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Porsche 911 Ducktail - Study/Alternate
Waiting for the snow to melt so I can take some field measurements of a building, so I cut up a business card and compared a Ducktail to an alternate location a bit higher.
Would be made of clear Polycarbonate or Acrylic. Not sure yet what would happen with the flow/vortex and pressure level above the engine cooling inlet. http://forums.pelicanparts.com/uploa...1520545657.jpg http://forums.pelicanparts.com/uploa...1520545657.jpg http://forums.pelicanparts.com/uploa...1520545657.jpg http://forums.pelicanparts.com/uploa...1520545657.jpg http://forums.pelicanparts.com/uploa...1520545657.jpg http://forums.pelicanparts.com/uploa...1520545657.jpg This is a side-by-side comparison, would not double Duck, although I guess one could. As I understand it, the Ducktail, Teatray, and Whaletail all try to correct the approximately 30 degree roof angle to mimic an approximate 20 degree slope (almost like a louver - steps). Image of wind tunnel smoke in link below. https://www.gettyimages.com/detail/n...re-id653712864 |
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Compare to sides that wrap forward more horizontally like the 4th Gen Pontiac Firebird. I think it would add a downward component to the vortexes generated and also capture more of the flow. Or not. The ducktail works by being opposd to the flow. :confused: I'm probably thinking about the tea tray. You could start with a Gurney flap at the top of the glass. That would simulate multiple base plates. I can't find a pic right now. |
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The Porsche 924 was introduced in 1976 for example, this rear spoiler might even fit - who knows? https://www.porsche.com/usa/accessor...924/924-turbo/ http://forums.pelicanparts.com/uploa...1520602046.jpg As far as doing a double duck and staging the airflow in a series of steps or ladders Merkur XR4i Bi-Wing style, that's like trying to fix something that isn't broken in my opinion. I'm exploring this alternate in part because I might be removing my rear Targa window to repair some rust likely hiding under the old rubber seals. Then replace the glass with lightweight scratch protectant coated Polycarbonate. Old thread - somebody did Targa bubble in Polycarb (page 2) http://forums.pelicanparts.com/porsc...rga-glass.html |
I retook the model pictures after removing the Ducktail and then played around with the "paint" program a bit to produce a marked-up composite.
http://forums.pelicanparts.com/uploa...1520694442.jpg And I remembered where I've seen this before, a Saab Turbo. Sourced the original photos from here: https://petrolicious.com/articles/th...f-swedens-eden http://forums.pelicanparts.com/uploa...1520695466.jpg Tried my hand at creating a composite photo with mark-up. https://petrolicious.com/articles/th...f-swedens-eden https://d39a3h63xew422.cloudfront.ne...-2000x1333.jpg Oh, and I have a name for it, UPPER-DUCK, not sure what it's really called. |
whaletail
With flow separation 'over' the aft-body,the 911 generates lift.
The whale-tail provides a surface for flow re-attachment to spoil the lift,while incorporating an embedded heat exchanger. If you look at the 1996 911 GT1 'silhouette' race car,you can see how Porsche corrected the too-steep backlight area to kill the rear lift,then double-downed with a spoiler for extra 210-mph,Mulsanne Straight stability. Cd 0.28 vs 0.40 if I remember correctly. |
upper duck
I would caution against the upper spoiler.I'd be concerned that you'd kill any downwash that is currently available to the engine bay inlet.
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https://pictures.dealer.com/l/longbe...y=resize&w=650 |
I found an image of a Porsche 924 without the rear spoiler while looking for Audi TT with and with-out rear spoiler.
https://rennlist.com/forums/924-931-...ictures-4.html http://www.seriouswheels.com/pics-pq...l-1024x768.jpg As Maxwell Smart would say.............."Missed it by that much". I can see why the later 924's and 944 had the rear spoiler. A much greater discrepancy on the older 911 design, but with a Ducktail it's a different story. I know it's not the favored "attached flow", but it's a step in the right direction. Porsche Says These Are the Best Wings Porsche Has Ever Made https://www.roadandtrack.com/car-cul...nd-rear-wings/ http://forums.pelicanparts.com/uploa...1520719340.jpg Quote:
aerodynamics? - VW GTI Forum / VW Rabbit Forum / VW R32 Forum / VW Golf Forum - Golfmkv.com http://www.golf5gti.com/upload/avata...04924_3041.jpg The thing I worry about is water getting trapped in the joint of the proposed "Upper Duck". If vented or weeped at the bottom some flow similar to the Audi above could feed the cooling air intake vent. That's a pretty big "could be" at the moment. Didn't someone in the forum build a scale model wind tunnel tester a few years ago? Quote:
My point is, as much as I've looked into the fan draw issue, I've never found a VW Beetle or Porsche 911 wind tunnel smoke study that included air being drawn into the engine bay. A great appointment for me, and even greater now that I'm pondering this proposal. |
IIRC the Audi Quattro Spider Concept introduce the DLO as a conceptual arch. The New Beetle and the TT coupe over-formalized it. Then they bowed to 'time's aero'.
