Fineness ratio vs drag coefficient

[aerohead]

Originally Posted by Vman455

I really think you've put yourself at a disadvantage working from such an old copy of the book. I have the 4th edition (1998), which isn't even the newest but is the last edition edited by Hucho.

On p. 53, under the heading 1.4 Aerodynamics and Design, Hucho writes:


You can go ahead and think that car design is all some sort of conspiracy, and that aerodynamicists have no say or are blinded somehow by corporate culture into producing shapes that have much higher drag than the lowest-drag experimental models or concept cars. But the reality is they work under constraints: people, who are motivated by cultural norms, buy cars; people buy cars for practical reasons and emotional ones; exterior design is dictated by both stylistic considerations (4 wheels, a standard-ish dimensional footprint, proportional wheels, aggressive faces, etc.) and technical ones (crash test performance, NVH, fuel economy, handling and performance, etc.).

The reason we don't have cars that look like tadpoles is simple: hardly anyone would buy one. Why? They look "abnormal." With a long tail, they won't fit in a standard garage, and if you make them small enough to do that they end up being tiny inside. They compromise packaging, interior volume, sightlines, and practicality.

Probably the best example of this so far is the original Honda Insight. That car is as close to a no-compromise car as have ever been brought to market. It had low drag and low weight. Consequently, it was a sales flop. People didn't want a two-seat car that didn't have an insane amount of power. People didn't want to pay extra for an all-aluminum body. People didn't want a tiny car with wheel skirts that looked different than every other car at their local Honda dealership.

It's stupid, yes, and buyers consistently buy impractical cars with feeble justifications--but this is not because of some conspiracy preventing their rational behavior. It's because we're irrational already.

We're seeing this start to change, as low-drag design becomes a premium feature, with cars like the Model S and 3, Taycan, and now S-class returning lower drag coefficients without significant changes to exterior design features. It remains to be seen how much lower they can go.

Cd 0.09.

[Tahoe_Hybrid]

Originally Posted by Vman455

I really think you've put yourself at a disadvantage working from such an old copy of the book. I have the 4th edition (1998), which isn't even the newest but is the last edition edited by Hucho.

On p. 53, under the heading 1.4 Aerodynamics and Design, Hucho writes:


You can go ahead and think that car design is all some sort of conspiracy, and that aerodynamicists have no say or are blinded somehow by corporate culture into producing shapes that have much higher drag than the lowest-drag experimental models or concept cars. But the reality is they work under constraints: people, who are motivated by cultural norms, buy cars; people buy cars for practical reasons and emotional ones; exterior design is dictated by both stylistic considerations (4 wheels, a standard-ish dimensional footprint, proportional wheels, aggressive faces, etc.) and technical ones (crash test performance, NVH, fuel economy, handling and performance, etc.).

The reason we don't have cars that look like tadpoles is simple: hardly anyone would buy one. Why? They look "abnormal." With a long tail, they won't fit in a standard garage, and if you make them small enough to do that they end up being tiny inside. They compromise packaging, interior volume, sightlines, and practicality.

Probably the best example of this so far is the original Honda Insight. That car is as close to a no-compromise car as have ever been brought to market. It had low drag and low weight. Consequently, it was a sales flop. People didn't want a two-seat car that didn't have an insane amount of power. People didn't want to pay extra for an all-aluminum body. People didn't want a tiny car with wheel skirts that looked different than every other car at their local Honda dealership.

It's stupid, yes, and buyers consistently buy impractical cars with feeble justifications--but this is not because of some conspiracy preventing their rational behavior. It's because we're irrational already.

We're seeing this start to change, as low-drag design becomes a premium feature, with cars like the Model S and 3, Taycan, and now S-class returning lower drag coefficients without significant changes to exterior design features. It remains to be seen how much lower they can go.

it's cooling system limitations as well ICE requires a bigger cooling system then a EV

[Vman455]

Originally Posted by aerohead

Cd 0.09.

Will never happen in a production car. Hucho doesn't think so, either--I asked him, and he wrote, "Now, more than 40 years later, cD = 0.20 seems to be possible for cars manufactured in large volume. And that’s it."

You can go on wishing for unicorns to become real. Or...you can be happy we have horses and look for the best horse possible.

[Tahoe_Hybrid]

Originally Posted by Vman455

I really think you've put yourself at a disadvantage working from such an old copy of the book. I have the 4th edition (1998), which isn't even the newest but is the last edition edited by Hucho.

On p. 53, under the heading 1.4 Aerodynamics and Design, Hucho writes:


You can go ahead and think that car design is all some sort of conspiracy, and that aerodynamicists have no say or are blinded somehow by corporate culture into producing shapes that have much higher drag than the lowest-drag experimental models or concept cars. But the reality is they work under constraints: people, who are motivated by cultural norms, buy cars; people buy cars for practical reasons and emotional ones; exterior design is dictated by both stylistic considerations (4 wheels, a standard-ish dimensional footprint, proportional wheels, aggressive faces, etc.) and technical ones (crash test performance, NVH, fuel economy, handling and performance, etc.).

