E86 lip spoiler aerodynamics
- Thread starter exdos
- Start date
Hey you should speak to these guys http://www.argon-creative.com/
They are really good and make one off or small batch stuff in various plastics and cf.
Their facebook page has a some pic of a few of their projects https://m.facebook.com/ArgonCreative?refsrc=http://www.google.co.uk/url&_rdr
They are really good and make one off or small batch stuff in various plastics and cf.
Their facebook page has a some pic of a few of their projects https://m.facebook.com/ArgonCreative?refsrc=http://www.google.co.uk/url&_rdr
mad4slalom
Senior member
clever bugger exdos! where do you find time for such epic and fun projects ? add me to list if you produce them for sale 
dubsesd said:
I can make a pattern to any shape, so there would be no problem in doing what you suggest. Whilst making the pattern seen in my photos in this thread, I started by shaping the profile along it's full length without the notch as below, so you can get some idea of what it might look like.
I played around with that in Photoshop, by colour coding the pattern and also giving it a carbon-fibre finish, and to me that just doesn't look right and I certainly wouldn't want to stick a lip spoiler of that shape on my car.
So I then set about putting a central notch in the pattern, and I started by having the notch quite a bit smaller than the two side profiles, as below, and to me, this is starting to look better.
The lip spoiler now starts to reflect the roof profile, which I've outlined in green. There are also two other design "accents" which sit roughly equidistant to a rear view, both above and below, which I've indicated with the green arrows. It seems to me that if there isn't a central notch in the lip spoiler, this visually "argues" with those design accents. So, from an aesthetics point of view, the central notch, which also includes the same design accent, is the most aesthetic format. However, when the pattern was at the stage shown in the photograph above, I delayed progressing further until I was sure about the rear view profile.
After deliberation and trials with Photoshop, I decided that a wider notch would be preferable, which would be almost the same size as the notch in the roof at the top of the rear window. So I increased the width of the central notch and the pattern that I now have is as below. The central notch is slightly smaller than the two side profiles and to me, it looks just right. The pattern has been painted an array of different colours as a guide to me during the sanding/finishing process and it is now in white gloss, and the shape I've now got (seen in different colours) just seems to blend into the car's design. I have to say that the OEM lip spoiler is extremely well designed from an aesthics point of view. Mine is slightly different to OEM but is essentially the same design.
If you now look at the way that air flowing over the car "sees" the spoiler, as in the photo below, the central notch doesn't actually reduce the effective height of the "Wickerbill" by very much, so the functionality of the part should be preserved, with or without the central notch.
As you can see from an earlier posted photo, a Wickerbill of 25mm will continue to allow the free flow of air.
However, a lip of 70mm clearly prevents free flow and would create a huge amount of drag as shown in the photo below.
As you can see, I've been through the thought processes and testing stages and have reached the conclusion that the OEM lip spoiler design, is both aerodynamically effective and aesthetically designed.
Graeme,
In the Undercar Aerodynamics thread a similar question was asked:
In other words, the direction of the flow of water/air will essentially be the same at all road speeds and this is determined by the height of the Wickerbill, as I think my demonstration photos have shown. A Wickerbill of between 10mm to 25mm will give the direction of airflow behind the car that I'm attempting to produce as per an illustration I previously produced in the Undercar thread, "Undercar Strakes + OEM lid wing", as below.
In the Undercar Aerodynamics thread a similar question was asked:
exdos said:
In other words, the direction of the flow of water/air will essentially be the same at all road speeds and this is determined by the height of the Wickerbill, as I think my demonstration photos have shown. A Wickerbill of between 10mm to 25mm will give the direction of airflow behind the car that I'm attempting to produce as per an illustration I previously produced in the Undercar thread, "Undercar Strakes + OEM lid wing", as below.
The painted prototype looks great! What are the next steps? Are you planning to make a mould?
Ed Winchester said:
Thanks Daniel! I've not gone to sleep on this and I've been in touch with a couple of different carbon fibre fabricators to get some idea of the cost of having the part made. I'm in no great hurry to get it finished so I'm still in the "consideration" phase.
In the meantime I've also been messing about designing front splitter/flippers using your old bumper and photoshop to produce something that I think would not get destroyed on a road car, provided the car isn't lowered too much and provided that you are aware of it's presence when going over sleeping policemen and parking by kerbs.
I've come up with a few different designs based on the "fangs" as the starting point. The following photos show the OEM front bumper and then with 3 different designs in carbon fibre and colour coded. If I opt for the colour coded versions, then I think that these could be made out of ABS plastic, which would be more durable than CF or GRP. As I've previously mentioned in our PMs, I can make any of these parts for myself, and I don't really want to get involved with going commercial, because I simply don't want the hassle, which most group-buys seem to produce. Then again, if there were enough demand and other owners really like what I've come up with, then in many ways, it would be a shame not to get copies made professionally to share, in the absence of availability of similar parts for the Z4M. As a note, my designs are Copyrighted by me.
I know which of the six designs that I like best for my car. Please feel free to comment.
As always, very interesting to read John. I actually like the en face view of the OEM bumper with the fangs as they are, so I think preserving these in the same colour as the car and adding to this in black would be aesthetically most pleasing - perhaps a halfway house between the last two with the sections that reflect the OEM shape in yellow and the additions in black. The visual effect will be different for different colours anyway...
