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Another vote for a dedicated aero subforum. People like Moti, etc have thoroughly demonstrated the power of aero mods on our cars. This thread is great, but even having read it, it's hard to go back and find the exact post I'm thinking of if I'm looking for an old reference.
Interesting how the splitter curves up. I never noticed that in this photo before.
Presumably to increase airflow under the car but I wonder if it significantly reduces the splitter functionality?
Given we (most of us anyway) are not using under flow to the same degree....
OK, So that brings up something I've been thinking about. I was at Gateway a couple of weeks ago testing and this Mustang was there. They were testing a new front splitter. It had a profile that reminded me of the splitters on the LMP1 cars.
What is the purpose of the raised center section? Is it to increase airflow under the splitter in that section to increase velocity and thus lower the pressure?
OK, So that brings up something I've been thinking about. I was at Gateway a couple of weeks ago testing and this Mustang was there. They were testing a new front splitter. It had a profile that reminded me of the splitters on the LMP1 cars.
What is the purpose of the raised center section? Is it to increase airflow under the splitter in that section to increase velocity and thus lower the pressure?
My understanding is that it is more aimed at underflow in regard to the rear of the car than the front as such. My guess is there is some pretty high end underbody and rear end diffuser stuff going on.
My understanding is that it is more aimed at underflow in regard to the rear of the car than the front as such. My guess is there is some pretty high end underbody and rear end diffuser stuff going on.
Stand to be corrected...
You are probably correct.
Here are shots of the side skirts and rear diffuser:
Some of the more advance splitters actually taper the airflow down to tighter stage then open back up again. The concept is similar to a velocity stack into a combustion chamber... the expansion at the end pulls air through the tighter part of the splitter at a higher velocity creating a lower pressure zone. The tapering at the front promotes more ideal laminar flow.
Its not something you can just slap onto any car as the shapes rely heavily on the airflow through the mouth of the bumper and what happens to the air behind it with the floor.
I was under the impression that the 3d splitters that have different heights at the front were primarily for safety to prevent the front and undercar aero from completely stalling. Such has hitting a puddle or bottoming out on a bump under braking.
Regarding the curved front edge vs flat edge on a splitter, it has nothing to do with the splitter itself and everything to do with the rest of the car. One is not better than the other in all applications, this is a great example of what we often say about aero - that everything on the car is an inter-related system, no single element can be examined out of context of the rest of the car.
At a basic level, you generally have two types of cars in terms of aero: those that rely on a wing and splitter to make the majority of their downforce because those items are relatively simple and easy to get right (i.e. all non-pro cars), and those that utilize ground effect under the car to make the majority of downforce (pro cars, when rules allow it). For the latter category, the entire underside is designed as a venturi (multiple venturis in many cases) and airflow under the car is essential to the function of the ground effect. Therefore in almost every example of a ground effect car you will see a front splitter edge with a raised section to feed that system and guarantee that the underside of the car always gets airflow. For amateur cars, and this is not to take anything away from the great development that goes into some "amateur" level cars, ground effect is simply out of reach because it requires advanced simulations and design. For cars at this development level it is better to go the opposite direction and reduce under-car airflow and thus reduce drag. A flat splitter accomplishes this best. It should be noted that a flat floor is NOT the same as complex ground effects. Flat floors are something that we can easily implement at an amateur level, and they are not at all as sensitive to a loss of airflow as a venturi system is. The splitter itself is also not very sensitive to a loss of flow underneath; the majority of downforce made by the splitter is due to the pressure on the upper surface, so as long as you maintain airspeed you have downforce, regardless of if flow is cut off below. For a car that does not utilize ground effects, it would not make sense to intentionally feed air under the car.
I always cringe when I see cars at a (high) amateur level trying to implement certain pro-level aero elements, because there's a high probability that they aren't getting it right and/or don't have the full system that makes it effective. That's not to say that some don't get it right enough, either by bright engineering or just sheer luck that it only took 3 permutations rather than 50 to get close, but even a team pushing the limits of budget and resources for an amateur/semi-pro level program, I would call it a gamble.
