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Old 10-10-2020, 07:03 PM   #11 (permalink)
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Quote:
Originally Posted by Vman455 View Post
... This excerpt considers the impact of practical factors, such as occupant room, and physical parameters, such as ground clearance, on the 'ideal' form. Even if we were building cars from scratch--which most of us aren't--slavishly following a 'template' will not by default obtain the best results for a marketable car. ...
Hi Vman455,

This is a great post. I add the words in bold just to point out that a core disagreement in aerohead/Edgar argument seems to me to be about expectations and goals. One position accommodates the mass market for cars as it is, with evolutionary changes perhaps) while the other position seems to advocate altering the underlying assumptions of what "the market" perceives as "practical" and "attractive."

I see affirmation of both positions in the quote you provide. Barnard clearly describes an ideal shape as to aerodynamics. As he says, "the 'ideal' form for a road vehicle is ... a cambered version, slightly flattened on the underside, with the optimum geometry being dependent on the ground clearance." That's not an affirmation of "The Template," obviously. And his following assertion that other design demands for the market require changes to the ideal form is reasonable. But he clearly does not disclaim the reality of an "ideal" shape (with optimazations).

FWIW, in general, I like and agree with the approach you describe. I just also love the ideal shape discussions because there is good learning in trying to understand them. Cheers!

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Old 10-10-2020, 08:34 PM   #12 (permalink)
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Quote:
Originally Posted by California98Civic View Post
Hi Vman455,

This is a great post. I add the words in bold just to point out that a core disagreement in aerohead/Edgar argument seems to me to be about expectations and goals. One position accommodates the mass market for cars as it is, with evolutionary changes perhaps) while the other position seems to advocate altering the underlying assumptions of what "the market" perceives as "practical" and "attractive."

I see affirmation of both positions in the quote you provide. Barnard clearly describes an ideal shape as to aerodynamics. As he says, "the 'ideal' form for a road vehicle is ... a cambered version, slightly flattened on the underside, with the optimum geometry being dependent on the ground clearance." That's not an affirmation of "The Template," obviously. And his following assertion that other design demands for the market require changes to the ideal form is reasonable. But he clearly does not disclaim the reality of an "ideal" shape (with optimazations).

FWIW, in general, I like and agree with the approach you describe. I just also love the ideal shape discussions because there is good learning in trying to understand them. Cheers!
Not sure if you're just being naive or you haven't actually been following how The Template is often used here. There'd be little debate if The Template were presented just as a low drag shape, that is (one of) the shapes that could be used to form a vehicle being done from scratch.

But it isn't, is it?

Instead it's used to try to 'achieve' all sorts of things - from setting rear spoiler heights, to deciding whether flow is attached or separated on an existing shape, to assessing the 'purity' of existing cars - and so on.

All are garbage.

(And you shortened the quote from Barnard to better meet your argument.)

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Old 10-12-2020, 12:50 PM   #13 (permalink)
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'template'

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Originally Posted by Vman455 View Post
I hope he doesn't mind my excerpting his book here, but this quote, from Chapter 4 "The Aerodynamic Design of Family Cars" in Road Vehicle Aerodynamic Design: An Introduction, is salient to the discussion surrounding the 'template' on this site in recent months:



A few comments:

We know from the literature on car aerodynamics and direct measurement that the range of variation of shapes that can support attached flow (that is, that are streamlined) is large; I posted a quote from a 2010 paper by Hucho on another thread here yesterday regarding the leeway available to designers to change fastback backlight angle without increasing drag, for example, and tuft test images posted here by a handful of people show attached flow over a range of shapes.

This excerpt considers the impact of practical factors, such as occupant room, and physical parameters, such as ground clearance, on the 'ideal' form. Even if we were building cars from scratch--which most of us aren't--slavishly following a 'template' will not by default obtain the best results.

Now, consider that most of us are modifying already-existing production cars, cars that are not half-bodies of revolution, cars that may have air dams or limited underbody paneling or extensive underbody paneling from the factory, cars with narrow tires or wide tires, cars with high ground clearance or low ground clearance, cars with varying rear-body shapes that translate to varying flow fields and pressure profiles, cars with all sorts of differently-optimized (or not-optimized!) aerodynamic and styling details.