Isn't what you've put on the aluminium sheet effectively a Gurney flap? The ever-reliable Wikipedia suggests that the height of the flap should be 1-2% of the wing chord. http://en.wikipedia.org/wiki/Gurney_flapexdos said:dubsesd said:As you can see from an earlier posted photo, a Wickerbill of 25mm will continue to allow the free flow of air.
However, a lip of 70mm clearly prevents free flow and would create a huge amount of drag as shown in the photo below.
Yes. If you consider the length of the Z4MC to be the chord length of an aerofoil, then it's 411.3cms long, the hypotenuse (the effective face) of my lip spoiler is 43.1 mm high, therefore, it seems that this fits in to that ballpark. 8)carl said:
At the end of the day, I'm just basically copying what BMW produced with the OEM lip spoiler and examining how it might work aerodynamically in practice and what I've seen suggests that it conforms to the theory. I've seen it time and again on forums, where people reckon lip spoilers are just cosmetic add-ons, but I've taken the trouble to find out what one might really do on a Z4MC before I permanently stick one on my car.
I suggested that this was effectively a Gurney flap when last there was debate about form vs function (IIRC this was stimulated by TomScott's OEM lip spoiler). My concern was that the OEM suspension lends a vagary to the steering at extremely high speed and that a Gurney flap might exacerbate this front end lift. Of course, with the soft front springs replaced, this shouldn't be an issue.
These are the figures for the Z4 3.0si CoupéBMWZ4MC said:
(A): 1.94 m²
(cd): 0.33
(cd × A): 0.64
at 200km/h
lift front 28kg
lift rear 43kg
So there's more lift at the rear than the front.
Here's a photo of the smoke trails over the Z4 3.0si Coupé. In the top photo, the air passing over the top of the car has to travel further/faster than the air passing under the car, which creates low pressure above the car and creates aerodynamic lift. In the bottom photo, I've manipulated the image showing the way that the smoke trails will appear if there's a lip spoiler/ gurney flap attached to the car: this is in accordance with typical smoke trails and my pressure washer experiments also illustrate this. Therefore, the upsweep of the air leaving the boot lid means that the air passing under the car, now has to travel further/faster to rejoin the air which travelled above the car, which lowers the pressure of the air passing under the car, so, overall, this should reduce aerodynamic lift along the length of the car, front as well as rear.
I suspect the perceived effect of the lift is greater at the front simply because the front wheels are largely responsible for providing feedback when making minor steering corrections. The OEM springs led to a wandering front end at speeds over 120-130mph, largely rectified by fitting Eibachs and absolutely resolved with my current setup. I've not driven a 3.0 Coupe so I don't know if they have the same handling characteristic at very high speed - do they have unusual spring rates as found with the OEM ///M suspension? How much rake is there with the OEM setup in either car vs Eibachs - perhaps this has some bearing? Perhaps the front suspension permits more travel than the rear in response to any lift created by the car, thus leading to a negative rake which exacerbates the front end lift. It's even possible that the vague front end at speed in OEM guise is not related to aerodynamic lift.
Dan Gurney himself found that a Gurney flap in isolation can increase rear down force to such an extent that the front of the car will lift leading to understeer and slower lap times. He responded to this by increasing down force at the front. With this combination, he was able to achieve higher straight line speeds as well as higher cornering speeds. Of course, he had the advantage of experimenting with race cars that had a flat floor pan and less turbulent under-car airflow as well as far greater straight-line and cornering speeds, so the results would likely have been more significant. If your splitter experiments come to fruition then you'll be able to increase down force at the front of the car too. Hopefully, with your existing strakes the effects of these will summate into a tangible performance advantage
Dan Gurney himself found that a Gurney flap in isolation can increase rear down force to such an extent that the front of the car will lift leading to understeer and slower lap times. He responded to this by increasing down force at the front. With this combination, he was able to achieve higher straight line speeds as well as higher cornering speeds. Of course, he had the advantage of experimenting with race cars that had a flat floor pan and less turbulent under-car airflow as well as far greater straight-line and cornering speeds, so the results would likely have been more significant. If your splitter experiments come to fruition then you'll be able to increase down force at the front of the car too. Hopefully, with your existing strakes the effects of these will summate into a tangible performance advantage
Hi John,
How are your experiments coming along? I'm also considering the OEM rear spoiler to increase rear downforce (hopefully not by such an amount that it leads to a wandering front).
I read you can't find an original OEM version anymore, but it seems like they do still have them e.g. on http://www.original-genuine-spare-parts.com/a/bmw/51710_/51710414770-heckspoiler_(bmw).htm. Any reason not to buy the original part?
Johannes
How are your experiments coming along? I'm also considering the OEM rear spoiler to increase rear downforce (hopefully not by such an amount that it leads to a wandering front).
I read you can't find an original OEM version anymore, but it seems like they do still have them e.g. on http://www.original-genuine-spare-parts.com/a/bmw/51710_/51710414770-heckspoiler_(bmw).htm. Any reason not to buy the original part?
Johannes
Johannes,jpeeters said:
Thanks for that. After your post, I sent an email to that company to ensure that they could actually send me the item, if I were to order and pay for the item on their website. In response they wrote; "Sorry, there is no delivery date for this item." I therefore assume that the part is unavailable to them also.