http://pictures.topspeed.com/IMG/jpg...spyder-2-1.jpg http://www.topspeed.com/cars/audi/19...ure179268.html Quote:
This isn't a photo, but a conceptualization based on ??? It suggests the intake air is sucked off the top of the detached turbulence. http://ecomodder.com/forum/member-fr...858-images.jpg Possibly a solution like the Mercedes retractable spoiler/Gurney flap? http://ecomodder.com/forum/member-fr...08-5-46-57.png |
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Meaning the side arches flow the air past the best they can, and the air over the top steps from roof to deck in an unattached but non-uplifting way (a giant louver). The deck or bed has to be just long enough, and the Aero-Template we use often in the forum has proven useful in showing us just where that is. EDIT: I found something interesting and related to what happens after a Gurney flap or wickerbill rear spoiler. I tend not to trust drawings and CFD as much as wind tunnel images but they have their uses. http://www.firebirdnation.com/forums...of-a-trans-am/ http://www.2gta.com/taairflo.jpg Quote:
The Trans-Am spoiler is a smaller version of the original Porsche Ducktail, the (+) plus signs indicate positive pressure, meaning an opening on top of the deck/trunk there would allow air in (downward). Hey, that's how these things create down-force, imagine that. |
I hope you didn't miss my edit four minutes later. The forum is so busy it's hard to keep up. I'm trying to build a metal kitchen cabinet to replace my plywood one. I'm hitting it hard for one hour a day.
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What you described is similar to a "Super Ducktail" (my term not an official name) I have on my old computer of a racing Porsche 911. It raised the Ducktail, widened it past the engine lid, and fluted it along the sides. Way to aggressive for what I had in mind, but marvelous in it's own right. I'll try and find an image of it, worthy of inclusion. Oh, and I found a wind tunnel for a model by happenstance. https://www.rctech.net/forum/electri...ricks-103.html https://www.rctech.net/forum/attachm...te-resized.jpg https://www.rctech.net/forum/attachm...ind-tunnel.jpg https://www.rctech.net/forum/attachm...-c-resized.jpg I found the "Super Ducktail", but the car I was thinking of was white. It's similar to the below in any case. http://germancarsforsaleblog.com/category/race-cars/ http://forums.pelicanparts.com/uploa...1520725034.jpg I'm not looking for all that down-force, nor all that bodywork. http://germancarsforsaleblog.com/mot...acing-replica/ http://germancarsforsaleblog.com/wp-.../09/M911R2.jpg Looks like they taped them on and liked the results before they glassed them in. http://www.racingsportscars.com/phot...-05-13-009.jpg |
That's what I was thinking, wider to catch more air and with the horizontal fillet.
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Different car from an old 911, same issue of disrepair for me, engine not running full tilt thereby drawing in air during wind tunnel testing - so what's the point if not simulating real world conditions?
