Aerodynamics Fundamentals: Front Splitters
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Front Splitters
10.38
| 00:00 | In this section of the course, we're going to be discussing the various aerodynamic devices that we typically see on club level cars. |
| 00:07 | We'll be going through them from the front of the car to the back, so let's start by taking a good look at the front splitter. |
| 00:13 | It's worth noting that with all things related to car aerodynamics, there are no hard rules. |
| 00:18 | Everything is situational and the key points presented are more guidelines than rules. |
| 00:23 | The splitter is the primary source of front downforce on most touring cars, and is a key part of getting the most out of a car's aero package. |
| 00:33 | It's also a component that is very car specific, and has quite a few different details going on around it that require attention. |
| 00:40 | The splitter's primary purpose is to make front downforce by capturing the high pressure region from the front of the car on top of it, and generating a low pressure underneath through the use of front diffusers and ground proximity. |
| 00:53 | Lastly, it also needs to send clean airflow rearwards. |
| 00:57 | The first thing we need to decide on all splitters is what planform shape to run on the splitter. |
| 01:03 | When I refer to planform shape, what I mean is the shape when viewed from the top. |
| 01:08 | Generally speaking, this is going to be dictated by our rules, and we're going to try to max out that rules box as we discussed in the previous section of the course. |
| 01:17 | In the eventuality that the rules do not constrain our splitter, what we're going to want to aim for is a splitter that reasonably matches our power level, aero goals and suspension setup with the car. |
| 01:28 | If we have a lower power build, say 200-300 hp, and we're going with a single element rear wing as a result, then we probably don't want to have the splitter stick out more than 100mm from the bumper. |
| 01:40 | If we have a higher power car, say 500-600 hp, we'll be running a reasonably sized dual element rear wing, and we can increase that splitter overhang to 150-200mm at the front and about 100 -150mm at the side, if we have a decent rear wing on it. |
| 01:57 | If we have 1000hp or over that, we can go bigger again. |
| 02:02 | A big dual or triple element rear wing combined with 200-300mm of front overhang and 200mm or so of side overhang is where the best performance can be found. |
| 02:12 | If we're getting to the larger side of splitter size, we may wish to consider trimming back the forward outboard corners a bit. |
| 02:18 | On corner entry where the weight transfer is already on the nose from braking, these parts of the splitter can scrape quite badly. |
| 02:26 | In these cases, it's a good idea to sweep the leading edge of the splitter back a bit towards the outboard portions, just to allow for a little bit more margin here and not to have to run crazy stiff suspension or otherwise compromise the front ride height. |
| 02:40 | A good static ride height for the splitter to sit at is around 70mm, factoring in that it will sit lower than that on track as a result of downforce compressing the car's suspension at speed. |
| 02:52 | Some rulesets will restrict splitters to 80mm or higher static ride height and we want to be as low as we can get on those rulesets. |
| 02:59 | For rulesets where we're able to go much lower, I typically don't advise mounting a front splitter on a club level car statically below 60mm. |
| 03:08 | This puts us very close to the ground at that point and will need quite stiff suspension to control the car and stop the splitter scraping. |
| 03:15 | As the car's ride height drops during end of straight braking conditions, the splitter will be very close to the ground. |
| 03:22 | This powers up the ground effect and results in the splitter suffering flow separation, which can lead to unexpected losses in front downforce and the car bouncing along the straight. |
| 03:31 | Some of these issues can simply be avoided by lifting the ride height a little bit. |
| 03:36 | At the front of the splitter, we need to make sure we have a rounded leading edge geometry. |
| 03:40 | We don't want to have a sharp, razor thin splitter. |
| 03:43 | At a minimum, we should target a 10mm radius. |
| 03:46 | But bigger is better. |
| 03:48 | I wouldn't say no to 40mm if you had the thickness. |
| 03:51 | Although, for most club level splitters made out of a flat sheet of material, you're going to struggle with having a radius that size. |
| 03:59 | The radius on the lower edge is far more important than the upper edge as the lower edge is the suction surface. |
| 04:05 | If I had a 12mm piece of plywood for example, I would put a 10mm radius on the bottom and a 2mm radius on the top, rather than a 6mm radius both top and bottom. |
| 04:17 | Adding a bit of thickness to the splitter will help structurally, but the key aerodynamic gains are a nice big radius at the start of the suction surface of the splitter. |
| 04:26 | If we have a sharp leading edge, the air will try to turn around the front of the splitter, however there will be a discontinuity in the curvature where the sharp edge is. |
| 04:35 | This will naturally cause the flow to separate around the sharp edge of the splitter, and that separation will cause poor performance both on the splitter and downstream. |
| 04:44 | At the end of the splitter we'll need some form of front end plate. |
| 04:48 | This end plate will sit on the end of the splitter and stops the high pressure air on the top spilling into the low pressure area underneath. |
| 04:55 | Generally speaking, I advise end plates to be about 100-150mm tall, covering the full length of the splitter's outboard portion front to rear. |
| 05:03 | The end plate should have an angled front when viewed from the side. |
| 05:06 | This will spin up a vortex on the outside of it which will help stop flow separation on the outside of the end plate. |
| 05:13 | When we run an end plate with a dead vertical leading edge, the outwash from the body typically causes a degree of flow separation on it. |
