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Para
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Dear Sir/Madam,
Is there an empirical data available on what the loads (lbs or Newton) are on a typical splitter for an average passenger car at various speeds?....or is there an easy way to calculate/estimate the force for a given splitter size/area ?
Thanks in advance
kindest regards
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Warren (Staff)
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I am not aware of any off the shelf data. Do you mean aerodynamic loadings or strength of a typical splitter? both could be quite different and are effected by different variables although one would hope any decent splitter is strong enough to resist the aerodynamic loads it is designed to take!
Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant
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Hanaldo
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Totally impossible to give a generic value for. The same splitter on one car will perform differently on another car, let alone different splitters. Variables like rake angle, leading edge thickness, ride height, distance forward of the bumper, diffusers if it has any, etc. etc. To calculate that sort of thing you need CFD data on the specific splitter youre using, and even then you can take those values with a pinch of salt without a full 3D scan of your car.
Splitters can generate massive aero loads though, so they do need to be very strong. The universal one I build Ive done free-air CFD analysis on, and in a perfect situation it will make 400kg of downforce at 200km/h. In the real world thats likely closer to 350kg at 200km/h, but still massive loads. So a 2mm thick carbon sheet wont cut it on a splitter that is actually doing anything!
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Para
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Hi Guys,
First of all, thank you to everyone for getting back back....much appreciated.
I realise that the splitter itself does not actually create downforce (unlike an airfoil). All it does is to increase the surface area over which high pressure can build up. The more high pressure there is above the splitter...and the more low pressure below the splitter, the greater the net downforce.
Also, my understanding is that splitter function is also very sensitive to ride height.
The lower the car is to the ground the greater suction that will be created by the ground effects, hence the reason why the splitter is located at the lowest possible point. However if the splitter is too close to the ground it will stall, producing less downforce and more drag because air cannot flow through the bottom part of the splitter, so the speed of the flow there will decrease, increasing the pressure.
I read somewhere that this sensitivity can be reduced by designing anhedral shaped splitter. The idea being that in the case that the car touches the ground, part of the splitter will continue to function and hence create downforce.
So yes, i understand there is no one answer without CFD. The splitter will be unique to the vehicle it is being designed for...as frontal are, stagnation point etc are all different on different vehicle types...
But i was quite surprised to read that splitters can generate between 300-400 kg of load....astonishing !
Thanks once again everyone...much appreciated
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Hanaldo
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Group: Forum Members
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+xHi Guys, First of all, thank you to everyone for getting back back....much appreciated. I realise that the splitter itself does not actually create downforce (unlike an airfoil). All it does is to increase the surface area over which high pressure can build up. The more high pressure there is above the splitter...and the more low pressure below the splitter, the greater the net downforce. Also, my understanding is that splitter function is also very sensitive to ride height. The lower the car is to the ground the greater suction that will be created by the ground effects, hence the reason why the splitter is located at the lowest possible point. However if the splitter is too close to the ground it will stall, producing less downforce and more drag because air cannot flow through the bottom part of the splitter, so the speed of the flow there will decrease, increasing the pressure. I read somewhere that this sensitivity can be reduced by designing anhedral shaped splitter. The idea being that in the case that the car touches the ground, part of the splitter will continue to function and hence create downforce. So yes, i understand there is no one answer without CFD. The splitter will be unique to the vehicle it is being designed for...as frontal are, stagnation point etc are all different on different vehicle types... But i was quite surprised to read that splitters can generate between 300-400 kg of load....astonishing ! Thanks once again everyone...much appreciated Splitters do create downforce, just not as much as an airfoil. The main function of a splitter is to reduce the amount of air going underneath the car. As with all aero structures, the high pressure zone on top of the structure contributes very little to the negative lift being created, it is all about that low pressure zone on the bottom that does all the work. But the splitters role is much more important than just that; not only does it reduce positive lift by reducing the volume of air underneath the car, but by doing so it improves the performance of other aero components like any canards or front wings, side skirts, rear wing, rear diffuser if there is one, etc. So the net benefit can be huge because not only does the splitter itself produce negative lift, but it also let's the entire aero package produce more negative lift. They can actually produce significantly more than 400kg, mine is a relatively simple design. The splitter/front wing combinations on cars at the pointy end of Time Attack are making more than 800-1000kg of negative lift - to put that in perspective, it means you should be able to park a small car on top of the splitter and not see any deflection... So they can be absolutely massive, and are a hugely structural component. That said, a 20mm lip stuck to the bottom of the front bumper without proper rake or rear extension, is not going to do that and is really only contributing to drag. So most splitters that you see on street cars and the likes are not making any downforce at all. If you cant stand on it, its not doing anything for you!
