308 rear spoiler (wing) | Page 11 | FerrariChat

308 rear spoiler (wing)

Discussion in '308/328' started by Crowndog, Feb 3, 2012.

This site may earn a commission from merchant affiliate links, including eBay, Amazon, Skimlinks, and others.

  1. johnk...

    johnk... F1 World Champ
    Owner

    Jun 11, 2004
    10,630
    CT
    Full Name:
    John Kreskovsky
  2. mike996

    mike996 F1 Veteran

    Jun 14, 2008
    6,685
    Full Name:
    Mike 996
    "The spoiler is most likely designed to remove this effect and help remove hot air."

    It's hard for me to accept that because if engine heat was the reason for the wing, ALL 3x8s would have been delivered with the wing rather than it being an option. As I said in an earlier post, if it actually served a purpose in some situation, Ferrari would have stated that the wing option should be selected IF the car was to be used in whatever that situation was.
     
  3. s219

    s219 Formula Junior

    Aug 26, 2021
    411
    My day job is aerodynamics (wind tunnel, CFD, and ground/flight testing) and my first reaction when seeing the wing years ago was that it was probably cosmetic. It’s possible it deflects some air down to fill in the base area behind the rear glass and reduce recirculation above the deck lid, but if that was the goal the shape could have been better.

    if there was clean CAD of the vehicle outer mold line, this would be easy to explore with CFD. But I’d be amazed if that existed.
     
  4. thorn

    thorn F1 Rookie
    Silver Subscribed

    Aug 7, 2012
    3,322
    Tallahassee, FL
    Can you put a model 308 car in a small wind tunnel to simulate?
     
  5. s219

    s219 Formula Junior

    Aug 26, 2021
    411
    From a practical standpoint, the car would probably have to be no smaller than 1/8 scale to properly resolve the geometry features, which drives you to a fairly large wind tunnel (university tunnel or larger). And then you'd need to be able to compensate for the small model size with higher speed or higher air density to get into the proper range of aerodynamic conditions. Need proper aerodynamic scaling for the results to be useful. That's always a challenge with wind tunnel testing.
     
    thorn likes this.
  6. hyenahf

    hyenahf F1 Rookie

    May 25, 2004
    2,603

    I don’t recall seeing anything remotely that small or an open or close tunnel. 1/4 is typically the smallest for modern day scale. Like you said, speeding up the air to compensate for the diminutive scale becomes a detriment for accuracy.

    Virtually EVERYTHING on wind tunnel today are modeled in at the late development stages, from functional intake ducting grills, radiators, underbody sheet metal, formations, drivetrain, exhaust, suspension, hubs and spinning wheels on a rolling road because they all have an holistic effective on the aerodynamics. The detailing is truly impressive now with 3D prt for RP.
     
  7. s219

    s219 Formula Junior

    Aug 26, 2021
    411
    The smallest vehicle model I have tunnel tested was 1/4 scale, but 1/8 scale is easily possible if the facility can meet the Reynolds Number. There is no reduction in accuracy in a good facility, We test even smaller model scales for aircraft which have very high requirements for accuracy in drag measurement (about 0.00005 increments in drag coefficient, or better) so vehicles are more forgiving. Really, the main risks with model scale are whether you can resolve the important geometry features, if there is enough room for instrumentation (pressure taps, internal sensors, etc) inside the model, and whether you can properly mount and support the model in the facility for accurate measurements (force & moment balance).

    Most auto development has moved over to CFD, since it can handle complex details much better at earlier stages in the R&D process, at a time when there is lower cost/risk and more chance to have an impact. There is still a fair bit of tunnel testing, but CFD has made huge inroads in recent years. If somebody had a good CAD model of a 308 or 328, I could spin up that simulation in a couple hours and have results within 1-2 days. For this particular spoiler question, a simplified model could be used (watertight vehicle outer mold line on a moving ground plane) and we'd only need to get more complicated if there were some noticeable concerns.
     
    thorn likes this.
  8. johnk...

    johnk... F1 World Champ
    Owner

    Jun 11, 2004
    10,630
    CT
    Full Name:
    John Kreskovsky
    Similar background, retired, buy I have a different take. If you look closely at the wing and it's mounting position, and visualize the flow over the roof, the wing would seem more like and extension of the roof creating more of a cavity behind the window rather than a simple back step. Seems more likely it would prevent air from deflecting downward. Plus, from the mounting height it would appear that the wing would be in the wake of roof boundary layer. Not exactly where you would want it of it had some aerodynamic effect. Not to mention that the rear deck is vented so it's not a simple back step or rear facing cavity.

