Porsche 911 Ducktail - Study/Alternate

[aerohead]

Originally Posted by kach22i

You mean to straighten out the air flow off a swirling fan?

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?

With a closed test section,a boundary layer builds up on the floor,walls,and ceiling,which thickens as you progress further and further into the tunnel.
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.

[kach22i]

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?


Now this:
Wheeler Dealers: S14 E1


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.






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.

[aerohead]

Originally Posted by kach22i

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


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/



This Audi TT below is a few years later than the 2001 model, I think this retractable one allows air to sneak between it's bottom lip and the trunk lid. The result appears to be some smoke gets under there, perhaps a good thing, I'm not sure.

aerodynamics? - VW GTI Forum / VW Rabbit Forum / VW R32 Forum / VW Golf Forum - Golfmkv.com


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?



It's a pretty strong fan, even the five bladed one I have. Discussions on replacing it with an electric fan were deemed unfeasible in the Pelican forum as the motor would be more powerful than a Prius electric motor. Updating my 5 bladed fan to a better cooling one would rob me of 5 hp, similar to lugging around an extra 50 lbs - no thanks.

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.

It doesn't matter as much if the flow into the engine compartment is at high pressure or not,as both have engine-driven,high-static-pressure fans for forced-air cooling to compensate.
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!

[freebeard]

That Escort RS needs a Red Baron paint job.

I suspect this works similar to my proposed Porsche 911 Sponge Bob tail.

Compare http://ecomodder.com/forum/showthrea...tml#post566231

[kach22i]

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.

[kach22i]

A couple of studies, still getting the hang of this new to me photo editing program.

[aerohead]

Originally Posted by kach22i

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.

Buchheim and his associates investigated rear slope angles and Hucho reported that Buchheim et al. reported that 23-degrees would be the maximum angle which could support attached flow.If you look at Buchheim's illustrations,you'll measure 22.5-degrees.
I've stuck with 22-degrees as a conservative figure.But feel free to 'go wild' at 22.5-degrees!

[aerohead]

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.

[kach22i]

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.

[aerohead]

Originally Posted by kach22i

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.

I think the change will help out with cooling.It would be better if everything was boxed in,as Porsche did,as there's only 'leakage' via the engine compartment.But hey,this is your rodeo!
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.