Front splitter

[TurboTed]

Hi, I am interested in making a carbon front splitter for my car to increase downforce in the front of the car. I've been told that if it is not mated with a full undertray and rear diffuser it is either useless or will create an imbalance in downforce that will negatively affect the car. Is this true or would it be worth it to just have a front splitter? BTW the car is a front wheel drive Honda Accord that will be used for HPDE's(high performance driving events). Thanks in advance.

 

[ivymike]

I can't say that I know anything specific about the geometry you've got in mind, but...

1) it is possible to make an effective wing and attach it to a car, even in front. It doesn't necessarily have to have other parts in other places to work. If you're going to rely on the overall shape of the car after installation of a small object for an aerodynamic effect, then the rest of the car will matter.

2) hanging funny-looking stuff all over your car will probably put it in a bad mood. Is that what you had in mind by a "negative effect?" It seems unlikely to me that the "downforces" on your car currently are particularly balanced - I expect that gravity dominates, and that the majority of the "downforce" from gravity acts on the front wheels, due to the weight distribution of the vehicle. Having more weight on the front than on the back, as well as more braking torque in front than in back, seem to be useful for making a car handle like a proper "daily driver." Adding substantial aerodynamic downforce at the front end without adding weight would probably have a noticeable effect on how the car behaves in corners. There are whole books on the subject.

Have you thought about making the "splitter" out of high-density polyethylene?

 

[TurboTed]

I have not considered polyethylene. I am pretty set on a carbon/e-glass hybrid with foam sandwich design which Im told should be plenty strong for my application and very light weight, which is important. What advantages/disadvantages would there be using polyethylene, I am not familiar with this material?

 

[MikeHalloran]

Poly won't cut your tires when it gets ripped off on a bump.



Mike Halloran
Pembroke Pines, FL, USA

 

[patprimmer]

Also unlike carbon/foam sandwich, it will deflect a lot before it breaks.

You will be familiar with it. It is used to make things like some milk bottles, some non carbonated beverage bottles, some Ice cream container lids, plastic fuel tanks, some motor bike mud guards and fairings. It is also extensively used for kitchen cutting boards and some plumbing fittings and pipes.

Basically it is extensively used anywhere that a very cheap light and tough plastic is required.

Regards
Pat
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[GregLocock]

The reason they say that it may harm the handling is that it will increase the downward force more at the front than the rear. This will increase the grip at the front, which is not a bad idea, except that it'll tend to make the car feel more tail happy. That could be bad for example the original Mini was rather tail happy, but I'd guess modern FWDs not so much.

I think that is a reasonable argument, but would be inclined to deal with that if and when it shows up, rather than fretting about it before hand.



Cheers

Greg Locock

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[evelrod]

Also, unless this "splitter" (diaplane, spoiler, whatever) is fitted very close to the roadway, it will be, largely, a waste of time and instead of decreasing lift (what a "splitter" actually does) it will just increase drag. It will, however, look rather "racery"...

Rod

 

[Tmoose]

Often in Conversations about lift/drag, statements will be offered about induced drag necessarily increasing whenever lift is generated. I'm not sure this is really a characteristic of non-airfoil aerodynamics, like cars, unless a design has pretty sophisticated body aero like Formula 1 etc. I think a big part of road vehicle drag is bluff body related, with vast areas at either end simply being subjected to high/low pressures. Similarly a lot of automotive lift/downforce is based on high under-car pressure from air "packing" under the car. Every aircraft pilot must consider substantially increased lift ("float") from "ground effects" when operating within a dozen feet(!) from the ground. Thus I think the mechanism for functional auto aero modifications changing lift or drag is often to subtly re-direct or share pressure between vertical and horizontal surfaces.

Here's some info from VW ca 1979 from VW. From the profile shown the car looks to be a Porsche 924, as Sciroccos of that era were much more angular. Applicability to modern cars is unknown.

- On the model fitted, Only one of the chin spoilers fitted increased Cd AT ALL.
- Most simultaneously reduced lift AND drag
- The meek looking B40 reduced Cd over 15% and Clf about 20% at the same time. At 100 km/h 60 mph the lift reduction was 3 kp or about 6.5 pounds (big deal).

I wonder which spoiler comes closest to the one fitted OEM.

http://www.mindspring.com/~blained/imgs/924weiss.jpg

 

[silverbullet1986]

Turboted, a splitter does not have to have a full under tray to work. Having a smooth under body and rear diffuser will help each of the aero items work better, but a splitter by itself will make down force.

Ivy mike, a splitter is different from a wing. A wing creates lift/downforce from its naca air foil inspired shape. A splitter is just a flat plate that protrudes out of the bottom of the front bumper. It "splits" a high and low pressure zone (high P on top, low P on bottom). The high pressure is created by stagnated air from the bumper.

