Fineness ratio vs drag coefficient

[aerohead]

Originally Posted by Grant-53

The 5th edition does not list fineness in the index but does discuss d/l ratio. Since an automobile is not a body of rotation tapered to a point this is more applicable to aircraft. Compound curved panels are more costly to stamp than flat panels generally speaking. My interest is chiefly in body shells for commuter bicycles. Drag and stability are issues to be addressed.

*The inverse is the fineness ratio for the mirror image, what the air always
'sees'
* The convention is to take half, as a half-body,and loft up to whatever ground clearance is chosen.
* For bicycle stability, aeronautical engineer, Al Voight chose a trike for his Vector, which HUFFY purchased and sold for $10,000/ pop. Cd 0.11 was claimed.

[aerohead]

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.

Hucho published that Cd 0.09 was technically feasible as of 1986. What a carmaker builds depends upon the technical specification of the committee which has oversight and authority over such decisions.
You may be entirely correct in what is decided, however it would not be driven by aerodynamic considerations. Those are for a different thread.

[aerohead]

Originally Posted by Tahoe_Hybrid

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

There are vehicles on the roads today in the USA, of 260" length. 'Extensible' tails as depicted by Fachsenfeld in the 1930s would enable 'parking'.

[aerohead]

Originally Posted by 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)...

After more name dropping you succeeded in providing us absolutely zero actionable information. Really appreciate it.

[aerohead]

Originally Posted by JulianEdgar

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



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



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!



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



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



I've never suggested that is the case



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.



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

Julian, do you know if the only difference between the Taycan Turbo, and Turbo S is the flip-up spoiler? Is there any other feature, like narrower tires in the equation? Thanks in advance!

[JulianEdgar]

Originally Posted by Grant-53

What makes it rigid? I've had 4 mm coroplast deflect from wind pressure at the front.

It had foam stiffeners inside, and of course the trike frame helped support it.

Most of the forces, except for a tiny area of the nose, would be outwards.

[JulianEdgar]

Originally Posted by aerohead

Julian, do you know if the only difference between the Taycan Turbo, and Turbo S is the flip-up spoiler? Is there any other feature, like narrower tires in the equation? Thanks in advance!

The graph in the paper Dr Wolf sent me is for the same car (Taycan Turbo), with the spoiler in up and down positions. Lowest drag occurs with the rear spoiler down, giving highest rear lift.

[JulianEdgar]

Originally Posted by aerohead

After more name dropping you succeeded in providing us absolutely zero actionable information. Really appreciate it.

Well I for one really appreciate hearing from the professionals actually working on cars - especially ones like the Tesla. Since Rob has now left Tesla, and is very frank in his communications, I thought it quite interesting that he could see no easy aftermarket way of lowering the Model S drag.

As I said, the law of diminishing returns is starting to apply with these cars.

[aerohead]

Originally Posted by JulianEdgar

The graph in the paper Dr Wolf sent me is for the same car (Taycan Turbo), with the spoiler in up and down positions. Lowest drag occurs with the rear spoiler down, giving highest rear lift.

That makes sense. While perhaps the best contour ( excepting racing cars ) the Taycan's is still a little too aggressive. Like Panamera, Cayman, etc..

[aerohead]

Originally Posted by JulianEdgar

Well I for one really appreciate hearing from the professionals actually working on cars - especially ones like the Tesla. Since Rob has now left Tesla, and is very frank in his communications, I thought it quite interesting that he could see no easy aftermarket way of lowering the Model S drag.

As I said, the law of diminishing returns is starting to apply with these cars.

Easy would be a slip-in, receiver-hitch, truncated boat-tail. Cd 0.18 would be a breeze.
A gap-filled, full-boat-tail trailer could take it to Cd 0.12, with extra batteries to boot! You'd be getting better mpg with the trailer , than without.