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Para
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Group: Forum Members
Posts: 8,
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+x+xHi Guys, First of all, thank you to everyone for getting back back....much appreciated. I realise that the splitter itself does not actually create downforce (unlike an airfoil). All it does is to increase the surface area over which high pressure can build up. The more high pressure there is above the splitter...and the more low pressure below the splitter, the greater the net downforce. Also, my understanding is that splitter function is also very sensitive to ride height. The lower the car is to the ground the greater suction that will be created by the ground effects, hence the reason why the splitter is located at the lowest possible point. However if the splitter is too close to the ground it will stall, producing less downforce and more drag because air cannot flow through the bottom part of the splitter, so the speed of the flow there will decrease, increasing the pressure. I read somewhere that this sensitivity can be reduced by designing anhedral shaped splitter. The idea being that in the case that the car touches the ground, part of the splitter will continue to function and hence create downforce. So yes, i understand there is no one answer without CFD. The splitter will be unique to the vehicle it is being designed for...as frontal are, stagnation point etc are all different on different vehicle types... But i was quite surprised to read that splitters can generate between 300-400 kg of load....astonishing ! Thanks once again everyone...much appreciated Splitters do create downforce, just not as much as an airfoil. The main function of a splitter is to reduce the amount of air going underneath the car. As with all aero structures, the high pressure zone on top of the structure contributes very little to the negative lift being created, it is all about that low pressure zone on the bottom that does all the work. But the splitters role is much more important than just that; not only does it reduce positive lift by reducing the volume of air underneath the car, but by doing so it improves the performance of other aero components like any canards or front wings, side skirts, rear wing, rear diffuser if there is one, etc. So the net benefit can be huge because not only does the splitter itself produce negative lift, but it also let's the entire aero package produce more negative lift. They can actually produce significantly more than 400kg, mine is a relatively simple design. The splitter/front wing combinations on cars at the pointy end of Time Attack are making more than 800-1000kg of negative lift - to put that in perspective, it means you should be able to park a small car on top of the splitter and not see any deflection... So they can be absolutely massive, and are a hugely structural component. That said, a 20mm lip stuck to the bottom of the front bumper without proper rake or rear extension, is not going to do that and is really only contributing to drag. So most splitters that you see on street cars and the likes are not making any downforce at all. If you cant stand on it, its not doing anything for you!
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Para
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Group: Forum Members
Posts: 8,
Visits: 20
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+x+xHi Guys, First of all, thank you to everyone for getting back back....much appreciated. I realise that the splitter itself does not actually create downforce (unlike an airfoil). All it does is to increase the surface area over which high pressure can build up. The more high pressure there is above the splitter...and the more low pressure below the splitter, the greater the net downforce. Also, my understanding is that splitter function is also very sensitive to ride height. The lower the car is to the ground the greater suction that will be created by the ground effects, hence the reason why the splitter is located at the lowest possible point. However if the splitter is too close to the ground it will stall, producing less downforce and more drag because air cannot flow through the bottom part of the splitter, so the speed of the flow there will decrease, increasing the pressure. I read somewhere that this sensitivity can be reduced by designing anhedral shaped splitter. The idea being that in the case that the car touches the ground, part of the splitter will continue to function and hence create downforce. So yes, i understand there is no one answer without CFD. The splitter will be unique to the vehicle it is being designed for...as frontal are, stagnation point etc are all different on different vehicle types... But i was quite surprised to read that splitters can generate between 300-400 kg of load....astonishing ! Thanks once again everyone...much appreciated Splitters do create downforce, just not as much as an airfoil. The main function of a splitter is to reduce the amount of air going underneath the car. As with all aero structures, the high pressure zone on top of the structure contributes very little to the negative lift being created, it is all about that low pressure zone on the bottom that does all the work. But the splitters role is much more important than just that; not only does it reduce positive lift by reducing the volume of air underneath the car, but by doing so it improves the performance of other aero components like any canards or front