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Author: Subject: front splitters?
omega0684

posted on 18/5/09 at 10:53 PM Reply With Quote
front splitters?

im after some general information on front splitters?

how do they work?

what are they for?

how are they attached?

what are they made of?

can they be used on 7 style cars effectively?

etc etc

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prawnabie

posted on 18/5/09 at 11:00 PM Reply With Quote
lol you carry on like this and your car will look like you've driven through halfords with double sided sticky tape all over it!
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blakep82

posted on 18/5/09 at 11:02 PM Reply With Quote
for a more useful answer

http://www.pts106.com/FB%20Aerodynamics%20Splitter.htm

bascially it seems to say they make a high pressure area above it, and low pressure below, so the low pressure is like a vacuum, sucking it down

[Edited on 18/5/09 by blakep82]





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omega0684

posted on 18/5/09 at 11:02 PM Reply With Quote
more like a trip through the 99p chav land store!

i take it that the underside of the splitter should be flat then and do as far under the car as possible?

does shape make a difference at all?

[Edited on 18/5/09 by omega0684]

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blakep82

posted on 18/5/09 at 11:14 PM Reply With Quote
i don't think the shape makes a difference, but i really don't know.
as far as i know though, they work best if the whole underside of the car is flat





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prawnabie

posted on 18/5/09 at 11:25 PM Reply With Quote
Our cars have downforce built into them - it comes from the pig iron engines!

Although in my case it counter-balanced by the upforce from the wings lol

Shaun

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Andi

posted on 18/5/09 at 11:41 PM Reply With Quote
Go the whole hog.



(Looks quite nice actually)

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blakep82

posted on 18/5/09 at 11:43 PM Reply With Quote
^ awesome! he's even got them on his helmet!





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Andi

posted on 18/5/09 at 11:49 PM Reply With Quote
Should have made one for his little bear mascot thingy.

Check the sister site across the pond. Loads of splitters
http://www.locostusa.com/forums/viewtopic.php?f=23&t=2302

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blakep82

posted on 18/5/09 at 11:52 PM Reply With Quote
if ytou like the look of them then go for it, but i think, with the nose of a 7 being so narrow, i don't think there'll be any downforce type benefit.
probably better with some kind of angled wing like the donkervoort in the link above

[Edited on 18/5/09 by blakep82]





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worcestersauce

posted on 19/5/09 at 07:42 AM Reply With Quote
If you are interested, I have a Westfield front splitter for sale as per the picture above. pretty rare now.

Andy

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craig1410

posted on 19/5/09 at 07:50 AM Reply With Quote
Hi,
I think a front splitter could be very useful in reducing front end lift on a seven. I have been reading a book called "Competition Car Aerodynamics" by Simon McBeath (ISBN 978 1 84425 230 5) and it explains it quite well.

Here is a link to the Amazon item: linky

I hope this helps,
Craig.

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procomp

posted on 19/5/09 at 07:56 AM Reply With Quote
Hi

In truth you are too far off the ground and going too slow for any benefit to really take place. The best you'll do is the same as the nurburgring 24 hr Caterham race car. And the mods that where carried out on that. I am sure Rob palin will be along to fully explain about that car.

Quite simply by going to length as the pic above all that resulted from the fitment of that body kit was negligible gain in handling but at around 130 mph without the kit when fitted it takes 6-10 mph of your top sped as we found out when we built the first Westfield with that kit. And even tried some extra bits to try and gain the speed back. But as for reducing front end lift you certainly do not need to go to those lengths.


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Cheers Matt






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sucksqueezebangblow

posted on 19/5/09 at 08:16 AM Reply With Quote
The principle behind splitters is the following; the faster you go the harder the nose of the car is crammed into the air. Some of this gets crammed under the car potentially creating high pressure, particularly if the underside of the nose is angled upwards. What the splitter does is exactly as it says on the tin, it splits the air going under the car from the air going over or around the car, and prevents the high pressure area under the nose (it may even create a little downforce if it is angled downwards slightly). You then get clean neutral pressure air going under the car, but it will be of little benefit unless you have a flat undertray.

If the car is nose down this can have a mild venturi effect as well. As the nose of a Locost is wedge shaped (looking from above) it would probably be appropriate to take the splitter all the way back along each side up to the bulkhead (i.e where the car reaches full width) in order to split all of the air going under the car.

Note that a full length undertray will prevent air exiting the engine bay so it would be necessary to vent the engine bay through the bonnet or sides of the car.

Most splitters are composite, and undertrays are often aluminium sheet. Carbonmods do carbon composite sandwich for making splitters.





