Quite impressive how they managed to get .15 drag coefficient in 1939 without modern materials and wind tunnels. I wonder whether modern materials and construction techniques wouldn't allow this again while still maintaining a road legal and practical design. The fact that the Tesla S has pretty much beaten all cars in their class shows that there must be quite some room for improvement in that area. Not requiring a certain brand shape for image reasons seems to be pretty helpful.
>The fact that the Tesla S has pretty much beaten all cars in their class shows that there must be quite some room for improvement in that area.
I like your comment but this seems like a total non sequitur? Are you saying that if it's not a multiway tie for the best in something, then that implies there "must be quite some room for improvement in that area"? Or how do you get to this conclusion?
I don't want to speak for the op but the fact that the first model designed by a company that did not exist until recently is currently leading all offerings from the rest of the 100+ year old industry in drag coefficient does to me intuitively indicate that there is some room for those competitors to improve.
> [...] while still maintaining a road legal and practical design.
It had a low drag coefficient, but there wasn't much of a practical design to maintain: "the car is so tall that a stiff crosswind could send it careening to the side."
>The fact that the Tesla S has pretty much beaten all cars in their class shows that there must be quite some room for improvement in that area.
The gains made by the Tesla S are mainly due to the form factor - it is uniquely advantaged by being a large all-electric sedan.
Longer vehicles have a significant aerodynamic advantage, because they can more closely approximate a perfect airfoil than a shorter vehicle. The Tesla S has a very smooth underbody because of the flat battery unit and because it requires no exhaust system. Air intakes are kept to a minimum, because it does not need to dissipate the copious waste heat produced by a combustion engine.
I don't mean to detract from the marvellous engineering efforts by the Tesla team, but the Model S is in a class of one. Large sedans from mainstream manufacturers come very close to the aerodynamic performance of the Model S, but the use of internal combustion puts them at an inherent disadvantage. Competing all-electric cars are predominantly cheaper and shorter vehicles, designed for the European city car market. The high price of the Model S allows Tesla to use a lot of trick aero features, like the bladed mirror mountings, active inlet vents and retractible door handles.
I have no doubt that the traditional manufacturers could match the aero performance of the Model S if they were to produce a car with a similar form factor and price; The Mercedes CLA BlueEfficiency exceeds the aerodynamic performance of the Tesla S, as one of the few large and expensive cars that have been optimised primarily for efficiency. Volkswagen manage a drag coefficient of just 0.159 with the XL1, but it costs $146,000.
The XL1 is exactly the kind of thing I mean. Only because it costs 150k doesn't mean this can't be produced cheaper, especially using all electric components once batteries become cheaper thanks to mass production. From what I get, the main reason why the Tesla S doesn't look similar to the XL1 is because they wanted it to appear 'normal' so people wouldn't feel estranged by it.
The Germans were really keen on aerodynamics for surface vehicles in the 30s; trains too! Here's some video footage of the Schienenzeppelin (propeller-driven diesel train) during it's preliminary 1930 test runs:
It later set a 143mph land speed record for a petrol-powered train, although it didn't exactly catch on (in no small part due to safety concerns concerning the passenger-mincer at the back). More here:
It was designed and built in 1939 to achieve 750km/h and very likely would have if it the war hadn't interrupted its development. It had rudimentary traction control and wings that generated downforce using the ground effect!
That 750km/h design target wasn't surpassed by a wheel driven vehicle until 2001!
> The Germans were really keen on aerodynamics for surface vehicles in the 30s
For good reason; _Wages of Destruction_ covers repeatedly how concerned the German government and corporations were about how much fuel Germany needed to import, which made the country more vulnerable and exacerbated their parlous foreign-exchange/currency situation. They went to the brink repeatedly and naturally, cutting down on petroleum consumption would have been very helpful.
That is excellent. I feel like there must have been a tremendous amount of interest in air, considering air cooled VW/Porsche and BMW boxer engines at that time, and indeed through the 1990 (and beyond).
The profile reminds me a lot of the Citroen Xsara Picasso¹ (older model) but in reverse; the front fender [bumper] is very like the Ford Ka's rear² too.
Drag coeffiecients are not absolute amounts of drag created so some things that improve the coefficient may increase the drag of the total car if they increase its size. It seems to be relative to surface area rather than cross section area so longer cars have an advantage in drag coefficient.
It's not surprising that a prototype-type of car has a drag coefficient of 0.15. Does it have AC, airbags, comfortable seats, audio system, power windows, ABS, etc?
Volkswagen XL1, a production car, has a drag coefficient of 0.189.
If you look at the modern experimental cars, they have much lower drag coefficients, like Aurora 101 is 0.08.
