Yarn test

If I go ahead and attach tufts of yarn all over the race car and get video of it at speed, what should I be looking for? 

Dead spots and active spots.  Active is where the air is flowing, that's where you can put aero, dead shows where you need to adjust your aero in order to redirect air flow.

Is the goal to get as many areas active as possible or to get air all flowing in the same direction?

loosecannon said:

If I go ahead and attach tufts of yarn all over the race car and get video of it at speed, what should I be looking for? 

What are you trying to accomplish?

Here's a pic of me using a car like mine for tuft test. Some things aren't what most people want to see. As an example the area by the fender vent opening, people want to see the yarn being blown straight back like there's a fan in the vent opening but that's not what occurs.

[URL=http://s240.photobucket.com/user/NOTATA/media/AERO/6f143724-b140-4041-afd0-9e28ebedf759_zpscvvsgdeg.jpg.html][/URL]

This pic shows the high pressure area at the base of the windshield doesn't extend far enough forward for a "Ram Air" Trans Am hood scoop to actually get a ram air effect. It gets more of a bullet effect as you can see by the yarn. And that only really occurs enough to notice in yarn movement when I opened the throttle enough to open the scoop flap. So really a "Ram Air" Trans Am scoop probably just increases drag other than providing ambient temperature intake air.

Note the turfs at the leading edge of the hood up waving "Hi!".

[URL=http://s240.photobucket.com/user/NOTATA/media/AERO/20160820_181315_zpstilrhaop.jpg.html][/URL]

There is also a liquid you can spray on a car to map airflow.

loosecannon said:

Is the goal to get as many areas active as possible or to get air all flowing in the same direction?

It depends on the area, and it depends on what your goals are for that area.  Also, sometimes tufts won't always tell you something, or you'll need a longer tuft and/or a 'suspended' one to get an idea of what's going on...

kind of like what KTR did with a FF Daytona Coupe:

Shouldn't that tuft behind the wing be kicking up?

In reply to BA5 :

yes it should. the wing is stalled and not working as intended.