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Old 11-11-2020, 11:52 AM   #21 (permalink)
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PURE Tuning Racing Progress Auto 205 mph Land Speed Civic

Try that. Really like that car’s shape, looks straightforward to do. I’m not sure about the front, though.

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Old 11-11-2020, 01:11 PM   #22 (permalink)
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runs counter

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Originally Posted by Vman455 View Post
kachi22, I don't mean to single you out here, but at the same time this needs to be addressed: This is way too simplistic, but it's one of those "rules of thumb" that get thrown around here constantly. Drag is one of the three components of the aerodynamic force resultant that forms from pressures acting on the entire surface of a car.

As I posted about in another thread recently, a well-shaped car can have a lot of forward-facing surface area subject to negative pressure differential from atmospheric--the implications of which (that this reduces overall drag because of the contribution of thrust) appeared to go over the heads of nearly everyone who subsequently commented in the thread.

Incidentally, Julian Edgar later told me that Rob Palin, former Tesla aerodynamicist, said that lowering pressures on forward-facing surfaces by careful shaping was a key strategy for reducing drag in the development of the Model S. This runs counter to the prevailing wisdom here that beyond a certain amount of rounding--just enough to support attached flow--shaping of the front of a car has little to no effect on drag and everything important happens at the back because the prevailing wisdom is overly simplistic to the point that it is not true.
* The Model S isn't necessarily the poster child for low drag. The are a dozen ICE automobiles on the road today with as low a Cd if 'electrified.' Some lower.
* As to the forebody, and it's effect on aft-body, you may recall Hucho discussing aerodynamic 'saturation,' a situation in which, at some degree of radius, any further 'softening' results in zero gain as to drag. This was 1976. SAE Paper No. 760185, Hucho et al..
* Drag reduction is the most important aspect of road vehicle aerodynamics, which makes the aft-body the most important area of the vehicle.
* And it may seem 'simplistic', because it is 'simple,' unless you introduce 'complex' body shapes, as Bearman discusses in his July 23, 1979 paper. Or Glenn D. Thompson, Standards Development and Support Branch, U.S. E.P.A., Figure 5, Page 11, ' Prediction of Dynamometer Power Absorption to Simulate Light Duty Vehicle Road Load,' shares in his 'template' advocacy.
* One can make aerodynamics as complicated as they like, however, since 1922, there's been no need. It's a 'Paris Dressmaker' issue.
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Old 11-11-2020, 01:42 PM   #23 (permalink)
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To add, I imagine it was a key strategy because of safety standards limiting a lot of rearward streamlining. Just a hunch, seems like cars are required to have a tall and flat rear end for “visibility”. If you’re limited like that, the importance of the front section becomes more important. Similar to cycling, the focus shifts to frontal area because the rear can’t really be improved under UCI rules. I could be wrong, though.
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Old 11-11-2020, 01:44 PM   #24 (permalink)
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rear wing

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Actually, the rear wing recommendation led me to Progress Autoís 205MPH Civic.
Itís pretty much my car, with a lot of aero work and engine tuning, etc. Wonder if it could be a good reference.
If you want to open a hornet's nest, get a copy of the book, ' Modifying the AERODYNAMICS of Your Road Car, by Julian Edgar, and look at Chapter 7, page 186.
*the text discusses SAE Paper 2011-01-0175, having to do with the 2010 Audi A7 Sportback ( fastback ).
* this car has rear body flow separation, including the entire backlight, which increases both drag and rear lift.
* Audi's solution is to add a deployable rear pocket spoiler, which reaches 72.5 mm upwards to the 'template' contour to cancel the separation-induced lift, then reaches a bit further ( 30 cm ) to add 'direct downforce.'
* the 2018 Audi A7 spoiler only goes as high as the 'template.' And it's Cd 0.26, vs Cd 0.28 for the 2010 model.
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When weather permits, you might construct a cardboard and duct tape rear wing for testing, and see if the performance gain ( if there is any ) justifies the trouble to fabricate a durable version.
The Tesla X, dual-position, active rear spoiler was quietly discontinued when it was found that snow and ice would build up below the 'wing', then cause problems when it attempted to lower, and stow itself back inside the hatch.
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Old 11-11-2020, 01:52 PM   #25 (permalink)
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visibility

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To add, I imagine it was a key strategy because of safety standards limiting a lot of rearward streamlining. Just a hunch, seems like cars are required to have a tall and flat rear end for ďvisibilityĒ. If youíre limited like that, the importance of the front section becomes more important. Similar to cycling, the focus shifts to frontal area because the rear canít really be improved under UCI rules. I could be wrong, though.
Rear visibility has certainly been an issue over the decades.
When General Motors did their Aero X concept car, the key personnel involved, mentioned GM's stringent rear vision standards which limited how streamlined the backlight area could be.
Soon, the Department of Transportation in the USA may allow 'camera' vehicles, with only synthetic, high-resolution, side and rear vision technology, like Volkswagen's XL1.
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Old 11-11-2020, 01:59 PM   #26 (permalink)
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If I can find a source, will do, thank you for the info. A deployable wing...why? For parking space? I don’t see much an issue with a static wing, but around here I’d agree on the ice. I’ll be purchasing lots of coroplast for the underbody, so I’ll snag some cardboard for tests like you say.

