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Old 04-10-2022, 02:19 PM   #91 (permalink)
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Originally Posted by Vman455 View Post
Tuft testing is one of the easiest, most effective, most useful forms of testing; you can trial things like separation edges, mirror changes, fences, vortex generators, air curtains, etc. and see what actually happens to the flow (which is worth an infinite number of guesses). That is a measurement: the tufts show flow direction and, as you learn to read them better, turbulence and speed. Most importantly, the tufts will show you exactly where on the body flow is attached and where it is separated.

An example of useful tuft testing: you asked about your muffler. Tape tufts to it, station a friend on the side of the road down low with a camera and take pictures as you drive by. Is the flow attached or separated? If it's attached, what do you think a plastic panel would "fix" exactly? If it's separated, throw a piece of cardboard on it temporarily and see if it's better, worse, or the same. Use your head rather than throwing up your hands and going, "Well, looks like all I can do is guess." I used to be that way. It's a giant waste of time.

For pressure testing, you can find digital manometers on Amazon for $50 or less; I bought this one, which came with two pitot tubes at the time but you can buy one separately. Disks are easy to make at home with metal bar stock and small brass tubing, which you can find at hardware or hobby stores. Julian's book walks you through the process. He was also nice enough to collect explanations of various test techniques in a single thread here.

This quote--from a 1963 paper on aerodynamics and body design by two GM stylists--is as true today as it was then:

"Technical apathy is often a far greater deterrent to the acquisition and application of vehicle aerodynamic data than any excessive expenditure of time or money" (Kelly, Kent and Harry Holcombe, "Aerodynamics for Body Engineers," SAE 640050).
Yeah driving by a friend on the ground is pretty hard to do in downtown Portland. Iíll have to do some gopro angle tests with the tufts. Iím envious of everyone having access to empty secluded roads for testing

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Old 04-10-2022, 03:28 PM   #92 (permalink)
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en.wikipedia.org/wiki/H._B._Van_Duzer_Forest_State_Scenic_Corridor

https://duckduckgo.com/?q=weather%20van%20duzer%20corridor%20oregon

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https://www.travelmath.com › drive-distance › from › Rose+Lodge,+OR › to › Portland,+OR
The total driving distance from Rose Lodge, OR to Portland, OR is 79 miles or 127 kilometers.
Closer that Bonneville Salt Flats. It's not level but has long straight inclines (compared to the rest of the Coast Range). The main thing is 80-100ft tall trees on both sides of the [two lane] road. It's like driving in a tunnel.
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Old 04-10-2022, 06:32 PM   #93 (permalink)
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en.wikipedia.org/wiki/H._B._Van_Duzer_Forest_State_Scenic_Corridor

https://duckduckgo.com/?q=weather%20van%20duzer%20corridor%20oregon



Closer that Bonneville Salt Flats. It's not level but has long straight inclines (compared to the rest of the Coast Range). The main thing is 80-100ft tall trees on both sides of the [two lane] road. It's like driving in a tunnel.
ive been thru there multiple times. i moved to portland from lincoln city a few years ago. that forest has pot holes, windy roads, and insane traffic lately. especially this time of year with crazy people constantly rushing to the coast. a good flat section ive seen is probably between mcminnville and spirit mountain casino, but thats a far drive just for some testing. i might as well do a lot of testing when im down in utah. girlfriends family lives in salt lake and we are there every month. just have never been to bonneville
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Old 04-10-2022, 10:32 PM   #94 (permalink)
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It's like another planet, when it's dry in August and September. The rest of the year it has brine creeks running through it.. I don't understand how Model Ts can have been there every year for a half century.

I have family in the hills above Willamina, and I was a some friend's house and saw the local news. They had a story about the tribal folk in Grand Rond reclaiming the old paper mill on the river to turn it into a tourist trap.

Maybe I can get up that way. For that long a trip [in the Metro] I'd air down the tires and take the gas mileage hit to save my posterior.
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Old 04-10-2022, 10:42 PM   #95 (permalink)
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It's like another planet, when it's dry in August and September. The rest of the year it has brine creeks running through it.. I don't understand how Model Ts can have been there every year for a half century.

I have family in the hills above Willamina, and I was a some friend's house and saw the local news. They had a story about the tribal folk in Grand Rond reclaiming the old paper mill on the river to turn it into a tourist trap.

Maybe I can get up that way. For that long a trip [in the Metro] I'd air down the tires and take the gas mileage hit to save my posterior.
the coast is pretty all year though. sunny summers or foggy winters with massive trees. i just had to leave because theres not much to do for us young millenials. got too boring ha

first test ill probably have to do out that way once it stops raining is tuft tests with and without rear wheel spats/covers. seems like the easiest thing
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Old 04-11-2022, 12:01 AM   #96 (permalink)
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When I was a kid we watched the hydroplane races on D Lake. Lincoln City came later. Here's the house my parents built in 1980, at Bayshore just North of Waldport. They had a view of the mouth of the Bay.