    As long as we're guessing, I say it's a handle so the Jolly Green Giant can pick the car up and carry it away. :D

    In other words, it's cosmetic.
     
  9. s219

    s219 Formula Junior

    Aug 26, 2021
    411
    I would have thought they'd put a simpler shelf spoiler if they wanted to do that. The basket handle (and its lower surface shape) really suggest more of a flow turning effect to me, if anything, but personally I think it's cosmetic.

    There has been an interesting trend in pickup trucks in the last 3-4 years where they want to enhance flow separation off the rear off the roofline with a small shelf spoiler. The rationale is that it creates predictable/stable recirculation in the bed and raises pressure on the rear window and aft-facing front wall of the bed, giving an overall drag reduction. They don't care about the base area of the tailgate as much anymore, since it's a smaller surface. This is all a big departure in thinking from decades past where you saw people jumping on fads of tonneau covers or mesh tailgates in an effort to minimize separation and recirculation in the bed. Now they want it and use it to get a drag reduction. Which of course means that folks who put on tonneau covers or mesh tailgates are probably hurting things.
     
  10. hyenahf

    hyenahf F1 Rookie

    May 25, 2004
    2,603
    CFD is used in conjunction with scales, and full size models are almost never replaced by CFD alone. Both have its limitations and attributes. There are plenty of 308 “skins” out there available, some are reasonable accurate judging by what I see all the video games. Building a low-res digital model without internals is relatively easy for a skill desk jockey.

    I have no experience with aircraft but I would say out of the shear size, it’s impractical to build a tunnel that large hence the use of scales. Automobiles are certainly more forgiving for the fact they don’t fall out of the sky, but most passengers vehicles are rigorously tested not only for drag and roll it plays for vehicle dynamics but cooling, hvac, wipers, noise and road grime in DLO’s and lamps. It’s not unusual for design to be opposed to absolute aero refinement. It’s a compromise.

    Trucks can be easily improve to a point you will loose the appeal to the customers. Yes truck beds are a liability in terms of aero, a tailgate up has lower drag than down or removed based on how the flow comes around the cabin.

    Nearly everything matters, aero operates as an entire unit. An alterations at the rear extremities of the vehicle will affect the front as well, at times dramatically.
     
  11. johnk...

    johnk... F1 World Champ
    Owner

    Jun 11, 2004
    10,630
    CT
    Full Name:
    John Kreskovsky

    Yep, on the pickup. But don't even need the roof spoiler. https://xplrcreate.com/2019/08/08/aerodynamics-of-tailgate-closed-vs-open/
     
  12. thorn

    thorn F1 Rookie
    Silver Subscribed

    Aug 7, 2012
    3,322
    Tallahassee, FL
    I have a 3D model of the 308, and can export in various formats... I highly doubt the model is completely accurate to real-world in every dimensional measurement (for example, the side intake doesn't quite look correct), but in a relative sense it might be of use. If you're interested, let me know what preferred formats you can use and I'll email you a file download link with and without the wing.

    (Other f-chat friends: please don't request this file. I'm unsure of the copyright restrictions, and offer it only for this particular one-time use.)

    Image Unavailable, Please Login
     
    hyenahf likes this.
  13. johnk...

    johnk... F1 World Champ
    Owner

    Jun 11, 2004
    10,630
    CT
    Full Name:
    John Kreskovsky
    A simulation would have to include the ability to consider the flow through the rear deck vents too. Oh, wait, they are different on cat and no cat cars as well. :)
     
  14. hyenahf

    hyenahf F1 Rookie

    May 25, 2004
    2,603
    Perhaps request a Gtb? It doesn’t have a trip-strip on the windshield header to reduce buffeting in the cabin when the roof is off …
     
  15. hyenahf

    hyenahf F1 Rookie

    May 25, 2004
    2,603
  16. hyenahf

    hyenahf F1 Rookie

    May 25, 2004
    2,603
     
  17. thorn

    thorn F1 Rookie
    Silver Subscribed

    Aug 7, 2012
    3,322
    Tallahassee, FL
    I tried to locate a suitable GTB, but found only too low a resolution or lacking the wing. If I had the *full source* version, I might be able to convert it to a GTB, but as the mesh has already been created it would be rather time consuming to start recreating and stitching the topology.

