Partial Boattail/Kammback on a sedan?

[Ecky]

Here's a thought: It's not as good as a kamm, but you could try grabbing the trunk lid spoiler used on the Civic Hybrid of similar year. I believe Honda made a few changes to them worth 0.03-0.04, the lid spoiler being one of them. You shouldn't have a hard time finding one in a junkyard.

[mpg_numbers_guy]

Originally Posted by freebeard

Somewhere near you vicinity there will be a recycler. At the very least Habitat for Humanity. In Bleugene Oregon it's BRING.

I've obtained a variety of materials there, Coroplast, double-wall greenhouse glazing, 1/8" ABS triangle cutoffs, sheet metal flashing, & etc. Your mileage may vary, but it would be less than full sheets for minimal cost. For a three-sided Kammback hood, I'd budget $50.

Sit in the driver seat and watch in your mirror while someone moves a shop rag or something around and note where the blind spots are. Then you can see what needs to be clear. ....or cut away. The transition onto any addition will be in the blind spot on the C-pillar.

It's good to have a plan. I try not to rush things too, eventual success counts.

...$50? Wow, from my research I calculated over $200 just for parts alone. I can see how a recycler would be a good resource though.

Maybe I could remove the rear window, rear hatch, etc. and use a kammback to double the storage space in my car...don't laugh at me for this lol.

Originally Posted by Ecky

Here's a thought: It's not as good as a kamm, but you could try grabbing the trunk lid spoiler used on the Civic Hybrid of similar year. I believe Honda made a few changes to them worth 0.03-0.04, the lid spoiler being one of them. You shouldn't have a hard time finding one in a junkyard.

7th gen HCH is 0.28 and the standard sedan is 0.36 (I think).

I thought spoilers in general added drag?


How about this as a mini-kammback? Or would this add drag? Fit 2001-2005 Honda Civic Em 4-Door OE Rear Roof Window Visor Spoiler Wing 1Pc
Or these vortex generators? Fit For Roof Shark Fins Spoiler Wing Kit 9Pc Vortex Generator Evo-Style PP
Or would they not be worth it?

[freebeard]

I'd budget $50

Cost plus?

The $40 part is similar to what kach22i has on his pickup IIRC. The 9 dollar part would require careful placement. In a wind tunnel.

[Vman455]

Originally Posted by mpg_numbers_guy

Or these vortex generators? Fit For Roof Shark Fins Spoiler Wing Kit 9Pc Vortex Generator Evo-Style PP
Or would they not be worth it?

If you tuft test the rear window, you'll find there's a bubble of flow detachment right in the center, at the base. I added 6 vortex generators a few inches down from the top of the rear window, angled at ~15 degrees to the direction of flow, and it kept attached flow across the entire window. Effect? Yes. Measurable effect? No.

[Ecky]

Originally Posted by mpg_numbers_guy

7th gen HCH is 0.28 and the standard sedan is 0.36 (I think).

I thought spoilers in general added drag?

Without a wind tunnel to test in, you're probably more likely to do harm than good with something like a spoiler, but they can help in some cases - I'm sure Honda did wind tunnel testing. Ditto with anything else you bolt or tape on which sticks out in the wind. Wings always hurt because by design they generate downforce at the expense of drag.

Pretty much the only easy, guaranteed DIY modifications are those which cover aerodynamically dirty areas with smooth panels, e.g. wheel spats, radiator blocks and belly pans.

[kach22i]

Originally Posted by freebeard

Cost plus?

The $40 part is similar to what kach22i has on his pickup IIRC. The 9 dollar part would require careful placement. In a wind tunnel.

Since all the Photobucket links are a mess, here is a shot of it from a few months ago.

random pics that YOU have taken....... - Page 605 - Pelican Parts Technical BBS


I put the American flag decal on it because it cracked recently - many years of service before it happened.

The smoked acrylic originally came off the side of the building of an architect I was helping out years ago, it had just been sitting there for years - I cleaned out his yard.

[freebeard]

Thanks, but I was thinking of the roof-top part.

[kach22i]

Originally Posted by freebeard

Thanks, but I was thinking of the roof-top part.

The way that works is the gap or air-slot between the roof and the wing. The air gets accelerated thereby lowering the pressure, the higher pressure air above it then drops (in theory).

I think one of the after-market roof wings (spoilers/visors) could be modified to have such a slot creating an air-fence down the back window.

https://www.ebay.com/itm/JDM-2000-CI...-/290780346895

Looks like they run +$100, maybe a home-brew creation will be more cost effective in retrospect, especially if you mess it up the cut.

Another approach is a bi-wing?

Harder to pull off by just guessing your way though it though.

http://ecomodder.com/forum/showthrea...-26678-10.html


Ford spent like a gazillion dollars to perfect that one I assume.

However, this is the similar direction I want to go in with my next experiment.

http://forums.pelicanparts.com/off-t...taken-606.html


Anything that plumps up the rear deck to near aero-template profile should work to some degree in my opinion.

This angle below (red car) is close to that of the Civic in question, maybe it isn't all that bad?

http://ecomodder.com/forum/showthrea...-26678-13.html

[aerohead]

If you like,go to the car blueprint website and check out the 3-view ,4-view images of:
*Cd 0.23 1993 Volvo ECC sedan
*Cd 0.23 2018 Audi A4 sedan
*Cd 0.22 2013 M-B CLA 180,Euro.spec.Blue.
*Cd 0.22 2017 BMW 5-Series G30 sedan
These are all non-Kamm,but industry-leading type low-drag sedan shapes,and if you'll study all the different views of their bodies,you might see some features you could use with the Honda.

[mpg_numbers_guy]

Originally Posted by Vman455

If you tuft test the rear window, you'll find there's a bubble of flow detachment right in the center, at the base. I added 6 vortex generators a few inches down from the top of the rear window, angled at ~15 degrees to the direction of flow, and it kept attached flow across the entire window. Effect? Yes. Measurable effect? No.

So you couldn't measure any benefit other than the airflow remaining attacked? Even non-FE related gains such as increased coasting distance?

Originally Posted by Ecky

Without a wind tunnel to test in, you're probably more likely to do harm than good with something like a spoiler, but they can help in some cases - I'm sure Honda did wind tunnel testing. Ditto with anything else you bolt or tape on which sticks out in the wind. Wings always hurt because by design they generate downforce at the expense of drag.

Pretty much the only easy, guaranteed DIY modifications are those which cover aerodynamically dirty areas with smooth panels, e.g. wheel spats, radiator blocks and belly pans.

Maybe I'm missing a point that's obvious to you. If the idea of a boattail/kammback on the end of a sedan won't work because the airflow goes over it and doesn't reattach, wouldn't it do the same thing with a spoiler, regardless of it having an aero shape or not?

Originally Posted by kach22i

https://www.ebay.com/itm/JDM-2000-CI...-/290780346895

Looks like they run +$100, maybe a home-brew creation will be more cost effective in retrospect, especially if you mess it up the cut.

How about something like this that I posted earlier?

Originally Posted by aerohead

If you like,go to the car blueprint website and check out the 3-view ,4-view images of:
*Cd 0.23 1993 Volvo ECC sedan
*Cd 0.23 2018 Audi A4 sedan
*Cd 0.22 2013 M-B CLA 180,Euro.spec.Blue.
*Cd 0.22 2017 BMW 5-Series G30 sedan
These are all non-Kamm,but industry-leading type low-drag sedan shapes,and if you'll study all the different views of their bodies,you might see some features you could use with the Honda.

One would have to basically rebuild the Honda for those...