Quote:
Originally Posted by TheTestPilot
That poses the question of, what are the results of tailgate down or removed with a hard tonneau.
I would like to try this but my 4y hilux ate no. 4 sparkplug at 556000kms , I think it's dead.
Alas poor Hilux.
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Sighard Horner's book, 'Aerodynamic Drag' is my only source for anything related.
Visualizing a 4-cup rotating anemometer:
* if the hemispherical cups are 'open' and traveling as the 'trailing' part of the cup, their Cd is 0.42.
* if the cups were filled in and 'closed' at the 'rear', their Cd is 0.37.
* a 11.9% delta-Cd between 'open' and 'closed'.
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With the tailgate closed, streamlines reaching and separating at the trailing edge of the gate will attempt to circulate around the corner, as a vortex sheet and collide with the boundary of the closed cavity, imparting some momentum.
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With the tailgate down, or removed, there's no longer a 'boundary'.
The flow separates, the vortex-sheet circulates towards the void, and collides with incompressible 'deadwater' under the tonneau, unable to impart any appreciable momentum ( punching a hand into a bowl of ball bearings ).