[JulianEdgar]

Originally Posted by aerohead

Without specifics, I can imagine a common situation where the comment would be spot on.
If the spoiler is there to provide a surface of reattachment, then it IS addressing a situation in which the low pressure over the backlight/boot region is caused by the early 'fast' flow separation.
By providing for flow reattachment, a locked-vortex is established, over which the fast inviscid flow CAN decelerate, and by the time it reaches the top of the spoiler, is at a higher static pressure, plus the spoiler acting as a dam, sequestering the low pressure immediately over the boot, away from the base of the car, where it cannot effect the wake.
In this case, both drag and lift are reduced do to the 'slower' air.

Yes, as I already said, it's possible to dream up a situation where a roof spoiler creates lift. (You seem to have missed the part about it being a roof spoiler.) But as I also said, with any modern car with attached flow on the rear window (and the quoted book shows a sedan) then it's extremely unlikely. And it's certainly not common.

So a good example of Aerohead writing material that is not relevant as he seems to be talking about a boot spoiler, not the roof spoiler that's under discussion.

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As to a 'wing' not being a 'spoiler', it may be a issue of semantics.
Anything that spoils lift is technically a spoiler, regardless of the actual device or technology. For example, a venturi is a 'spoiler.'
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If Aerohead is arguing it, black is white and white is black. A wing is not a spoiler, and a spoiler is not a wing. If Aerohead believes they are different only semantically, that's fine - another example of a misleading post from him.

Your comment about 'most lift comes from attached flow,' ought to include caveats, as there exists counterfactual evidence to your claim.

Again, a typical misleading Aerohead statement - he just loves misquoting what others write. I didn't just say: 'most lift comes from attached flow', I said:

It's highly unlikely that any spoiler will create lift on any modern car (where most lift comes from attached flow), unless something really weird is done so that the spoiler deflects air massively downwards.

Note my specific reference to modern cars: and yes, in modern cars, where there is attached flow over the upper surfaces, most lift does in fact come from attached flow.

Streamlined bodies have completely-attached flow, yet generate zero lift.

An aircraft wing is a streamlined body with attached flow - yet it generates no lift? Dear me - yet another wrong statement from Aerohead. (I think we've been here before, and if I remember correctly, Aerohead then had his own definition of what a streamlined body comprises.)

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Your book contains mistakes about 'wrapped' flow and lift. ' He who sins not, cast the first stone.'

I don't think so. I've now had chapter by chapter feedback on the book from:

• the head of Jaguar Land Rover aerodynamics
• an ex-Tesla aerodynamicist
• the head of Porsche aerodynamics
• a professor of aerospace engineering and author of two books on car aero
• a Formula 1 aerodynamicist

...not to mention of course feedback from the tech consultant when I wrote the book, who happens to be a world-renowned aerodynamicist.

None of them suggest any mistakes about 'wrapped flow' and 'lift'.

And you know what, I think I'd trust their opinions over Aerohead's ideas....