Quote:
Originally Posted by benphyr
So on my Odyssey which has large flat mirrors (almost like a pickup truck's) and which fold inwards rotating on a vertical pin it would actually be better aerodynamically to fold them horizontally? The folded frontal area would be exactly the same but the proportion that is right near the body of the van would be less and the proportion further away would be greater. (All other things being equal, etc.)  And does it matter if they are directly on the A-pillar?
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Generally if you must have a small flat object sticking into the flow, having it perpendicular to the body (or more specifically, equal angles on each side) is the best case. In the vicinity of the A-pillar though, not only is the flow very fast (and thus a high potential for drag), it may not be going in the direction you think it is, so a horizontal mirror might actually be at an angle to the airflow... this 'local' angle of attack will produce drag in itself, and acting like a little winglet, may have larger effects on downstream flow than even a mirror in normal position (for better or worse is hard to say, but 'better' would take a bit of luck).
Where they are
might be OK folding to horizontal, it's a fair way back from the A-pillar by the looks of it. But there is the safety / damage avoidance aspect (which is the original reason for folding, not aero) - I suppose it depends on what the local regulations are.