    Agreed on the rear bumper; I'll try and push it in a bit. For rim/tire size, I think we'll have to live with it. FWIW, I'm not even sure the wing gap is completely correct.

    Overall, it's certainly not an optimal model, but as this test is really just sort of for fun/sake of curiosity, hoping it will suffice.
     
  18. s219

    s219 Formula Junior

    Aug 26, 2021
    411
    Heck yeah, that looks plenty good enough to use. Based on the surface mesh I see there, the best format for me would be IGES. We may have to tweak a couple IGES export options to get the right format and entities, but let's start with your default IGES export and see how it looks. Send me download info through a private message here on F-chat.
     
  19. s219

    s219 Formula Junior

    Aug 26, 2021
    411
    We had two full scale wind tunnels capable of testing aircraft in the USA, but now we're down to one. I tested in the 30x60' tunnel that was demolished a few years back. A full scale fighter aircraft, or similar size aircraft, could be mounted in that tunnel and tested. We also tested cars and trucks in that facility in later years, and a lot of NASCAR race cars. Most automotive full scale tunnels are quite a bit smaller, roughly half the size, generally with test section widths on the order of 20-25'.

    The main problem with full scale testing for aircraft is the speed. Once you get out of the subsonic range, it becomes impractical to power large facilities. Our largest transonic tunnels have about 16' diameter test sections. Going higher into supersonic, size drops again and those are in the 4-8' range, with many quite a bit smaller than that but still very capable. So sub-scale models are a necessity, which makes everything else a challenge in terms of model fabrication, packaging, accuracy, etc. But if you look at sub scale models a company like Boeing uses, they have really perfected things. They can attain full scale flight Reynolds number with a 2-4% scale model in a cryogenic tunnel and get extremely accurate data.
     
  20. johnk...

    johnk... F1 World Champ
    Owner

    Jun 11, 2004
    10,630
    CT
    Full Name:
    John Kreskovsky
    If you are really going to fool with this may I suggest you save yourself some effort and just model a 2-D slice down the center of the car. And as I said, if you account for air exiting the rear deck vents the results will be meaningless. If you do 2-D you do a parametric study to see the effect of different vent flow by injecting air along part of the rear deck model at different rates.
     
  21. Brian A

    Brian A F1 Rookie

    Dec 21, 2012
    3,079
    SanFrancisco BayArea
    Full Name:
    1983 US 308 GTS QV
    Modelers/Aerodynamicists: thank you for letting us in the peanut gallery follow along. This has become a fascinating thread. Best wishes with the simulations and testing. Very cool stuff.
     
    MFlanagan likes this.
  22. johnk...

    johnk... F1 World Champ
    Owner

    Jun 11, 2004
    10,630
    CT
    Full Name:
    John Kreskovsky
     
  23. nerofer

    nerofer F1 World Champ

    Mar 26, 2011
    11,968
    FRANCE
    Note that it has the rear deck vents of an "euro" (= Non-Catalysed) 308, not those of the catalysed 308s and 328s.
    (328s have the same deck vents on catalysed & non catalysed cars)

    Rgds
     
  24. nerofer

    nerofer F1 World Champ

    Mar 26, 2011
    11,968
    FRANCE
    Indeed; and the study of the flow exiting the rear deck vents should be of interest (mass & speed).
    But you have quite a number of different options here as for the vents, as for the engine and ancilliaries (non-cat or cat, single and double cat...)

    Rgds
     
  25. johnk...

    johnk... F1 World Champ
    Owner

    Jun 11, 2004
    10,630
    CT
    Full Name:
    John Kreskovsky
    Yes, and all those variables tend to support that it was just cosmetic. After all, the Mitchelotto never had one, AFAIK. A couple from 1983. But I'm not expert on the Mitch....

    Image Unavailable, Please Login Image Unavailable, Please Login
     

Share This Page