Evelrod, that statement is not true. Being close to the ground will make it work significantly better due to ground effects but to say it is pointless with out being low is just flat out wrong. Also, I don't kno if its just because of ur wording but a splitter creates downforce to counter the lift of the car, not reduce the natural lifting effect.

 

[patprimmer]

silverbullet

Have you read your post when you were sober.

Regards
Pat
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[ivymike]

hhaa.. I wuz gonna say smthg but decided not 2, tho it wuz hard.

 

[silverbullet1986]

What do you disagree on?

 

[patprimmer]

Pretty well everything except your first paragraph, but especially your last sentence.

Regards
Pat
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[evelrod]

In the context of the original question...

A spoiler or airdam at the front lower valence of a passenger car such as the Honda Accord will likely lower (thanks for the link, Tmoose) the Cd and may or may not reduce lift. It is for certain that it will not be as effective for the intended purpose (low to medium speed performance driving/racing) if it is not close the the ground as possible. Being a FWD it may be a good move, overall, as the car may actually benefit from additional forward biased imbalance...test and tune.

As far as the current trend to the NASCAR looking "splitter"...In my own aero testing back in the 70's/80's, the effect of a front airdam was significant and varied widely from car to car. Some good, some not so good results were obtained from testing. One thing for sure, the shape and size were not what we expected. Aero as applied to our race car was NOT intuitive. I would love to see some data on how far the stagnate area extends in front of a car fitted with/without one of these "splitters". My guess is that they are more for looks than anything related to aerodynamic principals. Just a guess.

Rod

 

[jakethesnake180]

Sorry but silverbullet is exactly correct and to some extent so is evelrod, the addition of an airdam style front splitter will aid in reducing the lift by harnessing the stagnated pressure but it very much depends on the frontal area and shape of the accord as to where this pressure is generated and the dimensions of the splitter. The length of the splitter sticking out of the front of the car can create a negative effect if it is too big. without using a wind tunnel or some sort of modelling software i would suggest buying a book such as 'Competition car aerodynamics' by 'Allan Staniforth' and use some sort of cheap and easily manipulated material such as plywood to experiment initially before paying out for the expensive materials. Beware of the exhaust manifold though, no fires please.

 

[evelrod]

I've had a day or two playing about with high dollar race cars and a couple real geeky engineers. What I posted is what I found for MY race cars. I also posted that to be accurate, test and tune was an absolute necessity. There are no absolutes that I have found relating to the application of aero aids to automobiles. I use the term "aero aids" kinda tongue in cheek....

Relating to the silverbullet post...even a broken clock is correct twice a day!

Jake, we are just gonna have to agree to disagree on that one.

Rod

 

[b939625]

From the research I have done, silverbullet1986 and a few others explain really well how Wind Splitters work. Here’s a little additional information you made need for know in regards to the flow of air under your car.

Please note I am that leaving some things out of this due to people already addressing the issue above. For example: the splitters area of Low/high pressure at the stagnation point.

It all comes down to air flow underneath the car. It’s all about decreasing turbulent air underneath the car in order to sustain Laminar Flow. But to keep Laminar flow going “throughout” the undercarriage of the car you will also need: underbody panels and a good rear diffuser.... also Vortex generators help a great deal with the drag coefficient.

Research Air Dams, Vortex Generators (first used on Airplanes), Rear Diffusers, Stagnation Point (something I don’t want to get into but it is very important) and mainly Laminar Flow…..and that’s just to start….. a grasp of Reynolds numbers is good but confusing…… and know about the ability of splitters to alter the pressure in the engine bay which will cause problems with your radiator (Weird but true… and can be easily tested with a few inexpensive parts)

Here are a few good links to help get you or anyone else started……. Remember you are messing with the entire cars ability to stay on the road, (technically dealing with a reverse airplane wing) so tread lightly when modifying the airflow of your car because there is a lot more that goes into this than what I have said above…….

http://en.wikipedia.org/wiki/Laminar_flow

http://www.up22.com/Aerodynamics.htm

(part one)

http://www.autospeed.com/cms/A_2159/article.html

(part two)

http://autospeed.com/cms/title_Modifying-UnderCar-Airflow-Part-2/A_2456/article.html

http://autospeed.com/A_108646/cms/article.html

 

[b939625]

I forgot to add a few things up top...... research "Fluid Dynamics"...... also here is a good site.

http://www.strangeholiday.com/oops/stuff/annurev.fluid.38.050304.092016.pdf

 

[GregLocock]

What has laminar flow got to do with it?

Cheers

Greg Locock


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