Rounded corners vs. Straight edges on kammback

[Varn]

It has been since 73 that I had an R10. I always thought that the air entered the grill work in the top and went forward through the radiator and out underneath.

Originally Posted by freebeard

Sorry for using 'invoked' in two different senses in a single post.

As penance I will refute myself: There is such a car, the Renault R8.



I thought the cooling air exhaust created an invisible spoiler that flipped air downward with a vortex. But as the vented air probably bleeds straight back, the reported gains [citation needed] might be due to the Coanda effect.

[freebeard]

COcyclist --

Hijack??

As in 'threadjack'?

I believe this has been discussed?

[citation needed]

This thread is about rounded corners on a Kamm tail.

I thought it was about round corners vs square edges.

I try to not be a problem. Please don't take my going grammar nazi on myself as license to dog-pile on.

Varn -- I hadn't consider that possibility; but wouldn't that be wake-subtracting?

[MTrenk]

Hahahaha, the fights between the real aero guys and the black magic aero guys never cease. I think I shall start a Sensible Aerodynamics thread so perhaps we can enlighten the black magic guys, and remind the real aero guys that you don't have to make aero sound scary just so you can prove your credibility of knowledge on the subject. Aerodynamics principles are easy to understand, and to a certain extent can be utilized easy as well.

On the other hand, if you are not an engineer or physicist, and have never had wind tunnel or CFD experience, then you better shut your mouth instead of 'eye-balling' vortex physics.

2000neon, I can come up with a construction method that will allow you to easily create the radii you want! If you post pictures and dimensions of your vehicle, I'd be happy to work on designing the Kammback with you!

[ChazInMT]

Originally Posted by drmiller100

great study, and totally supports my argument on the angles.
if you look at page 75, they ran a CFD with 18.77 degrees, and a hard cut angle at the front, and hard angles at the sides, and the
FINAL RESULT IS EXACTLY AS I PREDICTED.
The minimum possible drag with no vortices.

Regards,
Douglas Robert Miller

drmiller, you are silly.


Here's the page you use as "Support".



Bigger version of pg 72 to contemplate

Nowhere does it state that the 18.77° angle is optimal, and on page 84 Feysel concludes that at 10°-12° the drag coefficient is optimal and as you go beyond 12° it increases. Just for kicks, on page 9 Feysel (the author) talks about the evils of the vortex generation I speak of, it's the last paragraph of the page.





Bigger version of pg 85...for your consideration.

Here is the page 85 which "Summarizes" the results. It seems pretty clear to me that the 18.77° is decidedly not the minimum drag. Now, I'm no math major, but the number .3091 looks to be greater than .2892, unless I'm not reading the graph right, it is decidedly less than the "minimum possible drag" you speak of.



So, Mr. Miller, it seems to me that you have used something completely out of context to try and bolster your stance. Science and engineering principles require that we look into all aspects of a study and not just focus on the ones that help us out.

Tell you what, since we've made a complete mess out of Steves thread, I have a proposal: I'd be more than willing to remove all my posts here regarding your posts 6,11, and 17 if you take them down. Like it never happened. See if you can salvage some dignity here or do you want your clever mental judo on display for all to see?

[Frank Lee]

I think I shall start a Sensible Aerodynamics thread so perhaps we can enlighten the black magic guys, and remind the real aero guys that you don't have to make aero sound scary just so you can prove your credibility of knowledge on the subject.

That's all fine and dandy except for the black magic guys that LIKE black magic and don't want to entertain reality.

"You can lead a horse to water but you can't make him drink."

[MTrenk]

Learning > Being Right
I just want to see a Kammback Neon, maybe I can help, and maybe this guy drives away happy from the gas station until his Neon bites the dust. :P

[ChazInMT]

Here's my analysis based on this template overlay.
Angle at front of Kamm 5°, overall 8°, rear of Kamm 11°. All angles are based on the ground being 0°. The top of rear window to trunk rear lip looks to be 17°. The car is "Leaning forward" in its design, the body side molding is 2° and the top of door line is 4°.

The Kamm looks to be about 7-8 inches tall at the back of the car based on a guess of 16" wheel size for this car, not exact but the best I can do without measuring a door er sumthin. The neon green line pictured is 8°, the red line is the template, the yellow orange thing is my quick & dirty side view of what the Kamm ends up looking like if it follows the template.

Hope this helps. Something to start with anyhow.




Since ecomodder isn't able to provide bigger pictures, I made a link to this so it's easier to see wassup.
Bigger Pic to LΘΘk At

[2000neon]

Hey Chaz, I have no problem with the added discussion at all in here. That picture looks great and pretty much what I have in mind as far as a side profile. I am hoping to be able yo be able to keep it as close to the template as possible, and maintain the curvature all the way through it. The roof of the car already has a pretty dramatic curve to it, and so I think by keeping it a smooth curve it will work better than a flat edged transition down the top of it.

As far as kamm height at the rear. I think you are pretty close. I'm pretty sure that the rims on that neon are 15" diameter, but with those hub caps, the total diameter of the caps is probably close to 16", so your guess of 7-8" seems pretty close. I would prefer the rear to be higher than lower, at least in the beginning, because it will probably be easier to take away height, than add it back on later. Plus rear visibility will be improved as height increases.

[2000neon]

MTrenk, thanks a lot, I am glad to have any and all help I can get.

To make things a bit easier to visualize and understand where I am coming from. Here are some pictures of my car.
The earlier "partial" kammback


Side profile, Due to space I couldn't get any farther back, and it is a little bit too high of a view for using the template, but still gives a rough idea of what I'm working with.



You can see how the rear bumper extends another few inches past the rear of the trunk lid. I might try to angle it rearwards at the back like Chaz has in his picture of the white Neon, I can go a few inches past the trunklid, without going past the bumper.

[MTrenk]

Thank you for the pictures Steve. I will try to have some drawings by tonight. I've never scanned anything to this computer before, so I might have to do the first rendition in Solidworks.
The plan in my head is to have the Kammback bolt to the trunk, yet still extend to the sides of the vehicle, hopefully mounting flush with the roof and C-pillars. In order for the trunk to open, the Kammback will have to be able to rotate upward at some location, and perhaps it can be as easy as using an aluminum door hinge from the hardware store.
Get back to you soon.