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Old 03-13-2012, 06:44 PM   #1
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Default Aero: Why do the guys with flat undertrays not run their splitters higher?

There seems to be plenty of packaging scope on lowered track Miatas to run the front splitter higher than the undertray, to maximise the amount of air flowing under the car. You track guys don't seem to do this though. What am I missing? I don't have a car here to clamber under and investigate, so I'm guessing it's something packaging-related that I've overlooked.
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Old 03-13-2012, 07:51 PM   #2
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...why would we want to maximize the air flowing under the car?
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Old 03-13-2012, 07:59 PM   #3
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You would want to "maximize" the airflow under the car... Not so much the ammount...
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Old 03-13-2012, 08:00 PM   #4
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Quote:
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You would want to "maximize" the airflow under the car... Not so much the ammount...
Gold star for this guy.
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Old 03-14-2012, 03:35 AM   #5
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Note the raised splitter of the generic prototype here: http://www.mulsannescorner.com/diffuser.htm

Also note the increasingly high noses of F1 cars since the high nose idea debuted on a Tyrrell in 1990.



A higher nose provides more air for underbody aero to work with. Obviously as the height of the front wing/splitter increases, its own ability to provide downforce decreases, which is why you don't see cars with splitters five feet off the track. Still, a happy medium is to have the splitter at least a small amount higher than the underbody.

It's [edit: not, entirely..!] the reason you see some bodykit bumpers with raised middle sections. For example, the fastest n/a car at Tsukuba Time Attack:

I can dig out further stuff from my one and only aero textbook if you want.
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Last edited by owenwilliams; 03-14-2012 at 05:05 PM.
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Old 03-14-2012, 08:42 AM   #6
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I'm not sure I would look to body kits as examples of proper aero.
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Old 03-14-2012, 09:05 AM   #7
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I agree, which is why I've looked to textbooks and Le Mans cars, and used a one-off bodykit on a very successfui and virtually unlimited-budget time attack car as an interesting example.
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Old 03-14-2012, 09:18 AM   #8
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Eh, the only qualms that I really have over that aero package is the boxed skirts. A virtual skirt of flat plate skirt probably would have netted them better down force via deflecting air from going back under the car. It looks ricey but those vented fenders reduce lift via high pressure relief in front wheel well's. The diveplate after the rear wheels helps create downforce via the same function in the vented rear wheel well.
Also the ducts up front, I certainly hope that they are functional. One for oil cooler and one for air box...?

A large reason you'll see that lifted section on cars as well is that it was discovered that the cars were getting very upset under situations of dive as they choked off flow under the car, it was losing downforce and the nose would pop back up. Similar yet exagerated effects of this (on much more 'wing like' designs) are the flipping 911 GT1 Porsche at Petite Lemans in 98 and Mercedes in 99. Around the same time frame, you'll see a lot of these lifted center sections in touring cars (DTM, BTCC, etc).

So take the lifted nose on a 'sedan' with a grain of salt and insight. The lifted nose on an F1 car is also used to put high pressure on the dive board just forward of the monocoque and to also help control airflow under the car.
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Old 03-14-2012, 12:30 PM   #9
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I understand all the above - but I thought the lifted nose concept applied to any vehicle with a flat, downforce-producing underbody.
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Old 03-14-2012, 12:54 PM   #10
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I LOVE reading Mulsanne's Corner. Everyone should "like" it on Facebook. Crazy cool stuff, all the time.
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Old 03-14-2012, 03:14 PM   #11
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But those are racing cars though... The raised middle...is style.
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Aero: Why do the guys with flat undertrays not run their splitters higher?-2005_leblanc_mirabeau1.jpg   Aero: Why do the guys with flat undertrays not run their splitters higher?-jaguar-xjr-14.jpg   Aero: Why do the guys with flat undertrays not run their splitters higher?-_s8_7384.jpg  
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Old 03-14-2012, 03:18 PM   #12
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The downforce created by a F1 car's splitter (or front spoiler as they call it), is amplified greatly as it goes lower. ie the whole recent debacle about flexible front spoiler on RB07.

