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  1. #151
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    Quote Originally Posted by NickRally View Post
    Couple of other thoughts after my first post on aero:

    1. Double diffuser on the Ford – it was mentioned on this forum and also such thought crossed my mind when I first saw the Fiesta small diffuser at the launch. I thought there was no way that was all the diffuser they have designed in and it also appeared like the original road car “diffuser” on top is used as an additional extraction device, though it wasn’t clear where on the underfloor this particular air would have been taken from, even though there are plenty of openings on the underside as it would appear. Nevertheless looking at images a bit later on, I couldn’t see an air passage between the dedicated WRC diffuser and the road car one so I discarded that thought, but once again none of the images I have seen so far is clear enough to say for certain what’s what and I haven’t seen one in person. Maybe people that have seen the real car with their own eyes can comment?
    Regarding double diffuser. I don't really think it is double. I was reading this book about aeordynamics (by Simon McBeath) and CFD analysis shows that efficient angle of diffuser is somewhere between 8-12 degrees. Now 8 degrees is quite shallow, any road car has this angle. And, as I understand primary function of diffuser is to balance downforce between front and rear (same as rake). So in Fiesta case it could be that front-end has enough downforce thus large difusser angle is not needed.

  2. #152
    Member NickRally's Avatar
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    Hi Marcco, the 8-10deg diffuser angle quoted was applicable to the flat bottom formula cars of the early 90's and it changed (the optimal angle got bigger) with the change in the rules specifying stepped floors for the F1 cars (that's pretty much what I do for living). As a general rule of thumb, the higher the distance between the floor of the car and the road, the higher the optimal diffuser angle. Also if we accept the theory that the diffuser will add equal amounts of downforce to both axles of the car (which probably wouldn't be the case with a bit more going to the rear being more probable), then higher diffuser angle than the one on the Fiesta would look more appropriate.
    Regarding the double diffuser, the only way it won't be doable is if the rules do not allow it (for one reason or another), otherwise there is no stopping the creativity of the designers.
    Regards,
    Nick

  3. Likes: drive (20th February 2017)
  4. #153
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    Quote Originally Posted by NickRally View Post
    ... the rules specifying stepped floors for the F1 cars (that's pretty much what I do for living). ...
    Nick
    I like this...

    @ Yaris: You didn't mentioned Yaris "nose up" floor design.
    Look:

    https://www.google.si/imgres?imgurl=...:&vet=1&w=1280
    https://www.google.si/imgres?imgurl=...:&vet=1&w=1280
    https://www.google.si/imgres?imgurl=...M:&vet=1&w=640
    http://cdn-9.motorsport.com/images/m...ota-racing.jpg
    https://www.google.si/imgres?imgurl=...M:&vet=1&w=790

    It looks like it is purposefully made to receive air under the floor... ground effect in mind.

    I see the "side skirts" diffusers looks like a clever trick, but I don't understand why the front part of the skirts is cut away, is there aerodynamic purpose or a mechanic (rocks flying) one.

    @ general underfloor aero: I think, we can not be sure that floor generated downforce is a vital part of car performance. Hyundai rear suspension cover were floating massively. As far as I can understand this should kill all floor aero performance.
    https://www.youtube.com/watch?v=gwyGvSPtgJ8 (0:41 to 0:47)

  5. #154
    Senior Member A FONDO's Avatar
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    For the guy who wanted the bottom of the car

    http://www.ewrc.cz/ewrc/image_browse.php?id=339519

    also can be seen the destroyed aero before the rear tyre, wonder how it happened

  6. #155
    Senior Member SubaruNorway's Avatar
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    Anyone know what the black boxes at the top of the fenders where the bumper is attached is?
    http://www.ewrc-results.com/image.ph...&entry=0&car=0
    "Die with memories, not with dreams" Scott McIsaac
    http://www.motorsportfilmer.net

  7. #156
    Senior Member jparker's Avatar
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    Good video for tech analysis:
    https://youtu.be/RfTeBPXkTps

  8. #157
    Member NickRally's Avatar
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    Before I have forgotten again:

    mozesii - thanks for the appreciation.

    OldF - great images, thanks, as you would have already seen, I have put them to good use.

    SlowSon - thanks, good photo.

    jparker - thanks, I will have a look.

