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wing v duck tail, Real data anyone?

Hi has any one got factual data regarding adding a 60" wing or GT3 996 cup car wing above a duck tail? SC track car
Ie lap times? , Hill climb times? feel of the car ?

Thanks John
Old 12-29-2017, 03:55 PM
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Someone posted lift vs. downforce comparisons between the ducktail and the 3.8RS wing like 10 years ago... Its still here... Maybe you can find it with search...
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Old 12-30-2017, 06:26 AM
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Search Jack Olsen posts, I think he did some actual testing
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Old 01-03-2018, 08:31 AM
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I think he's talking about whether there is a quantifiable benefit from combining the two, like Porsche currently does.

I've always combined the two, and there's no doubt that adding a wing to a spoiler makes for a large gain in terms of downforce. But whether, and if, the two are interacting in a meaningful way is something I don't have data on. I'd have to A/B a wing with and without a spoiler down below it.

I do have some 'dust data,' which suggests a pretty large low-pressure area. But that's not very scientific.



I recently purchased GT Racing's GT3-style base for the air-cooled cars. I doubt they did any meaningful testing with it (although I have no idea). The thing I like about it is that I will be able to eliminate my cross-supports with it.

Old 01-03-2018, 05:43 PM
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Jack, any noticeable drag or reduction on top end speed with that wing?

Tell us about your diffuser!
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Old 01-06-2018, 12:31 PM
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There's no doubt additional drag from the wing. But my top speeds on track are higher with the wing in place -- probably because I'm going through the corner before the straight faster. My highest speeds at Willow come when I have the splitter and side skirts reducing air under the car and the wing helping me through the turns that come before the long, fast sections.

But I've got no data on the real-world drag produced by the wing -- only theoretical stuff.

I copied an underbody piece that continued a flat bottom under the engine, but only as wide as I could get away with without compromising cooling. On track days, I add an extension and side skirts, which just bolt onto the original piece. No data on it, And while other people with just the cover piece report a seat-of-the-pants-sensed improvement, I can't say I can tell much of a difference. But it seems to carry a very low risk of increasing drag, and it's probably helping.



This is with the extension and side curtains attached. It's a single piece that rides to the track inside the car.



Bonus videos.

Diffuser POV, from below:

https://youtu.be/Ws5aSb8IwDM

And the whole package in use:

https://youtu.be/BdXzPvKPCro
Old 01-06-2018, 12:56 PM
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Thanks for the input on this i will do some track testing .
Old 01-23-2018, 02:21 PM
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I had that GT Racing GT3 tail for a while. It's a good part, a little lighter than a ducktail too. Required some sanding on the edges (especially the top edge). I need to get another GT tail for my 993 bodied car, the tail I have now works fine but weighs a lot.
Old 01-24-2018, 09:23 AM
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Hank Godfredsen, who sold GT Racing to his son who now runs it, told me that the information he had (he didn't test stuff like a race engineer would) was that you needed a spoiler of some sort under a wing. Which it looks like Porsche has always done, though not with a duck under a wing. But you wouldn't want a smooth stock rear lid and a wing, at least not for optimum performance.

Bill Walker from El Paso mounted a wing on his 911 with quick release pins. The wing was hardly a scientific purchase (someone gave it to him). He went out on the local track (Arroyo Secco) with the wing for several laps, then pitted and a couple of guys snatched the wing off and he went back out. He said his lap times didn't really change, but the car felt less stable without the wing. Mind you, neither the car nor the track supported Daytona like warp speeds. But how many have tried even this level of comparison?

With full data, like suspension potentiometers, you can measure how much lower one wing setting puts your rear than another. You can translate that, I think, into downforce. And you can compare your lap times, though that presupposes a driver of pro or near pro level skill, feel, and consistency. There are also ways of getting at actual drag figures without wind tunnels, though doing them at ordinary track days is a bit inconvenient, as no one expects someone to start coasting half way down a straight.

An then there is the placebo effect - with my wing I ought to be able to take corner X faster, so I will. And it worked, I'm still on the track. Well, did you go back and try that without it?

