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4th gen aero


boxkita

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Watching aero videos. Found this one for building an aero pressure kit -

 

Also has an ad for his book, Modifying the Aerodynamics of your Road Car, which explains more detail.

 

167 videos mostly on aero for the non-science consumer.

Edited by boxkita
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Not being able to post pics sucks. Just saying.

 

The rear undertray of the 2d models of the cars have been bugging me. I been looking at wagon & sedan butts to verify. The rear bumper skin extends forward to contact the spare tire well. This covers the center of the car between the frame rails. The oem mufflers are shaped to put a large glat surface of nearly the same shape as the bumper skin.

 

There was previous discussion of miata & s2000 rear bumper skins creating large amounts of drag because of the open space in front of under bumper. The legacy doesn't have that issue.

 

Wool tuft testing on the rear half of the wagon showed it was super smooth until the tailgate. It appears the tailgate designer just phoned it in.

 

Curious what a run of the wagon without the last divot looks like. The sedan looks really smooth. Watching white/blue smoke coming off the wagon, it very much curls and goes straight up the back window contacting the underside of the wing.

Edited by boxkita
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Interesting you bring up the mufflers. My '12 Jetta sport wagon has space for mufflers on both sides of the spare tire like the Legacy, but it only has one muffler so there is a tray to cover the hole between the rear/side bumper to the spare tire well.

 

Also VW has the under trays dimpled which likely causes more turbulent air at the surface to then allow the rest of the air to slip by smooth.

Wagon is LIFE! - 265,000 miles and climbing

Unofficial Build (Restoration) Thread

Steering Rack Rebuild

 

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very(relative to a gas car)...the soot builds up quick. I need to bring a rag for loading / unloading in the more mild winter days, otherwise muddy soot is getting on my pants. 40 to 50 mpg though. I wonder if a larger rear wing like the Legacy would help extend the turbulent air to reduce how much soot kicks back up

Wagon is LIFE! - 265,000 miles and climbing

Unofficial Build (Restoration) Thread

Steering Rack Rebuild

 

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very(relative to a gas car)...the soot builds up quick. I need to bring a rag for loading / unloading in the more mild winter days, otherwise muddy soot is getting on my pants. 40 to 50 mpg though. I wonder if a larger rear wing like the Legacy would help extend the turbulent air to reduce how much soot kicks back up

 

Same here.

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Been reading on this more because the rear hatch aero issue is what got me started on wagon aero to begin with. Driving down dusty mountain roads in a black wagon where only the tailgate was dirty.

 

On a race car (f1), the rear wing and diffuser are matched to bring the air flows together which greatly reduces drag while decreasing lift. On a hatch (wagon) car, the dirty rear comes as result of suction drawing air from underneath up the back window. Oddly, the rear spoiler actually makes it worse not better.

 

Before I exceeded Gunnar's patience with his freshly waxed wagon, we had determined adding vertical extensions at the trailing edge of the rear window helped airflow off the spoiler. Someone in one of the fb groups made a wagon spoiler with side pieces. It looked like a step in a better direction, however, I dropped off fb before any pieces shipped so no idea how it really worked.

 

Recent industry research has shown adding a sharp edge to the rear of the body work causes reduced dust on the rear of the hatch. Wraparound aero only works if the boundary layer doesn't detach. Once detached, you have more work to bring air flow back in line so to speak.

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very(relative to a gas car)...the soot builds up quick. I need to bring a rag for loading / unloading in the more mild winter days, otherwise muddy soot is getting on my pants. 40 to 50 mpg though. I wonder if a larger rear wing like the Legacy would help extend the turbulent air to reduce how much soot kicks back up

 

attachment.php?attachmentid=284925&d=1591410117

 

This pic shows the actual airflow at the back of the wagon. All the arrows pointing back are dirt :)

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When you say vertical attachment to the trailing edge do you mean like the fold out doors that come off the back of semis for aero?

 

That would make sense but probably wouldn't look super great lol. I wonder if the WRC cars run into that issue all being hatches. Maybe it's not enough to matter, or maybe that's part of the crazy wings.

 

 

Sent from my iPhone using Tapatalk

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When you say vertical attachment to the trailing edge do you mean like the fold out doors that come off the back of semis for aero?

 

That would make sense but probably wouldn't look super great lol. I wonder if the WRC cars run into that issue all being hatches. Maybe it's not enough to matter, or maybe that's part of the crazy wings.

 

 

Sent from my iPhone using Tapatalk

 

The fold out doors, yes. However, a .25-.5" inch protruding blade is enough. If you find the silt edge on the rear of your car, that's where the edge goes.

