Aero drag reduction potential

[aerohead]

Originally Posted by freebeard

This assumes a flat plate truncation?

Would ending in a box cavity create an inverted, 'virtual' (rather than inflated) extension to the boat-tail shape?

Edit: I notice Cd has the same question. Anyone have an answer?

*yes,all truncations would be like a loaf of bread,with simple vertical slicing.
*As to the box cavity,I'd really need to compare published empirical data.
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*A proper boat tail will have zero separation until it terminates and this will allow the continuous pressure rise until separation which will yield the highest base pressure and lowest delta-P across the vehicle;ie. minimum pressure drag.
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*The box cavity would have immediate separation,although would be designed for reattachment and capturing locked-vortices all-around.
*In theory,the outer flow field would pass over the locked-vortices and the base pressure would be based on the pressure of the modified separation point of the cavity's rear termination point,minus the energy lost to the continuous 'feeding' of the vortices.
*The wake of both boat tail and box cavity would be the same cross-sectional area at equal length,but the boat tail would have a bit higher base pressure due to its lack of circulation along the pathway.
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I'm not sure if this answers the question.

[freebeard]

Thanks for giving it a shot.

T'would be awesome to put one of Autospeed's Magnehelic gauges to work with a manifold of about 20 hoses you can valve on and off individually in a single run.

The reason I'm optimistic is that a half-tonneau on a pickup bed is essentially a box cavity facing up behind the obstruction of the cab, and it has a measurable effect.