Big Van Kammback/template help

[freebeard]

Curved is better than flat. Mair says 22° max, Hucho (IIRC) says never more than 12°.

[mwilliamshs]

How should the rear edges terminate? I think just a plain straight edge would create vortices around its edge?

If a plain straight edge is bad, it should either end in a curve (of what radius?) or in something else...

a) Gurney flap? (see below)

b) ???

If a GF is used wouldn't it benefit from a steeper taper, not that the specific degree of taper actually matters at this point but for clarity, maybe go from the ideal 12-20 degrees up to say 25-30 to prevent the GF from becoming more of a detriment than a benefit?

Since a GF helps airflow stay attached as though the degree of attack were less, I think increasing that angle and using a small GF would help attachment and make the tail work as though it were longer by maintaining attachment all the way to its very end without vortex inducing spillover at its tip. GFs do typically increase Cod though so it would need to be just big enough to work and hopefully there's a better answer for the end of the tail than a GF anyway. Most tails I see on Ecomodder are capped off but I'd be talking about a 5' x 6' cap and that's BIG. That's 5 feet by 6 feet btw, not inches, a panel size most vehicles on here would only have as maybe a belly pan.

[freebeard]

During the 30s a convex rounded end was in style (think 'Dymaxion'), but more lately a sharp crease for fixing the point of separation is in. See the crease added to the back bumper of the latest Prius.The panel inside that separation line can be convex, flat, concave or a recessed box. Concave or convex would be stronger for a given weight than flat, or a flat box.

Here's an example (I like) of a concave or boxed rear end.

http://jalopnik.com/the-renovo-coupe-is-an-electric-shelby-with-1-000-lb-ft-1621969757

[aerohead]

Originally Posted by mwilliamshs

How should the rear edges terminate? I think just a plain straight edge would create vortices around its edge?

If a plain straight edge is bad, it should either end in a curve (of what radius?) or in something else...

a) Gurney flap? (see below)

b) ???

If a GF is used wouldn't it benefit from a steeper taper, not that the specific degree of taper actually matters at this point but for clarity, maybe go from the ideal 12-20 degrees up to say 25-30 to prevent the GF from becoming more of a detriment than a benefit?

Since a GF helps airflow stay attached as though the degree of attack were less, I think increasing that angle and using a small GF would help attachment and make the tail work as though it were longer by maintaining attachment all the way to its very end without vortex inducing spillover at its tip. GFs do typically increase Cod though so it would need to be just big enough to work and hopefully there's a better answer for the end of the tail than a GF anyway. Most tails I see on Ecomodder are capped off but I'd be talking about a 5' x 6' cap and that's BIG. That's 5 feet by 6 feet btw, not inches, a panel size most vehicles on here would only have as maybe a belly pan.

I vote for rounded edges,same radius as front leading vertical edges and horizontal roofline edges.
Some of the sharp rear edges popular today were acoustic 'fixes' for bi-stable flow problems of initial designs which showed up in anechoic wind tunnels.
Kamm advocated bread slice 'burst' chopping,but never did it in practice for himself or clients.