| 05:20 | If the outboard edge of the splitter is inline with the bumper, I typically move the rear of the end plate about 50mm forwards of where it would meet the bumper. |
| 05:29 | This is just to allow some clean air to breathe through that junction. |
| 05:32 | If the splitter is wider than the bumper, this detail isn't necessary and we can go the full length with the end plate. |
| 05:39 | If going wider, a small gurney flap or upkick in the splitter should be used where the splitter protrudes from the bumper. |
| 05:46 | Don't worry, we'll be discussing the gurney flap in more detail soon. |
| 05:49 | This in most scenarios works out to be about a 20-30mm vertical plate on the rear edge of the splitter protrusion, which will help with downforce on the outboard portion of the splitter as it will increase the pressure on the top and decrease the pressure underneath by promoting more upwash. |
| 06:04 | A critical aspect of any splitter is the presence of front diffusers, also known as splitter tunnels. |
| 06:11 | These are ramps fitted to the splitter that expand air up from the low base plane of the splitter into the tyre well. |
| 06:18 | Going back to the Bernoulli's principle module, you'll remember that having a channel with expansion results in low pressure on the small cross-sectional area portion of the channel and higher pressure at the end of the expansion. |
| 06:29 | Well, the front diffuser is essentially acting as the expansion, with the wheel wells being the exit to the end of our expansion. |
| 06:36 | By providing expansion of the air behind the front splitter, the front diffusers can generate suction under the splitter. |
| 06:43 | Combined with the curvature of the tunnel, creating a local upwash of the flow, we'll see sizable front downforce gains with front tunnels fitted. |
| 06:51 | It's not uncommon to see the front downforce values double when a car transitions from a dead flat splitter to one with front diffusers. |
| 06:58 | Some general rules of thumb if we're making our own splitter tunnels are to target a ramp angle of between 10-12 degrees. |
| 07:05 | Why this angle? If you get too high, you'll suffer flow separation at low ride height. |
| 07:10 | If you go too low, you won't make much downforce at high ride height. |
| 07:14 | Generally, I aim towards the low side for angle if the ride height for the splitter is low, and the high side of angle if the ride height for the splitter is high. |
| 07:22 | At the kickline, which is what the point where the tunnel starts to curve up is called, I would try to aim for a bend radius of around 100mm. |
| 07:30 | The kickline usually starts about a third of the splitter length long for a short overhang splitter, and around half of the splitter length long for a long overhang splitter. |
| 07:40 | We should try to put the inboard vertical wall of the tunnel in line with the chassis rail, and the outboard wall about 50mm outboard of the inside tyre shoulder. |
| 07:50 | Typically, I'll flare the back of the outboard wall outboard to expand the tunnel a bit harder, while keeping the angle at the front straight to align with the incoming flows being sucked into the tunnels. |
| 08:00 | These aren't hard rules, but they are good starting points. |
| 08:04 | To be clear, this isn't to say that we're going to need a lot of custom work here. |
| 08:09 | There are plenty of good, low cost front splitter tunnel options off the shelf that can be used for a project. |
| 08:15 | Professional Awesome for example has a very low cost ABS plastic tunnel. |
| 08:20 | I would personally use their large tunnel over their small one. |
| 08:24 | AJ Hartman also has some decent carbon options, as does Sydney Composites. |
| 08:29 | These are all bolt-in options, so we can package them to fit whatever splitter geometry we have. |
| 08:35 | Ideally though, we would recess the splitter blade to adapt these tunnels seamlessly and bond them into the splitter design, making the transition between the blades and the tunnels as smooth as possible. |
| 08:46 | The final thing to consider on the splitter is mounting. |
| 08:48 | As we've already discussed, the splitter is very ride height sensitive. |
| 08:52 | If the splitter is mounted poorly, with limited support, it will start to flex down as the downforce on it increases. |
| 08:59 | This will typically result in the downforce increasing as the splitter gets closer to the ground, however it's worth noting that this happens most when we're at higher speeds. |
| 09:08 | This means that we end up with a more forward aero balance in high speed corners and under braking, which isn't good. |
| 09:15 | The extra flex means that the splitter can also scrape more often and can cause flow separation on the splitter at higher speeds. |
| 09:22 | If the splitter isn't mounted strongly, it may break off, the car will lose all its front downforce and that's going to quite likely result in a crash. |
| 09:31 | All of these are negative for performance, so it's important that we mount the splitter strongly and with good rigidity. |
| 09:37 | This covers everything we need to know about club level front splitters, so let's run over the main points again before moving on. |
| 09:44 | The front splitter is a critical component in generating front downforce for most race cars. |
| 09:49 | Its design and placement help capture high pressure on the top while creating low pressure underneath using front diffusers and ground proximity, while also sending clean airflow rearwards. |
| 10:00 | Splitters must be shaped to match the car's aerodynamic goals, with the size based on engine power and resulting rear wing size, and should be mounted at an optimal ride height to prevent flow separation whilst maintaining performance at low speeds and high ride heights. |
| 10:15 | Additionally, using front diffusers or splitter tunnels can double the downforce compared to a flat splitter. |
| 10:21 | Features like end plates or gurney flaps can also further improve performance. |
| 10:26 | Off-the-shelf splitter tunnel options can simplify customisation, while proper integration ensures smooth airflow and maximises aerodynamic gains. |