At the really high end of aero and power, my understanding is that there is a dead zone - if you enter over Y, you are fine as long as below Z. But if you enter under Y, you'd better be under X, because in between you won't have the downforce you need to stay on track. This has to be quite counter intuitive to the seats of our pants.

The paddock consensus among mechanics supporting Caymans is that their drivers would go faster if they took off the wings they fancied.

Jack is to be commended for his combination of resourceful changes of the sort which look like in theory they should improve this or that, his commitment to aesthetics, and his frank admission that he isn't super data driven. If professional top end race cars have diffusers, why shouldn't I try one on my car? And if it didn't put me off in the sagebrush, well at least it didn't hurt, and I have had the fun of design and fabrication.
Old 01-28-2018, 12:57 PM
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A significant part of the benefit is car/power dependent. My actual data/experience below:

'88 Carrera
This car is extremely sensitive to aero because it is low-powered and generally aero-inefficient. I recently pulled 150lbs out of the car and added a 55" wing on a 964RS deck. At willow the car went from 1:33's to 1:29's. Maybe 1.5 sec is attributable to weight, so really strong gains there.

As Jack referenced, the car can stall out with the added aero, but exit velocity can make up for that. Best data for this is: the car is 3mph slower entering 8, 5mph faster exiting 8 and 9 and 2mph faster at the end of the front straight. On a track with more straightaway and slower speed corners, the aero would probably be slower.

Another data point: Before adding the wing, I had an IROC tail on the car with an adjustable gurney. At cal speedway the ideal gurney length was 1.5". At 2.5" the car was 6mph slower down the front stretch! I mention this to emphasize that more aero on these older cars is not always better.


2002 996
This car has/had full aero. 2,670lbs at dead on 300bhp. I started with a full 997 cup wing, 997 cup front end and cannards. The car was fast and stable, but a pig in a straight line. I pulled the cannards off, blocked off the center radiator and went to a 5" smaller rear wing and picked up nearly a second at willow. Fastest part of that track for this car is turn 8 exit: went from 136 to 140mph.

Sometimes less is more.
Old 01-29-2018, 10:57 AM
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There was a time many years ago in IMSA when they where just learning about aero, they came up with a rear spoiler that popped up when you got on the brakes. That was outlawed right away.

Now I watched a F1 race the other day at Texas and low and behold their rear spoiler is doing that.
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Old 01-29-2018, 11:27 AM
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Quote:
Originally Posted by Mehoff View Post
A significant part of the benefit is car/power dependent. My actual data/experience below:

'88 Carrera
This car is extremely sensitive to aero because it is low-powered and generally aero-inefficient. I recently pulled 150lbs out of the car and added a 55" wing on a 964RS deck. At willow the car went from 1:33's to 1:29's. Maybe 1.5 sec is attributable to weight, so really strong gains there.

As Jack referenced, the car can stall out with the added aero, but exit velocity can make up for that. Best data for this is: the car is 3mph slower entering 8, 5mph faster exiting 8 and 9 and 2mph faster at the end of the front straight. On a track with more straightaway and slower speed corners, the aero would probably be slower.

Another data point: Before adding the wing, I had an IROC tail on the car with an adjustable gurney. At cal speedway the ideal gurney length was 1.5". At 2.5" the car was 6mph slower down the front stretch! I mention this to emphasize that more aero on these older cars is not always better.


2002 996
This car has/had full aero. 2,670lbs at dead on 300bhp. I started with a full 997 cup wing, 997 cup front end and cannards. The car was fast and stable, but a pig in a straight line. I pulled the cannards off, blocked off the center radiator and went to a 5" smaller rear wing and picked up nearly a second at willow. Fastest part of that track for this car is turn 8 exit: went from 136 to 140mph.

