Where is my Max Roof Camber?

[cfg83]

Hello -

I start with this image :



Then I look at a side view of my wagon and see that the maximum height *appears* to be above the rear seats :



That led me to this overlay, where the dark line of the tear drop shape is scaled to be "above" the outline of my car :



If I were to limit the extension of a "Kamm-Spoiler" to the rear bumper, that would imply a ~7 degree slope that would take me to this :



Does this look correct?

CarloSW2

[RobertSmalls]

You can see in your third picture, the image of the SW needs to be rotated slightly counterclockwise.

The template calls for that arrow to be lined up with the highest point on the roof, where the roof is flat. Then you use a sawzall behind that point to generate an ideal teardrop shape.

I propose that if your roofline is curved downward less steeply than the template and you don't want to sawzall, you can slide the template rearward until the angle of your roof matches the angle on the template. This is equivalent to lengthening the fore-body. In any case, the slope of the roof must match the slope of the template where you begin your modding. Otherwise you will have a crease running the width of your roof.

I recommend blowing up your images to a few thousand pixels wide before aligning the template.

[Piwoslaw]

Carlos, you can always move the max roof camber forward.



This would allow you to "Kamm" the whole rear half of the car (both roof and sides). The rear extension would be the ideal 12° cherry topping.

[cfg83]

Piwoslaw -

Ha ha, I was thinking about that last night, i.e. why didn't Saturn just make the car that way!?!?!? If I had the skillz you're proposing in the picture, I'd do a chop top to reduce the frontal area.

RobertSmalls -

I didn't rotate the image because I pulled it "as is" from tirerack.com, and it's only a 0.2 degree difference anyway. They use that picture as a base for imaging fan$y wheels on the car. Even when I use the "Print Page (PDF)" option, it's just a PDF of the same image. Scaling it up doesn't really buy me much. However, maybe this is a good excuse to do a picture of my real car from far away (to reduce the distortion from perspective).

CarloSW2

[aerohead]

Carlo,before you commit to a design,I would recommend you find 300-pounds (136-kg) of ballast for the front seats of the Saturn,so she'll have the 'rake' she'll have with a typical load.
If you can find a portion of level concrete,a simple bubble level will reveal the actual 'max camber' location on the roof.
Measuring the ground clearance at front and rear bumpers will help you adjust your drawing.
That should be confusing enough,right?
I apologize in advance for an up-coming thread that addresses the Ford Probe IV roof-line architecture.
That car achieves Cd 0.15 with very little aft-body,although it is really 'raked',the max camber point is waaaaaaaaaaaaay back on the roof,and roof-to-boot angle never exceeds 17-degrees in the low-drag configuration.
You might be able to cheat on your angles/curvature a little.I hope to know in a little more time.

[cfg83]

aerohead -

Thanks for the feedback. I never thought to put the weight when taking the picture. On average, I probably have me + 40 lbs O' Crap, so that makes about 200 lbs. The bubble level is soooo simple that it makes the process a lot easier.

CarloSW2