Reducing lift on different body shape cars

[JulianEdgar]

Originally Posted by aerohead

*On line 1) I prefaced my comments with respect to context.
* Whether a 'fastback' is a 'pseudo-Jaray', or 'Kamm-back' is the context.
-----------------------------------------------------------------------------------
A) on a 'pseudo-Jaray' body, a rear spoiler would have to address lift-due-to-separation, as well as 'direct lift' if that was desirable.
B) on a 'Kamm-back' fastback, no lift-due-to-separation would exist.
C) adding a spoiler to a Kamm-back would cause the streamlines to re-converge, the flow to accelerate up to a higher velocity, lower pressure, increasing the size of the wake, lowering base pressure, raising overall drag.
The 'active' spoiler attempts to navigate the dilemma. They don't obstruct rearwards vision when 'parked', can limit the hit to rear visibility at low speeds, ( Tesla Model-X original, 3-position wing ), then go for downforce at high speed, where one needs to pay close attention to what's ahead of the car.

OK, you're back to stuff from the 1930s about shapes and imagined airflow patterns.

As someone else pointed out, it makes it very hard for you to succeed in your understanding when you refuse to read the current best descriptions of how things like rear spoilers work. Refer to Aerodynamics of Road Vehicles, 5th edition. There is a lot there that differs from the 1987 edition.

(Or just do some tuft and pressure testing on some fastback cars.)

[aerohead]

Originally Posted by JulianEdgar

OK, you're back to stuff from the 1930s about shapes and imagined airflow patterns.

As someone else pointed out, it makes it very hard for you to succeed in your understanding when you refuse to read the current best descriptions of how things like rear spoilers work. Refer to Aerodynamics of Road Vehicles, 5th edition. There is a lot there that differs from the 1987 edition.

(Or just do some tuft and pressure testing on some fastback cars.)

A look at Fachsenfeld's book would disabuse you of that notion. This is the foundation of the Kamm-back. It's a 'known quantity'. There's nothing theoretical or abstract about it any of it. In use today on the highest performance and most expensive cars.
I know how spoilers work. No mysteries there.

[JulianEdgar]

Originally Posted by aerohead

A look at Fachsenfeld's book would disabuse you of that notion. This is the foundation of the Kamm-back. It's a 'known quantity'. There's nothing theoretical or abstract about it any of it. In use today on the highest performance and most expensive cars.
I know how spoilers work. No mysteries there.

Excellent! All that I have seen you write about rear spoilers here has been when they're working in separated flow (basically none of today's cars). But if you know how they work in attached flow too, that's great.

[aerohead]

Originally Posted by JulianEdgar

Excellent! All that I have seen you write about rear spoilers here has been when they're working in separated flow (basically none of today's cars). But if you know how they work in attached flow too, that's great.

Many months ago I began to compile a list of 'direct downforce' rear spoilers which meet the exact criteria you've touched on tangentially, and contextually, however, it will only be until after we can agree, and come to some sort of consensus on 'separated flow' situations that I'd even be interested in discussing it.
I'm uncertain what the product mix is in Australia. In the USA, there are dozens and dozens of modern cars with flow separation straight from the assembly line.

[JulianEdgar]

Originally Posted by aerohead

I'm uncertain what the product mix is in Australia. In the USA, there are dozens and dozens of modern cars with flow separation straight from the assembly line.

Apart from SUV-style pick-ups (that I don't call cars) I'd suggest that there are very few new cars sold worldwide that have complete flow separation prior to the end of the car. (Some have separation bubbles and flow that re-attaches - in fact, if you include the A pillars, probably all of them.) Do you have lots of pictures, or tech references, showing all these cars with flow separation?

[aerohead]

Originally Posted by JulianEdgar

Apart from SUV-style pick-ups (that I don't call cars) I'd suggest that there are very few new cars sold worldwide that have complete flow separation prior to the end of the car. (Some have separation bubbles and flow that re-attaches - in fact, if you include the A pillars, probably all of them.) Do you have lots of pictures, or tech references, showing all these cars with flow separation?

1) The conversation has been limited specifically to roofline flow separation. There are other separations, however, they belong in their own thread.
2) If the previous metric of 'post-1990' vehicles still stands, then the following will constitute a sampling of rooflines exhibiting premature separation:
1994 Ford Mustang
1995 Ferrari F355 Berlinetta
2012 NISSA GT-R Black Edition
2012 Chevrolet Camaro ZL1
2012 M-B C63 AMG BLACK SWRIES Coupe
2010 Audi A7 Sportback
2013 Aston Martin Vanquish
2015 Bentley Continental GT3-R
2015 Shelby Super Snake
2015 SCION FR-S
2016 Ford Mustang Shelby GT350R
2016 Porsche Cayman GT4
2016 Cadillac ATS-V
2016 Chevrolet Camaro SS
2017 Porsche 911 Turbo S
2017 M-B GLC Coupe
2019 M-B-AMG GT63 S4-Door
2020 Audi E-Tron
* Ford Aspire
* Ford Fusion
* Hyundau ACCENT
* Jaguar XE
* Jaguar F-Type R Coupe
* Jaguar XKR-S
* Kia Rio
* Mazda MIATA
* Mitsubishi Lancer
* Nissan Sentra
* Subaru WRX
* Tesla Model X
* Chevrolet Malibu MAXX
* Dodge Viper
* Honda CIVIC
* Audi TT
* Audi R8 GT
* Audi RS3
* VW New Beetle
* VW New, New Beetle/ Bugster
* VW Bugatti Veyron 16.4 Super Sport
* Porsche 993
* Porsche Panamera
* Porsche 911 GTR RS 4.0
* Porsche 911 Carrera GTS
* Porsche Taycan
* Suzuki had a small, entry level car with it
There are others, I can't bring my entire library with me. Sorry!

