Reducing lift on different body shape cars

[JulianEdgar]

Originally Posted by aerohead

Correct me if I'm mistaken, however, all I've seen so far, are uncorroborated statements, with no empirical, laboratory evidence. And quite the contrary.

Oh well, you must not have read (or perhaps understood?) what people have been writing here, with plenty of textbook citations and on-road tests shown.

I don't care what you believe, and thankfully general belief here in what you write seems to have diminished - probably impossible for it not to with the overwhelming amount of evidence that has been presented as to the errors in so much that you write.

[JulianEdgar]

Originally Posted by aerohead

At $ 4,000 / hour, are you prepared to underwrite all member costs? I believe we have, on the order of over 30,000 members.
Very generous of you!

Excellent aerodynamic testing and development can occur on the road or track, at little or no cost.

You know that, but you pretend otherwise so that interest is maintained in simplistic and incorrect notions like using templates - ie making guesses from drawings.

To put that another way, you deliberately choose to continue to mislead people here.

[aerohead]

Originally Posted by JulianEdgar

Oh well, you must not have read (or perhaps understood?) what people have been writing here, with plenty of textbook citations and on-road tests shown.

I don't care what you believe, and thankfully general belief here in what you write seems to have diminished - probably impossible for it not to with the overwhelming amount of evidence that has been presented as to the errors in so much that you write.

Textbooks written in Dayton, Tennessee?

[aerohead]

Originally Posted by JulianEdgar

Excellent aerodynamic testing and development can occur on the road or track, at little or no cost.

You know that, but you pretend otherwise so that interest is maintained in simplistic and incorrect notions like using templates - ie making guesses from drawings.

To put that another way, you deliberately choose to continue to mislead people here.

Wow! So the implication that simply adding a rear spoiler, or burst-edge to a run-of-the-mill passenger car will affect a miraculous drag reduction isn't insanely misleading?
The wing on your Insight, derived from an Abbott and Von Doenhoff 'template', that's okay, however an entire vehicle body, like a Douglas DC-3, or Hindenburg, derived from a 'template' is out-of-bounds?
Intellectual depth as can only be explored with a tunneling microscope.
I hope for the sake of creation that you haven't hired an architect for any help on your shop construction.

[JulianEdgar]

Originally Posted by aerohead

Wow! So the implication that simply adding a rear spoiler, or burst-edge to a run-of-the-mill passenger car will affect a miraculous drag reduction isn't insanely misleading?
The wing on your Insight, derived from an Abbott and Von Doenhoff 'template', that's okay, however an entire vehicle body, like a Douglas DC-3, or Hindenburg, derived from a 'template' is out-of-bounds?
Intellectual depth as can only be explored with a tunneling microscope.
I hope for the sake of creation that you haven't hired an architect for any help on your shop construction.

A rear spoiler can reduce drag, especially on a fastback shape. I wouldn't call it 'miraculous' - but you can if you wish.

Separation edges can reduce drag. Whether you think that occurs on 'run of the mill' passenger cars is up to you.

An airship is a good example of a low drag shape, yes.

No I haven't needed an architect - the shed comes fully engineered.

[aerohead]

Originally Posted by JulianEdgar

Excellent aerodynamic testing and development can occur on the road or track, at little or no cost.

You know that, but you pretend otherwise so that interest is maintained in simplistic and incorrect notions like using templates - ie making guesses from drawings.

To put that another way, you deliberately choose to continue to mislead people here.

