Quote:
Originally Posted by CrustyNoodle
C'mon! It's not the skin friction that causes all the drag, it's the low pressure zone so basically the size of the wake. Surely the size of the wake on a vert with the roof down has got to be double that of the coupe.
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At low Re skin friction drag dominates over profile drag. Also the velocity deficit (wake) would be about the same for a vert and a coupe. The verts would be slightly more turbulent - but in the context of flow control a turbulent velocity profile is not necessarily a bad thing.
What makes you think that the verts wake is "double" that of the coupe?
The verts advantage is much the same as the one experienced by pickups. It's called a recirculating vortex (the point that you both seemed to skip last time around)
Since friction is the main source of drag at low Re (and hence low velocities) the flow separation over what would be the roof of a coupe causes the air to bypass actually touching the roof. Reducing skin friction drag!
Quote:
Originally Posted by m7ammed
Isn't the vert heavier thus making it less efficient?
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Why at those two points coming up in a talk about constant velocity efficiency? there another concept called inertia that comes into play.
Inertia makes the difference in holding a 3650 pound car and a 3400 pound at speed almost nonexistent - so we can ignore it.
I'll go into more detail when I'm doing this on a computer and not my phone.
Here's another fun fact that blows people's minds - drag doesn't increase with the square of velocity. It's actually a parabolic curve.
Pilots should know the term "flying the backside of the drag curve". Well guess what. In most autos and day to day situations we drive on the backside of the curve. It's means that we can drive faster and create less aerodynamic drag! But only to a point.
I should generate a drag curve for the 135. It'd be fun