Zulu's Build Thread (Honda CR-Z)

[CigaR007]

Originally Posted by California98Civic

The block is coming along nicely. Do you remember Metro's Gen1 Insight with the boattail? There were a couple others too. Botsapper? 3wheeler? I forget who. Anyway, their testing showed MPG results. You could build a shorter version and test it. What I liked about MetroMPG's was he worked around the OEM taillights. Bring the edges of the rear box cavity closer to the sides of the car...

Build it with carboard and painter's tape at first and set up ways to measure aero effects, fine tuning in light of the results.

Great pictures!

That's the beauty of this online community. I will definitely re-explore their boat tail builds for inspiration.

Originally Posted by aerohead

I've not seen anything in the literature which addresses a partial cross-section box cavity. The sides would be isolated, leaving only top and bottom with access to the active flow. Pressure spikes would be likely. Vorticity.

I agree. Upon reflection, I might build a short-length cavity box (maybe a foot or so) that covers the sides, without blocking the OEM rear lights. Interestingly enough, the rear light assemblies have a protrusion that seem to mimic a vortex generator. I will add a photo soon.

[JulianEdgar]

Originally Posted by CigaR007

I agree. Upon reflection, I might build a short-length cavity box (maybe a foot or so) that covers the sides, without blocking the OEM rear lights. Interestingly enough, the rear light assemblies have a protrusion that seem to mimic a vortex generator. I will add a photo soon.

Why guess? Just build a few versions out of cardboard and test them. No one here can say with any certainty what the results of the different versions will be - no one.

[CigaR007]

Originally Posted by JulianEdgar

Why guess? Just build a few versions out of cardboard and test them. No one here can say with any certainty what the results of the different versions will be - no one.

I value this community's insight and I will follow an iterative process model. I understand your point, but some constructive feedback is always welcome, in my opinion.

There will definitely be many mockups of this box cavity, just for the sake of curiosity and learning.

Regards

[freebeard]

Originally Posted by aerohead

I've not seen anything in the literature which addresses a partial cross-section box cavity.

Searching the Ecomodder website returns 105 results for 'wake filling'. 106 henceforth.

With a notch for the tail light like the Insight's, add 2 or 3 clear plastic vortex traps. If they're Fresnel lenses the light or visibility would be augmented.

[CigaR007]

I attached the grille block and went for a drive.

I drove a 70km loop (round-trip) and a 180 km road trip (known route and average fuel consumption for each over thousands of kilometres) and recorded an average reduction of 0.2 l/100km in fuel consumption. Result is based on an average cruising speed of 96 km/h.

These are preliminary results but it looks promising given that the results were obtained in much cooler ambient temperatures 5°C vs 25°C).

As expected, coolant temperature has increased from a stable 79°C to a range of 84°C (cruising @ 2500 rpm) to 95°C under moderate load and acceleration.

Today's trip of 180km, fuel consumption was recorded at 4.5l/100km

Imperial values (US) :

An increase of 2.2 MPG (50.1 MPG to 52.3 MPG) at an average speed of 60 MPH over 112 miles. Roughly a fuel economy increase of 4.2 % vs the factory grille opening.

[aerohead]

Originally Posted by freebeard

Searching the Ecomodder website returns 105 results for 'wake filling'. 106 henceforth.

With a notch for the tail light like the Insight's, add 2 or 3 clear plastic vortex traps. If they're Fresnel lenses the light or visibility would be augmented.

One cautionary tale out of Norway's KH University, Stockholm, involved NASA's Project Shoebox.
The stinger addition to the truncated boat tail added little additional drag reduction due to the fact that it was already embedded within the turbulent wake, behind the separation line.
Their assessment was that, had the original rear slope angle not been as aggressive as it was, NASA would have realized greater results.
' Stuffing the wake', although imparting a marginal benefit, was very marginal. And that was for a 'full-perimeter' add-on. Limiting a tail extension to say, 33% of the wake area would have extremely dubious probability of significant benefit.

[freebeard]

I thought the more helpful part of the quote is the idea of using vortex traps. The only place I've seen them is in this graphic:



Lower right. On an Insight boat tail they would be lateral, in the notch for the taillight, clear and about 4x6".

[aerohead]

Originally Posted by freebeard

I thought the more helpful part of the quote is the idea of using vortex traps. The only place I've seen them is in this graphic:



Lower right. On an Insight boat tail they would be lateral, in the notch for the taillight, clear and about 4x6".

Hucho shows the drag reduction with a form of this technology.
In Funderburk's Masters Thesis references, he points out inflated gap-filler and inflated boat-tail returning the highest drag reduction since Fachsenfeld, pre-1939.
I don't have an explanation for never seeing the vortex capture device used in the industry.

[freebeard]

Hucho shows the drag reduction with a form of this technology.

Retractable Boat Tail Base Plates? [citation needed]

[Piotrsko]

Originally Posted by aerohead

I don't have an explanation for never seeing the vortex capture device used in the industry.

Trucking industry has never been noted for it's engineering educated drivers, they tend to be very pragmatic. The vortex capture device appears to cause issues with extreme city docking or drivers weight management