Let's Talk Aero

[dabossinnne]

Fascinating subject matter. Plenty of science but also the a lot of "black art" of application involved to get the most (or even anything worthwhile) out of aero additions or changes. There's a reason big-time pro race teams spend beau coup bucks on aerodynamicists, computer modeling and wind tunnel testing.

Pretty good, if very basic, race car aero 101-type stuff here from our P-car friends at Rennlist.com: https://rennlist.com/how-tos/slides...ide-to-aerodynamics-522480#lift-to-drag-ratio

 

[AJ Hartman]

I'll do a test with some ribbon and evaluate -- a teeny bit of downforce with a little more air "pulled" through the vent surely can't hurt, I suppose.

As far rearward as those louvers are, they have to be getting into the high pressure zone at the base of the windshield. I would not be surprised if they let air in. Its a toss up so a string test would be very good to do here.

 

[Big Black]

Thanks, AJ. I'll try to get some good video. Also the hood is designed with an "exit" for the scoop at the wipers. I'll look into this also and share results.

 

[ChrisM]

A few months ago I went and looked up the requirements to be an aerodynamic engineer for Ford Performance and the qualifications were...daunting...to say the least. Not that I blame them.

The undertray on my 07 is basically a square that's only as wide as the radiator. It doesn't fill in the corners or go back to the axle. What might be the effect of adding a full undertray without a corresponding splitter (not a complete underbody, just the front undertray)? And what exactly do the aero tunnels do that I see on high performance cars?

If I had to venture a guess I'd say that they may reduce drag for a higher top speed but not necessarily increase downforce? Or maybe they would, but not as well as a splitter. And I'd guess the tunnels direct air towards the brakes but also reduce turbulence from air shed into the wheel wells.

I get these random questions staring at pictures of cars...

Sorry to repost my own comment, but I was curious if anyone had any input here.

 

[Grant 302]

A few months ago I went and looked up the requirements to be an aerodynamic engineer for Ford Performance and the qualifications were...daunting...to say the least. Not that I blame them.

What were they?

What might be the effect of adding a full undertray without a corresponding splitter (not a complete underbody, just the front undertray)? And what exactly do the aero tunnels do that I see on high performance cars?

Continuing the splitter at the same level lets the level of suction drop off slower than it would with an abrupt end, assuming air intrusion from the sides. Tunnels and up-kicks can be used for various purposes. Direct air for cooling and if designed to do so, energize the incoming stream or an area downstream, smooth a transition for less drag.

The ones in front of the front wheels in that pic probably serve several functions: Brake cooling flow, additional downforce, fill the low pressure behind the front tires, energize a stream that maintains underbody low pressure. I'm sure other things I'm not thinking of...

 

[ChrisM]

What were they?

I don't recall exactly and the job listing isn't showing up anymore, but they have one for an aerodynamic engineer on the corporate website and it requires a Master's degree, a few years of experience with relevant programs, applications, and computational fluid dynamics, and they prefer a Ph.D and a whole bunch of words/programs that I don't understand.

The one I saw a bit ago had something like five years experience with the high performance auto/racing industry on top of all that. I was looking out of curiosity so I may not be remembering it correctly.

 

[Grant 302]

That sounds like other Ford jobs that I've viewed in the past. Like you would need to come from a competitor to qualify!

 

[302BOB]

I guess I need not apply............

 

[Grant 302]

Got a couple more of these for smaller point to point differential measurements and some static pressure tubes.

For the dynamic pressure, I'll just use the tube end pointed into the airstream instead of using pitot tubes.

 

[Grant 302]

As far rearward as those louvers are, they have to be getting into the high pressure zone at the base of the windshield. I would not be surprised if they let air in. Its a toss up so a string test would be very good to do here.

With the scoop from the 'black mamba' hood, I think they should normally vent. I had a hood scoop on my '00 GT for a top mount intercooler that clearly vented to the backside just in front of the cowl.

Testing on my '11 says that the hood would vent (if holes or vent present) all the way to the rear bulb seal. Removing the seal, however, does ingest air from the cowl. I have about 6" removed off the ends. They ingest a bit going straight, but vent a bit/intermittently with yaw on the outside of the turn.

 

[302BOB]

I compromise my aero by driving with my windows down. I need to hear my Boss talking to me...........

 

[Grant 302]

I compromise my aero by driving with my windows down. I need to hear my Boss talking to me...........

On a serious note, aero *should* be considered with the windows down! Or at least comparing both conditions.

 

[Big Black]

I promised to post the yarn test.

The vent as expected functioned as you might imagine, better with negative pressure in front as compared to the vent without a wicker. What was most remarkable was that after the intake of the KR hood was taped, the right (no wicker) vent stood up the yarn much more. Now, the question is how much underhood temperature increase will result from taping the intake. The other thing that I can't post is that the hood seemed much more stable after taping the intakes off. Some of that may be due to weatherstripping the seams, though. First image is the left with the wicker, right without, open intake, second is with the intake taped off, hope you can see the difference on the right, MUCH better extraction.

 

[ChrisM]

If having the intake taped off results in more air flowing out the vents, I imagine your underhood temps would go down, not up.

 

[Grant 302]

Interesting results BB. Scienced the _ _ _ _ outta it!

 

[Big Black]

If having the intake taped off results in more air flowing out the vents, I imagine your underhood temps would go down, not up.

Hoping. I'm going to figure out how to test that (wife's meat thermometer). Surely it will reduce lift and drag (good). If temp goes down, then we got all three.

 

[venom52]

@Big Black looks like we have some testing in the spring to do at hastings or RPM. Looking at the pictures you have two setups to consider. Wickers and intake blocked or just wickers and open intakes. I would be inclined to use open in the summer months and closed in the cooler months. Either way i think you'll see reduced under hood temps as well. You could also test with the fan kicking on as well.

 

[gripdriver]

How did you weather strip around the hood?

 

[Big Black]

AmeriSeal #13480 Multi Purpose Bulb Weatherstrip 3/4" W x 7/8" H x 8' L...

I did both sides of the hood, adhesive toward fender lip, and above both headlights as shown below. Used 7 1/2':

 

[Fabman]

AmeriSeal #13480 Multi Purpose Bulb Weatherstrip 3/4" W x 7/8" H x 8' L...

I did both sides of the hood, adhesive toward fender lip, and above both headlights as shown below. Used 7 1/2':
View attachment 2615

More pics please...