Aerodynamic Streamlining Template: Part-C

[aardvarcus]

I don’t understand what all the conundrum is about.

A person who is knowledgeable in the fields of aerodynamics created a useful tool based on generally accepted aerodynamic theory. (It’s just a half cross-section of an established shape.) That person then distributed that tool free of charge. It’s so easy anyone who can overlay a picture can get an idea of a good place to start. Yes the tool takes some adapting to get it to fit a typical vehicle, but it seems that most people who have created boat tails have figured this detail out, and it seems to work for them.

Is it the absolutely perfectly most aggressive but still yet optimal cross section to apply in top view and side view? I don’t know. I am sure someone who owns a wind tunnel and does extensive vehicle testing could develop a shape that would be more ideal for any given vehicle, but those people aren’t exactly on the internet giving out advice for free. Frankly I am appreciative that someone though enough of “the rest of us” to spend their time creating this reference, updating it, and answering questions about it.

I am also appreciative that there are those on here who question the established theories. I personally would love to see some of these different ideas designed, built, tested, and posted so that I can see your results.

It is pretty easy to see that the conversation here is no longer providing useful dialogue; it has disintegrated into an internet shouting match. I at one time provided free advice on double stud walls and a few other classically-based building systems on a few internet forums related to low energy housing. The help I provided very similar to the template; it was basic ideas on how to build something very close to standard but would perform very well. I am sure it wasn’t “perfectly optimal” but it was based on sound building theory, it was affordable, and I had some experience having actually built one house that performed excellently and started on my second. There were some other theories on those forums, SIP, ICF, Straw, OVE Stack with spray foam, etcetera. My double stud related posts were constantly criticized, mostly by people who had never built a low energy house, but were planning great things. Over time I decided to stop helping.

I hope those on this forum who have done don’t decide to stop helping. [/rant]

[kach22i]

Originally Posted by aardvarcus

I hope those on this forum who have done don’t decide to stop helping. [/rant]

I agree with everything you have said, and also hope the experts continue their forum participation.

[slowmover]

This thread might be sticky, but it is closer to being a sidebar conversation about an optimized tool. A tool applicable to DIY.

Perfection is fun, but hardly necessary past a certain point. Where that point lies will always be in contention for some.

If I can reduce the family transportation fuel budget by a comfortable percentage then I am home free . . the other ownership/operational costs of personal transportation are higher in aggregate.

Subsidized fuel and subsidized roads are what make any of this possible, after all. The larger forces mean more. The day they change ends all of this.

.

[ennored]

This may not be the exact right thread to post this, but so many threads seem to devolve into discussions about the ideal template, I'll try here....

What I don't think I have ever seen is a "template" that describes what the minimum rear "tail" needs to look like to achieve attached flow. This shape is NOT ideal relative to drag, but should have much less drag than say a flat rear like a semi trailer, or even a sphere. We see this over and over, less than ideal shapes making good aero numbers. From the Dryden van, to Trailer Tails, to Joe Schmoe's kammback, to the latest hybrid car, etc. We hear a lot about attached flow and tuft testing here as being a reasonable metric. Just what shape do we need to get that? (And just how good is it?)

[jime57]

Originally Posted by kach22i

To be of practical value, one could continue to use the template in profile, but not in plan view. The step to 3D and to fit typical body styles is yet another reach, for another day.

Let's get a working plan view first, and then resolve the transition from square to round.

I think that this is the essence of what you have been saying, and I agree to a considerable degree. But, as someone else said "the perfect is the enemy of the good" or something like that. Folks want to proceed and get some boattails built. Already, we are seeing folks build to the template profile and achieve considerable improvements.

Just a few days ago I was at a large Lowes parking lot eyeballing the cross sections of a bunch of various vehicles. In doing so, I realized that in the general case, the cross section is a hexagon. There are right angles at the bottom, an obtuse angle in the middle, where the windows taper inward, and obtuse angles at the top - with all the angles slightly rounded. I seems to me that if someone with CFD software and skill wanted to model the transition to a semicircular transom, this would be the correct "front end."

