Writer seeking examples of tested DIY aero mods for book

[freebeard]

I went looking for 'Epcot car' and found this from a DisneyWorld ride:


https://www.worldofwalt.com/facts-test-track-epcot.html

Cute little bug. The ride dates to 1999, i don't know about the car. But the back of the roof presages current practice by twenty years.

[JulianEdgar]

In the book's Chapter 2 on interesting aerodynamic cars from the past, I tried to feature mainly (1) production cars and (2) cars for which there was detailed technical aerodynamic development material available (eg an SAE paper).

I did add in a breakout interesting cars that often weren't production cars and/or for which there was less info available.

So I guess even with a Cd figure available for a PNGV car, I probably wouldn't have featured it. A full detailed tech paper? That would be a different story!

[JulianEdgar]

https://www.youtube.com/watch?v=piWgv60DTSY

[freebeard]

My attempt at an air curtain. I got this far, the system crashed and I never went back to it.



The outer face is flat but the air dam is compound curved to form a converging duct.

edit:
I just learned of the Bugatti Divo.



https://www.4legend.com/2018/paris-2...a-bugatti-divo

Bugatti's modeling skills are superior to mine. But the concept of the splitter upturned into a shark-fin shape open at the top is there.

[JulianEdgar]

[oldtamiyaphile]

Most cars of the same era are broadly the same shape, and most cars have huge expanses of 'fake grille'. It doesn't seem that difficult to pick up some ducting from a wrecked car, open up the grill and wheel arch liner, add some duct tape and done

OEM fog light holes can also serve as the inlet.

[Vman455]

Originally Posted by oldtamiyaphile

Most cars of the same era are broadly the same shape, and most cars have huge expanses of 'fake grille'. It doesn't seem that difficult to pick up some ducting from a wrecked car, open up the grill and wheel arch liner, add some duct tape and done

OEM fog light holes can also serve as the inlet.

I ordered air curtain ducts from a Hyundai Ioniq to do just this to my car, probably get around to it this summer.

[JulianEdgar]

Particularly important on low-drag cars that are often directionally not very stable:

https://youtu.be/p1u47xjR1aw

[freebeard]

I like the fins on your Insight. How did you adhere them to the glass?

I've always been curious about the logic behind the canted and slotted fins on the Bertone BAT


https://en.wikipedia.org/wiki/Alfa_Romeo_BAT

I thought that while in free air a car body might rotate around the Cp, the tire contact patch wants to rotate around a point ahead of the rear axle line. So there would be a hidden moment of force there. Also, you might have included mention of NASCAR roof-top fences in the subject.
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At Permalink #105 I'd asked what you thought about the magic butt trumpet exponential bell difusser.

I was searching for something else and I found a thread from 2016 where a forum member, stealth, applied CFD modeling to the question. Here's the result:

On the model that has 100mm of ground clearance, flat base, removing the inverted horn increased the drag from 5.4N to 5.9N, increase of almost 10%. The pictures shows that without the airflow that going through the horn and pushing up the wake, it allows the airflow from the top go down and push aside all of the other airflow.
....
However what's interesting is that for the 30mm ground clearance, the drag values are near identical. I think this is because of the size of the horn and the low ground clearance makes for a rapid expansion of the airflow which has similar drag level to having a solid back end.
....
It all depends on the size of the horn and the ground clearance but I think it can be used to reduce the drag if done correctly. In terms of the Cd accuracy, in terms of real world predictions, the software wouldn't be any good unless I can get some real world validation, but it's accurate and consistent for when comparing designs and their drag values.

My interpretation is that the second picture has the flat transom and the third has the bell. It appears to add order to the lower part of the wake. And with +70mm of air moving, 10% less drag.

[JulianEdgar]

Vortex generators:

https://youtu.be/uXYLCxq5YjA