Ford Sierra XR4i Bi-Wing Spoiler?
 

Hey all, do any of you have info/explanations of the aerodynamics behind the Bi-wing spoiler on the Ford Sierra/Probe III concept. I’ve read that it reduces drag, but I’ve also heard that it’s a measure for creating downforce. I’ve not found a concrete answer yet.

Just off-hand, looking at the angle of the back glass, the spoiler more than likely does reduce drag primarily by reducing lift. I've never seen an analysis of it on that car specifically however.

Here is a site-wide Google search for bi-wing. https://ecomodder.com/forum/google_s...5679j6676099j7

It's not helpful to me because I have Prefs set to max number of posts per page instead of 20, and Google's search is page oriented.

Maybe you'll find something there. F1 front wings have gone away beyond bi-planar.

It reduces pressure under the wing, so causing better flow attachment and allowing the rear spoiler to work better.

Not the vehicle you requested, but adjacent?

Porsche 911 Ducktail - Study/Alternate
https://ecomodder.com/forum/showthre...e-36229-3.html

https://www.topgearbox.com/cars/ente...t-rs-cosworth/
http://forums.pelicanparts.com/uploa...1616437886.jpg

I don't remember if the "25 lbs of down-force" comment was from a video or post in that thread.

I do recall finding the Escort RS Cosworth when doing a search on the XR4i, so there may be common material in videos and articles floating around the Internet.

Bet it's turbulent as sin back there.

Cosworth
 

I think I posted on this car a decade or so ago. I suspect it's in my lectures.
From memory, it was a homologation special for rally racing. The rear addition provided downforce at the expense of lower top speed. 20- to-30 counts extra drag. Two-to-three miles per hour slower.
I'll try and find it.

Interesting that this come up, I’ve considered a version of this for drag reduction on my Ion. Everything angled to reduce drag though

explanations
 

Lutz J. Janssen & Friedl W. W'u'lfing were the co-inventers.
If you can find a copy of United States Patent No 4,533,168, it has their full explanation.
I got mine off micro-film at the Dallas Public Library. It could be available online.

Thanks all. I’m still in search of a boat tail alternative, then. Still very interesting, and visually surreal.

Have you reviewed ecomodder.com: Morelli's 'Fluid Tail'?

http://i1271.photobucket.com/albums/...itled12_20.jpg

http://i1271.photobucket.com/albums/...titled7_22.jpg

I have not. Thanks for the heads up.

Wonder if this could be applied to a notchback car?

Volkswagen Golf GTI W-12 650

https://ecomodder.com/forum/member-f...w12-650-16.jpg

Technically, a hatchback modded into a bubble-top coupe.

Where have I seen this before? :)

Do you have any possible papers/info describing how the aerodynamics of the car function?

Wörthersee?

There are all the articles in the link I provided. I'm not sure which one is best.

Long story short, it was a one-off concept built for an annual meet at Wörthersee, Top Gear's verdict was 'not sorted'. It has a very short wheelbase for 200mph. :)

The idea was to preserve the hatchback roofline and get massive downforce without a tacked-on wing. One way to look at it is as three internal ducts feeding the wake. Another is as two flying buttresses tied to a towel-rack wing.

There's a custom bubbletop over the W-12.

No one seems to be mentioning that it was a lot more than you can see here - centrifugal fan fitted to rear wheels, inbuilt ducts within wheel arch, etc.

That’s kinda what I had in mind for my Saturn. The roof shape is reminiscent of a bubble top, and I planted big flying buttresses and it did occur to me to attach a “towel rack” wing to them to aid in aero. I figured if I made it adjustable I could find the best angle of attack for drag and then another one for downforce. You know, for when I wanna track it

..I got some studying to do, nowhere near as knowledgeable on this as you guys.

Here's something that surpasses my nderstanding.

https://ecomodder.com/forum/member-f...10-images5.jpg

A wind/electric hybrid that is pushed forward by quartering winds.

No idea either.

The effect does happen in certain crosswinds in a velomobile, though. That’s about all I know.

You've not sailed a boat? Sail boats can head into the wind, up to about 40 degrees of true wind direction. When I sailed a 14 foot catamaran, a very long time ago, the cat was fastest with wind at right-angles to my direction of travel, what is called a beam reach.

The trouble with a road vehicle though, is that the direction of travel is constrained by the road, so you can't tack for example.

https://upload.wikimedia.org/wikiped...f_sail.svg.png

Well, that's part of it. Also, the diagram shows the sail has reach. The windmobile is a fixed airfoil.

(I've not)

For a while John Roncz was designing sail/wings/turbine blades that would generate thrust in conditions typical sails cannot. I didn't understand the mechanisms then and still don't but I can see why those style airfoils could be used on vehicles if you accept the penalties for sub-optimal direction.