 

Note the lack of dust on the rear of this car and all the sharp edges from side to rear. Granted there's excessive mods, but look at taillights vs lgt.

Neuville-Henri-02-1536x1024.jpg

Link to article discussing details- https://www.wrcwings.tech/2020/06/08/hyundai-test-new-modifications-for-the-i20-coupe-wrc-in-finland/

 

And a legacy in dirt shows the difference in dust cloud attachment

2007-Subaru-Outback-XT-rear-three-quarter-dirt.jpg

 

Here's a static pic of Gunnar's wagon setup to test the side to rear turbulence. The in-motion pucs are currently in a storage container while our house is remodeled. The panel really smoothed the air flow and greatly reduced the suction effect under the spoiler.

57f2d59acadd12e4e5492f198c19946c.jpg

Edited by boxkita
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So there's the c west wing, which may be the Facebook group one you mentioned earlier.

 

 

https://uploads.tapatalk-cdn.com/20190601/8c6f62c8b00bfd2fcbe8c86c80a11d37.jpg

 

I just thought they looked cool.

 

Great link btw. I've been looking for something like that. I just get distracted.

 

 

Sent from my iPhone using Tapatalk

Edited by Nonamedude
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So there's the c west wing, which may be the Facebook group one you mentioned earlier.

 

 

https://uploads.tapatalk-cdn.com/20190601/8c6f62c8b00bfd2fcbe8c86c80a11d37.jpg

 

I just thought they looked cool.

 

Great link btw. I've been looking for something like that. I just get distracted.

 

 

Sent from my iPhone using Tapatalk

 

I remember cfd pics and a much bigger side plate. I think they finished it, but can't find a picture.

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K, working this weekend so I can get a few runs off. To clarify, what are we looking for on the wagon that isn't already in post 24 of this thread?

 

Look at you knowing what's been done. :)

 

There's a note in post #30: "EDIT: Oh derp, I left stuff in scientific notation. Pretty much, any time you see e+##, it means take the number before that, and multiply it by 10 raised to the power of the number. So 6.77e+01 in the velocity plot attached to this post would be 6.77x10^1 = 67.7 meters per second.

 

I can include freedom units in future plots, would be good to have both."

 

A translation would be nice. Im still looking at this on a cellphone. If you did them, which is it?

 

Asks (test in isolation if possible):

1. run the #24 wagon model at 60mph/100kph/27.7777m/s

2. " at 100mph/44. m/s

3. remove rear spoiler (just round radius the corner) and plot for 27.7 & 44 m/s. The plot with air flow arrows is super useful (its wool tufts without tickets).

4. Add a front lip (a line sticking out 6" (width of bumper) from bottom of car). Do 27 & 44 m/s tests. Colored & arrows.

5. " except draw a vertical line down to "ground" instead of horizontal.

6. On rear of wagon, draw a line extending underneath line out 6" or a foot. Simulates an actual diffuser. Use 27 & 44 m/s as speeds.

 

Curious which benefits more. Improving rear or front?

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Roger that. Here's the 60 mph run of the baseline wagon model - post 24 was already done at 100 mph. Note that the scales are different for some of the 100mph vs 60mph plots, so don't assume a certain color or arrow length means the same thing between the two runs - look at the actual scale in each plot.

 

For comparison, 60 mph run returns 155.4 N/34.9 lb of drag and 414.1 N/ 93.1 lb of lift.

100 mph run returns 406.2 N/ 91.3 lb of drag and 915.5 N/ 205.8 lb of lift

 

Again, given the nature of the model these lift/drag values are best taken with a grain of salt, and for apples to apples comparisons of different scenarios run w/ the same model.

 

On baseline/front lip/diffuser runs - makes sense to me to try a few different ride heights, since everything's currently at stock height. Thoughts?

pstat.PNG.ea3082ef844740239188edb97ad58a29.PNG

tke.thumb.PNG.b5e99f698419dd7b9e956a2596cef925.PNG

tke_zoom.thumb.PNG.d21863b15b284d47367c21eff3754744.PNG

vel.thumb.PNG.9e69f171871a5f2c5a25765406a4dd5e.PNG

vel_zoom.PNG.6df45e9d9601875d2bc39689c632d2e3.PNG

velvec_aft.PNG.f4e12043db17c8431085cf87aff95a60.PNG

velvec_front.PNG.309afa68df28306af4acfe9ebd7e0d33.PNG

Edited by awfulwaffle
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