I used to think, when I didn't know any better, that extending along a 'template' was the solution--based on what I read on this site. I now realize that this an incredibly simplistic view, and one that does not take into account the facts that 1) there is no single optimum 'template', and 2) the variation in shape and thus flow over the cars we modify is in no way consistent, so a "one size fits all" approach simply cannot produce the best results possible.

For example, a few weeks ago I measured surface panel pressures and found that the flow speed down the center of the roof of a Prius is faster than at the outside edges, and that over the rear window the opposite is true. The 'template' assumes uniform pressure and thus uniform flow speed over its circular section. Given that this is not the case on a Prius, why would a person assume that extending it with a half-circular tail at a specific angle is automatically the best solution to decrease drag? Maybe it isn't. Perhaps the optimum solution doesn't involve fitting a tail at all, if doing so would increase difficulty of parking or not being able to fit in a standard garage, for instance, but looking at other areas of the car to decrease drag. Perhaps a tail that does not have a half-circular cross section would reduce drag more than one that does. How on earth would one know without testing? Without measuring, I would never have known that the flow speed over the rear body is not constant side-to-side in the first place!

'Templates' are like security blankets: someone guarantees results with a minimum of thought or effort. But after trying it, testing is infinitely more rewarding, not very expensive, and not that difficult; the hardest part is really just finding the time to do it, and that's not a huge hurdle. More importantly, testing will reveal what the air is actually doing over your car--no guessing or predicting necessary. Go try it!
1) sounds like Barnard is describing the Morelli CNR 'banana' shape, developed in 1976, from a theoretical, 2-D, numerical model of WW-II era, which is constrained for zero lift and pitching moments.
2) Goro Tamai covers this technology at length in his book, "The Leading Edge.' MIT utilized the Morelli form with their solar race team.
3) at 'normal' ground clearance, the Morrelli form has 79% higher drag than the 'template.'
4) at 'ideal' ( drag minimum ) ground clearance, the C.G. is so high that the NHTSA might deem it unacceptable as a candidate for commercial passenger car manufacture.
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5) as to the velocity profile over the 'template', you are correct.
6) no extrapolation to the Toyota Prius is implied.
7) the original premise of the 'template' was as a guide for roofline elongation modification, a prerequisite to low drag.
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8) your 2010 data from Hucho may be conditional, contextual, as well as any tuft-test imagery.
9) Hucho provided quite a lot of design latitude for vehicles up to Cd 0.15.
10) below Cd 0.15, a designer is much more constrained.
11) in order to approach Cd 0.09, to Cd 0.07, a designer would be required to keep with the half-body of revolution, with no rear slope angle any steeper than 22-22.5-degrees.
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12) the body cross-section may morph longitudinally, from a half-semicircle, to more rectangular section, and back again, as long as the pressure profile is maintained. This was already demonstrated by Jaray as of 1922, Kamm, General Motors, Funderburk, etc.. Commercial/ Industrial ASHRAE, HVAC ductwork technology takes advantage of this capability, and I have nearly 6-years of firsthand experience working around it with the company's Pitot-tubes, MAGNEHELICs, anemometers, flow-hoods, U-Tube manometers, and inclined manometers
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13) 'Parking' was addressed by Fachsenfeld in the 1930s. I reproduced the technology and tested in the latter 1990s. That should be in my photos album here at the forum.
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14) As to 'testing', the 'template' is already pre-tested. It's simply off-the-shelf-technology, for 98-years now. That's the whole point to the exercise. It's a known quantity. It's not an unproven hypothesis. It can be taught as 'theory' in fluid mechanics because it's been corroborated, time and time again, worldwide
15) whatever you're modifying, the ground reflection, mirror-image criteria remains. Whether 'square' or 'round' the aft-body contour must not deviate from from Hucho's ( Julienne's, Lanchester's, Eiffel's, Jaray's, Lay's, Heald's, Aberdeen Proving Ground's, Electric Boat Division of General Dynamics Corp., Prandtl's, Reid's, Horner's, Kamm's ) l/h = 5:1 streamline half-body if you ever expect to achieve really low drag. If you have a problem with it, take it up with NASA. I'm just the messenger.
16) And as to Barnard, why the supposition that he's the sharpest knife in the drawer?
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Old 10-12-2020, 01:58 PM   #14 (permalink)
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aerodynamic testing