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omega0684

posted on 19/5/09 at 09:37 AM Reply With Quote
i was thinking of something alone the lines of this


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craig1410

posted on 19/5/09 at 10:16 AM Reply With Quote
quote:
Originally posted by omega0684
i was thinking of something alone the lines of this




Yes, having read the book in my last post, I am in no doubt that something like this would help the seven quite a bit. Having said that, one of the worst areas of a typical seven aerodynamically is the cycle wings which can produce a lot of lift. You need to replace these with the ugly long arches to get maximum benefit.

Cheers,
Craig.

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brianthemagical

posted on 19/5/09 at 11:06 AM Reply With Quote
The main limitations on sevens is the lack of solid frontal area, if you consider that the picture above may have approx 0.5m of splitter, where as tin tops and GT/Sports cars have around 1.5-2m to play with.

As for shape or design, ideally it's infinitely thin, strong enough to be stood on, the onlyeffect of which would be the suspension compressing, thus it needs to be attached to the chassis, not body. They are more effective if closer to the ground. The front edge usually conforms to the front of the nose, to give a fixed length at all points, said length should be around 10cm at least.

The way they wrok is by effectively raising the stagnation point on the front of the vehicle, thus less air is able to travel under the car as it's entry is at a lower pressure, this speeds the airs velocity under the vehicle lowering pressure. above the splitter, infornt of the nose is a large high pressure region, this acts to create downforce on the splitter, and car also increase airflow into the radiator or grill, but unless adequately vented it will increase the form drag.

I'll try and get some CFD pics up if i get a chance.

Edited to respond to the above post. The main drag ic caused by the wheels then selves and the rear of the vehicle, fitting swept arches will have little effect, maybe even worse as the wheel is no longer covered as with a cycle wing. the only real advantage is gained by fully enclosing the front, and continuing that to the rear, in effect having a full bodied seven. the cockpit can also have great implications, aero screens being one of the best, closed cockpit being the best, verticle windscreens bing the worst, doors helping, no screen is so so.

[Edited on 19/5/09 by brianthemagical]

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omega0684

posted on 19/5/09 at 11:07 AM Reply With Quote
quote:
Originally posted by craig1410
one of the worst areas of a typical seven aerodynamically is the cycle wings which can produce a lot of lift.
Cheers,
Craig.


this is becoming common discussion at alot of meets and i had a quite in depth chat with a fellow DAX owner at stoneliegh about it. obviously the way to reduce lift is to reduce the pressure on the underside of the wheel arch by cutting holes in the back of the cycle wing to increase/encourage air flow through or cut/drill holes in the top of the wing to relieve presure,

personally i think that drilling holes into my carbon mods cycle wings isn't going to happen, period, but a neat and tidy couple of slit at the rear of the arch might not look to bad, but then 'where do you stop?' all of a sudden your cycle wing looks like a slab of swiss cheese , i think that its all a little extreme for a road only car.

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brianthemagical

posted on 19/5/09 at 11:12 AM Reply With Quote
The wheel will do far far worse than the cycle wing, the best comprimis would be having a very close fitting arch thet extends down the front of the wheel, but that'd look funky.
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MikeRJ

posted on 19/5/09 at 11:13 AM Reply With Quote
quote:
Originally posted by craig1410 You need to replace these with the ugly long arches to get maximum benefit.



The clamshell wings produce even more lift than the cycle wings!

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craig1410

posted on 19/5/09 at 11:38 AM Reply With Quote
quote:
Originally posted by MikeRJ
quote:
Originally posted by craig1410 You need to replace these with the ugly long arches to get maximum benefit.



The clamshell wings produce even more lift than the cycle wings!


I wasn't meaning that type of wing I was meaning the ones where the front edge of the cycle wing comes right down to the ground almost. This prevents the cycle wing from scooping air up and directing it downward which is what causes the lift problem.

quote:
Originally posted by brianthemagical
The wheel will do far far worse than the cycle wing, the best comprimis would be having a very close fitting arch thet extends down the front of the wheel, but that'd look funky.


What he said in fact ^^^

Sorry for the confusion...
Craig.

[Edited on 19/5/2009 by craig1410]

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sucksqueezebangblow

posted on 19/5/09 at 01:02 PM Reply With Quote
The air going between the cycle wing and the tyre does probably contribute to the lift they create but by far the biggest contributor will be the curved profile of the top of the cycle wing.

Many of us will recall the tendency of early Audi TTs to go through hedges backwards on high speed corners, and many years before the early Sierra waggled its arse at high speeds.

Both of these problems were caused by the smooth curved back-ends of the cars creating lift, effectively lifting the back of the car and so reducing grip. On the Sierra they fixed this with a tiny spoiler built into the rear windscreen trim to break the airflow away from the car to stop it creating lift. With the Audi they added a small wing like gurney flap or spoiler to break the airflow away from the back of the car.

This is what is required on cycle wings; a small gurney flap or spoiler. Spoilers do what they say on the tin; they spoil the airflow over a curved surface causing it to break away and thus prevent it from causing lift.

