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Intersting Things in the Data


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After studying the data, I find myself most attracted to three columns in particular.

 

Drag(lbs.) - Lift(front) - Lift(rear)

 

Drag ranges from 342lbs. to 270lbs.

Front lift ranges from 374lbs to -154lbs

Rear lift ranges from 117lbs to -176lbs

 

Those are some pretty HUGE ranges. It looks like we really can't change drag too much but we definitely can effect lift. The good news to me is that almost nothing you did in the tunnel made the drag dramatically worse. Even by adding a decent amount of downforce, drag didn't come into play.

 

Basically, the front of the car is where we need to spend most time and the rear of the car is pretty easily addressable. VERY VERY nice work guys. I can't wait to get into more details.

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i was going through the data and began piecing together mods to apply to the car per the data that will match each other, front to back. it looks like the you can put too much downforce to the rear of the car and make the front end come up. i.e. whale tail or wing and nothing done to the front looks like it would be bad. i think more attention to the front of the car is needed and then almost anything added to the back would be a benifit. more info and testing is needed. i wonder if the west coasters can put something together on a "trial basis" ($ wise) at a tunnel and do a second set of tests. i know that the best whould be to keep the tunnel set up the same, but in an effort to save some green, just an idea.

 

jimbo

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I wouldn't even think about the side force or yaw moments. Unless you take a lot of time centering the car in the tunnel, they are worthless. We didn't spend any time on that, thinking the time was better used on something else.

 

I was pretty surprised that almost everything we did had some positive effect, some just more than others. Drag being fairly constant was also a big surprise. I thought the whaletail and wing would eat a lot of hp, but that's not the case.

 

jt

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That's what I tried to capture in the article. This series of testing was truly an eye opener, and I personally think that our efforts should next be spent on blowing smoke, and testing pressures.

 

Mike

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I must be confused. By run #6 the car was still worse off than the base line in terms of drag and lift.

 

-Joe

 

I was pretty surprised that almost everything we did had some positive effect, some just more than others. Drag being fairly constant was also a big surprise. I thought the whaletail and wing would eat a lot of hp, but that's not the case.

 

jt

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I must be confused. By run #6 the car was still worse off than the base line in terms of drag and lift.

 

-Joe

 

It looks like the 16" Panasport rims with larger tires in case 5 and 6 are responsible for most of the increase in drag up to that point. I know wheel width can add considerable drag, but maybe the higher ride height allowed more air to flow under the car too.

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It looks like the 16" Panasport rims with larger tires in case 5 and 6 are responsible for most of the increase in drag up to that point. I know wheel width can add considerable drag, but maybe the higher ride height allowed more air to flow under the car too.

 

Ding ding ding!

 

Now go down to runs 20-25 and take a peek... Frontal coverage helps those bigger tires/wheels considerably.

 

Mike

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Add negative camber to all this and my tires stick out even more into the airflow. There was a reason they added the ZG flares with the G-nose.

 

The real issue is for a daily driver/fun car and whether these mods will produce the benefits desired if the appearance changes in ways an owner has issues with.

 

Now on our club race car, that we can mod to get as slippery as hell...

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I should have been more specific with the drag comment, because I was thinking of the rear spoilers. I "expected" to see more drag from the rear spoilers, because circle track guys are always laying them down or shortening them. Several of the mods did increase drag, but they also had a positive downforce result.

 

But, each of the rear spoilers produce a lower cd than the car with nothing on the rear. This amazes me, and I haven't been able to come up with a common sense explanation.

 

jt

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I should have been more specific with the drag comment, because I was thinking of the rear spoilers. I "expected" to see more drag from the rear spoilers, because circle track guys are always laying them down or shortening them. Several of the mods did increase drag, but they also had a positive downforce result.

 

But, each of the rear spoilers produce a lower cd than the car with nothing on the rear. This amazes me, and I haven't been able to come up with a common sense explanation.

 

jt

 

Funny, on the way to work this morning I was thinking the exact same thing. How is it that an "air catcher" spoiler on the tail of the car DECREASES drag. I was looking at the backs of cars on my commute and trying to visualize how the air flows off the tail of the car. I don't quite understand this either. It must have something to do with the way the air coming off the top of the spoiler, curls and releases the trapped air from the tail panel. Kind of like peeling a suction cup off glass.

 

Based on this phenomenon, maybe we should try some small vertical spoilers to the left and right sides of the tail lights on the rear vertical edges of the quarter panels to increase the effect.

88438699-L_thumb.jpg

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But, each of the rear spoilers produce a lower cd than the car with nothing on the rear. This amazes me, and I haven't been able to come up with a common sense explanation.

This is due to the location of the wake or "pressure drag" behind the car. The spoiler deflects air upward causing some downforce and that also pushes the wake upward as well. Without the spoiler the wake is directly behind the car. With the spoiler the wake is moved further away from the body and higher up and so it can't "suck the back of the car" as well.

 

This link talks about pressure drag in aeronautics terms: http://selair.selkirk.bc.ca/aerodynamics1/drag/Page2.htm

 

There was quite a bit of discussion about changing the location of the wake and how that could reduce drag on these threads:

http://forums.hybridz.org/showthread.php?t=117165

http://forums.hybridz.org/showthread.php?t=115294

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Funny, on the way to work this morning I was thinking the exact same thing. How is it that an "air catcher" spoiler on the tail of the car DECREASES drag.

 

Im not completely sure but doesnt this have to do with how air moves over air better then metal kinda like the tailgait up or down myth? Instead of the air moving on the car it goes over the top of the higher pressure?

 

Any opinions on if the different roofline of the 2+2 would be better aerodynamically?

 

No ideas?

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