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Old 06-13-2018, 11:25 AM   #732 (permalink)
aerohead
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disparity

Quote:
Originally Posted by freebeard View Post
I think The Template is ideal in theory only, but I will ask: Do you think the disparity from 30 to 50% is more significant than what's at 80%? It certainly involves more cross-sectional area.

aerohead Can you comment on 'phantom tail' truncations and the reflex curve add-on to the Baby Template? I forget, was it same-same with or without it?

Whoa! Simul-post. I'll have to go back and read that.
*Most of the gains occur early in the boat-tailing.
*Additional elongation suffers diminishing returns.
*Fachsenfeld and Kamm,at the FKFS, considered that a 'practical' length car would be truncated at 50% frontal area,to allow a motorist to navigate urban environments and hazards.
*An extensible tail would allow additional drag reduction on the open highway,when aero would be most important.(like Mercedes has done recently with their concept car).
*The FKFS' best,full-tailed,knife-edged body came in at Cd 0.12,as with Walter Lay's 1933 'car.'
*Unfortunately for us,they never tested this 'ideal' body with a truncated tail at 50% frontal area.
*The Template came in at Cd 0.1487 truncated,and Cd 0.1209 as a long-tail.
*Whether the 18.7% drag reduction of the tail was worth the trouble would be up to the consumer,policy maker,etc..
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*As to the phantom tail on Baby,the smoke indicated its presence.
*The von Mises,reflexion was a concession to extant DOT requirements for tail lights and license plate.(I wanted to simulate a legal road-going automobile)[ I suspect that she paid a price for losing plan taper of the boat tail]
*Using the Cambridge University Eco Racer CUER as a guide,it's conceivable that Baby would have measured in the neighborhood of Cd 0.11 with trailing knife-edges (as Layne commented on) and more closed-in wheel fairings (Goro Tamai).
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