Scaling the Template

[freebeard]

I've been examining my own actions. The loaded terms slipped right past me, but the name questioning stuck out like a sore thumb to me.

So, we're all good then? How about that Morelli Shape?

[aerohead]

Originally Posted by freebeard

I've been examining my own actions. The loaded terms slipped right past me, but the name questioning stuck out like a sore thumb to me.

So, we're all good then? How about that Morelli Shape?

Morelli got Cd 0.16 off the ground without wheels.
When he chopped the tail it went to Cd 0.161.
When he lowered it onto the ground it went to Cd 0.35.Ouch!
After a bunch of hours in the Pininfarina tunnel they were able to chisel that down to Cd 0.201 for a 'production-ready' vehicle.'
It was a coup in 1978.
It doesn't seem so dramatic today.
Aptera didn't get any spectacular results with it either.Center of gravity is kinda spooky too!

[kach22i]

Originally Posted by aerohead

*When the Template is coming at you,you see a semicircle minus the area removed for its 'ground clearance.

This confirms my worst fear about the use and fitting of the template to an existing rectangular automobile and or truck.

Thank you aerohead for the full disclosure and explanation.

We have talked at length about the best way to fit the template in longitudinal section, if I may indulge; how about some pointers on how to use it in cross section?

Automobile 2 - Odds And Ends Photos by kach22i | Photobucket


Or this?



As a design professional I constantly have to think of things in 3D, and I assumed others on this board were in the same position (for the most part). Frankly, I'm embarrassed that I did not realize before now how absolutely silly using this template in any capacity has been.

Yes, there is more than one way to aerodynamic bliss, but using the aero-template does not appear to be one of them, at least for a non-half round in section vehicle.

Originally Posted by ChazInMT

Kach has come out and basically called the template worthless in all but a very narrow range of circumstances.

You jumped ahead of me, but this statement is certainly true after today.

I still think as a fully realized 3D shape it works as advertised, and as a guide for transitional curves to the 22-degree limit (scaled down or not) is an excellent guide. Beyond that there has been much misguided silliness with I'm sure nothing but good intent behind it.

The emperor has no clothes.

[Sven7]

I'm not going to comment on the bull crap being thrown around. It's not worth my energy. Kach, you obviously would want to get as close as possible to that form when you build a boat tail. This is why we always recommend putting large radii on boat tails. Capiche?

Originally Posted by aerohead

For Klemperer's Cd 0.15 -0.16 model :

I believe the 1978 Morelli-Pininfarina vehicle you're speaking of is this one:

[freebeard]

The emperor has no clothes.

Emperor...Citizen? I'm glad you didn't get chased off from the thread. When I first logged in to the forums, the first real insight I received was when I posted this VW Trekker and you improved it.


I've taken the same journey as you—that's what prompted the 'Does it have to be a half-body...' thread. I was asking how much violence you can do to the template and still have it respect you. Nobody addressed it as I had hoped. My thinking is if the lateral section is semi-elliptical, say as tall as it is wide, then the air movement in section will be faster than the movement in plan; so the taper in plan increases and the taper in section decreases to subdue lateral air movement. How much?

A squircle can range from almost a square (vortexes) to almost a circle (no vortexes). How close can you approach square comfortably?

Sven7 -- "How about that Morelli Shape?" was linked to a thread from 2010. I was thinking about that *thread* more than the design aerohead deconstructed. It ran 19 pages and who appears on page 19?

• ChazInMT
• kach22i
• NeilBlanchard
• autogyro
• aerohead

It's like it's coming around again on the old guitar.

[kach22i]

Originally Posted by Sven7

This is why we always recommend putting large radii on boat tails.

I've done some research into hovercraft ducts where we go from round to square/rectangular in a convergent taper. Building a boattail would be similar in that we would be going from square to round with a convergent taper.

Other than a generalized arc from the template which must be twisted in 3D to even be considered relevant, I see no direct application of the template in long section if the cross section is a total bust.

This is a classic case of trying to fit a square peg into a round hole (half round hole actually), maybe there should be vetting process to avoid such situations in the future.

Originally Posted by freebeard

I've taken the same journey as you—that's what prompted the 'Does it have to be a half-body...' thread. I was asking how much violence you can do to the template and still have it respect you. Nobody addressed it as I had hoped.