Sometimes less is more.
Near same set up; same rear deck with 50" wing and 1/2 gurney flap.
Reduced wing angle from 6 degrees to 2, this was worth 1.5 seconds @ Fontana Roval. Forgot to change back to 6 when at Chuckwalla, pace off from priors by 2 seconds.
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Old 01-29-2018, 12:24 PM
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I'll add some seat of the pants data for fun:

Narrow body SC (16x7 / 16x9 wheels), 2400lbs, 300hp (I turn my turbo down to min), ducktail
Top speed at The Ridge Motorsport track in Shelton, Wa = 134mph
Best Track time = 2:00.xx

After my 'super' wide body conversion (17x10 / 17x12 wheels), 2400lbs, 300hp, GT-1 wing
Top speed at The Ridge Motorsport track in Shelton, Wa = ~126mph
Best Track time = 1:59.65

I felt faster in the corners but noticeably slower at the end of the straight.
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Old 02-06-2018, 11:18 AM
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Quote:
Originally Posted by kent olsen View Post

Now I watched a F1 race the other day at Texas and low and behold their rear spoiler is doing that.
Not really, they have a drag reduction system (DRS) that they can deploy on some straits if they are closer than 1 second to the car in front.
At the end of the straight te wing must go back to the original position.
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Old 02-07-2018, 08:32 AM
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I did some testing with a home-made DRS system. The data I got was inconclusive -- the airflow for a 1972 widebody 911 is so crazy, I think this was making a negligible difference. I opted to remove it, ultimately, since it added weight and (more importantly) increased the likelihood of driver-error problems.

Some video clips:

https://youtu.be/bnJPK532mlI

https://youtu.be/a2PVC5k3CHI

https://youtu.be/yk5g-7gn7H0
Old 02-07-2018, 08:39 AM
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All of that setup looks perfect to my eye. Except the angle of the wing looks too aggressive. But that might just be the wide-angle lens that took the pictures.

So, for the sake of other people reading this who might not know -- if you're measuring an 8 angle of attack from level ground, then your angle of attack is actually about 19, which would almost certainly be well into stall. The airflow down the back of the car where it hits the wing is 10-12 down.
Old 02-17-2018, 07:39 AM
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Mr. Jack,
So, even with the wing at the top of the uprights, the airflow angle approaching the leading edge of the wing is still conformed to the angle of the rear window area?
How far up from the rear window is this angled mass of flowing air present?

BTW, that car is sweet, like the rear tow hook also
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Old 02-17-2018, 08:30 AM
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Yes. Even above the roofline. I tested it with wool tufts.

In this picture the lower angle is -11.



So in testing my wing, a 5 angle of attack became a ~16 angle when corrected. And my ride-height data generally lined up with that.



Of course, it changes direction once it passes under/over the wing. Here's my goofy "glitter gun" test.



Some of my testing is completely unscientific. But it looks cool.



https://youtu.be/yk5g-7gn7H0
Old 02-17-2018, 10:56 AM
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The angle of the rear 996 GT3 cup car wing ( off my cup car) was measured when the car was sitting on level ground using a digital level, sitting on a straight edge across the full depth of the wing.
Jack ,You are correct, the full 9 degrees created too much drag( see above lap times)
going back to the least "wing "position it felt like more Hp to drive and dropped lap times.
The stability, smoothness and control of the car was the greatest improvement along with lap after lap of constant lap times, not 1 lap wonders.
All done on R spec AO50 Yokohama tires.
Old 02-17-2018, 02:17 PM
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Great info here as I’m currently looking at wing options (again)

Background:
I ran a raised centre element on a 3.8 tail base on my previous car and found i lost about 3mph top end in drag even at modest AoA, but the stability outweighed the drag penalty. Previous car didnt have the power to go any bigger, new car has a 3.6 so I’m looking at options again.

Already have a banana style carbon wing that came with a tail 3.8 base deal (pictured).
Then my recent chassis purchase came with another smaller 60” banana style so i now have two!



Im looking at getting rid of one and fitting a larger straight wing.
On a widebody car, is 70” the recommended size, taking it right out to the bodywork limit?

Jack, i know you made you own, but which section/chord profiles have people found best?

Also end plates sizes and shapes?

Last edited by DHE11; 02-17-2018 at 02:55 PM.. Reason: Pic
Old 02-17-2018, 02:54 PM
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