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Old 06-03-2017, 01:07 PM   #11 (permalink)
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40-mpg

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Originally Posted by GKRenegade View Post
I'm wanting to get as close to 40 mpg as possible. I am currently at 26 mpg for my first tank. Not sure what I should do to the belles Pam besides just run a custom sized full sheet of diamond plate under it.
*for talking points,let's say she turned out averaging 26-mpg.
*to get to 40-mpg with strictly aero would require an 89.6% drag reduction,ending up with Cd 0.0362 (if you were starting with around Cd 0.35).
*Cd 0.10 would be considered the lower limit for a road car and it would have to be electric,with no openings in the body.
*basjoos is looking at Cd 0.17 with his AeroCivic.If you haven't seen it yet,check it out.It'll give an idea what 0.17 would require.

*to go below you'd want to look at something like CUER

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Old 06-05-2017, 02:56 AM   #12 (permalink)
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Seems the renegade has recessed headlights and grill. If I put thin clear plastic to smooth it all out, that should help quite a bit with drag yes? If I did that with each recessed item and light on the front, it would have next to no drag especially if I were to silicone all edges. Any thoughts? And I did look under the jeep. No belly pan of any kind. But looks like I can find mounting points. Any reason I shouldn't just wall up the entire underside? Do I need to leave any gaps?
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Old 06-05-2017, 08:53 AM   #13 (permalink)
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May I suggest doing a forum search on belly pans, I think there are several threads showing different methods and materials.
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Old 06-05-2017, 10:01 AM   #14 (permalink)
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Quote:
Originally Posted by GKRenegade View Post
Seems the renegade has recessed headlights and grill. If I put thin clear plastic to smooth it all out, that should help quite a bit with drag yes? If I did that with each recessed item and light on the front, it would have next to no drag especially if I were to silicone all edges. Any thoughts? And I did look under the jeep. No belly pan of any kind. But looks like I can find mounting points. Any reason I shouldn't just wall up the entire underside? Do I need to leave any gaps?
The front of the vehicle is nearly irrelevant, relatively speaking, when compared with the rear. Drag comes mostly from turbulence in your wake.



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Old 06-05-2017, 10:36 AM   #15 (permalink)
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Quote:
Originally Posted by GKRenegade View Post
Seems the renegade has recessed headlights and grill. If I put thin clear plastic to smooth it all out, that should help quite a bit with drag yes? If I did that with each recessed item and light on the front, it would have next to no drag especially if I were to silicone all edges.
The general consensus is that stopped cavities on the nose of the vehicle are more or less null, aerodynamically speaking. The nose of the vehicle "piles up" a sort of stagnant nosecone of air in front of it; headlight buckets, having no flow through them, don't really change how that nosecone of pressure behaves. That's kind of the idea behind grille blocks; closing off more of the nose creates a more cohesive high pressure zone in front of the car that helps guide more air smoothly over the rest.

I think I understood that right. Anyway, the point is that your bigger gains are going to be found somewhere besides the nose. At least at first. If you make the rest of the vehicle very aerodynamic, attention paid to smoothing out the flow at the nose pays off greater dividends as the air moves aft.

That doesn't mean there are no gains to be had from doing what you're talking about, it's just that the results will be small, possibly invisible signals against the noise of everything else.

As to the belly pan, I would make sure that it was NOT a seamless unit from front to back. The engine bay has to have openings from which to shed its hot air for proper cooling. You will need to satisfy yourself on that score as to whether it's open enough for cooling.

If you're concerned about the material you use melting, look at some of the belly pans that have already been written up in this forum. In some cases coroplast (corrugated plastic) even covers the exhaust system areas without harm (though I wouldn't put it there myself). And in any case, coroplast will be lighter so that's probably your better choice wherever you can choose it instead of some other, heavier material.

MSDS for Coroplast: http://www.coroplast.com/pdf/Coropla...2020140505.pdf

This calls out its melting temperature at 324F, not sure at what temp it starts to become soft but with sufficient support and restraint, it may not be an issue.
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Old 06-05-2017, 04:50 PM   #16 (permalink)
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Two things. First, definitely leave a hole in the belly pan for engine air to escape. I have mine starting at the back edge of the radiator, extending back about 12-18 inches, and the opening is 18-24 inches wide. I do not have a full pan, just the beginning of one under the front. In our desert heat, there is a ton of air that is being pushed and pulled into the engine bay through the radiator and AC condenser coils. All that air needs an easy escape route.

Second, one of the major sources of "drag" is the AC compressor. I lose 1-2 mpg in the summer because of this. Just keep it in mind when looking at your numbers and where you want to get to...since not using it is not an option (in my opinion). Good luck! :-)
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Old 06-10-2017, 12:42 PM   #17 (permalink)
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grille

Quote:
Originally Posted by GKRenegade View Post
Seems the renegade has recessed headlights and grill. If I put thin clear plastic to smooth it all out, that should help quite a bit with drag yes? If I did that with each recessed item and light on the front, it would have next to no drag especially if I were to silicone all edges. Any thoughts? And I did look under the jeep. No belly pan of any kind. But looks like I can find mounting points. Any reason I shouldn't just wall up the entire underside? Do I need to leave any gaps?
The nose of your JEEP constitutes less than 6% of it's overall drag.

And even though the grille is recessed,all the radii around are generous enough to provide fully-attached flow there.It takes very little to be effective

Your problem is the horrific wake

You need some sort of boat-tailing to tame that drag.It's the only thing known to work in 95-years of research.
It could be something like in the lower image,a box cavity combined with extra cargo storage

This is the goose that lays the golden eggs.
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Old 06-11-2017, 08:47 AM   #18 (permalink)
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So in trying to look at what I could do for a boat tail or kam back, I'm getting kinda lost. I really don't want to take away from the functionality of the renegade's hatchback and curved rear window. I was thinking, what if I did side skirts to essentially lower the car without actually lowering it? Like what the 18 wheelers have under them? And I thought there used to be some sort of overlay for the boat tail diagram to see what to do to your car? Would anyone with more knowledge be able to help me design a partial kam back or boat tail?
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Old 06-11-2017, 10:45 AM   #19 (permalink)
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Quote:
Originally Posted by GKRenegade View Post
So in trying to look at what I could do for a boat tail or kam back, I'm getting kinda lost. I really don't want to take away from the functionality of the renegade's hatchback and curved rear window. I was thinking, what if I did side skirts to essentially lower the car without actually lowering it? Like what the 18 wheelers have under them? And I thought there used to be some sort of overlay for the boat tail diagram to see what to do to your car? Would anyone with more knowledge be able to help me design a partial kam back or boat tail?
Side skirts are proven to work, as are front air dams, belly pans, rear wheel skirts and smooth wheel covers.

I see a lot of these on the roads around here:

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Old 06-11-2017, 12:42 PM   #20 (permalink)
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Quote:
I really don't want to take away from the functionality of the renegade's hatchback and curved rear window... Would anyone with more knowledge be able to help me design a partial kam back or boat tail?

http://www.jeepspecs.info/2015-jeep-renegade-sport-4dr-fwd-specifications-features-full-floor-console/

Nor do you want to reduce the functionality of the taillights. The overhang above the rear window pretty much is a Kamm-back. A full boat tail would be the length of the vehicle's wheelbase. I see these possibilities;
•Single-wheel boat tail trailer

Reddit has a little freakout over Bam Zip Pow's aero pickup & boat tail trailer
•retractable boat tail


•box cavity

•perforated base plate

Morelli's 'Fluid Tail'

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