The reason we don't have cars that look like tadpoles is simple: hardly anyone would buy one. Why? They look "abnormal." With a long tail, they won't fit in a standard garage, and if you make them small enough to do that they end up being tiny inside. They compromise packaging, interior volume, sightlines, and practicality.

Probably the best example of this so far is the original Honda Insight. That car is as close to a no-compromise car as have ever been brought to market. It had low drag and low weight. Consequently, it was a sales flop. People didn't want a two-seat car that didn't have an insane amount of power. People didn't want to pay extra for an all-aluminum body. People didn't want a tiny car with wheel skirts that looked different than every other car at their local Honda dealership.

It's stupid, yes, and buyers consistently buy impractical cars with feeble justifications--but this is not because of some conspiracy preventing their rational behavior. It's because we're irrational already.

We're seeing this start to change, as low-drag design becomes a premium feature, with cars like the Model S and 3, Taycan, and now S-class returning lower drag coefficients without significant changes to exterior design features. It remains to be seen how much lower they can go.

the average car is 185inches long(i.e 2020 civic, corolla ) you can fit a Chevy suburban 225" in the average garage

[ksa8907]

Originally Posted by Vman455

Will never happen in a production car. Hucho doesn't think so, either--I asked him, and he wrote, "Now, more than 40 years later, cD = 0.20 seems to be possible for cars manufactured in large volume. And that’s it."

You can go on wishing for unicorns to become real. Or...you can be happy we have horses and look for the best horse possible.

I've skipped through a lot of this thread but I 100% agree with the above. "The juice has to be worth the squeeze."

At some point it is not worth the small increase in efficiency to lose comfort, capability, style, safety, etc.

[JulianEdgar]

The law of diminishing returns is obvious.

Someone asked me the other day what aero drag improvements I would recommend on a Tesla Model S.

I said: "None that I'd be confident with."

That was in the context of Rab Palin (Tesla aerodynamicist on the Model S) telling me he'd been having discussions with an aftermarket company developing Tesla Model S bits to - purportedly - reduce drag. Ones he said, that would not do so.

And hell, who would better know than he?

But still leaves us many billions of vehicles where it's easy to reduce drag (and/or lift)...

[skyking]

Your'e obsessed with posting about lift. Is it because you've got the instrumentation to measure it?
In the realm of economic driving, the destabilizing effects lift are not an issue. Neither is adding downforce.
What we care about here is drag. We do indeed measure it with adding mods, then doing tuft testing, A-B-A testing, coast down tests. Long term gathering of data over the same ground, day after day.
We don't have many million dollar wind tunnels.
In the speed ranges in question, measuring lift is a roundabout way of measuring a component of drag. It is by no means the source of all drag. Not even close.
I suggest you climb down off your well beaten dead high horse and try participating in a civil manner.
You have a great deal to add here. Try adding it and not contesting every other thing you see.

[JulianEdgar]

Originally Posted by skyking

Your'e obsessed with posting about lift. Is it because you've got the instrumentation to measure it?

I can measure changes in drag and panel pressures too, and I often write about those as well.

In the realm of economic driving, the destabilizing effects lift are not an issue. Neither is adding downforce.

Unless you never exceed 80 km/h, not true.

What we care about here is drag. We do indeed measure it with adding mods, then doing tuft testing, A-B-A testing, coast down tests. Long term gathering of data over the same ground, day after day.

Well, any coast down testing that you can perform on a normal road is quite invalid - it's one of the things that Aerohead states here that is right. I am not sure what your point is with your other tests - they're great!

We don't have many million dollar wind tunnels.

Neither do I - I am not sure of your point.

In the speed ranges in question, measuring lift is a roundabout way of measuring a component of drag.

That does not appear to be the case. An example is the Porsche Taycan that has lower drag at higher lift (ie spoiler down).

It is by no means the source of all drag. Not even close.

I've never suggested that is the case

I suggest you climb down off your well beaten dead high horse and try participating in a civil manner.

Well, the 'civil manner' of the group has allowed complete misconceptions and erroneous advice about car aerodynamics to flourish for a long time. Might be a bit better if BS is called out and not brushed under the carpet.

You have a great deal to add here. Try adding it and not contesting every other thing you see.

I contest only misconceptions, errors and misleading advice. Unfortunately, there is a lot of it.

[freebeard]

I contest only misconceptions, errors and misleading advice. Unfortunately, there is a lot of it.

We learned in the sixties and forgot this again: To fight is to feed it. Counter bad speech with good speech.

Propose a template framework for a first approximation across a range of use cases for airflow management.

Something like Morelli's Urban Car.

[JulianEdgar]

Originally Posted by freebeard

Propose a template framework for a first approximation across a range of use cases for airflow management.

Something like Morelli's Urban Car.

Why? For car modification, I think it is the completely wrong approach.