Sorry, I have failed you (and myself), other forums dedicated to aerodynamics must be reading this and having a good laugh on us all. Like I said I feel embarrassed, and now embarrassed for anyone suckered into this great folly.

I like the aero-template as a concept which I can keep in the back of my mind, but as the tool it was intended to be, it's fallen short, way short in my opinion.

Perhaps a better tool would be a box in section proportioned to a typical road car's length and a typical windshield, then given a "known to work" boattail.

Such a template would be applicable to retrofitting existing cars/trucks, but the gold standard Part-C template could be reserved for scratch built projects with a hemispherical cross section.

Just my thoughts.

[freebeard]

Perhaps a better tool would be a box in section proportioned to a typical road car's length and a typical windshield, then given a "known to work" boattail.

My vote is for prolate ellipsoid.

Sorry, I have failed you (and myself), other forums dedicated to aerodynamics must be reading this and having a good laugh on us all.

This is relevant to my interests. You weren't responsible for the other thread, and you should see what passes for aerodynamic speculation on other car sites.

[kach22i]

Originally Posted by freebeard

......... and you should see what passes for aerodynamic speculation on other car sites.

I know some car sites and design sites (illustration/Industrial design) have some frightful things being posted, which is why I think despite all the friction, this site is head and shoulders above those.

I was referring to sites dedicated to aerodynamics, although I'm not exactly sure if I know of any. Post a few and I'll check them out, a good way to get rid of me - haha.

The closest I've gotten to is the Physics Forum:
Physics Help and Math Help - Physics Forums

On the Physics Forum site there is much bleed though into other topics because they tend to look at everything. If you were to post something on aerodynamics or Cd alone without considering other factors such as lift, handling and other fundamentals you will pretty much have to spend some energy getting the one answer you want. However you will learn a lot, and might feel fairly stupid in the end, especially if you have forgotten much of your college studies.

In my own defense, from what I can recall all of my car/truck studies have been 3D in nature, but like I said maybe not when using the template as advertised.

The cross-section is a deal breaker, I should have remembered building all those balsa aircraft models as a young teen. I made a killer 36 inch wingspan Spitfire, talk about ellipsoid (fuselage section and wings).

Similar to this:
Guillow’s Spitfire MK-1 – {part 6} | Monogram F-15 Eagle - 1:48 scale kit


http://www.rchobbyhub.com/phpBB3/vie...p?f=204&t=3534
[IMG][/IMG]

[kach22i]

Originally Posted by ChazInMT

All due respect,
Charlie

With all due respect Charlie I have stated the full sized template works as a stand alone entity, but is not the tool needed nor promoted in this forum by it's developers and their following.

I have stated many times in many ways that scaling down the template is scaling down success, and I suspect that there is a mathematical factor which can be applied to this.

I have suggested that a 3D boattail template/tool be develop to retrofit to existing cars/trucks and made suggestion as to what it may look like in cross section and so forth, therefore I have done much more that criticize - read up.

I admit that I need to learn more on the scaling of models (not doing any model testing at this time), however very few things posted in the forum lend a clue. The comment that a 1/6th scale model would need to be doing 120 mph means what exactly? An intriguing comment, one which I appreciate but no context or comparisons to add value or pattern. 120 mph verses what other speed of the full scale body, 20 or 250 mph? No clue, sorry if I missed it. Is the air going to detach on the scale model before the full scale model? Now that would be useful information and make some sense. Crickets.

I understand that one cannot fit a square peg into a half circle hole, which puts me one up on you Charlie - your emotions on this topic have blinded you to the painfully obvious.

[kach22i]

You sure have a big head about yourself Charlie, living in an alternate universe must be hard on you.

Now back to something more productive, pages 24-30-ish have several post by ERTW which is the missing link several people remembered but could not locate.

http://ecomodder.com/forum/showthrea...c-9287-24.html

http://ecomodder.com/forum/showthrea...c-9287-25.html


http://ecomodder.com/forum/showthrea...c-9287-26.html


More than one person expressed misgivings about the template's application and usefulness other than in the abstract. I am not alone on that one.

EDIT-1:

The below overlays based ERTW's work, but I don't have his 3D skills. They should get the point across to even the most obtuse.

Automobile 2 - Odds And Ends Photos by kach22i | Photobucket


A different fitting attempt to convey the message.


Close up detail