wings, side skirts, rear wing, rear diffuser if there is one, etc. So the net benefit can be huge because not only does the splitter itself produce negative lift, but it also let's the entire aero package produce more negative lift. They can actually produce significantly more than 400kg, mine is a relatively simple design. The splitter/front wing combinations on cars at the pointy end of Time Attack are making more than 800-1000kg of negative lift - to put that in perspective, it means you should be able to park a small car on top of the splitter and not see any deflection... So they can be absolutely massive, and are a hugely structural component. That said, a 20mm lip stuck to the bottom of the front bumper without proper rake or rear extension, is not going to do that and is really only contributing to drag. So most splitters that you see on street cars and the likes are not making any downforce at all. If you cant stand on it, its not doing anything for you! Hi Hanaldo, Thanks for that. Indeed those are huge loads. However if you look at data from passenger cars modified into track cars, you will see that no such vehicle capable of generating more than about 1.4g centripetal acceleration. I can only think this is due to unbalanced load as it difficult to get comparable loads at the back of the car without substantial aero bits such as diffusers and matching rear wings to ensure non turbulent return of the low pressure flow back up to ambient. On the contrary a proper race car generates half of it’s downforce by ground effects alone (flat bottom and diffusers….the Venturi effect) so a passenger car is never going to get into the 2.5g lateral acceleration as in a Radical of similar. Incidentally, has anybody modelled a front splitter with an aerofoil cross-section and noted the effects?...although this may not be work that well… as an aerofoil needs smooth flow over both surfaces to be effective….given that it is mounted on the front of a car where there is a massive stagnation point….so that may be pointless. Anyway the reason for the original post was to gauge what sort of loads we can get from a splitter so that I could work out the loads that the connecting rods and attachments would be subjected to….attached is an example showing a 90 kg downforce and it’s effects on attachments etc For this I have assumed that the 90 kg (198 lb) force will be evenly distributed along the splitter length. We can then model this force acting at a single point at the centre of the splitter and treat the whole set up as a framework that has external forces acting on it. From a framework perspective, the rods and the splitter itself carry out one of two operations: These can stop the framework from collapsing inwards by exerting an outward force, or THRUST….ie acting as a STRUT or prevent the joints from flying apart by exerting an inward pull (TENSION) at each end…acting as a TIE. The calculations show the thrust and tension loads on the rods and the retaining attachments. I solved for the various loads acting through the system simply by taking moments about appropriate points and resolving vertical and horizontal components of all the forces.  
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Hanaldo
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I'm not talking about Radicals or the likes, I'm talking about Time Attack cars. Take a look at any of the Pro or Pro Am cars competing at WTAC. These cars are all making more downforce than an F1 car, they're looking at numbers in excess of 3000kg of aero loading. Yes, in those classes the cars are a tube frame chassis with tunnels in the floor, so they are proper aero cars, but they are based on passenger cars. I was sort of more making the point about how open ended your question was - a splitter can quite literally make anywhere from no downforce at all to over 1000kg of downforce. Its simply impossible to estimate a value without knowing anything about the design or the car its going on.
Yes, the total aero package needs to be designed so that it is properly balanced. You need a proper weight distribution including aero loading so that the centre of gravity is as close to the centre of the car as you can get it, but this often comes down to class rules and the actual base car you are starting out with. But with good design it is certainly possible to balance the aero loads and produce very high downforce.
As for front airfoils, yes I have designed and built these, and yes they can be superior to a splitter. Again, take a look at any cars running at the pointy end of time attack, they will all have front wings (except the Lyfe GTR, but ccompare them to the competition and you can see they would gain a lot by having some better front aero). RP968 and the 1:1 R8 are probably the best examples of a full front airfoil rather than a splitter. Lots of the other cars will have a combination of splitter and front wings, and this is especially more common in the lower Open Class cars, as this category is still a stock chassis design with flat floors and tunnels prohibited.
To throw you another design curve ball - attachment points should all be behind the bumper/air dam. Mounting solutions like splitter tie rods and cables are absolutely horrific when they are external and placed in the air flow. These create so much drag and destroy so much lift potential that you would be better off running a much smaller splitter design in order to do wothout them. Any aero car that has been properly designed will not have any mounting points in the air flow.