Ryan is right on. Back in the 80's there was a lot of drivers killed in cars running a early version of this setup, so it was dropped. The way it worked was with the bottom curving up at the front flowing underneath and exiting out the back with a slope upward, it was like a upside down wing. You have to keep the air channeled though or it well just spill out the sides, and may even lighten the car. The early versions channeled the air with side skirts that ran under the cars to channel the air and that was the problem. The car would hit a bump in a corner and tear the skirt off in the middle of the corner and it was instant shut off of down force and some terrible wrecks and drivers killed. A buddy of mine and I screwed around with this on a shifter kart and we won a regional race with it and you guessed it, when they inspected us it was instantly outlawed. When we first start playing with it we didn't have the skirts underneath and the kart would get light in the front as most of the air was hitting the front curve and then just spilling out the sides right away in stead of staying stuck to the bottom and actually push the nose up..
That is why the modern day ones are molded high in the center to form a channel and some have ends on the front that curve downward to help keep the air in the center channel. With all this being molded in you well hit the flat part of the splitter and keep the channel with no skirts to tear off. Nascar on the other hand as Ryan said keeps most of the air above their splitter and from going under it as they run a dirty bottom like we do. Their splitter stick out from the car is pretty short. so their goal is to keep the air from going under the car. It is only about 12" or so front to back and the rear edge is basically the same curve shape. Nascar runs basically no suspension up front, the tires being the only suspension in the front under braking and corners to the apex.. They run soft springs and they adust the shocks with shims that lets them bottom out and just keep the splitter off the pavement. Different strokes for different folks.
View of the transom. The sides curve in at 15 degrees. Some strange ideas I’m working on.
Skateboard laminates are thin, can be cut with scissors, and should work... Maybe using aluminum flashing to fill the gaps. Or plywood. In any case, you can see how much narrower the fastback is at the front edge. I’m hoping it helps keep the wind out of the cabin. We have to race with windows open.
Last edited by Occam’s Racer; 05-04-2018 at 07:44 AM.
Reason: Add pic
I was under the impression that the 3d splitters that have different heights at the front were primarily for safety to prevent the front and undercar aero from completely stalling. Such has hitting a puddle or bottoming out on a bump under braking.
That is correct. It reduces sensitivity to underbody starvation, which can cause aero instability (porpoising), at the expense of front downforce.
There are also other considerations like cooling for the exhaust (so it doesn't melt the flat floor) and trans / diff heat exchangers.
I would not recommend copying that car's aero setup; it looks less than ideal... where should I start?
1) The splitter chord is quite small. Is that really a 7" front chord from the outline of the OEM bumper cover?
2) There are no end plates on the splitter, so the air just spills over the sides and is wasted.
3) The tires stick out from the wheel well and create a ton of drag. Look at all the exposed frontal area of the tire! He could at least try to shield it with some canards.
4) There are no struts/supports on the sides, so it's doubtful that splitter is under much load.
5) I have yet to see an effective rear diffuser setup with a stick axle without significant modification to the chassis (cut the trunk floor out & modify the floorpan in front of the axle). He is also pouring more air under the car from the raised splitter and flat bottoms are prohibited, so underbody drag will be higher.
6) He has all kinds of strakes and doodads hanging off the diffuser, but the stock bumper cover is there acting as a wind sock (I'm sure removing the rear valance did wonders).
Dollars spent: ~$100 for splitter, ~$1600 Singular kit
Hours spent: ~12
How effective: Splitter =2 Wing = 3
0=slower, 1, no improvement, 2 =slightly better,3= big improvement
Materials used: Birch, aluminum flat stock
Size/thickness of materials: 1/2'' birch, 1 and 1/4'' aluminum
Bracket location: front crash support, sway bar mount, tabs near steering rack, trunk rails
Tracks tested on: Buttonwillow 13CW
Race/TT class built for: N/A
The rear wing provided massive improvements in stability in long sweepers, and under braking. I had to re-calibrate braking points (and my thinking) and was still wary as to how much grip I could actually generate. Shortcomings were definitely the driver. I was nowhere near the limit of the setup. Very little drag at low AoA.
Front splitter was too high and small to achieve proper balance. Quick and dirty mounting brackets due to time constraints. Decent levels of understeer. Splitter is 4'' when measured from vertical of bumper. Airdam is on the list, but ran out of time.
Even with my poor driving, I dropped 2+ seconds off PB at Buttonwillow 13CW.
Looking good. More splitter. Since you don't have an airdam shrouding the front tires, add some front tire spats rising from the back edge of the splitter at the corners. Lap time will continue to fall as you get get comfortable with what the car is happy to do now.
04-18-2018, 01:34 AM
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