It is just a suggestion. I have neither the s/w nor skills to do the model. I do think that such a model might have considerable potential to take the template idea to the next level. I have no clue as to how difficult this CFD process might be.

[freebeard]

Originally Posted by kach22i

Template away, I found your car.

Colani! Rear screen wipers in 1970! Mounted on the transaxle!

Thanks for the link, his work is pretty extensive; I'd never seen the F1 cars before. And new pictures of the C-Form.

Originally Posted by aardvarcus

I don’t understand what all the conundrum is about.

Sturgeon's Law‎. "ninety percent of everything is crap" Ya gotta read with your skepticals on.

ennored -- Colani is the master at pushing (twisting and punching) the envelope.

[kach22i]

Originally Posted by jime57

I seems to me that if someone with CFD software ........do think that such a model might have considerable potential to take the template idea to the next level. I have no clue as to how difficult this CFD process might be.

I have no clue either, but such a tool would take into account the amount of air going over the top of the car, in lieu of the near equal flow over the surfaces found in the 3D version of the Part-C template.

Double Post - from the Scaling Thread.

It's funny when things come to you, I just started cleaning my cast iron pan for lunch and I guess found this relaxing enough to have an "Aha!" moment.

I'd like to thank everyone for their participation in this thread, without some of the push and shove I may not have been challenged enough to have this little epiphany.

Industrial Design - Transportation Photos by kach22i | Photobucket


A closer look at the sketches.


Feel free to ask questions, I'm now the one in the position of defending a theory (please be gentle).

Before this all I really had was the right questions, and the mistakes I made only helped me learn more and lead to the final outcome.

I'm just about positive there is nothing new here, just new to me. In fact I'd bet my lunch money that some guy 100 years ago did all the calculations and tests on this.

The mathematical equations and so forth may all be out there in some old text book. However in terms I can relate to, and the twist of perspective I've lent to this issue may help some of us want-a-be aerodynamicist, or at least I can only hope.

Click on the images to make them larger and more readable.

[kach22i]

Originally Posted by ChazInMT

So, in other words, you're saying VW screwed up when they created the lowest Cd value on a production car with the XL1...

...........Below is a chart showing foil sections and their associated drag based on how long the foils are compared to how tall. (Fineness ratio....reference sledge hammer girl for a 10).

You can keep trying to alter the original template and shorten it all you want to, to match your own reality. Isn't that what all the redesign of the template is about? Knowing it's wrong and fighting desperately to change it? I've done the overlay with the old green template, did you miss it? Where exactly is the template you are using posted in the forum, or is it just something from a link of your own making?

FYI: Foil sections are not 3D shapes, you are missing the importance of thinking in 3D.

Air goes almost equally all the way around this object........
http://ecomodder.com/forum/showthrea...e-25975-5.html


Air goes over the top................mostly
Aerodynamics... Diggity!!

[justme1969]

Boat tail is not an option for my sedan model. but something rarely touched upon here is adding a diffuser and vortex generation / turbulence Ideas.
I cant seem to post pictures here or I would post my crayon sketch "LOL"
Company only added CAD reader to my new puter, impossible to undo a stupid move like that here.
Anyhow theres a few piks that show my rear end attempts to date in garage. Spoiler reversed and tucked behing rear glass, shorter ride height for rake,dam n skirts to reduce parachute effect.
Well if I add a diffuser similar to the weak attempts on a few recent new mini vans just above the top of my rear window it will confuse the air mass and react similar to a boat tail if I add rear bumper extension or trunk extender to divide the massed air before it creates the vaccume behind rear of car.
not a cam back a true diffuser with ported air and spoilers similar to small trim tab devices??? Anyone gone this route b4? Am I cutting edge of 1950s aircraft technology installed on modern aerodynamic automobile???

[kach22i]

No time to talk today, did some quick sketches and a composite image sheet this morning, enjoy.

Industrial Design - Transportation Photos by kach22i | Photobucket