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Old 09-11-2020, 04:40 PM   #31 (permalink)
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' BEST'

* The nose is 'best' according to Daugherty and Franzini, page 297.
* The tail satisfies Daugherty and Franzini's ' attention in streamlining must be given to the rear end, or downstream part, of a body as well as to the front.' page 297.
* ' for streamlining against subsonic flow a rounded nose and a long, tapered afterbody generally result in minimum drag.' D & F, page 315
* ' The drag of bodies with finite thickness mainly consists of friction drag, which is small in all cases in which no flow separation occurs. This can be achieved by slender shapes on the rear part of the body which produce only a weak pressure rise in the flow direction. Shapes of this kind are aerofoils and 'streamlined' bodies.' Professor Dietrich Hummel, page 57, Hucho, 2nd-Ed.
* ' [T]he shape of the body should be designed so that the flow remains attached and the pressure rise is as large as possible.' Hummel, page 59.
* ' The main contributions to the drag force originate from the rear part of the body.' Hummel, page 61.
* ' [I]t is very important to design a rear body surface which brings the divided streamlines smoothly together.' Hummel, page 61.
* ' Optimum shapes are 'streamlined' bodies having a very slender rear part.'
* Page 61, Table 2.1, 3rd from bottom: ' Streamlined body L/D = 2.5, Cd 0.04. ( the template)
* ditto, bottom of table, 'Streamlined half-body @ zero ground clearance = Cd 0.09. ( the template)
* ' Vortex type flow separations, related to inclined shapes of the base of a vehicle, may cause considerable contributions to the overall lift.' Hummel, page 64 ( Porsche 912 / 911 ).
* ' [W]ith refinements in aerodynamics progress is towards the body of revolution.' Hucho, page 107. ( just skip to the body of revolution and have all the progress in a single stroke )
* ' Separation-induced vortex trains : Fastback : induces downwash , leading to low separation line, short wake ( prismatic model ), drag. page 112.
* ' At points where the flow is opposed by a high pressure increase, it tends to separate from the contour.' ( Porsche 911 ) Hucho, page 117.
* ' drag induced by any vortices.' Hucho, page 118.
* ' Aspect ratio is very small for vehicles ( 0.3 ).' Hucho, page 122.
* ' there is not a simple relationship between the overall lift and drag for this profile drag / vortex-induced relationship.' Hucho, page 123-4.
* ' Three-dimensional longitudinal vortex pair' page 140.
* ' base pressure also depends upon the angle at which the flow separates from the contour.' page 141
* ' Mair's boat tail and 22-degrees, page 141.
* ' The highest drag.... results from vortex drag.' page 149.
* Figure 4.59, Ahmed body, attached flow = lower lift, page 151.
* ' [C]onvex surfaces must be matched to prevent high pressure variation along the flow path.' ( template ) page 160
* ' risk to sales.' page 188
* page 199 ( template )
* page 200 ( template )
* page 202 ( template )
* page 203 ( template )
* ' [T]he drag of the ( Cd 0.09 ) basic body is achievable. To what extent this can be approached in the development of a production vehicle is therefore more of a question of the balance of the requirements of the specification than of technical feasibility.' Hucho, page 209.

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Old 09-11-2020, 06:15 PM   #32 (permalink)
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Quote:
Originally Posted by aerohead View Post
In Figure 4.54, at the bottom of the table you can see the separation-induced vortex-drag increasing with the down-slope angle, up until 'burst' occurs. This is very important with respect to cars like the 911/ 912.
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In Figure 4.55, all the data presented is for separated flow and high vortex-drag. The drag minimum, and lower lift occurred at 15-degrees. You can clearly see the trend line down towards the 15-degree point on the table. And above, in Figure 4.54, you can actually see what the vortex-drag component is @ 15-degrees. The lowest lift occurred at the original roof contour ( actually on the 'template', but at high truncation ).
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With respect to fastback rear lift exceeding notchback rear lift, some counterfactual evidence is presented in Hucho's Figure 5.9, on page 221.
* A close examination of the lift table reveals a CL 0.4500 for the fastback, while the notchback version of the same car is CL 0.5085.
* The lift relationship for the two cars remains until 29-degrees of yaw, where they're identical rear lift values, then the fastback overtakes the notchback as the table ends, at 30-degrees yaw.
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The squareback shown, registered CL 0.2390, however this car is a Type 36, not a Type 31, as with the upper two cars. It, technically would not be an apples-to-apples comparison.
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The table also provides the asymptotes for each car's maximum crosswind CL.
Normal mix of errors (eg comment re Fig 4.55) and irrelevancies (eg bringing in old-shaped notchbacks with separated flow).

I'll let people look at the diagram and make up their own minds as to what it shows with regard to:
  • separated flow, attached flows and resulting wakes.
  • lift of fastbacks versus squarebacks



You would honestly think the diagram is clear enough for anyone to understand...
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Old 09-11-2020, 08:16 PM   #33 (permalink)
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Quote:
* In front elevation, the 'template' car approximates a semicircle in cross-section. There isn't a flat surface on the car anywhere. It's all compound surfaces.
This is why the Template has virtually no application to a passenger vehicle. And heaven forfend driving it sideways. That's where the fun is.
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Old 09-16-2020, 10:58 AM   #34 (permalink)
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errors and irrelevancies

Quote:
Originally Posted by JulianEdgar View Post
Normal mix of errors (eg comment re Fig 4.55) and irrelevancies (eg bringing in old-shaped notchbacks with separated flow).

I'll let people look at the diagram and make up their own minds as to what it shows with regard to:
  • separated flow, attached flows and resulting wakes.
  • lift of fastbacks versus squarebacks



You would honestly think the diagram is clear enough for anyone to understand...
* ' [T]he vehicle aerodynamicist must refer to a huge amount of detail resulting from earlier development work.' Hucho , Preface
* The new Ford Bronco, upcoming Rivian pickup, HUMMER, and others will fall under these dimensional considerations.
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Old 09-16-2020, 11:02 AM   #35 (permalink)
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no application

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Originally Posted by freebeard View Post
This is why the Template has virtually no application to a passenger vehicle. And heaven forfend driving it sideways. That's where the fun is.
Would you like to argue your thesis scientifically?

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