REPOST: http://ecomodder.com/forum/showthrea...d-26678-3.html Quote:
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https://www.total911.com/porsche-993...sport-raw-993/ http://t911.wpengine.com/wp-content/...12/AC_3531.jpg My thoughts on that line of exploration was to blend or flute the inlet into a sugar-scoop tapered into the body just under the rear glass belt-line. Just so that it wasn't hanging out there like elbow macaroni. :D Sooooooooooo.........blending a "chime" (jet aircraft term) onto some kind of aft aero-device has been of interest. Even thoughts of reusing the roof wing on my pickup truck or the similar contraption as seen above my hovercraft duct have been sketched up. In most of my schemes there is an air-gap between the car body and aero-device so that the engine lid can be raise and there is no disruptive joint in the assembly. In essence, just want to keep the wing/spoiler simple and in one piece. Right now I'm thinking a foil or spoiler with an open bottom drainage slot in the location shown on the last model photo composite image is one last possible direction before this line of thought dead-ends. Gotta take a thought until it dead ends. I can't help myself. EDIT: What I was trying to describe as my last design attempt in this direction is perhaps an adaptation of the 993 basket hoop third brake light. https://www.ecklers.com/porsche/993-...iABEgI3R_D_BwE https://www.ecklers.com/assets/eam/i...ku/P906484.jpg Only bigger, better and of different function. The hoop above was to work with work with the adjustable grille. https://www.luxsport.com/1998-porsch...rera-c-317.htm https://www.luxsport.com/galleria_im.../317_p23_l.jpg http://pilotesanciens.blogspot.com/2...er-dealer.html http://1.bp.blogspot.com/-wSF2pVB0eZ.../Resized-3.jpg Quote:
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Having more fun with my model and aerodynamic concepts.
When I first put it on it was level flat, and realized it was under the aero-template too much, plus could not open the engine lid. I curved it up to resolve both issues - could be a bit smaller/thinner in retrospect. http://forums.pelicanparts.com/uploa...1520790897.jpg http://forums.pelicanparts.com/uploa...1520790897.jpg http://forums.pelicanparts.com/uploa...1520790897.jpg Also posted below if you need to see them a little larger. random pics that YOU have taken....... - Page 606 - Pelican Parts Technical BBS Now look again at the below image, how the flow sneaks under the air-slot under the rear spoiler much as it does on the roof wing of my pickup truck. aerodynamics? - VW GTI Forum / VW Rabbit Forum / VW R32 Forum / VW Golf Forum - Golfmkv.com http://www.golf5gti.com/upload/avata...04924_3041.jpg I know that many of the images regarding my truck were lost to Photobucket's 3rd party BS including the CFD images, but the long and short of it is, the air getting under is accelerated and this draws the air above it downward. In this case the backside of the wing/spoiler engages the airflow, causing a build-up of pressure, this pressure can escape downward and into the cooling vent, or attempt to fight the flow above and probably lose and end up as a vortex aft, which in turn would once again cause down-force and downward airflow on the engine lid. All just my imagination at work currently, but this is much closer to being worthy of testing in some manner - in my opinion. If I had to say this design reminds me of most, I'd say the New Beetle hoop wing. FS/WTT: retro new beetle - NewBeetle.org Forums http://newbeetle.org/forums/attachme...e-p3130001.jpg http://newbeetle.org/forums/attachme...e-p3110008.jpg I'm wondering if that would fit my car now. :D |
I had the camera too close to the car/object on the top overhead views and this was distorting things.
Here is a better aerial true view. http://forums.pelicanparts.com/uploa...1520795182.jpg |
At the Darko wind tunnel, a wire mesh screen moderates airflow 40ft away around a corner. Perhaps there is application here?
If you're going to publish correct geometry you should put a Creative Commons bug in the corner. :) https://upload.wikimedia.org/wikiped...served.svg.png |
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I looked at a couple of PDF's and a website on the subject, not sure that you mean exactly. I have cardboard, mirrors, drinking straws and cigars.......................maybe I should blow some smoke? :cool: |
Thanks for asking :thumbup: I hadn't posted these pictures from Darko:
http://ecomodder.com/forum/member-fr...6-100-1191.jpg http://ecomodder.com/forum/member-fr...7-100-1187.jpg The story is that after they finished the coke-bottled test section it had attached turbulence which reduced the effective cross-section. The solution was the (double-pass) 2" welded wire mesh wall. It had a wire mesh man-door in it. Somehow it moderated the flow through the test section. Crazy world or what? |
exactly
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This boundary layer,unless it is blown,or suctioned,can effectively choke down the cross-sectional area of the test section,increasing the local velocity. Also,a boundary layer is forming and growing on the test vehicle itself,aggravating the situation. And as a rule,anything tested,should not have a frontal area which exceeds 5% of the test sections cross-sectional area. This is one reason why Cds can vary,from tunnel to tunnel. |
Below similar to the TV show Wheeler Dealer episode with the 1985 Ford Escort RS - Cosworth.
