Why don't vehicles have aerofoils to partially take the weight of the car?

[seifrob]

You know, from my point of view (that means thousands of miles away from you, living in different culture, not to mention language barriere, I woud say its time to close this thread.

Sometimes you are giving expert knowledge without realizing you are posting in a chat.
This forum is a think tank (expert ring) and Facebook at the same time, and that is what makes it special. It is its beauty and its awe, and we should never forget it and learn to go on.

It saves a lot of frustration.

[freebeard]

I wou[l]d say its time to close this thread.

Hold one second. I have a question open with aerohead.

And I asked a question in Julian Edgar's New Book thread that is relevant here.

Any comparison with Facebook is odious.

[JulianEdgar]

Originally Posted by freebeard

Hold one second. I have a question open with aerohead.

And I asked a question in Julian Edgar's New Book thread that is relevant here.

Any comparison with Facebook is odious.

Aerohead deliberately misinterpreted by post, by pretending that what I wrote ("As far as I am aware, there has never been a road car of any type, ever created anywhere, where aerodynamic lift was a positive.") was somehow saying that no cars had lift.

I couldn't be bothered explaining "a positive" (i.e. something good) isn't the same as "positive" (i.e. the mathematical sign opposite to negative).

So I doubt the point is worth pursuing.

I am not interested in discussing Buckminster Fuller; I've said everything I have to say on him in my aero history book.

[JulianEdgar]

Originally Posted by seifrob

You know, from my point of view (that means thousands of miles away from you, living in different culture, not to mention language barriere, I woud say its time to close this thread.

Sometimes you are giving expert knowledge without realizing you are posting in a chat.
This forum is a think tank (expert ring) and Facebook at the same time, and that is what makes it special. It is its beauty and its awe, and we should never forget it and learn to go on.

It saves a lot of frustration.

I am not sure I am correct in my understanding of what you have written, but it seems to me you are implying that since it's just a chat, forum, Facebook equivalent, it kind of doesn't matter.

Maybe it's because I am very old (and so see putting something in writing as being significant), or because I actually have spent thousands of hours modifying my cars, but I never see it that way. Surely we want the best advice possible being given to people doing the hard yards modifying their cars?

(Of course, lots of people here never get their hands dirty, so for them it's all a wonderful hypothetical, where there are no consequences of any sort for promoting bad outcomes.)

But this is called Ecomodder, and I'd prefer to think that people here are actually interested in successfully modifying their cars.

[freebeard]

I couldn't be bothered explaining "a positive" (i.e. something good) isn't the same as "positive" (i.e. the mathematical sign opposite to negative).

So I doubt the point is worth pursuing.

The question wasn't differentiating quantity and quality, it was specific to what he sees in the 1969 model. Not for you to decide.

But then, sure smother this thread with a pillow.

[JulianEdgar]

Originally Posted by freebeard

The question wasn't differentiating quantity and quality, it was specific to what he sees in the 1969 model. Not for you to decide.

But then, sure smother this thread with a pillow.

Ah yes. I forget your propensity for disappearing down rabbit burrows. All wonderful when we never actually do anything, personally, in modifying cars (at least, not that I have seen from you in the few years I have been here - maybe you did previously).

[AeroMcAeroFace]

Originally Posted by AeroMcAeroFace

Doing a bit more research yields this, https://core.ac.uk/download/pdf/195212282.pdf

Further to the above, here is a graph showing the reduced rolling resistance and also total drag.

They also quote "For safety, stability and/or economy, positive use can
be made of aerodynamic forces/moments (lift,
download, side force, yaw, roll) which are not
currently employed in Heavy Vehicle operation, and
drag control can be used for braking as well as fuel
efficiency."

While only a proof of concept it is still interesting.

[aerohead]

Originally Posted by freebeard

In what way are they counterfactuals? Esp. the 1969 Squareback. 1970 was the first year for the long nose IIRC. And that was about luggage capacity and the safety bumpers. What was different about the '69 to the '62?

1) Julian's text can be interpreted to mean that no car was ever sold which had positive lift.
2) In that context, the three vehicles listed are examples of vehicles, manufactured and sold, which had front and rear lift.
3) The two Volkswagens were tested and reported by ROAD & TRACK.
4) The Porsche 911 and Carrera data were provided by Hucho.
5) I don't have any road test data for other years of Volkswagen so I can't address the '62 model year.

[aerohead]

Originally Posted by Vman455

I think we're all oversimplifying in this thought experiment. The analyses of vehicle stability by Scibor-Rylski, Gilhaus and Hoffman, and Barnard (to pick just 3) are complicated, with lots of calculus--because they depend on understanding not just forces and moments in three directions, but the derivatives of these forces and moments with respect to angular speed of body rotation, steering angle, and tire slip angle (i.e. the problem of lift and stability cannot be brushed away with a simple, "Imbalance of lift is the issue"; there are many more variables in play). Each comes up with a slightly different set of equations and parameters; S-R calculates a "critical velocity" for stability and a "static margin" (note, this is different than the static margin used in aeronautics); G and H reference two other authors who calculated a "stability index." Barnard doesn't bother with either of these, choosing to reference other authors' work instead and summing up, "In addition to the reduction in drag that usually accompanies a reduction in lift, the favourable stability characteristics of low or negative lift provide good reasons for reducing the (positive upward) lift coefficient of vehicles."

The conclusions of these authors are similar: lower lift is better than higher; balanced lift is better than unbalanced; lower rear lift than front is preferable to the reverse.

We can sit here and debate, but I don't think we will somehow arrive at a conceptual solution better than these, especially since none of us here are even considering all the variables introduced in these sources (or, at least, I haven't seen anyone mention them in this thread). We need actual comparison of a high-lift and low-lift vehicle on the road, or the same vehicle in different configurations, to answer the initial question.

* Everyone, using the same vehicle, would at least get everyone on the same page.
* A vehicle that's been tested would be a value-added choice.
* Hucho mentioned one which travelled the world circuit of wind tunnels.
* From there, we could explore every avenue of inquiry.

[aerohead]

Originally Posted by Ecky

I skipped over a few pages in this thread, so this may have been addressed, but my ultimate questions are these:

1) Does generating lift necessarily generate drag? All else being equal? Certain you can take an aerodynamically dirty vehicle and clean up the wake in a way that creates lift and may not add drag, but that's not what I mean.

2) If creating lift *does* create drag, wouldn't it be the case that, at the speeds where this lift matters, rolling resistance is a much smaller component of total drag? At 30mph/50kph, where rolling resistance is dominant, very little lift would be generated. At 80mph/130kph, where aerodynamic drag is the vast majority of total wasted energy and rolling resistance approaches negligible, is it worth adding more aero drag to cut rolling resistance?

* If we can agree to analyze a specific vehicle, the math will answer our questions.