Drag per aft-body length/roof angle

[aerohead]

I've added 11-additional drag tables at the #1 permalink on page -1 just to muddy the waters.Some of you are talking about actual boat-tailing and these might help.
I've also completed Xist's drag table and if Al can shake free,we'll get that scanned and posted.
I'm also going to prepare a new table derived from the original wind tunnel work of the Golf/Rabbit-I.It will take a week to complete it.

[Xist]

Aerohead, somehow I had not seen your response. I will wait for my girlfriend to come over, ask her how to determine the angles, and like I do far too often, groan in exasperation, and then she will laugh at me.

Beluga and Aerohead, I apologize for not using words like a big boy, but as usual, like right now, I really needed to be doing something else, so I hoped that you guys could figure out what I intended. Beluga, instead of building a giant boat tail, I bought a Civic HX, and went from twenty-seven to forty-seven MPG.

Aerohead, how come the sharp angles that do not follow the template are inherently more aerodynamic? It looks like the earlier and the sharper the taper, the better.

Would completely removing a truck bed be more aerodynamic than building an aerocap?

[aerohead]

Originally Posted by Xist

Aerohead, somehow I had not seen your response. I will wait for my girlfriend to come over, ask her how to determine the angles, and like I do far too often, groan in exasperation, and then she will laugh at me.

Beluga and Aerohead, I apologize for not using words like a big boy, but as usual, like right now, I really needed to be doing something else, so I hoped that you guys could figure out what I intended. Beluga, instead of building a giant boat tail, I bought a Civic HX, and went from twenty-seven to forty-seven MPG.

Aerohead, how come the sharp angles that do not follow the template are inherently more aerodynamic? It looks like the earlier and the sharper the taper, the better.

Would completely removing a truck bed be more aerodynamic than building an aerocap?

Xist,I'm going to try and answer your question with some additional visual drag tables which I'm currently working on.
You'll find that things are extremely conditional/contextual.
The sharp angled test models were a way for Buchheim and his team to start with extremely fundamental shapes,collect data,and then expand out from there.Buchheim ended up with the 'Template',producing bodies as low as Cd 0.14.Kamm did the same thing,starting in the mid-1930s.Kamm's 'Template' produced Cd 0.12.Same as Walter Lay's 'Template' of 1933.THe original 'Template' dates to 1922,with Paul Jaray's airship-inspired 'pumpkin seed' half-body car of Cd 0.13.
I've completed some photo-copy work on the new tables and will work on them through the week.Hope to post next Saturday.
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With respect to the pickup truck,I removed the bed from my Dodge pickup and lost 2-mpg,as well as causing an overheat condition.
Constructing a custom,streamlined bed/cover would be better than just an aeroshell.I have one of those as a work-in-progress which I hope to complete before the world ends.
From some of the other tables you can already see that the sharp angles don't deliver the 'lowest' drag,they only beat the 'Template' when all the other parameters which allow the 'Template' to function are abandoned.

[Xist]

Originally Posted by aerohead

From some of the other tables you can already see that the sharp angles don't deliver the 'lowest' drag,they only beat the 'Template' when all the other parameters which allow the 'Template' to function are abandoned.

Does that mean "When the laws of physics are ignored?

[aerohead]

Originally Posted by Xist

Does that mean "When the laws of physics are ignored?

It comes down to the committee who determines the technical specifications and respecting what the stylist has penned for the design.
An example would be the original VW Golf/Rabbit which could have had Cd 0.34,instead of Cd 0.43,but the car would not 'look' like what the stylist drew,so it was a non-starter.

[Xist]

Originally Posted by aerohead

It comes down to the committee who determines the technical specifications and respecting what the stylist has penned for the design.
An example would be the original VW Golf/Rabbit which could have had Cd 0.34,instead of Cd 0.43,but the car would not 'look' like what the stylist drew,so it was a non-starter.

I have had win8 issues and reinstalled the OS several times in the last week or two. Somewhere in there, I lost my version of the diagram. I did not see that you had figured out the angles and discussed them until I tried to find the picture that I posted.

Let's say I make a CarXist. Should I follow the Template or just cut an angle from the windshield to the rear bumper?

The original version of the chart does not make sense to me, especially compared to the next chart that you posted, where the closer that semi trailers followed the template, the more aerodynamic they were.

CarXist! That sounds like way too much work!

[aerohead]

Originally Posted by Xist

I have had win8 issues and reinstalled the OS several times in the last week or two. Somewhere in there, I lost my version of the diagram. I did not see that you had figured out the angles and discussed them until I tried to find the picture that I posted.

Let's say I make a CarXist. Should I follow the Template or just cut an angle from the windshield to the rear bumper?

The original version of the chart does not make sense to me, especially compared to the next chart that you posted, where the closer that semi trailers followed the template, the more aerodynamic they were.

CarXist! That sounds like way too much work!

The short answer is yes,but I'd like you to see the new drag table I've worked on this week which should be ready by tomorrow,then you'll see from Hucho's own research,another reason why I promote it.

[aerohead]

I've added the new drag table # 14 which is based upon Wolf-Heinrich Hucho et al' SAE Paper # 760185,from 1976.
This work applied to the Golf-1,Scirroco-1,and Polo-1.Since these are 'real' cars we see that they respond differently to the rear slope compared to simple, crude test models.
I've included a more full explanation of the work in the preamble above the new table up at the 1st page #1 permalink.
You can see the origins of the 'Template' taking form.

[Xist]

Originally Posted by aerohead

The short answer is yes,but I'd like you to see the new drag table I've worked on this week which should be ready by tomorrow,then you'll see from Hucho's own research,another reason why I promote it.

Again, the closer to the template, the more aerodynamic. I am going to try to stop obsessing about this...

Okay, that is not going to happen, but I will stop posting about it.

[aerohead]

Originally Posted by Xist

Again, the closer to the template, the more aerodynamic. I am going to try to stop obsessing about this...

Okay, that is not going to happen, but I will stop posting about it.

It's extremely important that you be skeptical,and marshal all your critical thinking skills when considering a project.You want to make all your mistakes on paper,or the computer screen,not out in your work area.
Many of the aerodynamic pioneers said that achieving low-drag was the EASY part.Selling the idea was the real challenge.
92-years after Jaray's big breakthrough people still can't wrap their mind around the concept of a single solution.
*Nuclear submariners don't question look-a-like submarine hulls.
*Commercial airline passengers don't question look-a- like aircraft fuselage.
*Shooting enthusiasts don't question look-a-like ammunition.
*Plumbers don't question look-a-like pipe fittings.
*Meteorologists don't question look-a-like anemometers.
*We can go on and on.
In the automotive industry there has been a high grade paranoia over look-a-like automobiles since the 1920s.Citizen consumers have been conditioned over the decades to accept planned automotive absolescense.
We may have bred out our ability accept stasis when it comes to vehicles.It's a fascinating conundrum.