Roof Spoiler
 

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

It's hard to tell because it all depends on how it fills out or does not fill out the aerodynamic template.

I'm guessing it's this profile below - correct me if I'm wrong.

https://www.nadaguides.com/Cars/2018...0-FWD/Pictures
https://cdn.jdpower.com/ChromeImageG...001_640_03.jpg

Guessing where that top of rear window spoiler is, I suspect it is in the airflow and interacting with the attached airflow.

Spoilers spoil the airflow, causing rolling vortexes that can pull down the layer of air above it - a good thing but it takes energy - a bad thing.

I'm not a fan of this upper location because the spoiler is not at a 60 degree angle, the angle required for creating a good vortex.

In effect this spoiler is not a spoiler, it is a flatish plate that allows for a clean release of air, but it's a clean release of air where attachment would normally be, so it's kind of a stupid location.

The effect is a larger hole in the air than without it.

Again, this needs to be verified with a template overlay - go for it Joggernot.

https://youtu.be/Fq8hkPobpes

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

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.

Sounds about right, roof spoilers upset the air flow of a clean aerodynamic car, and upsets the air further down the line of less clean cars with a real trunk lid.

I do see room in life for keeping an open mind on this in only a very limited scope pending wind tunnel verification.

1. Historic examples from late 1970's of redirecting roof foils on BMW and Lancia Class-B type race cars with notch-back roof lines.

Example
https://www.scalemates.com/kits/tami...racing--128154
https://www.scalemates.com/products/...0-pristine.jpg

2. Spoilers on notch-back cars that angle down at about a 7-degree angle and give the air a clean edge to release from.

I use words of caution about blind rage or blanket ridicule on any topic as it invites group think over actual analysis, and that's the sort of thing that made these idiot devices popular to begin with.

One last point, none of the spoilers in the video were true +60 degree Gurney flaps that I was talking about earlier as the narrator focused on aftermarket junk. I would be very interested in seeing wind tunnel or CFD diagrams of Wickebill/Gurney flaps on roof edges if anyone finds them.

The yellow spoiler you drew in might misrepresent the majority of aftermarket roof spoilers. From what I can tell many of them are rather flat 180 degree plane.

However some do angle up a bit at the lip similar to your addition.

I think that some of these roof spoilers are small enough and flat enough as not to cause as much damage as others of more aggressive design.

Meaning one is still shooting one's self, but not a head shot, just shooting one's self in the foot.

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

https://ecomodder.com/forum/member-v...520-105825.jpg

The word "spoiler" is applied to any trailing edge device that's been added on including those of modest negative slope and those of +60 degrees.

In that context just about every SUV and Crossover made today has one, and so do the last of the wagons and hatchbacks.

Just want to point this out for clarity.

https://www.hendrickhondasc.com/used...ZZMCAXGC025606
https://www.hendrickhondasc.com/inve...jpg?height=400

https://www.grandmotorcars.com/detai...7fbb98380.html
https://photos5.motorcar.com/used-20...7822-9-800.jpg
https://photos5.motorcar.com/used-20...7822-4-800.jpg

https://www.consumerreports.org/smal...ooper-preview/
https://article.images.consumerrepor...-Cooper-r-1-18

It's just not the location at the back of the car that makes the examples above better than the ones in the video. It is their design and angle of attack.

roof spoiler
 

My first question would be,is this an OEM Hyundai part for the Genesis,or some aftermarket piece?
The Genesis is capable of in the neighborhood of 150-mph.If the car was found to be unstable at this speed,Hyundai may have added it as a palliative,as Audi did with their TT.And Daimler did with their Mercedes-Benz 190 EVO.Mitsubishi Lancer.Subaru WRX.
Car companies don't want their customers killing themselves.It's bad press.
You can legally drive the Genesis at top speed on portions of the Autobahn,so it would be an issue,at least in Europe.

The person was very proud of the new after-market add on. Not an OEM piece. Yes, it was on a Hyundai Genesis, but the year wasn't given.