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Old 06-22-2021, 06:58 PM   #11 (permalink)
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I can see how they could test the front spoiler easily. But, were the five data points modifications to a complete test shell? Full scale?

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Old 06-22-2021, 07:04 PM   #12 (permalink)
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I can see how they could test the front spoiler easily. But, were the five data points modifications to a complete test shell? Full scale?
Yes, they were testing full scale with the cars made from polystyrene and having interchangeable bits.
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Old 06-22-2021, 07:45 PM   #13 (permalink)
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Thanks.

It always bothers me when they reduce a compound curved surface to a single angle. You can do a lot with three or four points on a Spline Curve.

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In the computer science subfields of computer-aided design and computer graphics, the term spline more frequently refers to a piecewise polynomial (parametric) curve. Splines are popular curves in these subfields because of the simplicity of their construction, their ease and accuracy of evaluation, and their capacity to approximate complex shapes through curve fitting and interactive curve design.

The term spline comes from the flexible spline devices used by shipbuilders and draftsmen to draw smooth shapes.
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Old 06-23-2021, 01:01 PM   #14 (permalink)
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'smaller'

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Originally Posted by JulianEdgar View Post
I am going to post some aero cars - not every day, as the thread name implies, but whenever I feel like it. (Unlike the Random Aero Cars thread, I will always try to provide some measured data.)

All the cars are covered in my book - A Century Of Car Aerodynamics (link below).

Today's car - the 1983 Fiat Uno.



The Uno was a low-cost car made in huge numbers over 8 million were built. Most interesting from an aerodynamics perspective, it was a small hatch. The smaller the car, the harder it is to achieve a low Cd. And since a hatch will always have a large wake, with that shape we have another aerodynamic negative. But Fiat took great care to optimise the aerodynamics especially drag at a time when few manufacturers were bothering much about the aerodynamics of their cheapest cars.

Cd was 0.34 (standard car), 0.33 (economy special) and 0.30 (Turbo). Lift figures were also good - and across the whole range of yaw angles.

One might want to provide some context with respect to a qualifying adjective as 'smaller'.
We know from verisimilitude that there exists no prohibition from 'shrinking' the proportions of a very low drag vehicle, creating a 'smaller' vehicle of identical Cd.
An example would be Morelli, who took a small, 1976 FIAT of Cd 0.44, and turned it into Cd 0.23.
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Old 06-23-2021, 04:21 PM   #15 (permalink)
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One might want to provide some context with respect to a qualifying adjective as 'smaller'.
We know from verisimilitude that there exists no prohibition from 'shrinking' the proportions of a very low drag vehicle, creating a 'smaller' vehicle of identical Cd.
An example would be Morelli, who took a small, 1976 FIAT of Cd 0.44, and turned it into Cd 0.23.
Most people understand what a smaller car is. I don't know of any smaller production car that looks exactly like a big one but is just shrunk proportionally in all directions.
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Old 06-23-2021, 04:52 PM   #16 (permalink)
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1975 Porsche 924



Aerodynamic development of the 924 began using one-fifth scale models that were tested in Paris Laboratoires Eiffel. The results gained from these tests were then applied to full-size prototype that was optimised in the Volkswagen wind tunnel.

With the headlights retracted, the Cd was 0.36. With headlights up, it increased to 0.38. Projected frontal area was 1.76m2, giving a CDA of 0.634m2 with the headlights down, and 0.669m2 with the lights raised.
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Old 06-23-2021, 05:19 PM   #17 (permalink)
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I don't know of........

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Most people understand what a smaller car is. I don't know of any smaller production car that looks exactly like a big one but is just shrunk proportionally in all directions.
That's not even germane to the topic.
If you're going to make a simplistic, overgeneralized comment about 'small', then It's my opinion that you haven't properly served the reader.
The 1987 Renault Vesta-II remains one of the lowest drag 'cars' ever created, in spite of it's 139-inch overall length.
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Old 06-23-2021, 05:28 PM   #18 (permalink)
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Is there enough data to make the 924 the next car of the week?
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Most people understand what a smaller car is.
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History - Another look at the Cord 810 | Page 2 | The H.A.M.B.
https://www.jalopyjournal.com/forum/....772659/page-2
Pray went on to make some very highly regarded Auburn Speedster replicas, while the company he started managed to make about 100 Cord 8/10″ cars, as they were branded, reflecting the fact that they were 8/10th scale replicas of the original Cords.
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Old 06-23-2021, 11:17 PM   #19 (permalink)
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Very interesting ad for the 924:

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Old 06-24-2021, 03:25 AM   #20 (permalink)
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Re the above ad. It's interesting on a bunch of levels.

1. It gives the power to propel the car at 55 mph - 15hp.

2. It gives the lift forces at front and rear at 100 mph - 46 and 105(!)lbs, respectively.

3. From the above, and knowing the projected frontal area, we can work out the front and rear lift coefficients, and so work out lift forces at all speeds.

4. It states that the lateral centre of pressure is behind the centre of gravity, so we know it has decent straightline stability

5. It shows the centreline surface body pressure measurements, including in the wake (but not, unfortunately, under the car) so we can see how much of the upper surface of the car is experiencing low pressure (ie lift - see #2 above.)

Good ad!

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