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Para
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+xI'm not talking about Radicals or the likes, I'm talking about Time Attack cars. Take a look at any of the Pro or Pro Am cars competing at WTAC. These cars are all making more downforce than an F1 car, they're looking at numbers in excess of 3000kg of aero loading. Yes, in those classes the cars are a tube frame chassis with tunnels in the floor, so they are proper aero cars, but they are based on passenger cars. I was sort of more making the point about how open ended your question was - a splitter can quite literally make anywhere from no downforce at all to over 1000kg of downforce. Its simply impossible to estimate a value without knowing anything about the design or the car its going on. Yes, the total aero package needs to be designed so that it is properly balanced. You need a proper weight distribution including aero loading so that the centre of gravity is as close to the centre of the car as you can get it, but this often comes down to class rules and the actual base car you are starting out with. But with good design it is certainly possible to balance the aero loads and produce very high downforce. As for front airfoils, yes I have designed and built these, and yes they can be superior to a splitter. Again, take a look at any cars running at the pointy end of time attack, they will all have front wings (except the Lyfe GTR, but ccompare them to the competition and you can see they would gain a lot by having some better front aero). RP968 and the 1:1 R8 are probably the best examples of a full front airfoil rather than a splitter. Lots of the other cars will have a combination of splitter and front wings, and this is especially more common in the lower Open Class cars, as this category is still a stock chassis design with flat floors and tunnels prohibited. To throw you another design curve ball - attachment points should all be behind the bumper/air dam. Mounting solutions like splitter tie rods and cables are absolutely horrific when they are external and placed in the air flow. These create so much drag and destroy so much lift potential that you would be better off running a much smaller splitter design in order to do wothout them. Any aero car that has been properly designed will not have any mounting points in the air flow. So what sort of lateral acceleration can these Time Attack cars muster? I couldn’t find any data on that, but I suspect no where near an F1 car…or even a Radical ….i guess one of the limiting factors is the mass of the Time Car….. given that the friction forces (tyres/road surface) would need to overcome m.v^2/r….therefore the greater the mass m, the greater the counter force (grip needed) that needs to be generated to negotiate a bend
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Hanaldo
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Group: Forum Members
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+x+xI'm not talking about Radicals or the likes, I'm talking about Time Attack cars. Take a look at any of the Pro or Pro Am cars competing at WTAC. These cars are all making more downforce than an F1 car, they're looking at numbers in excess of 3000kg of aero loading. Yes, in those classes the cars are a tube frame chassis with tunnels in the floor, so they are proper aero cars, but they are based on passenger cars. I was sort of more making the point about how open ended your question was - a splitter can quite literally make anywhere from no downforce at all to over 1000kg of downforce. Its simply impossible to estimate a value without knowing anything about the design or the car its going on. Yes, the total aero package needs to be designed so that it is properly balanced. You need a proper weight distribution including aero loading so that the centre of gravity is as close to the centre of the car as you can get it, but this often comes down to class rules and the actual base car you are starting out with. But with good design it is certainly possible to balance the aero loads and produce very high downforce. As for front airfoils, yes I have designed and built these, and yes they can be superior to a splitter. Again, take a look at any cars running at the pointy end of time attack, they will all have front wings (except the Lyfe GTR, but ccompare them to the competition and you can see they would gain a lot by having some better front aero). RP968 and the 1:1 R8 are probably the best examples of a full front airfoil rather than a splitter. Lots of the other cars will have a combination of splitter and front wings, and this is especially more common in the lower Open Class cars, as this category is still a stock chassis design with flat floors and tunnels prohibited. To throw you another design curve ball - attachment points should all be behind the bumper/air dam. Mounting solutions like splitter tie rods and cables are absolutely horrific when they are external and placed in the air flow. These create so much drag and destroy so much lift potential that you would be better off running a much smaller splitter design in order to do wothout them. Any aero car that has been properly designed will not have any mounting points in the air flow. So what sort of lateral acceleration can these Time Attack cars muster? I couldn’t find any data on that, but I suspect no where near an F1 car…or even a Radical ….i guess one of the limiting factors is the mass of the Time Car….. given that the friction forces (tyres/road surface) would need to overcome m.v^2/r….therefore the greater the mass m, the greater the counter force (grip needed) that needs to be generated to negotiate a bend Yeh you won't find that sort of data published, the teams will keep that information pretty close. I know the race engineer for the Tilton Evo, I'll see if I can get it out of him. However these cars are past the limits of the R-Compound control tyre, the Advan A050. Every year there is a tyre failure from aero loading. They could actually generate more downforce and more grip and go faster, but the current tyre regulations are what holds them back. Which for me is great, you play within the rules, but it makes it a little bit incomparable to most other racing series that run on full slicks. But even on R-Compound tyres, these are 1000kg/1500hp+ cars going full throttle (~300km/h) through Turn 1, which is just unheard of in any other racing category that Sydney Motorsport Park hosts. Even our pinnacle motorsport category here, the V8 Supercars, are completely blown out of the water and running 12 seconds a lap slower.
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