comment on 1st-gen Porsche 911/912 lift

[kach22i]

Originally Posted by freebeard

Bucky Fuller used to say that an epiphany was just the answer coming back to a question you'd forgotten you asked yourself. In this case it was Youtube:

My answer is at 7:47. The last 2:30 is an ad [for baby wipes?]

Long but good video.

Thank you for posting it.

[aerohead]

1) no one will argue your pressure measurements.
2) if you'd consider the actual aspect ratio of any particular vehicle, it's effective wing area, wing loading, and actual lift, for that same vehicle, at half-load, with two occupants, and the balance of the weight in the trunk, at the legal maximum speed limit in The United States of America, and compare that to the static loading of the vehicle, then tell us why we need to be concerned?
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And using your Porsche 911 as a thought experiment ' truth table of logic', consider:
* If the airflow 'wrapped' the 911's body, it would have Cd 0.14. ( Buchheim et al. )
* The 911 demonstrates Cd 0.40. ( Hucho)
* Since aerodynamic drag is pressure drag, the 911's excess drag can be explained by pressure drag. ( Hucho)
* Pressure drag is a function of flow separation. (Hucho)
* By default, the 911's body has flow separation. ( Hucho)
* And since flow separation is essentially at the rear of an automobile, the 911 is experiencing aft-body flow separation, which is counterfactual to any claim of flow attachment. The cannot exist 'flow 'wrapping''.
* The flow separation is explained by the fluid mechanics and ground rules of fluid mechanics Hucho said was 2 of the 3 objects of his book, in the Preface.
* Between Mair's and Buchheim's boat-tail research, Hucho presents that the maximum downslope of any aft-body contour which can maintain attached flow is 23-degrees, clearly violated by the 911.
* It's extremely unfortunate that the Porsche 911 tuft-study photographs were not published with flashing lights and huge disclaimers, as to the implications of interpreting 'attached' flow, when that entire region of the car was already heavily compromised.
* Taken out of context, it is tantamount to standing physics on it's head.
* Nobody should ever interpret tufts as indicative of attached flow, unless viewed within the context of vortical flow.
* And this is where you commit your 3rd sin: On the very first page of Hucho's textbook, he admonishes ' ... the vehicle aerodynamicist must refer to a large amount of detail resulting from earlier development work.'
* You've thrown out all this 'earlier' development work with the baby. Hucho published that it is from this vast body of empirical data: ' the essential experimental results, presented as ground rules of the fluid mechanics...design strategies, showing how many existing single results can be combined to provide general solutions.'
* This is where you shoot yourself in the foot.
* And it's from this 'obsolete' data that the 'template' is derived, dating to the ' Le Precurseur', airship of Pierre Julien, France, 1850.
' It ain't what you know. It's what you think you know, that just ain't so.' Samuel Langhorne Clements