Quote:
Originally Posted by aerohead
* Cd 0.15 is for Klemperer's 1922 half-body with wheels.
* Cd 0.10 without wheels, maintaining the same ground clearance.
* The 1981 Volkswagen 'Flow' body long-tail, by Buchheim et al., is Cd 0.14.
Its half-body, at maintained ground clearance is Cd 0.0913.
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* Jaray's 'pumpkin seed' of 1922, with diffuser ( his invention ) is Cd 0.13.
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* The baby 'template' car measured Cd 0.121 with 'loose' wheel fairings and chopped tail.
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* Cambridge University's CUER solar racer is 'template'-esque, and with knife-edge trailing surfaces measured Cd 0.11.
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* The flow on the sides of the 'template' is essentially the same over the top. It's a half-body. That's what half-bodies do.
It says very clearly, and multiple times in your favourite book that isn't the case, and was found in 1922
* ' The main contribution to the drag force originate from the rear part of the body.' Hucho, page-61, 2nd-Edition.
* ' [I]t is very important to design a rear body surface which brings the divided streamlines smoothly together. Optimum shapes are ' streamlined' bodies having a very slender rear part.' Hucho, page 61, ditto.
* ' [T]he optimum shape in terms of drag is a half-body, which forms a complete body of revolution together with its mirror image- produced through reflection from the roadway.' Hucho, page 15, ditto.
Complete body, meaning not on the ground, I don't see many flying cars
* ' [L]ow drag can only be achieved when the separation at the rear is eliminated.' Hucho, page 16, ditto.
* ' [A]n effective fineness ratio in free air of 2.27..... approaches the drag minimum recognizable.' Hucho, page 210, ditto. ( 'template' is 2.5:1 )
Again, that is in free air, most cars can't fly
* The pressure recovery... provides for the reduction of the drag.' Hucho, page 144, ditto.
* ' [P]ressure drag is the largest component in the aerodynamic drag. Its minimization is the true objective of motor vehicle aerodynamics.' Hucho, page- 119, ditto.
* ' A closer approach to the value of the basic body without wheels is only achievable through further integration of the wheels into the body.' Hucho, page- 201. ditto.
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All the above are defining the 'template.'
* Hucho shows it in Table 2.1, page 61, from Horner's book of 1951. Cd 0.04 in free flight ( actually lower ). Half-body would technically be Cd 0.08.
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All I can reasonably take from that is, the template is low drag, especially without wheels, and even more so nowhere near the ground.
But actually, reading through the bits of that book I can access, it says "Klemperer (1922) recognized that flow over a body of revolution... changed drastically and lost symmetry when the body came close to the ground"
Seems pointless to follow something like that to me when designing cars, which live on the ground.
"Despite their extreme length, flow separates from the rear of streamlined cars. By truncating the rear shortly upstream of the location where separation would take place, shapes of acceptable length were generated with no drag penalty"
So that says to me that using a template may actually increase drag, a bit like extending a kamm-back can be pointless.