Was this: VWVortex.com - So who didn't catch the Escort RS Cosworth episode? https://res.cloudinary.com/carsguide...pa-%286%29.jpg Now this: Wheeler Dealers: S14 E1 http://www.motoringbox.com/wp-conten...t-cosworth.jpg That middle wing shown above added 25 lbs of down-force in the wind tunnel, no idea how much drag it added though. I suspect this works similar to my proposed Porsche 911 Sponge Bob tail. http://forums.pelicanparts.com/uploa...1520790897.jpg http://forums.pelicanparts.com/uploa...1520790897.jpg http://forums.pelicanparts.com/uploa...1520790897.jpg http://forums.pelicanparts.com/uploa...1520795182.jpg Now I'm wondering what it would look like with three tails terracing down. One off the roof line/Targa bar, one as shown in the middle, and a third at the bottom of the deck lip just above the rear tail lights. Total overkill, but I have lots of business cards that I can cut up and play with. I would terrace or step them, not stack them as in the Escort RS. |
VW/Porsche fan draw
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As to spoilers: *The 924 Turbo reached out to Buchheim's 23-degree contour *The VW Student is AST *The VW H2 concept is AST *The VW Bugatti EB110 is AST *Porsche 911 GT1 is AST *VW L1 is Buchheim *'09 Audi A2 is Buchheim *VW Lambo Murcielago is AST *Porsche 918 is AST *Porsche Panamera S is AST/Buchheim *VW Lambo Sesto Elemento is AST *Audi R8 GT is AST/Buchheim *VW Lambo Aventador is AST *VW Bugatti Veyron is AST/Buchheim *Audi A9 concept is Buchheim *VW XL1 is AST *Porsche 911 GTR RS 4.0 is AST *Audi A8L is AST *Audi A7 spoiler is AST *Audi RS5 is AST *Audi S3 2.0 Quattro S Tronic spoiler is Buchheim *Audi SQ5 is Buchheim *Porsche Macan Turbo is AST/Buchheim *Audi R8 V10 Plus is AST *Don't have Audi TT with me VW Group appears to favor the 22-23-degree maximum down-slope.Even if there's longitudinal vortices,at least they've got enough center-line flow reattachment to control rear lift,as many of these cars are really fast! |
That Escort RS needs a Red Baron paint job.
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Forgive my thick skull, but I've only figured out that;
AST = Aerodynamic Streaming Template As found here: http://ecomodder.com/forum/showthrea...c-9287-54.html And I've figured out that R. Buchheim is an author of aerodynamic works, but I don't know what his specific contribution is and the importance of his name as a reference is. Given time I could probably figure it out, but spelling it out will help me. |
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A couple of studies, still getting the hang of this new to me photo editing program.
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Buchheim et al.
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I've stuck with 22-degrees as a conservative figure.But feel free to 'go wild' at 22.5-degrees!:) |
911 tails and engine cooling
I'd be very leery of any flow obstruction leading to the cooling air inlet on the engine cover.
The whale tail type spoiler would capture the downwash,ensuring high pressure into the gill slits,and it's added length would help capture a vortex above the spoiler,like a half-tonneau does on a pickup. |
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Thanks Aerohead, your early input on some ideas I've been tossing around is appreciated.
The next round of changes will be a scheme that attaches the deflecting plane (wing/spoiler) to the engine lid instead of the rear window lip. This is another level of simplification and functionality. It will be neither a Ducktail nor a Whaletail/Teatray but something that is a little of both and a further development of the Sponge Bob model. In my opinion only the very first concept shown (Saab-style) had the possibility of interrupting airflow in a bad way, and my concerns about it have paved the way to a better direction so it was a necessary step. EDIT: Posted new photos - I took the wing, flipped it upside down, bent the edges and stuffed it into the joints of the engine lid. Kept the angle not too aggressive but there is room for experimentation there. Now it's looking similar to any other aftermarket wing on any other car? I don't care if it looks similar or oddly different, as long as it works. EDIT-2: To be clear, I don't expect free flowing airflow to engage the wing. I expect the trailing edge of the wing to extend the profile of the car to a near Aero-Template profile thereby lowering the Cd. Some of this air flow is getting drawn down into the engine grille via the engine cooling fan prior to the wing's affects so this should not alter existing engine cooling for better or worse. I also expect some slight squeezing of air (acceleration) of air traveling between car body and underside of wing. At a micro level this means there is anti-lift or down-force on the wing. At the macro level of pressure wave/bubble; I'm not so sure what sort of swirling turbulence from possible pressure differentials of air traveling under and along the sides of the car as it meets the air coming over the top of the car causes. I'm looking for slight improvements and not an entire overhaul. |
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Also,I don't think a wing can be effective unless it's raised up into the inviscid flow,above the separated wake,as Mercedes did with their 190 Evo,Mitsubishi Lancer Evo,Subaru WRX,and Chrysler Aerospace' Dodge Charger Daytona. A wind tunnel would be handy. |
Porsche 'ducktail'
The December, 2022 MOTORTREND, page 65, contains a vignette on the 1972 911 Carrera RS 2.7, by Aaron Gold.