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Old 04-11-2022, 10:41 AM   #97 (permalink)
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IONIQ tail


1) If you'll look at 2:23 into the video, you'll see how the 'fully-boxed' tail elongation is capturing the smoke in the wake.
2) This is what you're after.
3) Flow @ top, sides, and bottom, is decelerating along the reducing cross-section of the 'tail', and recovering pressure the entire way.
4) When it separates from the new trailing edges, it's at lower velocity, higher pressure, according to the Bernoulli Theorem.
5) This increases base pressure.
6) Increased base pressure reduces pressure drag.
7) The reduced pressure drag is the 'streamlining.'
8) Upper and lower 'spoilers' might provide a drag reduction, however, nothing is going to compare to a box-cavity or boat-tail.
9) Technically, the sides must be included in the 'system.' Without them, you'll experience transverse pressure contamination.
10) And the tail will be useless without 'clean' onset flow. That means rear skirts, as much of a full belly pan as you can get away with, and a diffuser designed for low drag, not downforce.
-------------------------------------------------------------------------------------
11) The blueprint for the IONIQ doesn't indicate much boat-tailing in plan-view.
12) You need it, and the tail will have to respect whatever exists, then add to it, along a streamlined pathway, to provide for attached flow, the desired pressure recovery along the sides, and smaller wake, free of vortex-drag.
13) It's going to be a 'French-curve' environment, integrated into the OEM burst-edges.
--------------------------------------------------------------------------------------
14) The tail itself will be complex. The solution will be simple, not easy.
15) Solutions to drag reduction comparable to your target suggest a required 22-inches of elongation.
16) Since a receiver-mount cargo carrier is 24-inches, you may want to think in that direction, hence Basjoos' recommendation.
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Last edited by aerohead; 04-11-2022 at 11:11 AM.. Reason: add text
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Old 04-11-2022, 01:32 PM   #98 (permalink)
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Quote:
Originally Posted by aerohead View Post

1) If you'll look at 2:23 into the video, you'll see how the 'fully-boxed' tail elongation is capturing the smoke in the wake.
2) This is what you're after.
3) Flow @ top, sides, and bottom, is decelerating along the reducing cross-section of the 'tail', and recovering pressure the entire way.
4) When it separates from the new trailing edges, it's at lower velocity, higher pressure, according to the Bernoulli Theorem.
5) This increases base pressure.
6) Increased base pressure reduces pressure drag.
7) The reduced pressure drag is the 'streamlining.'
8) Upper and lower 'spoilers' might provide a drag reduction, however, nothing is going to compare to a box-cavity or boat-tail.
9) Technically, the sides must be included in the 'system.' Without them, you'll experience transverse pressure contamination.
10) And the tail will be useless without 'clean' onset flow. That means rear skirts, as much of a full belly pan as you can get away with, and a diffuser designed for low drag, not downforce.
-------------------------------------------------------------------------------------
11) The blueprint for the IONIQ doesn't indicate much boat-tailing in plan-view.
12) You need it, and the tail will have to respect whatever exists, then add to it, along a streamlined pathway, to provide for attached flow, the desired pressure recovery along the sides, and smaller wake, free of vortex-drag.
13) It's going to be a 'French-curve' environment, integrated into the OEM burst-edges.
--------------------------------------------------------------------------------------
14) The tail itself will be complex. The solution will be simple, not easy.
15) Solutions to drag reduction comparable to your target suggest a required 22-inches of elongation.
16) Since a receiver-mount cargo carrier is 24-inches, you may want to think in that direction, hence Basjoos' recommendation.
definitely smoothing out under belly and adding rear wheel skirts. ive seen some people on the ioniq forum say they may not do much because you have to SLIGHTLY curve them outwards for wheel clearance and that that will add frontal area and will just offset the benefits. wouldnt covering the whole wheel well with a skirt offset the few inches of front area added by a lot? especially if id be maintaining attached airflow? personally i feel like the attached airflow is way stronger than adding a inch or two of front area sticking out. obviously ill test it, but what are your thoughts?

extending the sides for the box cavity boat tail will be the harder thing to do, versus just extending the top and bottom spoilers
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Old 04-11-2022, 01:48 PM   #99 (permalink)
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added frontal area

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Originally Posted by Phase View Post
definitely smoothing out under belly and adding rear wheel skirts. ive seen some people on the ioniq forum say they may not do much because you have to SLIGHTLY curve them outwards for wheel clearance and that that will add frontal area and will just offset the benefits. wouldnt covering the whole wheel well with a skirt offset the few inches of front area added by a lot? especially if id be maintaining attached airflow? personally i feel like the attached airflow is way stronger than adding a inch or two of front area sticking out. obviously ill test it, but what are your thoughts?

extending the sides for the box cavity boat tail will be the harder thing to do, versus just extending the top and bottom spoilers
1) The most important part of the car is it's rear.
2) OEM longitudinal body camber, along the sides may 'hide' any rear skirt 'bulge', placing it in the 'shadow' of the body projection.
3) Even if there was an increase, the 'GOOD' the skirt would do for the tail extension would be orders of magnitude better than any frontal area penalty.
4) You'd want full rear skirts because of the onset flow issue. There are no really low-drag vehicles lacking full skirts.
5) If you had a bridge-fiducial, or perfectly-aligned laser, you could directly investigate any frontal area aggravation.
6) The boat-tail on my CRX was responsible for most of its speed at Bonneville. 'Bulging' rear skirts to get clean air onto the tail was a structural necessity.
7) Af penalty, if any, still netted an overall 26.5% drag reduction.
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Old 04-11-2022, 02:30 PM   #100 (permalink)
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wouldnt covering the whole wheel well with a skirt offset the few inches of front area added by a lot?
Consider the modern hypercar. They all taper through the doors and then have swollen 'haunches' to clear the rear tires.

If the skirt starts at the door opening instead of the wheel well, or even has a fillet added to the door, it would smoothen the airflow even more.

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