official numbers on COSWORTH upper wing
 

Pages 96 and 99 of the May, 1993 issue of AUTOMOBILE Magazine provided some FoMoCo numbers for the Ford ESCORT RS Cosworth.
* The upper wing degraded the Cd from 0.34, to 0.38.
* Top speed was reduced from 145 mph, to 140 mph.
* @ 110 mph, the car developed 10-pounds front downforce, and 37-pounds rear downforce.
* Over 200- hours were spent in the Ford of Cologne, Germany wind tunnel to aerodynamically tune the car for the downforce and engine turbocharger cooling.
-----------------------------------------------------------------------------------------
As an aside, I applied Hucho's, December, 1986, rule-of-thumb for delta-Cd vs delta- Top Speed.
The result's accuracy was over 98%.:)

fixed
 

There would be a spectra of relative wind angles at which the airfoils would generate enough lift to propel the car. Otherwise she'd be dead on the ground.
The Lubbock Avalanche Journal carried a story about this windmobile being stopped by Department of Public Safety patrolman for speeding. The driver was a 'foreigner' and had misinterpreted the US State Highway-82 sign as the posted SPEED LIMIT. The patrolman didn't cite him, just explained the situation.:p

A couple old threads where we make mention of the car in question.

https://ecomodder.com/forum/showthre...tml#post517762

Curbside Classic: 1986 Merkur XR4TI – What’s In A Name?
https://www.curbsideclassic.com/curb...ats-in-a-name/

https://ecomodder.com/forum/showthre...-16550-16.html

https://ecomodder.com/forum/showthre...tml#post517797
http://kep.cdn.indexvas.hu/1/0/437/4...1230532_wm.jpg

journal article
The New Ford Aerodynamic Wind Tunnel in Europe
Rüdiger H. Volkert and Wigbert R. Kohl
https://www.jstor.org/stable/44470081?seq=1
https://encrypted-tbn0.gstatic.com/i...5ifNk&usqp=CAU

https://encrypted-tbn0.gstatic.com/i...6Uzho&usqp=CAU

https://encrypted-tbn0.gstatic.com/i...2LEBo&usqp=CAU

https://encrypted-tbn0.gstatic.com/i...zTv0w&usqp=CAU
NOTE TO SELF: To get the images above, use Google images with search term "Ford Probe X | Cunningham ID" click on first "ecomodder" image link, then see related images in far to the right side dialog box and scroll down.

Related?

I did a still screenshot of the video.

#2295. Ford probe 3 1981 (Prototype Car)
https://www.arcar.org/video-video-video-u0egl-suh0y
http://forums.pelicanparts.com/uploa...1616921626.jpg

https://www.imcdb.org/v594864.html
http://forums.pelicanparts.com/uploa...1616921911.jpg

https://www.aronline.co.uk/cars/ford...pment-history/
http://forums.pelicanparts.com/uploa...1616922758.jpg

About half way down in the comments section is perhaps a clue to Ford's concern for extra down-force at speed?


https://www.aronline.co.uk/cars/ford...pment-history/

Probably just downforce. Possibly, a mix of both? I don’t doubt that the cars would need some aid for stability, but the double wing on that Probe concept raises questions; I’m sure they weren’t looking for downforce.

The Probe is all horizontal surface. The Escort RS Cosworth has those fat arms that act like trim tabs vortex generators if not rudders.

Sierra stability
 

One journalist had nothing but good things to say about Sierra's very stable high-speed characteristics. He drove at up to 120-mph, and in the rain.

I think this is an issue of context. In terms of other similar class cars, it probably did compare favorably, but up against other more sporty models it was still lacking.

It's odd what works for stability and what does not. As a teenager, my parent's F-250 felt great at 115 MPH. Later on, the second generation MR2 I had started feeling like a complete handful at that speed with a Cd of 0.28. It had the low spoiler, and now I wonder what one without it is like.

(And at 51, I have no idea what the top speed of any of my current cars would be. :D)

115-mph
 

112-mph was set as the benchmark for the fatalities experienced in the Audi TT.
The pre-production 1963 Corvette Stingray was reported to have 'uncontrollable lift at 140-mph.'
The nose of the reproduction Cobra Daytona Coupes are said to get light and wander around at 125-mph.
Seems like a mixed-bag out there.
It's probably a good thing that the MR2 had the spoiler.

Stability is a bit more complex than is being described.

1) If rear lift is higher than front lift, the car will be more unstable - so it's not just the absolute values but also the ratio of lift values. Recent papers from Porsche describe this very well.

2) Lateral stability depends largely on the lateral locations of the centre of pressure versus the centre of gravity, with a rearwards centre of pressure required for stability. (ie more side profile area towards the back of the car than the front.)

Re the Sierra, I haven't explored it in detail but I understand that they added separation edges to the sides of the rear glass to improve stability, so perhaps there was an oscillatory flow at those locations.

The adjoining issue with F/R ratios is additionally, there is seldom an aero system in place that the ratio remains constant over the useful speed band. Meaning one has to compromise and try to remain within the band where the stability is acceptable, to state the obvious,

Only if the CLf and CLr change dramatically with speed - and as far as I know with road cars, they don't.

Would love to see a video on the aerodynamics of this double wing, Julian.

Frank Stephenson, designer of iconic car designs; the Mini, Maserati MC12, Ferrari F430 & FXX and the McLarens P1, 675LT, 570S & 720S, was also the Cosworth designer. He originally drew on an aerodynamically 'Fokker DR-1 Tri-wing' spoiler design on the race car and for the road car. The Ford bean counters deleted his third wing, it cost 5 deutschmarks too much!

https://www.youtube.com/watch?v=kFTepo8MzHY&t=258s

Wheeler Dealers' RS Cosworth episode, Ant Anstead fabricated the third wing! @4:40
https://www.youtube.com/watch?v=JzXlmjUNgUA