This car would have the same problem as early Saabs that had covered front wheels: when driven in the snow, the snow thrown off of the wheels will pack in and fill the cavity around the wheels and you won't be able to turn when you need to.
"For example, the car is remarkably sleek head-on and moves through the wind almost effortlessly, but the car is so tall that a stiff crosswind could send it careening to the side."
This statement in the article is odd to me. It's no taller than many modern vehicles, nor is the frontal aspect ratio as bad as say, a SUV. It seems like the side stability has more to do with the wheel placement or suspension, or maybe weight balance.
It's a light, tail heavy car, with a shape that generates a lot of aerodynamic lift. At speed, it was probably hard to keep on the road even without a crosswind hitting it.
Because the wheels are faired, they have to be placed closer to the centerline of the vehicle. Especially the front wheels as they need to have space to turn. This makes the vehicle more susceptible to side wind tipping moment.
The Italians used a similar concept (forward control, teardrop shape) for their Fiat 600 Multipla.
Smaller and not quite as aerodynamic, but nevertheless it was shipped, and widely used as taxis which proves its versatility.
Not sure why, but I just love the teardrop concept.
No matter how flat and squared the front of the vehicle, add a taper to the rear and all's well with airflow.
Drag coefficient alone is almost meaningless for passenger cars. Aerodynamic drag is proportional to both the drag coefficient and the frontal cross-sectional area. This product (typically named CdA) is what's useful to compare.
For example, the Prius has a frontal area of about 2.3 m², giving a CdA of 0.58 m². The Schlörwagen has a frontal area of closer to 2.8 m² (thanks to its nearly 7-foot width), giving a CdA of 0.42 m². Still better, but not 40% better like Cd alone would lead one to believe. (The original Insight, for reference, has a CdA of 0.47 m².)
The wikipedia article [1] mentions the "reference area" is part of the equation to calculate Cd.
My understanding was the the Cd is taking into consideration the area in question, that's why it's a "coefficient" [2] If it's not taking into consideration the area, surely then it's not a "coefficient" of anything, it would just be "drag".
Also worth noting that a scale model of something (plane, auto, whatever) has the same Cd as the full-size version, showing that Cd does take area into consideration.
Also worth noting that a scale model of something (plane, auto, whatever) has the same Cd as the full-size version, showing that Cd does take area into consideration.
We're not disagreeing; we understand English differently. You say "Cd does take area into consideration" to mean that area has been divided out from drag measurements to produce an area-agnostic number; I say "Cd does not take area into consideration" to mean that Cd does not vary based on area (because area has been divided out).
These are the same statements. Both underscore my point that CdA, which is (by definition!) proportional to both frontal area and to drag force, is the worthwhile figure of merit for passenger vehicles (where lesser drag force translates directly into fuel savings).
Because you can't shape the car any way you want, you have to fit all these things in, while still being bound by box-like constraints (for driving on normal roads, parking, stability while turning, etc) and having to be slightly elevated to drive over bumps and small rocks.
It's pretty damn hard to build a practical and safe car with a very low drag.
Focusing on aerodynamics is important because they dominate the efficiency at high speeds but you can get pretty far without going to this extreme. For example, the Honda CR-X HF was getting over 50 MPG in the early 1980's and it was a very nice looking car, mostly because it was small, well shaped and had a small efficient engine.
The original 1.3 liter car (chassis code AE532) had an EPA Highway mileage rating of 52 miles per gallon (MPG)in 1984 and was reported to often achieve over 70 MPG in favorable driving conditions
35 comments
[ 2.8 ms ] story [ 49.2 ms ] threadI like your comment but this seems like a total non sequitur? Are you saying that if it's not a multiway tie for the best in something, then that implies there "must be quite some room for improvement in that area"? Or how do you get to this conclusion?
It had a low drag coefficient, but there wasn't much of a practical design to maintain: "the car is so tall that a stiff crosswind could send it careening to the side."
The gains made by the Tesla S are mainly due to the form factor - it is uniquely advantaged by being a large all-electric sedan.
Longer vehicles have a significant aerodynamic advantage, because they can more closely approximate a perfect airfoil than a shorter vehicle. The Tesla S has a very smooth underbody because of the flat battery unit and because it requires no exhaust system. Air intakes are kept to a minimum, because it does not need to dissipate the copious waste heat produced by a combustion engine.
I don't mean to detract from the marvellous engineering efforts by the Tesla team, but the Model S is in a class of one. Large sedans from mainstream manufacturers come very close to the aerodynamic performance of the Model S, but the use of internal combustion puts them at an inherent disadvantage. Competing all-electric cars are predominantly cheaper and shorter vehicles, designed for the European city car market. The high price of the Model S allows Tesla to use a lot of trick aero features, like the bladed mirror mountings, active inlet vents and retractible door handles.