-------------------------------------------------------------------------------------- Aerodynamicist Hermann Burst was charged with addressing the rear lift/high-speed instability of the 911, associated with the drawbacks of the sloping rear. -------------------------------------------------------------------------------------- Burst was a graduate of the FKFS at the University of Stuttgart, where the 'Kamm-back' was developed from Fachsenfeld's patents, with Dr. Wunibald Kamm riding shotgun on the research. And Burst already had success in Porsche's Le Mans-winning long-tail kammtail racing cars. The 1968 907 long-tail was Cd 0.27. The 1969 908 long tail was below the 907's. -------------------------------------------------------------------------------------- Burst's 'solution' for the 911 was an airdam, along with a kammtail roof. Porsche management was okay with the front, but shot down the K-form roofline. The silhouette of the 911 was not negotiable. ------------------------------------------------------------------------------------ Over three days, three rear spoiler designs were hashed out. The 'ducktail' is the one-out-of-three designs approved for homologation and production. -------------------------------------------------------------------------------------- The spoiler was incrementally increased in height until lift and drag reached a 'reversal point,' after which performance degraded again. ( Sweet-spot ). Drag dropped from Cd 0.4239, to Cd 0.40. Top speed improved from 149.2-mph, to 152-mph. Separation-induced lift was killed off. Engine cooling was improved. Taillight back-soiling was mitigated. As Wolf H. Hucho had commented in 1986, the spoiler performed almost as well as simply lofting the roofline up to where the 'tearing edge' of the ducktail ended. ------------------------------------------------------------------------------------- In 1973, the kammtailed ROVOMOBIL debuted, with Cd 0.23. Presently, Porsche is using the 1930s K-form roofline. The lower performance variant of the Taycan is Cd 0.22, close to ROVOMOBIL. |
jalopnik.com/: Meet The East German Beetle-Based Supercar With Better Aero Than Tesla -- By Jason Torchinsky
I suspect that in 1974 the commies ripped off Luigi Colani's 1960 Colani GT Quote:
https://www.carstyling.ru/en/car/1965_colani_rs/ |
PORSCHE using aerodynamic streamlining template 'again'
Curiosity led me to print off the blueprint for the 911 Carrera 2.7.
I scaled it to my stack of 'rooflines' and took a look on the X-ray reader. The engine air inlet below the backlight is slanted on a 23.5-degree angle. The 'ducktail' tearing edge lofts the 'body' at that location up to a 17-degree slope. Extrapolating the contour happens to generate a perfect match the 2013 AST. Aerodynamicist Hermann Burst's original 'solution' for instability was to add a kammtail roofline, intersecting the 17-degree tearing edge position. Had this been done, the lift issue would be gone, the car would have lower drag, engine cooling would have been improved, and the higher base pressure mitigate the taillight lense back-soiling issue. The car would no longer 'look' like a 911, so it was shot down by the Paris Dressmakers. Fortunately, in the intervening years since 1972, Porsche has incrementally 'raised' the back of the 911 in each new iteration. Today, Porsche finally has the contour Tony Lapine co-designed with Larry Shinoda, for the Chevrolet Corvair Monza GT of 1962. GM's head of design,'Wild Bill' Mitchell hated the kammback too! |
VW also relented on the New Beetle. The new New Beetle had a roofline relaxed from the original archetype
https://cartype.com/pics/1594/full/w..._2012_plug.jpg cartype.com/pics/1594/full/wv_beetle_2012_plug.jpg |
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https://www.paledog.de/Automobile/19..._rear.jpg.html http://forums.pelicanparts.com/uploa...1667815104.jpg Quote:
http://forums.pelicanparts.com/uploa...1667816843.jpg https://www.paledog.de/Automobile/1990s/ http://forums.pelicanparts.com/uploa...1667815221.jpg |
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