As for nose location on F1, I wouldn't take that as an indicator of right or wrong aero as regulations change to limit aero every year. Note this year the front nose (after the suspension mount location) has been forceably lowered.
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Old 03-14-2012, 03:21 PM   #13
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NAAAH THIS IS THE ----.


http://jalopnik.com/ground-effect-cars/
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Old 03-14-2012, 03:43 PM   #14
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In the 3 photos of the racing cars above, two are pre-90s designs, and the other is a new, no-tweaking-required car, like a Radical. That's how I'm choosing to explain to myself why they don't have raised noses :P Then again, the raising is very slight even on new Le Mans prototypes, but it is there, so it might be there on those designs.
Re. F1, I'm aware of most of the >general< aero regs that have come in over the years, and should point out that the raised nose was originally to provide more air for the diffuser/barge board/everything under the car to work with, and was soon considered a safer (in a crash) design, which might be why it's one of the few big design changes that's not been banned. I'm also aware that the lower the front wing the better in F1. Open wheel cars have the advantage of being able to run the front wing as low as possible, while still being able to get a load of air to the diffuser under the nose.
I seem to be fighting a losing battle with y'all here. I'm confused.
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Old 03-14-2012, 04:20 PM   #15
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I think your problem with understanding this situation is that you are cross-referencing completely and totally different forms of cars, which require completely different aero applications to suit their needs. Aero is not something designed by theory, or looking at pictures. You can guess based off of theory and track testing, but you also need to consider what you are using the aero for. Do you want to cut drag? Or maybe you need the absolute max amount of downforce, and drag is not as much of a concern, because you have the hp to muscle through it.

In the case of that lifted center section on splitters, "Homemade WRX" is correct from what I have read about it. The center is lifted, because cars that are very low to the ground (below 4" or so) become pitch sensitive depending on how long the splitter protrudes from the bumper.
There's a decent discussion on it in the MotoIQ forums.
http://www.motoiq.com/forum/afv/topi...2/aft/445.aspx
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Old 03-14-2012, 04:31 PM   #16
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Quote:
Originally Posted by owenwilliams View Post
I understand all the above - but I thought the lifted nose concept applied to any vehicle with a flat, downforce-producing underbody.
Well 'lifted nose' refers to a formula car, who's undertray doesn't go far enough forward to pinch the ground and they also have front wings/spoilers.

The raise in the center of the undertray is largely seen on cars that CAN have the splitter touch the ground on course and it is to keep air flow and prevent an aero enduced 'buck' and raising of the nose. I know Daytona Prototypes are careful of this despite thier limited returns from an undertray as they have some strict rules on them being flat, ending point, etc (or at least use to). This is something that I learned working with them in a wind tunnel during a college internship that I scored through my motorsports engineering minor. So I learned enough to get myself into troubl

Exagerated example:
1)Think of two kids balanced on a see-saw (car at speed with aero/suspension balanced)
2)The kid on the left suddenly jumps off (loss of the majority of the front downforce when undertray touchs).
3)The kid on the right suddenly picks up the left as he no longer has resistance (the rear is still making the majority it's downforce via a large wing and the front isn't).
4) now in a race car that lifting of the front allows air under the car which if enough will lift the car....or in the two forementioned cases, lift it into the air.

This is where the raise comes. It allows continued flow under the car.


Quote:
Originally Posted by owenwilliams View Post
I seem to be fighting a losing battle with y'all here. I'm confused.
I'm here with ya
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Old 03-14-2012, 04:56 PM   #17
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God ------- damn it.
I've been studying my book/bible for the last hour.
You are correct. In saloon cars, the splitter is raised to stop the diffuser choking and/or the front porpoising under extreme yaw. In formula cars, the nose is raised to allow more air under the car for the diffuser/tunnels/whatever to work with. The THEORY is correct about raising the splitter muchly in a saloon car purely to feed the diffuser, but in practise it doesn't happen because the reduction in front downforce from the reduction in ground effect makes it impractical.

So, I'm gonna say I was 50% correct. I'm a glass-half-full guy, which means that 50% is rounded up to being 100% ------- CORRECT YOU ***** SO SCREW YOU GUYS
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Old 03-14-2012, 05:18 PM   #18
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Quote:
Originally Posted by owenwilliams View Post
So, I'm gonna say I was 50% correct. I'm a glass-half-full guy, which means that 50% is rounded up to being 100% ------- CORRECT YOU ***** SO SCREW YOU GUYS
Hyper has returned?
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Old 03-14-2012, 05:24 PM   #19
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always thought:

1. if you have a flat bottom car, air going under the car is a good thing. speed up the flow, lower pressure, more downforce.
2. on a Miata, where it is an aero nightmare underneath. you wouldn't want air under the car.

also never look at F1 (or most spec race cars) for aero idea, they are most often regulated by rule.
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Old 03-14-2012, 05:30 PM   #20
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Quote:
Originally Posted by bellwilliam View Post
also never look at F1 (or most spec race cars) for aero idea, they are most often regulated by rule.
This is another cool part about Mulsanne's corner. When he takes a pic of a work-around, he tells you about it.
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