind when setting up a car. Ideally add as much front downforce as possible then balance the rear by adding wing or diffuser or both to achieve the balance you are looking for, that may not mean 50/50% front to rear downforce. Having a triple element wing running at an insane angle of attack will not make the car faster if it lifts the front of the car. Splitter size is usually dictated by the class you intend to race in and is often used to restrict aero within a class, by limiting the front splitter size and the potential for front end downforce you can limit the entire amount of downforce that makes since to run.

3. Air management through the grill is as important as air management under the car or over the top. In the video AJ posted with the BMW the amount of downforce generated off the large splitter and dive planes was negated by the lack of ducting to the radiator and having a place for the air to go after it exits the radiator. In general the smaller the grill opening the better, limiting air to just enough to cool the car is better, and trying to control the air after it exits the radiator to go over or to the side of car is usually better than under the car. I say usually because cars with tunnels and extensive air management under the car can make use of this airflow to increase downforce.

There are many variable that will dictate the effectiveness of any areo bit you decide to run, the challenge is to be able to measure the change and know if the desired effect was achieved.

Dave

 

[AJ Hartman]

ddozier is pretty much right on with his 3 points. Aero can be looked at like suspension. You don't all of the sudden bolt on every single little suspension compent to the car and expect it to work. First you add CC plates. Then a bump steer kit. Then nicer shocks, and on and on and you measure and adjust as you go. Aero is the same. Add some parts, see what happens and adjust as necessary. We were able to get to around 150lbs of Df in the front at 100mph on that BMW after having lift in the baseline runs. I bet with good radiator ducting we could have maybe doubled this. I went to the tunnel with an Audi a few months before this car and that car made 189lbs on the front with a little 3" splitter cause it had good rake to it, and was ducted very well on the front side of the radiator. We were able to get an OK balance to the car since we can trim the wing out as well. Thats why the wing was so flat in the smoke stream parts of the video since that was done at the end of the day.

 

[AJ Hartman]

Heres the other tunnel video if I never posted it here.

 

[flyhalf]

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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[ddozier]

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?

Not all splitters generate downforce the same way, some help to create a low pressure region under the nose of the car sucking it down closer to the pavement, others dam or restrict air from moving from above the splitter to below the splitter and this generates a large high pressure zone above the splitter and is pushing down on the top side of the splitter. These two forces are what you are trying to capture and take advantage of, both yeild downforce and its the combined forces that create the total downforce.

Here is a CFD of a small splitter on a S550 front end that I borrowed from Verus Engineering S550 aero study.


Notice in the image that the area above the splitter is yellow, red, and orange and the area below the splitter is blue, green and violet. look at the scale to the left and you can see the pressure differential of the two areas. This is with a simple flat splitter and a bunch of other assumption like a closed off grill I am betting but it will help you see how a splitter effects the air in front of the car and below the car. You can do more to increase the effectiveness of a splitter by adding tunnels to move the air where you want it to go under the car, and dive planes and winglets above the splitter to keep the two pressure zones separated.

Dave

 

[AJ Hartman]

Heres 2 more wind tunnel videos. Yes, its not a Mustang, but a lot of the concepts and weather something was an improvement or not will generally hold true for Mustangs. I don't really give exact numbers but try to mention in the clips if something was of a benefit or not. Also keep in mind that a "benefit" can also be different based on what you are trying to achieve.

 

[cholmes1]

Anyone doing anything involving underbody aero for the S197 or has it been shown to be more detrimental?