Kammback Angle Okay?

[Xist]

Originally Posted by Sven7

Seriously, we do airflow testing here at work and some stuff comes out the exact opposite of what you'd think. I obviously can't go into detail. Just be aware that in many aero circumstances, how a thing looks has little bearing on how it actually works. If you're trying something that deviates from conventional wisdom, you need to test it.

Can you give me any examples? Just whisper into my microphone--I mean, my ear!

I think that it was Aerohead that said that in a windtunnel, the air going over the trunk of a 914 actually flowed forward!

Stuff like that?

I have seen this diagram several times lately and when Aerohead shared it in http://ecomodder.com/forum/showthrea...rag-25845.html I responded:

Originally Posted by Xist

I guess that "filling the wake" still helps, even if we do not maintain attached flow.

and he answered:

Originally Posted by aerohead

Yes,it looks like even a compromised aft-body will still provide some drag reducing potential as with Chrysler's experiments with their De Soto Airflow test mule demonstrated.
Their 'fast' rearend helped get the Cd 0.51 of the orig. car down to Cd 0.244.
Not too shabby for 1934!

You guys seem to have agreed that attached flow is not enough, but would you have even that much if the angle is too steep?

[blowncopcar]

Hey kach22i, I never actually said my goal was to just keep the air attached... My goal is just to make it most effecient and get the most MPG, no matter how I do it... so that mainly what im asking, is just is it set up to get the most mpg, air attached or not, id like to know how but that why I was asking you guys cause yall know more about that.... I believe aerodynamics means a lot to my car especially because 90% of my miles are interstate and I drive a lot.... so any more info is appreciated but I will by lifting it slightly while I also extend it and give it a nice curve... I will post pictures then. BTW... my vision is not restricted at all even when I extend it the majory of the whole middle part (non-curved) is a big sheet of lexan... and its clean lol SORRY THIS POST IS ONE HUGE SENTENCE

[kach22i]

Originally Posted by Sven7

....Next time, if you're thinking about using the template improperly, just STOP and think about what you're doing.

Tyler, next time you feel like coming off as some snotty kid and know it all, just stop and think about it - seriously.

There have been several recent postings on the late 1970's and early 1980's work NASA did at out at Dryden. It's information like this which investigates things outside an idealized 3D shape which I find most useful to our DIY backyard applications on real world vehicles.




The Dryden truncated boattail has been discussed many times in this forum without anyone suggesting the that template is in error. I don't see why it cannot be done again.

One of many NASA/Dryden PDF's posted in the forum:
Access forbidden!

Photo Gallery on several of their research projects"
NASA - Dryden Image Gallery

EDIT-1 ............image added:
Automobile 2 - Odds And Ends Photos by kach22i | Photobucket

[aerohead]

Originally Posted by Xist

Can you give me any examples? Just whisper into my microphone--I mean, my ear!

I think that it was Aerohead that said that in a windtunnel, the air going over the trunk of a 914 actually flowed forward!

Stuff like that?

I have seen this diagram several times lately and when Aerohead shared it in http://ecomodder.com/forum/showthrea...rag-25845.html I responded:

and he answered:



You guys seem to have agreed that attached flow is not enough, but would you have even that much if the angle is too steep?

If the contour is steeper than the 'Template' it puts the boundary layer in a very precarious position.The sudden pressure rise will trigger separation and your wake begins right there,with a tremendously low base pressure,killing you with pressure drag.
The 1922 Klemperer' streamlined brick runs a 'fast' rear contour but it won't go below Cd 0.15.It's right at 22-degrees and it gets there pretty fast.

[kach22i]

Originally Posted by blowncopcar

Hey kach22i, I never actually said my goal was to just keep the air attached... My goal is just to make it most effecient and get the most MPG, no matter how I do it...

If you can do some rolling down a hill coasting test I'd like to see your numbers on the original stock car, with roof spoiler added and roof spoiler with leading edge air-slot of about an inch.

See my roof wing thread in my signature below to get an idea why.

[ChazInMT]

Kach, apply the template however you want for yourself. When you apply it wrong in open forum, don't expect us all to fall all over ourselves heaping praise on you for your insightful genius. I have patiently tried numerous times to explain where your thinking is in error. Your post #33 is proving to me that you disregard what I say and are unwilling to listen to anyone but yourself. I'm done trying to help you.

[kach22i]

Originally Posted by ChazInMT

Kach, apply the template however you want for yourself. When you apply it wrong in open forum, don't expect us all to fall all over ourselves heaping praise on you for your insightful genius. I have patiently tried numerous times to explain where your thinking is in error. Your post #33 is proving to me that you disregard what I say and are unwilling to listen to anyone but yourself. I'm done trying to help you.

ChazInMT, I never said that you were wrong, Tyler was wrong or the aero template was wrong - remember that.

I've stated that rescaling the template for smaller scale protrusions like the Gurney Bubble works and achieved agreement.

The earlier +2005 Mustang example also caused some people to rethink how the template could be interpreted.

The trailing edge roof spoilers on econoboxes and the roof garnish on pick-up trucks also seems to be cases where increasing the angle of inclination over that of the aero-template (at full scale) works.

At some point you have to admit my discovery of a connection between the template and rescaling has validity. One size in fact does not fit all.

You have seen and noted several Japanese hybrids veering from the idealized 3D aero shape at least in profile, and this raised a question. This very question I have attempted to answer with rescaling exercises.

If you cannot see what is before you, then you are surely blind.

Automobile 2 - Odds And Ends Photos by kach22i | Photobucket


How much more obvious can I make it?

The aero-template works.

Rescaling the aero-template works to some degree, but it is not the maximized application of this tool.

EDIT-1:

A more detailed examination of this body style and rescaling of template.

http://s184.photobucket.com/user/kac...?sort=3&page=1

[Sven7]

I try reason and it just bounces off. I'm going to try one more time. This is the last one.

-Gurney bubbles and trailer A/C unit are not applied to the trailing edge of the vehicle.

-New hybrids are designed as entire vehicles, where the designers are able to tweak and test virtually any part or surface of the vehicle.

-There are more factors in overall Cd than the center profile. Tumblehome, mirrors, plan taper... many if not all of these are adjusted and tinkered with in the design phase of high-efficiency cars.

-The only thing the OP is changing is the trailing edge of the greenhouse.

-You're taking a lot of liberties with the NASA truck, suggesting in one image that it is simply 22 degrees and in another that it matches a scaled template.

-The Volkswagen Golf was designed in the early 70's and was by no means an aerodynamic masterpiece. Picking apart the exact curvature from a non-orthographic image is pedantic.

-I've listened to reports from the aero lab at work and can tell you the car needs to be considered as a whole, not just some 30cm long segment on the back of the roof.

Originally Posted by ChazInMT

Kach, apply the template however you want for yourself. When you apply it wrong in open forum, don't expect us all to fall all over ourselves heaping praise on you for your insightful genius. I have patiently tried numerous times to explain where your thinking is in error. Your post #33 is proving to me that you disregard what I say and are unwilling to listen to anyone but yourself. I'm done trying to help you.

Yep.

[Sven7]

Originally Posted by blowncopcar

is it set up to get the most mpg

Not yet; you'll want to do this. Seven degrees on the top.



And yeah, the longer the better. When you revise it post up some more pics!

[Xist]

I will repeat that filling the wake seems to provide benefits, but should not achieve the full potential.