Quote:
Originally Posted by NeilBlanchard
I had fun doing it -- and I now know how I'm going to build my CarBEN EV prototype shell. The 1/4" polystyrene is a revelation for doing compound curves.
The 12 degree slope in the thesis was for a straight surface, and the slope was only on the top. The 3D cap shows how a curved surface can work better -- and there have been a lot of discussions here on EM with 15d slope being ideal, and even 18d works on cars like the EV1 because of the air flows in from the sides, as well.
I'll look around for the "ideal profile" image and see how it lines up with this cap? And it is no "recurve" like the prototype, so the main descending surface is much longer than previously.
[Edit: Here's the "ideal profile compared to the SU cap model:
So, the cap may be a little steeper than ideal -- I'll try a less steep version.]
The comment about the side mirror sight lines not being blocked by the cap is something I had not thought about.
[Edit 2: On the other hand, here's the EV1 compared to the ideal profile:
As you can see, it deviates as much or more than the cap. And here's the Dolphin:
I think the profile is a fine 2D guide, but is 3D, the air can flow in from the sides so the taper can be steeper *if* the sides are also tapered?
What do you folks think?] |
The sides have got to be tapered and well radiussed at the top to get the best benefit.Just like the back of an airship(Met Life,Goodyear,FUJI).
You can go as steep as 22-degrees but you've got to be more than a car height behind the point of max roof camber before you can get there.
I think I put Mair's boat tail graphic in the thread for the Aero.Stream.Template.Check that and see.It will give you the dimensions.The 'Template' gets to 22-degrees also.I set it as the limiting geometry because of Mair's work.
Many researchers used slab-sided models in wind tunnel experiments and never achieved the low drag of the Jaray/Klemperer 'zeppelinesque'forms.