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Originally Posted by JulianEdgar View Post
When you can point to the aerodynamic testing you've done, and be able to compare that to your guesswork, we can have a discussion about the relative merits. Otherwise...
I did have friends photograph Spirit from a chase car, while undergoing tuft testing at 100-km/h on a local highway. Those images were published here many years ago. Those may be of interest to some.
The T-100 with aero add-ons, including the inflated boat-tail was tuft-tested and photographed by John Gilkison from a cliff-side overlooking the highway near his home in New Mexico in the early 2000s, and posted here.
The 1970 Volkswagen Transporter was my senior project at Texas Tech. The particulars of that are in my unpublished 'thesis'. 27 mpg @ 55-mph, went to up to 35-mpg @ 55-mph, only aero mods and steel radials. Ala 'Crisis Fighter Pinto.'
My dad photographed tuft-testing of the Dodge D-100 pickup project from an overpass in Lubbock, Texas back in the the late 1970s. Those photos were also published here.
In 1990, after setting a land speed record at Bonneville in 1989, I assisted Kenny Lyons in getting a scale model of his record BMW-powered motorcycle streamliner tested at Texas Tech University's College of Mechanical Engineering's scale wind tunnel. It was there and then that Pat Nixon, Graduate Student Advisor, turned me on to a recent SAE publication on flow imaging and the $1,100 ( US) smoke generator used in their lab, which complemented tuft-testing, water tunnel, and water tank testing. Smoke was the only technology which allowed visual observation of vorticity, with any ease or accuracy. I 've been 'sold' on smoke ever since.
The 1984 ITworks CRX HF set a USFRA land speed record at Bonneville in 1990. All data from the California Timing Association, official timers of the FIA. Speeds are accurate to over 5-decimal places. Fuel economy data was from 'tank' mileage. Texas, to Bonneville, to California, and back to Texas @ 55-mph. ( 430,000 mile data base recorded for this vehicle ).
The 1984 ITworks CRX HF was then fee-tested at the Chrysler Proving Grounds, East Chelsea, Michigan, by third-party technical staff of CAR and DRIVER. Data reduction supervised by Technical Editor, Csaba Csere. Top speed was verified on the 8-mile oval. Coastdown testing was conducted to SAE specifications, on a tree-lined testing grounds track dedicated for that specific purpose. Skidpad testing was conducted for free. C&D brought their own weather station with them, for continuous air density monitoring during testing.
Glen Scharf of the General Motors Aerodynamics Laboratory helped me reverse-engineer a Cd 0.235 from the Bonneville, tank mpg, and proving ground data. The CRX was designed to the 'template' specification.
'Spirit' as you know, is a work in progress. One of the racing teams at Bonneville provides an on-line calculator for top speed. With the numbers from the first DARKO outing, SPIRIT is estimated at 128-mph terminal velocity. She's returned as high as 39.9 mpg on three occasions out on the open road. We have a record of all fuel consumption for the truck since day-1, when purchased new in 1994 by John Gilkison ( aka Aero Stealth ).
The second trip provided additional data for SPIRIT, as well as 'baby' the 1/3rd-scale model of the 'template.' Cd 0.1201. At under 4-sq-ft frontal area, compared to 29-sq-ft for SPIRIT', I'm unsure if 'baby's' blockage-ratio would enter into the calculus of this 'tiny' wind tunnel.
With $144,000 worth of Honeywell load cells below the floor measuring strain, their accuracy might just eclipse something I might attempt to accomplish with shade-tree engineering practice. Especially over different days of testing.
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Old 10-12-2020, 02:08 PM   #15 (permalink)
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sorry

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I am sorry, but you don't seem to have taken anything on board from the first post in this thread.