I have no doubt that the traditional manufacturers could match the aero performance of the Model S if they were to produce a car with a similar form factor and price; The Mercedes CLA BlueEfficiency exceeds the aerodynamic performance of the Tesla S, as one of the few large and expensive cars that have been optimised primarily for efficiency. Volkswagen manage a drag coefficient of just 0.159 with the XL1, but it costs $146,000.
https://www.youtube.com/watch?v=E-ID_ktSoLY
(Part two of the video: https://www.youtube.com/watch?v=ZY7PIIV0nIs )
It later set a 143mph land speed record for a petrol-powered train, although it didn't exactly catch on (in no small part due to safety concerns concerning the passenger-mincer at the back). More here:
http://en.wikipedia.org/wiki/Schienenzeppelin
Here's another great example, the Mercedes T80: http://en.wikipedia.org/wiki/Mercedes-Benz_T80
It was designed and built in 1939 to achieve 750km/h and very likely would have if it the war hadn't interrupted its development. It had rudimentary traction control and wings that generated downforce using the ground effect!
That 750km/h design target wasn't surpassed by a wheel driven vehicle until 2001!
For good reason; _Wages of Destruction_ covers repeatedly how concerned the German government and corporations were about how much fuel Germany needed to import, which made the country more vulnerable and exacerbated their parlous foreign-exchange/currency situation. They went to the brink repeatedly and naturally, cutting down on petroleum consumption would have been very helpful.
I can't recall the source, but there are those who posit that the international spot markets mean war never need be fought over oil supply again.
1 - http://thumbs2.ebaystatic.com/d/l225/m/mWFPlYob-ONd0k2waRJ1j...
2 - http://www.theaa.com/images/allaboutcars/testreports/2005076...
https://www.youtube.com/watch?v=yGNaEDAooBI&feature=youtu.be...
http://www.webroad.ch/monotracer/
Coincidence that it is also Swiss? Are these designs somehow related?
The monotracer actually exists by the way. Quite a few have been built and sold.
Volkswagen XL1, a production car, has a drag coefficient of 0.189.
If you look at the modern experimental cars, they have much lower drag coefficients, like Aurora 101 is 0.08.
This statement in the article is odd to me. It's no taller than many modern vehicles, nor is the frontal aspect ratio as bad as say, a SUV. It seems like the side stability has more to do with the wheel placement or suspension, or maybe weight balance.
It was certainly not because it was too tall.
The Italians used a similar concept (forward control, teardrop shape) for their Fiat 600 Multipla.
Smaller and not quite as aerodynamic, but nevertheless it was shipped, and widely used as taxis which proves its versatility.
Not sure why, but I just love the teardrop concept. No matter how flat and squared the front of the vehicle, add a taper to the rear and all's well with airflow.
For example, the Prius has a frontal area of about 2.3 m², giving a CdA of 0.58 m². The Schlörwagen has a frontal area of closer to 2.8 m² (thanks to its nearly 7-foot width), giving a CdA of 0.42 m². Still better, but not 40% better like Cd alone would lead one to believe. (The original Insight, for reference, has a CdA of 0.47 m².)
The wikipedia article [1] mentions the "reference area" is part of the equation to calculate Cd.
My understanding was the the Cd is taking into consideration the area in question, that's why it's a "coefficient" [2] If it's not taking into consideration the area, surely then it's not a "coefficient" of anything, it would just be "drag".
Also worth noting that a scale model of something (plane, auto, whatever) has the same Cd as the full-size version, showing that Cd does take area into consideration.
[1] http://en.wikipedia.org/wiki/Drag_coefficient
[2] http://en.wikipedia.org/wiki/Coefficient
We're not disagreeing; we understand English differently. You say "Cd does take area into consideration" to mean that area has been divided out from drag measurements to produce an area-agnostic number; I say "Cd does not take area into consideration" to mean that Cd does not vary based on area (because area has been divided out).
These are the same statements. Both underscore my point that CdA, which is (by definition!) proportional to both frontal area and to drag force, is the worthwhile figure of merit for passenger vehicles (where lesser drag force translates directly into fuel savings).
It's pretty damn hard to build a practical and safe car with a very low drag.
The original 1.3 liter car (chassis code AE532) had an EPA Highway mileage rating of 52 miles per gallon (MPG)in 1984 and was reported to often achieve over 70 MPG in favorable driving conditions
https://en.wikipedia.org/wiki/Honda_CR-X