Check out the bottom of the civic hybrid

[James]

check out the bottom of my dad's civic hybrid. The Cd is supposedly .27, and it has a partial belly pan under part of the front of the car and near the back. It is suspiciously missing sections on either side behind the rear wheels.

Wouldnt there be less drag with these areas covered? it doesnt seem like it would cost very much to cover these areas, if they were already putting a plastic panel in that area. Any guesses why they wouldnt cover those areas?
At least on one side, it wouldnt be anywhere near the exhaust...even on the exhaust side, some improvement could easily be made. also, the lip of the rear bumper is a sharp edge that sticks out and overlaps the belly pan, it looks as if it would catch some air.

[omgwtfbyobbq]

A couple wild guesses
-It doesn't matter. With air flow exiting near the low pressure trunk area anyway, there's no point to smoothing the air stream right before turbulent separation.
-They also may want to induce some turbulence right before the back of the car, so that some of the air flowing under the car will curve up into the low pressure area behind the trunk, and the separation of airflow over the top/sides of the car wouldn't be influenced as much.

[brelandt]

All I could make out from that picture was an upside down coil spring....

[James]

yeah, sorry the pic is upside down. what you are looking at is the back corner of the vehicle, looking toward the rear wheel.

Could be that they left it like that to create turbulence. Initially, I would have thought that Honda would have optimized everything on the car, but after seeing the aero results of Phil Knox and Bajoos, I am starting to give everything a closer look.

[The Toecutter]

A couple wild guesses
-It doesn't matter. With air flow exiting near the low pressure trunk area anyway, there's no point to smoothing the air stream right before turbulent separation.
-They also may want to induce some turbulence right before the back of the car, so that some of the air flowing under the car will curve up into the low pressure area behind the trunk, and the separation of airflow over the top/sides of the car wouldn't be influenced as much.

Another wild guess

-Some bean counter wanted to save about $1 off the materials costs without regard to the impact on the car's quality, basically telling the engineers to **** off.



Happens all the time in industry.

[omgwtfbyobbq]

Heh, yeah... VW uses plastic water pump impellers, plastic!

[red91sit]

I almost wonder if something is missing? The only reason i ask this is there is that empty circle ring thing, looks like it could be used to attach another plate, same with the bolt hole in the corner. The wheel spoilers also seem as if they were designed to work with more underbody. Hmmm

[James]

Yeah,
Maybe honda will just start adding the panels in a couple years, as the MPG competition between the hybrids gets more intense??
I just wish they would have done a better job with it...I dont think my dad would like me putting coroplast under there!

[cfg83]

red91sit -

Originally Posted by red91sit

I almost wonder if something is missing? The only reason i ask this is there is that empty circle ring thing, looks like it could be used to attach another plate, same with the bolt hole in the corner. The wheel spoilers also seem as if they were designed to work with more underbody. Hmmm

Maybe the circle ring thing is for a ground effects kit for a non-Hybrid Civic sedan. Maybe the new Si.

CarloSW2

[tjts1]

Theres always room for improvement even on supposedly very efficient cars. A first gen Prius (97-99, never sold in US) owner in Australia was able improve fuel economy at 100kph from 42mpg to 47mpg with a simple front belly pan. You would think the manufacturers would have installed on it from the factory if they were trying to build the model of efficiency.

He went from this


To this


In the end every component goes through a cost vs benefit analysis. Filling in that area behind the rear tire will probably improve fuel economy by a point or two but it wasn't worth it to Honda. It might be to you.
I still find it outrageous that hybrids like the Prius and Civic don't come with rear wheel skirts from the factory.

[invisiblegold]

Yeah, I agree. There was some old story about GM calculating the cost of fighting lawsuits compared to fixing the bolt that hooked a muffler to the gas tank. I guess they were exploding and killing people.

I have the notion that Macnamara talked about it in his movie "The Fog of War"...and that the few dollars per car was more than the hundreds of thousands in lawsuits. Then again, I have a terrible memory so it might have been an urban myth.

I'd like to think that they found other problems with the underbelly pans that we don't know about (like rust from water collection or cooling issues.) Or perhaps that it wasn't as important as we think.

[invisiblegold]

PS: I also remember that the old Porsche 911s (1970s at least) were fully contained underneath. (until the way back) Motorheads have pointed out that it enabled Porsches to go faster with less horsepower than the American muscle car equivalents.

[caprice]

[quote=tjts1;38274]
To this


Nice belly pan. Where is there more info on this one? Thanks.

[tjts1]

The story is from Autospeed, an Australian online magazine which I subscribe to.
http://autospeed.drive.com.au/cms/A_2456/article.html
The same car was also turbocharged for more power and even better fuel economy.

[The Toecutter]

How much horsepower and FE did the car have with the turbo?

I've read of turbocharged Honda Insights that do 0-60 mph in 7 seconds and in normal driving haven't lost any fuel economy. Man, how fun that would be at speed with an optimized gear ratio...

[rh77]

I've been noticing on HCH-II's here that a small lip spoiler is standard. I always thought that a spoiler was for downforce -- but apparently it must serve some function of "finishing" the air over the car for efficiency:



RH77

[MetroMPG]

Rick (and others):

rear drag-reducing spoiler explained: http://www.gassavers.org/showthread....kpot#post20378

[rh77]

Originally Posted by MetroMPG

Rick (and others):

rear drag-reducing spoiler explained: http://www.gassavers.org/showthread....kpot#post20378

Perfect! Thanks...

-Rick

[James]

Yes I think the spoiler was put there for aero reasons. If you look at it from farther forward, you can see that it is not "flat" or parallel to the trunklid, but has about a 30 degree slope. This corresponds to what Phil Knox told me: the optimal angle for a trunklid spoiler was 30 degrees (I think-let me check back in my emails). He said angles above or below this would create more drag (on a typical sedan shape).
I think that a flat extention(or slightly downward sloping) would be beneficial for vans trucks and hatchbacks.

[James]

now that the picture is there, how much do you think the antenna on the top affects aerodynamic drag. I take it off when I am driving the car on the hwy.

Here is the message from Phil:
I think the chin spoiler is a good way to go,although I am
surprised that Toyota didn't already do that on the Camry.And I agree
with Dave about the effectiveness of the spoiler,as compared to a full
undertray.Extending the roofline out at an angle not to exceed 12-13
degrees should allow for attached flow 'til the end of the foil.The
rest of the air will swirl into a smaller version of the "locked"or
"captured" vortex,that presently preceeds your trunklid's rear
edge.Darin has succesfully pulled this off with his Firefly/Metro.I
ran a vey long version of this on my CRX to my advantage.Also,a rear
decklid spoiler,which leans back at an angle no greater than
30-degrees (as measured from the horizon)and projects rearward to a
point which intersects that 12-13 degree angle coming off your
roofline,would approximate an ideal fastback.Anything higher would
increase drag.Anything lower would increase drag.Steeper angles would
also raise drag.Just for giggles,you might want to project that line
out behind the car,just to see how close Toyota came to a "cleaner"
form.A round dowel about 18-inches tall, inserted into a shallow piece
of wood,and taped to the trunklid of the car,with six-inch strips of
bright yarn taped to the dowel every six-inches or so,would tell you
alot about the airflow there.A friend could drive as you sit in the
backseat watching "which way the wind blows".Happy experimenting,and
let us know how things progress,Phil.P.S. If you wanted to experiment
with Vortex-generators,those yarn tufts would reveal whether or not
they were pulling the flow down without separation.