Quote:
Originally Posted by JulianEdgar
Honestly, the one really good thing that Aerohead's posts do is make me check my facts. That is, why, I think to myself, am I so confident Aerohead is quite wrong, especially when he has good citations to (purportedly) back it up?
That's why, where I can, I go look at his citations.
So this was a good example.
Aerohead writes:
...and I think, nah, I've never measured high downwards pressures on the nose of any normal car. And in published (and my measured stuff), downwards pressures on the rear of a car come only with a rear spoiler (or, in very unusual vehicles - like solar race cars - by fully attached flow).
So then Aerohead nominates Fig 6.8 in Hucho (second edition) as his evidence.
So maybe I am wrong? Better go take a look.
No, there it is.
The only downwards pressure occurs ahead of the windscreen of the Transporter - the peak (Cp of 1) - is in a very clear stagnation zone... so acting backwards, not up or down!
You need to look not only at the pressure, but also the direction in which it is acting. A big, flat, vertical surface on the front of a vehicle is going to develop high pressures, but that's all drag, not downforce!
Furthermore, the idea that "all the low pressure of the suction peak can be overwhelmed by the high local static pressure acting at the nose and tail" is obviously wrong when the area of the graph is far greater in the negative pressure zone (let alone that acting vertically) than the positive!
So, either Aerohead cannot read and understand the diagram, or he is confused, or his theory is wrong, or he is deliberately prosecuting an argument by being deceptive - you choose. |
1) the transporter's front bumper is essentially a splitter. I own one.
2) full local static pressure of stagnation is acting directly on top of it.
3) and as quite often, there's never a mention of the pressure distribution under the vehicle, nor lift-related palliatives known in the public domain, as if it's not part, nor could ever be a part of the calculus.
4) and the wider picture in which Hucho has claimed that for 'passenger' vehicles are concerned, just target 'neutral,' neither positive or negative lift.
5) 'Normal' cars aren't designed for downforce.
6) I suppose you missed the part about the Nissan LEAF, with the 'template' roofline, having the lowest Coefficient of Rear Lift, measured in the 'Drag Queens' article in CAR and DRIVER. Fully-attached flow up to the truncation, no rear spoiler necessary.
7) Hybrid-notchback, Mercedes-Benz CLA 250, having the highest rear lift of the five cars measured.
8) This is part of the prima facie evidence validating the claim that a 'streamlined' body can produce zero-lift.
9) do not make any association between the VW Transporter and the 'template'. It's an invalid comparison.
And let's quit with the 7-year-old's attempt at profiling and clinical psychology. You don't know me. You don't know what's in my mind.
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'seems to me that your greatest concern would be falling from grace as an aerodynamic guru, directly threatening book sales, should the buying public ever get wise to you, realizing that you're out of your depth in many things aerodynamics.
Perhaps you thought that, by including us in your book, that we'd be willing to submit to your dominance rituals, and peck corn from your feces.