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

[freebeard]

Now that would depend on the spring rates. High lift might mean a fractional inch.

* Some teams have a higher threshold for risk than others.
* You could win, you could lose.

*Some times you win, and then lose it on the backup run.

[JulianEdgar]

Originally Posted by freebeard

Now that would depend on the spring rates. High lift might mean a fractional inch.

Really? Tell me of a road car that would lift on its suspension by a 'fractional inch' when subject to 50 per cent lift (the last lift figure I saw being used)?

Or is this just another 'thought experiment' where every aspect of reality can just be brushed away?

[freebeard]

Ask aerohead

*At Bonneville, for instance, cars have no suspension.

Or anyone driving a stanced Beemer. I'm stuck with stock spring rates and 3.5" road clearance.

Was 'high-volume production automobiles' inherent to the posited 'what if...'?

[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.

[JulianEdgar]

Originally Posted by Vman455

I think we're all oversimplifying in this thought experiment.

[....]

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.

In a nutshell, this is why I really dislike "thought experiments" on web discussion groups. (Not just this thread - all of them.)

Anyone - anyone at all - can come up with ideas that might possibly work. But does an idea alone have any value? I'd suggest that in the field of modifying cars, no, it doesn't.

What has value is coming up with the idea then proving (through actual testing) that it works.

Maybe I have a different perspective because, as a magazine editor, I used to get maybe one or two of these a week sent to me for my thoughts. Someone, dreamily looking into space, said "But what if we did...? Wouldn't that be great? I know, I'll send it to that bloke Julian Edgar for his thoughts." I have one in my in-box right now.

Is it a good idea? Who knows? Who cares? I don't, much. Unproven ideas are easy. I'd go so far as to say: trivial. Only two of those hundreds of ideas that I have been presented with over the last 30 years, have, to my knowledge, ever been commercially successful. And not serendipitously, both had been well tested before being presented to me.

But the real reason I dislike thought experiments is this: they spread likely falsehoods. The idea may have been a mere postulation, but soon it takes root. The idea initiator has plausible deniability ("I didn't say it was true or would work!"), but they're the one who initially promoted it. Just look at US politics for many classic examples.

Suggesting that lift is a good idea in road cars - and 99 per cent of this website is about modification of road cars - is an especially bad idea to spread... there is literally truckloads of evidence against it.

[j-c-c]

Originally Posted by JulianEdgar

In a nutshell, this is why I really dislike "thought experiments" on web discussion groups. (Not just this thread - all of them.)

Anyone - anyone at all - can come up with ideas that might possibly work. But does an idea alone have any value? I'd suggest that in the field of modifying cars, no, it doesn't..................

Nearly EVERY solution starts with an "idea", if that doesn't have a value, then stick to textbooks. Adding "alone" is only stating the obvious.

The fact "everybody" can up with an idea, is a universal motivation individually for everybody to discover the best idea, IMO.

There are many who can only generate an idea, and likely another group that can't discover an idea but can test it, no matter who does what, progress can still be made.

Your stated inability above to see this is, not in a pejorative sense, stunning.

[kach22i]

Originally Posted by AeroMcAeroFace

.....................

Partial lift has been employed by solar cars, but these cars had high front lift and low rear lift in a straight line and low front lift and high rear lift in a cross -wind. The aerodynamic and form priorities of a solar car would not easily align with the aerodynamic and form priorities of a partially lifting body car.

...........Do I think that this concept is practically applicable? Given the right conditions, priorities and restrictions yes I do. Do I think that those will ever arise? No, I don't.

It was a good question because it forces us to think and challenge dormant assumptions that lay hidden in our minds.

Originally Posted by aerohead

*At Bonneville...............

* You could win, you could lose.

One thing I learned going from scaled model experiments to full scale experiments is that the time, money and consequences also get scaled up.

Yea, I'd imagine that losing at Bonneville isn't a pleasant experience should one survive.

Originally Posted by JulianEdgar

One reason that lift causes increases drag is that more of the tyres are exposed.

Cars with high lift have both increasing Cd with speed and increasing CdA.

I don't think that has been mentioned in this thread.

Good point, not to mention the suspension is designed around certain sprung and unsprung weights that once altered could lead to mishap.

In another thread sometime ago someone mentioned the tires actually grow a bit in height as the rotational momentum stretches out the sidewalls at high revolutions. Kind of like dragster slicks that start out partially flattened and become doughnut like once the green light flashes.

Also in another recent thread someone mentioned the suspension at speed may be forced downward or upward depending on lift and or down-force, which in turn affects the CdA.

FREEBEARD, the doughnut shaped things you mention are 2 foot and not 4 foot and called tires?

You lost me buddy, please clarify for those that just woke up and the coffee hasn't kicked in yet.

[JulianEdgar]

Originally Posted by j-c-c

Nearly EVERY solution starts with an "idea", if that doesn't have a value, then stick to textbooks. Adding "alone" is only stating the obvious.

The fact "everybody" can up with an idea, is a universal motivation individually for everybody to discover the best idea, IMO.

There are many who can only generate an idea, and likely another group that can't discover an idea but can test it, no matter who does what, progress can still be made.

Your stated inability above to see this is, not in a pejorative sense, stunning.

Ah well, be stunned!

I don’t see the point - and I see a lot of negatives - in sharing ideas for which there is little / no evidence, and of which no testing has been done. Basically every conspiracy theory, for example, matches that description.

[kach22i]

Originally Posted by JulianEdgar

Really? Tell me of a road car that would lift on its suspension by a 'fractional inch' when subject to 50 per cent lift (the last lift figure I saw being used)?

Or is this just another 'thought experiment' where every aspect of reality can just be brushed away?

I'm not familiar with actual data on this, but phrases/experiences like the "steering got light" when going fast, and seat of the pants experiences going fast on a secondary highway with rolling hills feeling the car lift like a roller coaster ride is conformation enough for me.

The physics is there, the automobile will react to those forces be they F = ma in the vertical or aerodynamic.

[kach22i]

Originally Posted by j-c-c

Nearly EVERY solution starts with an "idea", if that doesn't have a value, then stick to textbooks. Adding "alone" is only stating the obvious.

The fact "everybody" can up with an idea, is a universal motivation individually for everybody to discover the best idea, IMO.

There are many who can only generate an idea, and likely another group that can't discover an idea but can test it, no matter who does what, progress can still be made.

Your stated inability above to see this is, not in a pejorative sense, stunning.

Yes, philosophy is lost on much of the modern world. Could we, should we, and how shall we get there, human will and curiosity shall lead the way.

Pessimism has it's place as does peer review.

I am always amazed by humans, one person knows one thing, another knows another and somehow progress is achieved. Like ants building a massive ant hill.