Hatchback Vs. Sedan (why does a sedan have a better Cd?)

[spacemanspif]

Originally Posted by E.Roy

So it appears the sedan is 180.3" long, a whole 5" longer, which to me makes no sense. Why cut down the interior room on a hatch?

I worked at pepboys about a year ago and we had 2 feistas for delivery cars, 1 hatch and 1 sedan. And these cars were the first time I noticed what car companies were doing with these small cars. The sedan definitely had a larger trunk than the hatch and I always thought that the hatchback had a completely useless cargo area.

Best I can tell is that Americans don't like station wagons because of the stigma of being "old lady cars" or whatever. So instead of extending the roof over a sedans trunk, they chop off the trunk and add a door and just like that the magazines call it a "hot hatch" so people want to buy it. In the mean time, people who want a useful vehicle like a wagon are left with nothing but what the Germans have to offer....

To me its stupid to cut a car down but I see tons of hatches running around town all the time. Best I can figure is the salesman says "the sedan has 50cubic ft of cargo space, but the hatch has 62, so its got more space for when you go on vacation with the family" and people eat it up...except the hatch has vertical space that is useless unless you want your luggage falling on top of your children...


Off my soapbox and back topic: The wheel skirt threads all seem to say that skirts have more impact as the wheels get closer to the back of the car. Could the added Cd be from the turbulence caused by the hatch's wheels being closer to the back of the car?

[Cd]

Originally Posted by spacemanspif

Best I can tell is that Americans don't like station wagons because of the stigma of being "old lady cars" or whatever.

Agreed ! That is why that the SUV replaced the minivan which replaced the station wagon. Stigmas !
SUVs are a cross between station wagons and pick ups, but people don't see it that way.

Even minivans are starting to have truck like front ends to lose the stigma that comes with driving a minivan.

I wonder what will replace the SUV. Hopefully something more efficient ! ( Already SUVs are labeled 'soccer mom vehicles' )

Back to the aerodynamics discussion, has anyone here ever tried to contact the manufacturer directly with a question like this ?

This site is filled with brilliant minds that i'm sure someone in the aero department would be more apt to speak with one of you.

Sure beats guessing !

And one more thing : If the manufactures wont give out information due to it being a " trade secret "* then perhaps one of you could contact the guys at the A2 wind tunnel and ask some advice there if they are willing.

* I contacted Lexus about the LS430 and asked some questions about the drag, but was given the "it's a trade secret" line.

A2 wind tunnel :

Address: 117 Godspeed Ln, Mooresville, NC 28115
Phone: (704) 799-1001
A2 Wind Tunnel

[gone-ot]

Originally Posted by Cd

And one more thing : If the manufactures wont give out information due to it being a " trade secret "* then perhaps one of you could contact the guys at the A2 wind tunnel and ask some advice there if they are willing.

* I contacted Lexus about the LS430 and asked some questions about the drag, but was given the "it's a trade secret" line.

A2 wind tunnel :

Address: 117 Godspeed Ln, Mooresville, NC 28115
Phone: (704) 799-1001
A2 Wind Tunnel

TIP -- You can contact EPA to get the "coast-down" data the manufacturers MUST supply to EPA as justification for the MPG values they provide to EPA for publication!

Then, assuming you're not math-adverse, you can simply backsolve the PWR-vs.-VELOCITY equation at 55 MPH(*) to find the vehicles CdA number.


(*) EPA assumes 55 mph for many tests, including coast-down.

[t vago]

Originally Posted by Old Tele man

TIP -- You can contact EPA to get the "coast-down" data the manufacturers MUST supply to EPA as justification for the MPG values they provide to EPA for publication!

Then, assuming you're not math-adverse, you can simply backsolve the PWR-vs.-VELOCITY equation at 55 MPH(*) to find the vehicles CdA number.


(*) EPA assumes 55 mph for many tests, including coast-down.

The test results can be found here:

Test Car List Data Files | Cars and Light Trucks | US EPA

[aerohead]

Originally Posted by t vago

I've been thinking about putting a kammback on the Karen-mobile...

She'd be a good candidate.

