Zulu's Build Thread (Honda CR-Z)

[AeroMcAeroFace]

Looks like it is working really well with good attached flow on the topside bits but not great attachment on the part by the brake light, but then it reattaches before the end so I would guess at that being a positive.

There is an audi a2 study using a box cavity and they found that the best diffuser varied based on the box cavity. https://www.a2oc.net/community/index...642#post165642

I don't see people doing things like this nearly enough anymore

Completely agree.

[aerohead]

https://ecomodder.com/forum/member-a...ing-effect.jpgHere's a $425,000 box cavity. https://ecomodder.com/forum/member-a...ion-plates.jpg
All the trailing edges are positioned where the trailing edges of an ideal boat-tail would be.
Between the separation line and the trailing edges, vortices are captured within the confines of the intentional void.
Outer flow follows over the outer 'surface' of the vortex, creating a virtual boat-tailed 'surface' of this 'dead' pool of air, on top and sides. ( the bottom is ruined because of the rear wheel turbulence and DOT bumper.
In order for the vortices to be captured, the rear edges of the cavity must be located at the 'streamlined' position.
* Your top is fine, it's a flush continuation and extension of the profile.
* The bottom seem okay as well.
* The sides however, seem too far inset to allow for vortex capture, producing unstructured turbulence instead.
I've added W.A. Mair's boat tail. It's outer contour would illustrate where 'edges' should be positioned.

[California98Civic]

If you do a rear diffuser, you should re-test. A really good comprehensive study of box cavities I saw, found that the cavity intereacted a lot with the diffuser. You'll want to tune the combination.

[CigaR007]

Thought I would share some updates on my CR-Z.

I made the fibreglass grille block more permanent by securing it onto the bumper with screws. I also added two electrical plugs to accommodate the engine block heater and the intelligent battery charger/maintainer. Makes it look more OEM/Stealthy.






Following Bernoulli's principle, I made a somewhat air-tight duct leading to the radiator. So far, it seems to help, as the coolant temperature is stable at cruising speeds (95C or 203F).



I opted to install a basic 8" android tablet for displaying various gauges through an OBD2 Bluetooth dongle (ELM327). My Scangauge II is still going strong, but it has limited displaying capabilities.



With the tablet, I can view up to 10 gauges simultaneously compared to 4 with the scangauge. The android app is called InfoCar. I also bought Torque Pro, but I don't really like the interface. I might revisit it later though.



The downside with android apps is that I don't have access to the specific x-gauges from Scangauge, especially pertaining to the hybrid system. I can add custom PIDs, but converting the x-gauge codes to PIDs is very difficult.

I will be building a partial boat tail or a kammback tail. To help with the process, I recently installed a hitch receiver. It will serve as the mounting base for the structure.







Below is a "napkin" sketch of my vision...haha.





User Cd was kind enough to do these two sketches to help me further visualize the project.





The plan is to make it OEM-looking and removable. It will follow the car's existing curves and aerodynamic design cues. Wheel skirts and rear diffuser will also be added afterwards.

I am currently trying to decide what material to use as the base for the structure. Maybe some aluminium strips to form some sort of brace. The structure will be made of carved foam to attain the best shape prior to the fibreglass layer. The first stage will be a 12" kammtail extension.

Cheers !

[freebeard]

Maybe an aluminum box? An interior finsh with the foam adhered to the outside?

Cd set the bar pretty high for fit and finish.

[CigaR007]

Currently working on the metal bracing. Here are a few pics.

Still need to add the bracing for the sides. It will be much sturdier when the xps foam sheet will be installed, to form the bottom of the kammtail.















Cheers.

[aerohead]

I'm all in with the side elevation of skirts and tail, however, personally, I'd lose the rear flip-up spoiler. It would only add drag.
----------------------------------------------------------------------------------------
In CD's rendering below your's there's a 'kink' in the contour, which is a no-no!
'... surfaces must be matched to prevent high pressure variation along the flow path... care must be taken that no kinks are present in the curvature.'
W-H Hucho, p.160, 2nd-Edition.
The upper 'tearing edge' at the rear is okay. And it's okay to use all of the length of the sides.
-------------------------------------------------------------------------------------
The plan-view image shows no continuity of the taper of the boat-tails flanks, in relation to the HONDA's. This lack of evolving cross-section reduction could cost up to a 33% loss in drag reduction according to Mario & Hirz' research.

[CigaR007]

Added rough tapering to the sides and glued the rigid foam sheets. Still need to increase the overall rigidity. We will see how sturdy it is after the glue has cured. I might have to fibreglass the base prior to continuing the build.










The sides protrude a bit in order to accomodate the future rear wheel skirts.




Cheers !

[CigaR007]

I glued another xps foam sheet and it feels more solid. Started working on the transition between the rear wheel and the kammtail.















Trying to assess how to continue the build. Perhaps assembling an inner box structure in the middle, between the tail lights. The CR-Z has a lot of complex curves, so I will probably have to use 2-part expanding polyurethane foam. It will be much faster, but costlier, versus cutting rigid pieces of foam and gluing them together to achieve the desired curves/taper.

I also need to fix the wobbly receiver hitch draw bar, as the whole structure has some play in it. Need to figure out a way to clamp it.

Cheers.

[freebeard]

Cd's design shows both with and without rear wheel skirts. What's the plan?