[aerohead]

That's the trick.And the jury is still out,with respect to the "best" solution.I did a fan-powered inflated tail also and it worked well.It was a crude proof of concept and I'll probably re-visit that one.If you look carefully at the NASA link photo,you'll notice that the tail starts out with very little curvature.The further it goes,the steeper it gets,to a point where it follows basically a constant angle from there back.If you start too steep,the flow will separate,with little benefit to your wallet.Scale that photo to your van,and you ought to be good to go!