RE: NACA ducts - how do they work?

> From: Steve Wiseman
> 
> Where they're particularly useful is in a flat sheet with a laminar
> (smooth) flow over the surface. In that regime, you run them with
> the narrow end pointing into the airflow - the sharp edges allow
> little vortices to start, dropping down into the of the duct. As the
> duct widens, the vortex grows (and vice versa - that's why the
> ducts are the shape they are). By the end of the duct, you've got 2
> countra-rotating vortices, without patrticularly disturbing the
> airflow over the rest of the sheet, and those vortices can be routed
> into a duct nice & easily.

I also posted this to BC (for a wider audience). Chap says they can be
used to inlet or expelling air depending upon which way they are
oriented. So they could be used pointing backwards to expel air from the
engine bay in place of the louvres.

CF bonnet looking more likely. ;-)
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