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Old 09-02-2020, 12:57 PM   #1 (permalink)
aerohead
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Fineness ratio vs drag coefficient

According to Hucho, and with respect to vehicles that are developed for the lowest possible drag ( something which might be of interest at this forum ), fineness ratio is the single most important criteria.....
'Lower drag can only be achieved by extending the length of the vehicle's body.'
Hucho, 2nd-Ed., page 201.
After examining some commercially-available BEVs ( which lack conventional cooling systems, and enjoy smoother bellies), concepts, as well as converting some previously-tested, simplistic wind tunnel models, by adding Tesla-grade' side mirrors in order to simulate those bodies as BEVs, I compiled a list, which illustrates the correlation between fineness ratio and drag coefficient.
I used the Length/ Square-root of frontal area in all cases. This converts each vehicle to a square,rectangular bar section which can be assembled into a bar-graph as has been done by marine biologists to compare the hydrodynamic efficiency of, for instance, fast pelagic fish and marine mammals.
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2006 i-MiEV.................................. 2.219827.................................. 0.35
2012 Chevy Spark......................... 2.510446.................................. 0.325
2017 Chevy Bolt............................ 2.705049.................................. 0.312
2012 Toyota RAV4.......................... 2.837229.................................. 0.30
2018 Jaguar I-Pace......................... 2.956080................................. 0.29
2018 Nissan LEAF........................... 2.908106.................................. 0.28
2019 Audi E-Tron (raked-roof).......... 2.98404................................... 0.28
2020 Porsche Taycan Turbo S........... 3.269224................................. 0.25
2020 Tesla Model S......................... 3.216863................................. 0.24
2014 VISIO.M................................ 2.745537................................. 0.24
2017 Tesla Model X......................... 2.76212................................... 0.24
2017 Tesla Model 3......................... 3.110366.................................. 0.23
2020 Tesla Model Y......................... 2.9182387................................. 0.23
2020 Lucid Air................................ No available data........................ 0.21
1941 FKFS K-5 (kurz-heck).............. 3.29665................................. 0.2166
1996 GM EV1................................ 3.1069501.................................0.197
1941 FKFS K-5 ( m-h).................... 3.69486.................................. 0.1813
2012 VW XL1................................ 3.011834................................ 0.1769
1992 GM Ultralite........................... 3.131837................................ 0.1733
1941 FKFS K-5 ( Lange-heck).......... 4.30126.................................. 0.1662
1993 GM 'Yellow-Ferret' LSR EV1...... 3.435861................................ 0.15
1981 VW 'Flow' body ( k-h )............. 3.346776................................ 0.16
1981 VW 'Flow' body ( lange-heck)... 4.432975................................. 0.15
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In 1922 Paul Jaray demonstrated low drag via an elongated body form.
In 1933, Dr. Walter Lay established the relationship between drag and elongation.
In 1935, Dr. Kamm and Baron Fachsenfeld re-created Lay's research, re-establishing the link between drag and body elongation.
In 1978, Liebhold et al. demonstrated a drag reduction of the D-B,M-B C-111 III, from Cd 0.237, to Cd 0.178, with body elongation ( fineness ratio )
In 1981, Buchheim et al. demonstrated drag reduction of the VW 'Flow' body with elongation.
In 1991, the IT works Honda CRX-HF set a club record at USFRA World of Speed, and verified the body elongation as primary source of drag reduction, later backed up at the Chrysler Proving Grounds, East Chelsea,Michigan.
In 1993, General Motors Corporation established a land speed record, at the Bridgestone / Firestone Proving Grounds, Ft. Stockton, Texas; with their Impact/ EV1, in part through body elongation, achieving Cd 0.14, compared to Cd 0.197, for the standard production version.
In the last session at DARKO, the 'baby' template car demonstrated a drag reduction with elongation ( fineness ratio). ( Cd 0.151, to Cd 0.121 ).
In the same test session, Spirit of Ecomodder indicated from Cd 0.44, to as low as Cd 0.214, as a simulated BEV.
2015's Mercedes-Benz IAA demonstrated a drag reduction with elongation ( fineness ratio ).

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Last edited by aerohead; 09-02-2020 at 12:58 PM.. Reason: typo
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