The Template gives absolutely zero valid guidance to making modifications on cars. It is not a benchmark; it is quite irrelevant.

Read any SAE paper on the aero development of a specific car. The use of a standardised shape is never even mentioned.

Read any current textbook on car aerodynamics. Standardised, ideal shapes are given a few pages out of perhaps 500.

Seriously, in what you have written, you've quite lost the wood for the trees.
I agree. Your command of road vehicle aerodynamics could aptly be described as 'sorry.'
I recommend the family physician check that corpus collosum. I seems like inhibition of your R-Complex has been compromised, and fear of lost books sales is overcoming any vestigial critical thinking you may have possessed.
Extreme conformation bias.
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Old 10-12-2020, 02:15 PM   #16 (permalink)
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presented

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Originally Posted by JulianEdgar View Post
Not sure if you're just being naive or you haven't actually been following how The Template is often used here. There'd be little debate if The Template were presented just as a low drag shape, that is (one of) the shapes that could be used to form a vehicle being done from scratch.

But it isn't, is it?

Instead it's used to try to 'achieve' all sorts of things - from setting rear spoiler heights, to deciding whether flow is attached or separated on an existing shape, to assessing the 'purity' of existing cars - and so on.

All are garbage.

(And you shortened the quote from Barnard to better meet your argument.)
I think you'll find English tutors available in your area. They may be able to turn you onto critical thinking coaches.
Your comments and conclusions belie a superficial understanding of some of your chosen topics. It's important that you know what you're talking about.
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Old 10-12-2020, 02:55 PM   #17 (permalink)
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I think you'll find English tutors available in your area. They may be able to turn you onto critical thinking coaches.
I'd be careful. Critical race theory has corrupted critical thinking in all levels of education. It will take years to root that out. I'm not sure what to recommend as an alternative. Funk & Wagnalls - Wikipedia?
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Old 10-12-2020, 03:58 PM   #18 (permalink)
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education

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I'd be careful. Critical race theory has corrupted critical thinking in all levels of education. It will take years to root that out. I'm not sure what to recommend as an alternative. Funk & Wagnalls - Wikipedia?
Oxymoron.
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Old 10-12-2020, 04:00 PM   #19 (permalink)
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16) And as to Barnard, why the supposition that he's the sharpest knife in the drawer?
In my experience, those whose ideas can stand on their own do not have to resort to ad hominem attacks.

Barnard makes his living as a consulting aerodynamicist to automotive manufacturers, who are apparently perfectly happy to engage his expertise on their projects. He has a PhD in engineering. He was a lecturer in automotive and aerospace engineering at the University of Hertfordshire. Those credentials suggest he knows what he's talking about, yet you choose to overlook them and attack his intelligence anyway (as you have several times on this site, basically whenever any of his writings or comments are posted).

As far as English tutoring: "onto" != "on to."
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Old 10-12-2020, 04:22 PM   #20 (permalink)
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Barnard

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Originally Posted by Vman455 View Post
In my experience, those whose ideas can stand on their own do not have to resort to ad hominem attacks.

Barnard makes his living as a consulting aerodynamicist to automotive manufacturers, who are apparently perfectly happy to engage his expertise on their projects. He has a PhD in engineering. He was a lecturer in automotive and aerospace engineering at the University of Hertfordshire. Those credentials suggest he knows what he's talking about, yet you choose to overlook them and attack his intelligence anyway (as you have several times on this site, basically whenever any of his writings or comments are posted).

As far as English tutoring: "onto" != "on to."
It's not ad hominem attacks, this is just normal everyday speech conventions from Australia. Right?
It only feels like an attack when you're on the receiving end.

What's the lowest drag production automobile Bernard is associated with?
Perhaps Bernard will be better remembered for making a killing.
I'm certain that those PhDs at I.G. Farben, who succeeded in scaling up the commercial - production of Tesch und Stabenow's Zyklon-B for the Third Reich were highly credentialed.

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