[JulianEdgar]

Originally Posted by aardvarcus

Julian,

Did I comment on your diagram use incorrectly? You are using the AST-I for all your overlays, are you not? In your videos and posts and such?

I am using the template that I see widely used here - the one in the Tools section of the site.

I really don't see that many users using that diagram (AST-I not II) on this site for those purposes.

Oh well, that's pretty well all I have seen being used! But it changes almost nothing: the use of any predetermined template to do any of these things is absurd:

- Show where there is separated and attached flow on existing cars
- Guide the shape of rear extensions
- Show how rear spoilers on sedans should be positioned and shaped
- Allow the assessment of the ‘aerodynamic purity’ of cars)

Using a diagram at all may be absurd, but in terms of relative absurdity I would consider using a diagram that exactly matches the XL1, Prius, Insight, etcetera to be less absurd than applying a diagram intended for a use on a vehicle that is in cross section a hemisphere. Once again, I don't have any hemispheres parked outside.

The template (whichever one you have now chosen) matches the font, side and underneath profiles of all these cars you've cited, does it? Er, no it doesn't...

If the notion of someone who does not have development resources mimicking the rear curvature as a function of height of some of the most respected low drag vehicles is absurd, then yes please count me among the absurd.

Well, it's just as absurd as blindly copying the full-load air/fuel ratio from another engine and saying it's good for your engine. Or spring rates, or....

I saw a really good quote on this the other day, it said "This is one occasion when copying one of the generic low-drag shapes will probably get you 90 per cent there."

Sure, I said that. Now why not give the context? The development was of a velomobile from scratch - not the modification of a car. In that context, yep, follow any of the at least five (!) low drag shapes that have been published.

The professionals may not use a diagram, but it is funny how so many of their "low drag" designs end up with almost exactly the same rear curvature as a function of height.

And so many of their low drag shapes do not. See a problem here!?

I don't think it is a groundbreaking revelation to make a higher drag vehicle (e.g. Toyota Tacoma) to have a rear curvature as a function of height that matches a respected lower drag design (e.g. Toyota Prius).

Just like copying another engine's air/fuel ratio. It works on that small turbo four so it's sure to be best for my large naturally aspirated V8...

But I also don't think that measured long term tank to tank 10% better MPG is the "wrong track." Perhaps it is a "non-ideal track", and there is perhaps a percent or so left on the table.

How would you know if you've not tested alternatives?

If I was a professional, with all the professional modeling resources at my fingertips I could know for sure about that percent.

Professionals don't use a template - and barely even mention them in their textbooks - because templates are of such little consequence. If they were the fundamentals some people here try to pretend then the textbooks would be full of them. And they aren't.