The lift caused by air going between the cycle wing and the tyre can be reduced two ways; mounting the wing so the front edge is close to the tyre (reducing the area the air can get through), and by venting the back of the wing (behind the spoiler if you have fitted one).

[Edited on 19/5/09 by sucksqueezebangblow]





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brianthemagical

posted on 19/5/09 at 01:28 PM Reply With Quote
The area between the tyre and arch will have little effect on anything, one surface is traveling at the free stream velocity, the other at higher velocity in the opposite direction, thus the interatin of the boundary layers will negate most of the air at it's entry, and there will likely be a higher pressure under the arch, thus the air will be unable to flow into it. The wheels have a far greater effect than the arch itself, it's effectivley trying to climb over the air, which will be high pressure at the base of the tyre.
The airflow over the wing will offer some contributions. CSR wings may go some way to help, as it detaches the flow at the rear of the wing, but this may contribute to drag, maybe not though due to the divergance angle of the rear of the wing and the low pressuer and stall that this would create.

Maybe some louvres in the upper surface may help, with a carefully increase area under the top of the arch to eject the high pressure build up above the wheel. Or maybe bringing the rear edge of the wing up so as to detach the flow and involve the turbulance of the wheel in the wake of the arch.

[Edited on 19/5/09 by brianthemagical]

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Rob Palin

posted on 19/5/09 at 08:43 PM Reply With Quote
Going back to the first bit of the original question, a splitter acts to produce a downwards force by encouraging air to slow right down (stagnate) on its upper surface whilst making it very difficult for air to pass around its front edge, causing a separation and a low pressure due to the 'void' which air cannot get in to fill. In most cases this low pressure will also be augmented by an effective increase in the constriction of the main flow under the front of the car.

The diagram in the link given in the 3rd post is correct and very useful, but the accompanying explanation is wholly incorrect, and represents a fundamental (but surprisingly common) misunderstanding of Bernoulli's equation and pressure.

A splitter does work on a 7-type car but not terribly effectively, mainly due to the shape of the nose, insufficient stagnation above it and there being plenty of options for air to take other routes around what it sees as an inconvenient obstruction rather than a powerful aerodynamic device.

Since generating either lift or downforces both generate drag, it's a better strategy to eliminate the sources of lift already on the car rather than just try to overpower them with additional downforce-creating items.

As discussed on here previously, the front wheelarches are the primary source of lift at the front of a 7. The lift is caused mainly by the flow up the front of the arch and the flow 'water-wheeled' up from the back by the rotation of the tyre, but some of it is from flow acceleration over the top of the arch.

The main things you can do to target these lift mechanisms are to extend the front edge of the arch further around (to at least 3 o'clock on a front right wheel, but preferably more), introduce louvres in the top surface (from about 11:00 to 1:00, still using the clock analogy), and put a sharp feature line at the rear of the top surface (preferably around 10:00-10:30) to get the air to separate cleanly from it and a little earlier than it perhaps would normally. If you feel fancy, you can dish the surface a little ahead of the separation edge to increase the pressure there and generate a tiny amount of local downforce.

Between these three measures it's possible to reduce the front lift of a typical 7 by more than half. Add a splitter too (a bit like the first pics, not the Westfield one), preferably just below a number plate or other place where a hefty stagnation is largely unavoidable, and make sure that the cooling flow exits out the top or the sides, and you'll not be far off zero lift at the front and with lower drag.

The rear doesn't tend to generate much lift and actually often has downforce, though much of that is because of the pitching moment from the lift generated at the front. Once you sort the front out that apparent rear downforce pretty much disappears, but you can claw some of it back by applying the same flow management measures to the rear wheel arches as at the front.

Hope this helps!

[Edited on 19/5/09 by Rob Palin]

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craig1410

posted on 19/5/09 at 11:00 PM Reply With Quote
Hi Rob,
What you have just said makes a lot of sense. Having read the above mentioned book on competition aerodynamics I have absorbed a lot of information but sometimes it is difficult to focus on which parts of that information are important and then apply them effectively. Your post certainly helps in this regard.

Interestingly, the bit about the number plate being part of the air dam above the splitter is exactly what I was thinking of doing because at the moment my number plate is too high and partially obstructs the grill. I wanted to make it lower but then it wouldn't be supported as the nosecone slopes downward at the front. My thought was to square off this downward sloping section of the nose by making an air dam and mounting the number plate on the front. Then extend a splitter around the lower edge of the air dam. It might catch the speed bumps though...

With regards to aerodynamics in general, I found that the most important thing I learned was that total pressure = static pressure + dynamic pressure and that dynamic pressure is increased with increasing air velocity. When you add the fact that total pressure is always the same along a given streamline then you can quickly visualise how the static pressure might vary and thus provide lift or downforce at any given point on the vehicle.

Thanks,
Craig.

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