1) I don't know that within the context with which you imply.
2) A 'Kamm-back' based fastback, of any length, would already have the smallest wake, highest base pressure, lowest lift, and lowest drag. A spoiler wouldn't alter that situation. A spoiler could add 'direct downforce,' however, historically, would come at the expense of higher drag, or danger to pedestrians if not thoughtfully conceived.
3) I'm in total agreement that a pseudo-Jaray 'fastback' could certainly benefit from a rear spoiler, as the flow would already be compromised. A perfect environment for a spoiler.
4) And I also fully agree that for a high-performance vehicle, of which its specification would easily provide for high-speed operation, that the incorporation of a rear spoiler would not only be beneficial, it would be a safety requirement.
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From Hucho's 2nd-Edition, page-23, Figure 1.26, 2nd from bottom, the 'template' of Lay's multi-element, multi-configurational, wind tunnel test model, allows prediction of Cd, in a range from Cd 0.30, to Cd 0.13., as a function of body elongation, with which Hucho discusses in the context of future vehicles design as of December, 1986. ( The actual research presented by Baron Koenig-Fachsenfeld indicated Cd 0.12 as the minimum ).
Hucho himself presented dozens of 'templates' in his chapter on detail optimization. Hoerner's book is also full of them. Both recommended reading.
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Finally, another aspect of vehicle aerodynamics and design, often mentioned here at EcoModder, which could explain WHY anything like a 'template' would never be expressed in vehicle design, and worthy of its own dedicated thread is, 'styling'.
As early as page-6, Hucho wrote: ' [M]inimizing the drag of a passenger vehicle must be accomplished with less conspicuous methods which conform to current styles.' ( Law of the Paris Dressmakers, 1927 )

[JulianEdgar]

Originally Posted by aerohead

1) I don't know that within the context with which you imply.
2) A 'Kamm-back' based fastback, of any length, would already have the smallest wake, highest base pressure, lowest lift, and lowest drag. A spoiler wouldn't alter that situation. A spoiler could add 'direct downforce,' however, historically, would come at the expense of higher drag, or danger to pedestrians if not thoughtfully conceived.

I am talking about modifying real cars, not theorising about shapes. A rear spoiler on a fastback shape can reduce drag and lift: refer to Page 304, Aerodynamics of Road Vehicles, 5th edition.

[aerohead]

Originally Posted by JulianEdgar

I am talking about modifying real cars, not theorising about shapes. A rear spoiler on a fastback shape can reduce drag and lift: refer to Page 304, Aerodynamics of Road Vehicles, 5th edition.

1) okay, 'real' cars.
2) The VW XL1 is a 'real car.' The VW XL1 is a 'fastback. It has an AST-II roofline, zero separation over the roof, and the lowest Cd of any extant production car. According to VW, with the governor defeated, the car will do 112-mph. No spoiler.
3) The Porsche Cayman is a 'pseudo-Jaray' fastback, it suffers flow separation over its roof and requires a rear spoiler, not only for direct downforce, but also to correct lift-due-to separation. Like the Taycan, also a fastback. Hyundai Prophecy concept car, ditto.
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Whether a rear spoiler can reduce drag and lift has never been a bone of contention.
Going back to Hucho, simply lofting the vehicle's rear profile to where you'd terminate an add-on spoiler, would in all likelihood, produce even more favorable results.

[JulianEdgar]

Originally Posted by aerohead

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A spoiler could add 'direct downforce,' however, historically, would come at the expense of higher drag

a few posts later....

Whether a rear spoiler can reduce drag and lift has never been a bone of contention.

Gosh it's hard to keep up. One moment a spoiler will add drag, and the next moment, it won't!

Soon we will be back to your completely incorrect theory of how rear spoilers work on modern cars.

Ah, here it is.

Going back to Hucho, simply lofting the vehicle's rear profile to where you'd terminate an add-on spoiler, would in all likelihood, produce even more favorable results.

How did you go with the reference I cited on how spoilers reduce drag and lift on fastbacks? I can tell you one thing: it is not at all as (you think) Hucho stated it back in the 1980s.

[aerohead]

Originally Posted by JulianEdgar

a few posts later....



Gosh it's hard to keep up. One moment a spoiler will add drag, and the next moment, it won't!

Soon we will be back to your completely incorrect theory of how rear spoilers work on modern cars.

Ah, here it is.



How did you go with the reference I cited on how spoilers reduce drag and lift on fastbacks? I can tell you one thing: it is not at all as (you think) Hucho stated it back in the 1980s.

*On line 1) I prefaced my comments with respect to context.
* Whether a 'fastback' is a 'pseudo-Jaray', or 'Kamm-back' is the context.
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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.