Interesting Aerodynamic Cars (Mike Vetter's ETV, also Avion)

[kach22i]

As usual I've been drawing up one version or another of an aerodynamic car, been attempting to avoid using a custom very curved windshield and yet still have a teardrop shaped glass canopy. My fear is this would make for some acute angles that air might have a hard time staying attached to, plus might look funny at certain angles.

Unfortunately, the car below confirms the front 3/4 view is most odd, but is it lack of curved (Stratos Lancia style) windshield, or is it just all the other quirkiness?

Hispano Suiza Carmen Boulogne 2021
https://mobile.twitter.com/hispanosuizacar




I guess it's not so bad, kind of Daytona Prototype first generation with that too vertical side glass..

EDIT:

https://hum3d.com/blueprints/hispano...019-blueprint/

[Piotrsko]

Afaik, curved windshields arent necessary if you do the edge treatments on the A pillar correctly

[aerohead]

* a set of blueprints would help, especially in plan-view.
* in the favorable pressure gradient of the A-pillars, flow attachment there could be a walk in the park, as Piotrsko mentioned.
* changing the T-100's windshield to that of the Dodge Viper only gained Spirit delta- Cd 0.005.
* As Hucho says, once flow is saturated, no further rounding makes any difference.
* The 'big-booty' on the Hispano would counteract some of the benefit of the greenhouse's plan-taper.
* For instance, the 2021 Maserati MC20, @ Cd 0.38, might have been Cd 0.319, according to Elliott G. Reid's plan-taper research at Stanford University. That would be McLAREN F1 Longtail territory, really good for a supercar.
* And speaking of, if McLAREN ever publishes a Cd for their Speedtail, it would be insightful. It also suffers the wide rear, compared to the greenhouse.
PS In 1986, Hucho mentioned the high cost of compound shapes, 'enjoyed' by the air. A windshield for LeMans GP car was $ 10,000 at the time.

[kach22i]

Originally Posted by Piotrsko

Afaik, curved windshields arent necessary if you do the edge treatments on the A pillar correctly

The mathematical formula Aerohead posted about a decade ago in a VW van thread involved knowing the "frontal area" but did not account for any rake angle.

As I recall per discussions regarding radius corners on truck boxes (think U-Haul cargo van) 100mm or about 4" was the diminishing returns radius (see chart in link below.)

https://ecomodder.com/forum/showthre...o-38795-3.html


It makes sense that a large vehicle sees benefit with 4" leading edge radius when smaller areas on car windshields are half that on the lowest of CD cars on the market. I mean just look how boxy looking a Prius is.

NOTE: While going between hand sketches and AutoCad I've been using the "draw ellipse" command for front bow/bumper and windshield top/bottom.

[kach22i]

Originally Posted by aerohead

1. * a set of blueprints would help, especially in plan-view................

2. * in the favorable pressure gradient of the A-pillars, flow attachment there could be a walk in the park, as Piotrsko mentioned..............

3. * changing the T-100's windshield to that of the Dodge Viper only gained Spirit delta- Cd 0.005..........

1. Updated the post

2. Understood

3. Thanks, I didn't know that. Great choice, maybe a bit wide for my design exercise, right now using a Mini Cooper Coupe (the 2-seater) windshield after looking at a couple of dozen cars. My struggle seem to lay in not the curve so much as that I wanted a more vertical rake than most modern cars have.

[freebeard]

The Hispano Suiza Carmen Boulogne windshield is recessed an inch or more at the A-pillar.

My 1958 VW convertible had a flat, upright windshield that was recessed maybe a quarter of an inch. The snow would build up and overpower the admittedly wimpy wipers.

Consider the three-piece windshield. My Clark Cortez had that.


https://i.ebayimg.com/00/s/MTIwMFgxNjAw/z/2w4AAOSw8vRhFKd6/$_1.JPG

[aerohead]

*From SAE Paper 860212, FIAT found, that for a test model very similar to the 1st-gen Golf / Rabbit, that airflow attachment saturated with a 40mm body edge radius.
* Starting with all hard edges, and going to all upper body edge softening, the drag dropped from Cd 0.4858, to Cd 0.313, a 35.5% delta Cd.
* Also, between a squareback, notchback, and fastback, the fastback body type was the most sensitive to tumblehome angle, which varied by 3.53% delta-Cd, between zero-and 35-degrees.

[aerohead]

* Hucho gets into this in his chapter on drag optimization. I left the book in the car and don't have that with me.
* As with all the body areas addressed, windshield inclination also indicates for 'saturation' at a particular angle.
* Light refraction is also part of the calculus. At some specific glass angle, the outward vision becomes a 'county fair, house-of-mirrors, optical fantasmagoria', and a danger ( the 1981 VW ARVW research vehicle was reported by one auto journalist who drove the car, to possess such vision difficulties that he struggled to drive it ).
* In the 1980s, Mitsubishi constructed a 'future car' of which, in autonomous mode, the front seats fully reclined, driver napped, while the roof fully lowered into the body, to cut drag.

[freebeard]

* Light refraction is also part of the calculus.

I would include being able to reach the glass, for cleaning it if nothing else.

3/4 tonneau, helmet and goggles.

[kach22i]

40mm is just over 1-1/2 radius, that's really small.

I don't think my 1986 Diesel Golf had rain gutters, which may act as Gurney spoilers on some cars I would guess.

Aside: Read a few days ago that the AMC Pacer was one of first cab-forward and rain gutter-less cars, and originally designed for a Wankel engine.

My wife has a 2015 Prius, her mom a 2017 Prius, either for light refraction or ease of entry the newer car has less slope to the windshield which accounts for a longer post high point travel length.