    J_n_z - thanks.
    On a crcuit racer the answer to the question you asked without a doubt would be yes to a raised centre section of a front splitter. On a rally car with its higher ground clearance the effect will be less pronounced, but I suppose (short of this being done to simply increase the ground clearance in the middle of the vehicle to go over road obstacles) it can still help.
    The side tunnels on the Yaris - if I was doing it, then my reasoning for moving the leading edge rearward would be to ensure that the tunnels get a slightly cleaner air away from the front wheels and in general increase the mass flow of air to them rather than being shadowed by the front wheels too much.
    The importance of aero on a rally car - you are most likely correct about the Hyundai's flapping suspension guards, but that is why I like the rally cars, aero is not king (in massive difference to F1), the mechanical side is of utmost importance. At the same time, with the new rules, aero becomes more and more important without overshadowing the other engineering sides and whoever gets to do the best job on all design fronts will end up with the fastest car overall.

    Regards,
    Nick
    Last edited by NickRally; 17th February 2017 at 22:41.

  9. Likes: drive (20th February 2017)
  10. #158
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    Quote Originally Posted by NickRally View Post
    Here is my first attempt at creating an aero analysis of the 2017 WRC cars. There is always a risk of making oneself look like a fool when doing this, but I’ll give it a go . I will start with the Fiesta and will expand with all the other cars as and when I have the time, but I can already see some very interesting features on the Yaris. I am also no expert on the regulations and although I have downloaded them, the nature in which they are presented is very different to the world of ground up designed racing cars where I come from, which makes the WRC tech regs a real challenge for me to follow.

    1. Ford Fiesta

    Attachment 1235

    The diffuser on the Fiesta appears to be the shallowest (1) of them all, this is not necessarily a disadvantage in terms of aero, but it is quite modest in comparison to the rest of the field. The transition area into the diffuser (2) is quite narrow as dictated by the suspension arm protectors (3), which in turn, at their trailing edge, do not form a continuous transition into the diffuser, though they probably provide a nice skirted area around the central floor into the diffuser transition, which would help with accelerating the air flow and reducing the air pressure further there. Nevertheless, integrating the trailing edges nicely into the diffuser surface (notwithstanding the technical challenges involved in this) may deliver an added benefit (something that appears to be done on the Yaris on some of the images). The diffuser streaks appear to extend below the surface of the flat floor in front of the diffuser, but I suspect this is optical illusion and like in many other forms of mototsport they are not allowed to do so, but once again a proper read of the tech regs should provide an answer to this question.
    Moving towards the front of the car, there appears to be a non-flat area, which I don’t know if it is because of the tech regs/homologation or it is done for creating an aero benefit. The image is not clear enough for me to see what happens there, but I can see similar features on the Yaris, though on some of the images of the Toyota from testing, I can also clearly see additional diffusers in front of the rear wheels, though more on this later.

    Regards,
    Nick
    Thanks for doing a serious aero analysis a la Mulsanne's Corner.

    It's interesting to see all the different solutions being tried by the teams because of the current freedom in the rules!

  11. #159
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    Quote Originally Posted by NickRally View Post
    Hi Marcco, the 8-10deg diffuser angle quoted was applicable to the flat bottom formula cars of the early 90's and it changed (the optimal angle got bigger) with the change in the rules specifying stepped floors for the F1 cars (that's pretty much what I do for living). As a general rule of thumb, the higher the distance between the floor of the car and the road, the higher the optimal diffuser angle. Also if we accept the theory that the diffuser will add equal amounts of downforce to both axles of the car (which probably wouldn't be the case with a bit more going to the rear being more probable), then higher diffuser angle than the one on the Fiesta would look more appropriate.
    Regarding the double diffuser, the only way it won't be doable is if the rules do not allow it (for one reason or another), otherwise there is no stopping the creativity of the designers.
    Regards,
    Nick
    I had mentioned the double diffuser in another thread. It's hard to validate, but if they are using it as such, the air has to come from somewhere? The M-Sport diffuser is very shallow compared to the others. Could it be as or more efficient than the others? Time will tell, we will see who copies who! As a matter of fact, are aero changes allowed during the season or is everything pretty much homologated for the whole season?

  12. #160
    Member NickRally's Avatar
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    Quote Originally Posted by jparker View Post
    Good video for tech analysis:
    https://youtu.be/RfTeBPXkTps
    Thanks again jparker, it is amusing to see how it never occurs to them to point the camera to the underside, which is where a lot of the interesting aero stuff takes place. Of course this is understandable considering that floors so far have not been massive differentiator in performance, but with the new rules, who knows. Funnily though, the Hyundai (the car in the video) has one of the roughest undersides if some of the distant images I have seen are anything to go by.
    Last edited by NickRally; 20th February 2017 at 12:15.

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