Roof Spoiler

[Tahoe_Hybrid]

Originally Posted by Joggernot

Saw this on another forum. Looks like it would be worst aerodynamics.

this gives you the visual eliment at 60 MPH

ignore the fire

[JulianEdgar]

Originally Posted by Vman455

I came across this in a textbook last winter. It seems relevant here.

I just saw this, and immediately thought: that must be from about the worst current textbook on car aero. And I was right - 'Theory and Applications of Aerodynamics for Ground Vehicles'.

That para is absolute garbage. To show the 'quality' of this book, note how reference 9, cited in the para, isn't even in the chapter references...

A spoiler, common in sports cars, is a negative lift device.

Yes.

It reduces the lift by slowing down the flow over its upper surface.

What surface? Not the spoiler, as this suggests.

A negative lift wing is the most common type of spoiler.

No, a wing is not a spoiler - how basic a mistake can be made?

When lifting devices are used, it is important to place them in the proper location at the rear of the vehicle, or they may turn out to negate the very effect for which they have been incorporated [9].

Ref 9 not included in chapter references (there are none for the book as a whole). It's highly unlikely that any spoiler will create lift on any modern car (where most lift comes from attached flow), unless something really weird is done so that the spoiler deflects air massively downwards.

For example, a spoiler on the vehicle rear roof only adds to the lift.

I don't think this is the case - in fact I think this is balderdash on any modern car with attached flow over the rear window. But OK, now where is the evidence for this? None is presented.

The book is full of mistakes - staggering that it was published by the SAE. If you want to learn about spoilers/wings/etc, Katz, Hucho or Scheutz are the gold standard - especially when compared to this book!

[Vman455]

Originally Posted by JulianEdgar

I just saw this, and immediately thought: that must be from about the worst current textbook on car aero. And I was right - 'Theory and Applications of Aerodynamics for Ground Vehicles'.

You're starting to sound like aerohead, repeating yourself--you've commented on this book before!

To paraphrase C.S. Lewis, I was young then--I hadn't started any engineering coursework when I posted this, and to quote another of my teachers (John Walter Hill, longtime musicology professor at the University of Illinois), "that was back when I believed everything I read."

[JulianEdgar]

Originally Posted by Vman455

You're starting to sound like aerohead, repeating yourself--you've commented on this book before!

To paraphrase C.S. Lewis, I was young then--I hadn't started any engineering coursework when I posted this, and to quote another of my teachers (John Walter Hill, longtime musicology professor at the University of Illinois), "that was back when I believed everything I read."

Yes I have commented on that book before, but not that part. My main point, that you have paraphrased, is that people should be skeptical about what is posted here.

Note that no-one at the time said that the extract was obviously wrong - the confusion of wing and spoiler should have alerted even the greatest tyro. (Instead, two people 'liked' the post!)

[AeroMcAeroFace]

My main point, that you have paraphrased, is that people should be skeptical about what is posted here.

This is the most important thing, chase the original references. I believe the person who wrote a paper more that the person who references the paper, and far more than the person who read it a while ago and thinks/believes it to be the case.

The thing is that the reference [9] , which I can't find either, may have found that their spoiler on the roof increased lift in some way, maybe by stopping a boot lip spoiler or sculpted and lift reducing body after the hatch from working properly.

Note that no-one at the time said that the extract was obviously wrong

It may not be wrong but it may be misleading, their findings may show an increase in lift. But those results are only useful in that specific scenario, which is not analogous to every car and probably not even representative and should never be taken as such.

[JulianEdgar]

Originally Posted by AeroMcAeroFace

It may not be wrong but it may be misleading, their findings may show an increase in lift. But those results are only useful in that specific scenario, which is not analogous to every car and probably not even representative and should never be taken as such.

Yes that is the case.

But I was referring to the confusion in the piece between a spoiler and wing - and the fact that is so wrong was a red flag re credibility.

[aerohead]

Originally Posted by Joggernot

Saw this on another forum. Looks like it would be worst aerodynamics.

* Do we know if that's an OEM part, standard on the Genesis, or an add-on aftermarket part ?

[aerohead]

Originally Posted by 2000mc

https://youtu.be/Fq8hkPobpes

Take away seems to be “roof spoilers are just stupid”

* An American Motors Javelin had a cosmetic roof spoiler which made no difference to performance.
* One Toyota Celica Supra also had an iconic, cosmetic roof spoiler, also of no effect.
* Mercedes-Benz built a 190 Evo, with a combination roof spoiler, rear wing, which was effective aerodynamically.
* Today's SUV rear spoilers have been shown to affect drag.The further back they reach, along the Kamm-Back contour, the lower the drag and lift. You can see it between the Porsche Cayenne and Toyota RAV4. The Porsche is Cd 0.36, while the RAV4 is Cd 0.30, and Toyota went to great pains to extend the D-pillar extensions back, almost to the Kamm truncation line.
* As MetroMPG emphasized years ago, we ought to take vehicles on a case-specific basis, and steer away from generalities.

[aerohead]

Originally Posted by Joggernot

Excellent views with the hydrogen bubbles to show the effect. I'll attach my effort with the template. Seems clear that the roof spoiler would disrupt the template and create drag.

I've come to the same conclusion. The 'kicker' might create what Hucho refers to as 'overshoot,' actually aggravating the ability for the flow to reattach on the boot/ trunklid, losing the attached vortex, and increasing drag/ lift.

[aerohead]

Originally Posted by Vman455

I came across this in a textbook last winter. It seems relevant here.

As there are fastback and notchback sports cars, we might want to qualify things with respect to a specific sports car.
A MIATA Club Car would require a different solution compared to a modern Corvette coupe.