[JulianEdgar]

Originally Posted by aerohead

1) The conversation has been limited specifically to roofline flow separation. There are other separations, however, they belong in their own thread.
2) If the previous metric of 'post-1990' vehicles still stands, then the following will constitute a sampling of rooflines exhibiting premature separation:
1994 Ford Mustang
1995 Ferrari F355 Berlinetta
2012 NISSA GT-R Black Edition
2012 Chevrolet Camaro ZL1
2012 M-B C63 AMG BLACK SWRIES Coupe
2010 Audi A7 Sportback
2013 Aston Martin Vanquish
2015 Bentley Continental GT3-R
2015 Shelby Super Snake
2015 SCION FR-S
2016 Ford Mustang Shelby GT350R
2016 Porsche Cayman GT4
2016 Cadillac ATS-V
2016 Chevrolet Camaro SS
2017 Porsche 911 Turbo S
2017 M-B GLC Coupe
2019 M-B-AMG GT63 S4-Door
2020 Audi E-Tron
* Ford Aspire
* Ford Fusion
* Hyundau ACCENT
* Jaguar XE
* Jaguar F-Type R Coupe
* Jaguar XKR-S
* Kia Rio
* Mazda MIATA
* Mitsubishi Lancer
* Nissan Sentra
* Subaru WRX
* Tesla Model X
* Chevrolet Malibu MAXX
* Dodge Viper
* Honda CIVIC
* Audi TT
* Audi R8 GT
* Audi RS3
* VW New Beetle
* VW New, New Beetle/ Bugster
* VW Bugatti Veyron 16.4 Super Sport
* Porsche 993
* Porsche Panamera
* Porsche 911 GTR RS 4.0
* Porsche 911 Carrera GTS
* Porsche Taycan
* Suzuki had a small, entry level car with it
There are others, I can't bring my entire library with me. Sorry!

No, I wasn't asking for guesswork based on your theories.

I asked: do you have lots of pictures, or tech references, showing all these cars with flow separation?

[aerohead]

Originally Posted by JulianEdgar

No, I wasn't asking for guesswork based on your theories.

I asked: do you have lots of pictures, or tech references, showing all these cars with flow separation?

I have technical drawings ( it's nearly a miracle if you can find a photograph which depicts dimensions in true-length ) for all vehicles listed, and their geometric parameters. Drag coefficients and CdA will allow reverse-engineering of critical performance. The numbers speak for themselves. The very reason for non-dimensional coefficients in the first place.
There are papers which address some of the vehicles listed.
For the others ,the geometric data analytics themselves provide for a high prediction confidence, whether others subscribe to the concept or not. Engineering is guesswork. Like estimating.
A good reason for all the geometric data analytics published for nearly a hundred years now for which to create such a toolbox.
We don't need an authors permission to engineer their work. We don't have to measure anything to predict with high confidence what the actual performance will be.

[JulianEdgar]

Originally Posted by aerohead

I have technical drawings ( it's nearly a miracle if you can find a photograph which depicts dimensions in true-length ) for all vehicles listed, and their geometric parameters. Drag coefficients and CdA will allow reverse-engineering of critical performance. The numbers speak for themselves. The very reason for non-dimensional coefficients in the first place.
There are papers which address some of the vehicles listed.
For the others ,the geometric data analytics themselves provide for a high prediction confidence, whether others subscribe to the concept or not. Engineering is guesswork. Like estimating.
A good reason for all the geometric data analytics published for nearly a hundred years now for which to create such a toolbox.
We don't need an authors permission to engineer their work. We don't have to measure anything to predict with high confidence what the actual performance will be.

Ah, back to the template - completely discredited as a means of ascertaining whether a car has attached or separated flow.

So in fact you actually don't have lots of pictures, or tech references, showing all these cars with flow separation?

[aerohead]

Originally Posted by JulianEdgar

Ah, back to the template - completely discredited as a means of ascertaining whether a car has attached or separated flow.

So in fact you actually don't have lots of pictures, or tech references, showing all these cars with flow separation?

1) the template can reliably predict separation.
2) comparison allows a visual representation of the separation-affected region.
3) Repeating myself: I don't have 'pictures', I have technical drawings.
4) Repeating myself: I have SOME technical references for SOME of the vehicles.
5) re-read 1)
I led you to water. I can't force you to drink. You don't know about templates yet. I've given you the sources. Until you explore those materials, you'll lack the proper educational foundation from which to make distinctions. It's extremely disrespectful to those who preceded you.