I think I’ve building up would be fine on a fixed wing. I can take my car into my heated shop and let it melt down every now and then, so I’m not that worried about ice. I think it should work okay.

What Id like to know currently is opinions on a boat tail design. With clear Lexan, I think I can keep the visibility, but the junction between the top of the trunk and rear windshield makes me feel like this is a lipstick-on-a-pig situation. I’d like to know the shape to use to make shortest (and preferably least strange looking) boat tail that still helps to streamline the airflow. For now it’s purely conceptual, but it’s something I’d like to know.
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Old 11-11-2020, 02:06 PM   #27 (permalink)
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The Xl1 reminds me somewhat of the EV1, interesting. I personally haven’t been convinced I can trust a very technological car, which is why I’ve got a civic. I’m very mechanically-enclined. I know my mom’s flex has a rear camera, and I can’t stand it. I meant moreso visibility in terms of another person seeing your car. It seems like cars are mandated to be very visible in both front and rear.
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Old 11-11-2020, 02:12 PM   #28 (permalink)
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Quote:
Were I to make a boat-tail, I’d need to make it from Lexan to keep the lights shining through it and in view at all angles.
Were the Civic wired for trailer lights, it would be possible to add new lights in the boat tail.

For visibility you have the Military Theme thread ecomodder.com/forum/showthread.php/military-theme-fun-function-22468

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Old 11-11-2020, 02:28 PM   #29 (permalink)
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I think I’ll stick to the wing for now, until whenever my velo is done. From then on, I’ll tackle a boat tail, and nose, for there’s a lot more work involved. That’s a sweet looking machine. A hinge and piston for the top section would be coolest of cool. I think if I were to go through the steps of making a boat tail, I’d go through the steps of changing the angle of the rear windshield, so I don’t have to trail the tail out as much. The other idea is Lexan behind the current windshield, but I’m not sure how I feel of that. Good information and pictures, though, I’ll be saving these.

I’ve changed my mind on the skirts, for the rear wheels anyways. I’ll do some cardboard testing driving through snow, but I think they might work in the rear. Hinges at the top can make for easier access to clean them.
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Old 11-11-2020, 02:31 PM   #30 (permalink)
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deployable why ?

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If I can find a source, will do, thank you for the info. A deployable wing...why? For parking space? I donít see much an issue with a static wing, but around here Iíd agree on the ice. Iíll be purchasing lots of coroplast for the underbody, so Iíll snag some cardboard for tests like you say.

I think Iíve building up would be fine on a fixed wing. I can take my car into my heated shop and let it melt down every now and then, so Iím not that worried about ice. I think it should work okay.

What Id like to know currently is opinions on a boat tail design. With clear Lexan, I think I can keep the visibility, but the junction between the top of the trunk and rear windshield makes me feel like this is a lipstick-on-a-pig situation. Iíd like to know the shape to use to make shortest (and preferably least strange looking) boat tail that still helps to streamline the airflow. For now itís purely conceptual, but itís something Iíd like to know.
I believe that the actual reason has less to do with aerodynamics, and more to do with commercial car washes, which could damage a structure like Tesla produced.
Hyundai / Kia recess their car's windshield wipers for this very reason.
You'll notice also that modern cars don't have exposed radio antenna as in the past.
Vortex generators would also to subject to damage unless 'Touchless' systems were used exclusively in lieu of hand washing.
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As to the boat-tail, as far as aerodynamics, all I can recommend is the 'template' for the side elevation contour. For the sides of the car, it would be the same in plan-view, as it's highly modelled after W. A. Mair's boat-tail research. You'll have to integrate onto the existing contour, and go from there. All compound surfaces, the most difficult to fabricate. Or 'planar' surfaces, like the Chevy VOLT, maintaining all the 'character' lines original to the car. Still a complicated build.
Rear visibility efficacy will fall on your improvisation.
I drove commercial vehicles in the military , had a commercial drivers license for a couple decades after, and drove with my side mirrors, so direct rear vision issues weren't 'issues.'
If you thought you had to, you could construct flying buttresses, with a vertical backlight embedded. I've done this with my truck. It has a captured separation bubble which travels along, air flowing over as if it's solid. Plan-B.

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