Rear diffuser?

[Phase]

Can anyone explain why the Mercedes eqxx rear diffuser reduces drag by just extending the bottom rear? It doesn’t even reduce the wake side

Can someone explain the physics behind just sliding out the back rear diffuser in length lowers drag?

[freebeard]

Wake size?

This EQXX?


greencars.com/post/the-mercedes-eqxxs-remarkable-626-mile-road-trip

I would speculate that the wake eventually dies down into the ground and this might decouple it in some way.

Anotehr example:

[Phase]

Originally Posted by freebeard

Wake size?

This EQXX?


greencars.com/post/the-mercedes-eqxxs-remarkable-626-mile-road-trip

I would speculate that the wake eventually dies down into the ground and this might decouple it in some way.

Anotehr example:

Well I’m about to buy some abs plastic and try to design one like the eqxx and then drill it into the rear back bumper

[aerohead]

Originally Posted by Phase

Can anyone explain why the Mercedes eqxx rear diffuser reduces drag by just extending the bottom rear? It doesn’t even reduce the wake side

Can someone explain the physics behind just sliding out the back rear diffuser in length lowers drag?

Any elongation, which maintains attached flow, while simultaneously allowing divided streamlines to converge, vectoring slower, higher pressure into the wake, is doing the only thing that can reduce drag.
It would be 'better' if the sides were equally filled in. M-B did this with C-111 III, Bionic Boxfish, and IAA. Their stylists may have wanted what is referred to as 'directionality' to be given to the side silhouette; rather than a more proper 'K-form' truncation. Only they can answer factually.

[aerohead]

Originally Posted by Phase

Why’s the Ioniq ev got the same or higher CD then if that has a smooth flat under body and a mini rear diffuser? That’s what I don’t get

I’m pretty worried about cooling when trying to cover the underbody mufflers and exhaust pipes

The BEV IONIQ-5 is more of a CUV, than a sedan like your IONIQ.
The fineness ratios should be compared.
The rooflines should be compared.
The IONIQ-6 is the Porsche 911 knock-off, with the same problems of the 911.
I'm unsure which IONIQ you're referring to. I can't seem to keep up.
It may be that Hyundai/KIA/Genesis doesn't want to risk patent or copyright infringement with Tesla, so they've settled for a little higher drag.
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If you'll do additional heat-shielding, exhaust wrap, or both, heat shouldn't be an issue. ICBM missile silos use nothing but concentric rings of sheet metal shells with dead air spaces in between to insulate them.
Kenny Lyon's BMW exhaust system was completely-wrapped on his Cd 0.11 streamliner motorcycle. And he was 'inside' the body at all times, with the exhaust!
If you keep the car long enough, the mods will easily pay for themselves.

[Phase]

Originally Posted by aerohead

The BEV IONIQ-5 is more of a CUV, than a sedan like your IONIQ.
The fineness ratios should be compared.
The rooflines should be compared.
The IONIQ-6 is the Porsche 911 knock-off, with the same problems of the 911.
I'm unsure which IONIQ you're referring to. I can't seem to keep up.
It may be that Hyundai/KIA/Genesis doesn't want to risk patent or copyright infringement with Tesla, so they've settled for a little higher drag.
--------------------------------------------------------------------------------------
If you'll do additional heat-shielding, exhaust wrap, or both, heat shouldn't be an issue. ICBM missile silos use nothing but concentric rings of sheet metal shells with dead air spaces in between to insulate them.
Kenny Lyon's BMW exhaust system was completely-wrapped on his Cd 0.11 streamliner motorcycle. And he was 'inside' the body at all times, with the exhaust!
If you keep the car long enough, the mods will easily pay for themselves.

I’m already above 110k miles and don’t plan on keeping the car for more than another 3-4 years so the heat shielding is already jacking up the price. Maybe on my next car I’ll go crazy off the dealership lot with all of that

And Hyundai made 3 ioniqs that look the same in 2017/2018. Hybrid. Plug in hybrid. And full ev

Not talking about the Ioniq 5. Just Google 2019 Ioniq ev and you’ll see it’s the same body style as my Ioniq, just a fully smooth front grill, and smooth under body.

[Phase]

Originally Posted by aerohead

Any elongation, which maintains attached flow, while simultaneously allowing divided streamlines to converge, vectoring slower, higher pressure into the wake, is doing the only thing that can reduce drag.
It would be 'better' if the sides were equally filled in. M-B did this with C-111 III, Bionic Boxfish, and IAA. Their stylists may have wanted what is referred to as 'directionality' to be given to the side silhouette; rather than a more proper 'K-form' truncation. Only they can answer factually.

I’ll be building a similar diffuser the the eqxx and have it extend about 8 inches like they are doing

I’ll be filling In the “ parachute” gap between the horizontal Muffer and the rear bumper. There’s about a foot of just open airspace under neath. Wonder how close of a gap I should make between the abs plastic and rear muffler. Clearly don’t want them touching. Thinking maybe one once or two inches then just wrap that corner of abs near the muffler with cheap heat foil or some aluminum heat tape or something

[aerohead]

Under Federal Trade Commission rules, Hyundai is allowed to call anything from Cd 0.2400, to Cd 0.2499, 'Cd 0.24.'
Their brochures at the dealership attribute all styles, with all wheel types and sizes with Cd 0.24.
The likelihood of that being 'exactly' correct is about 'zero.'
So the IONIQ EV could be Cd 0.0099 lower and we'd never know it unless we tested it independently.
If it's heavier and uses wider tires, that would degrade its drag.
We know that the Lucid Air's Cd is a function of tire width.
' Unknown quantities.'

[aerohead]

Knauf Insulation makes some great non-asbestos, high-temp insulation wrap.
I was involved in a Cleaver-Brooks high-pressure boiler-fed hydronic heating system for American Airlines Headquarters during the record freeze of 1983.
All the steam pipes were wrapped, then clad with an aluminum jacket.
These are commercial products. I don't know if 'individuals' can purchase from them.
Your friends the welders should have non-asbestos heat shields for close-quarters work. That material is local purchase.
And fiberglass welding blanket cuttings could be slipped between heat shield and ABS.

[Phase]

Originally Posted by aerohead

Knauf Insulation makes some great non-asbestos, high-temp insulation wrap.
I was involved in a Cleaver-Brooks high-pressure boiler-fed hydronic heating system for American Airlines Headquarters during the record freeze of 1983.
All the steam pipes were wrapped, then clad with an aluminum jacket.
These are commercial products. I don't know if 'individuals' can purchase from them.
Your friends the welders should have non-asbestos heat shields for close-quarters work. That material is local purchase.
And fiberglass welding blanket cuttings could be slipped between heat shield and ABS.

I’m still shocked that Hyundai didn’t add a rear diffuser to the Ioniq hybrid. Even Hyundais Elantra and Sonata hybrids have decent looking rear diffusers for gas engine cars. Toyota Prius even has a rear diffuser. I don’t get the flat bumper reasoning for the Ioniq when they were making a low drag fuel efficient car