[aerohead]

Originally Posted by Cd

Agreed ! That is why that the SUV replaced the minivan which replaced the station wagon. Stigmas !
SUVs are a cross between station wagons and pick ups, but people don't see it that way.

Even minivans are starting to have truck like front ends to lose the stigma that comes with driving a minivan.

I wonder what will replace the SUV. Hopefully something more efficient ! ( Already SUVs are labeled 'soccer mom vehicles' )

Back to the aerodynamics discussion, has anyone here ever tried to contact the manufacturer directly with a question like this ?

This site is filled with brilliant minds that i'm sure someone in the aero department would be more apt to speak with one of you.

Sure beats guessing !

And one more thing : If the manufactures wont give out information due to it being a " trade secret "* then perhaps one of you could contact the guys at the A2 wind tunnel and ask some advice there if they are willing.

* I contacted Lexus about the LS430 and asked some questions about the drag, but was given the "it's a trade secret" line.

A2 wind tunnel :

Address: 117 Godspeed Ln, Mooresville, NC 28115
Phone: (704) 799-1001
A2 Wind Tunnel

Once upon a time you could phone GM's Aerodynamics Lab and chat with Glen Scharpf (sp?)who ran things there.He was very helpful in sorting out the CRX's speed/mpg/drag data.And he was very open about discussing GM products.
That's all history now.
I have found that if you'll write to the public information officer for any respective automaker,that they'll be happy to mail you press kits from some of the concept cars which include a lot of technical data.
I've received packets from:GM,Ford,Volkswagen AG,Volvo,Honda,Renault,Chevrolet,Citroen,Adam Opel AG,Ford Werke AG,GMC/White Truck,Freightliner.
If more consumers talked to reps at auto shows about Cds and CdAs 'n frontal areas,they'd report back to headquarters and convey that there was actually consumer interest with such things.

[kach22i]

I'm suffering from some 'déjà vu' today, going back to an old but not real old post.

http://ecomodder.com/forum/showthrea...tml#post374147

Originally Posted by kach22i

I was doing a little research on Cd, scale, models and Reynolds numbers and found this paper.

This is curious, the "Estate Back" (think of a Chrysler 300 wagon) has a higher Cd than the "Fastback".

http://delphi.com/pdf/techpapers/2012-01-0168.pdf

Based on doing many many template overlays and just eyeballing it, I'd have to say the Estate Back fits the template, and the fastback falls short.

What's going on here?

http://ecomodder.com/forum/showthrea...tml#post374147

Originally Posted by kach22i

I've only skimmed it, but so far it looks like the smaller the aft area of the car (as long as you have flow/attachment) is more important than maintaining the template arc at full scale.

NOTE: The following page in the link above (page 6) has some template overlays as a visual aid.

[aerohead]

Originally Posted by kach22i

I'm suffering from some 'déjà vu' today, going back to an old but not real old post.

http://ecomodder.com/forum/showthrea...tml#post374147


http://ecomodder.com/forum/showthrea...tml#post374147


NOTE: The following page in the link above (page 6) has some template overlays as a visual aid.

The thing about the 'Template' is that if you want to approach Cd 0.07-0.08 territory,as Hucho cites,that you need the profile of the streamline half-body,and you also need the effective fineness ratio which the 'Template' provides in order to protect the boundary layer.Remember,streamlining is all about reducing pressure drag and that means minimizing,or eliminating separation.The 'Template' cannot produce separation,nor can it produce longitudinal vortices.Notchbacks can and do both.
Compare the Ford Probe-IV to the Probe-V.Do you see what Ford does with the aft-body to go from Cd 0.15,to Cd 0.137?

All of Hucho's Cd 0.15 forms are 'fastbacks.'
If you want to go below Cd 0.15 you elongate the fastback.It's the only way you can get there.

[gone-ot]

Here's an older Edmunds article giving 0.25-0.26 Cd values for the Lexus LS430:

2001 Lexus LS 430 First Drive

[botsapper]

...hatchbacks and wagons have a more abrupt transition and at a larger cross section of the vehicle, while three-box sedans have a stepped and smoother transition into the wake zones. AutoSpeed - Low Drag Car Aerodynamics