[aerohead]

1) I spent the last two days picking this paper apart.
2) So far, Levon Larsen and Sudesh Woodiga have created more questions than they've answered.
3) If, frontal area- based coefficients of aerodynamic drag are still defined by frontal area, then all but one Cd reported in the drag table are extremely dubious, as all are associated with a different frontal area.
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4) The February, 2015 edition of MOTOR TREND shared most of the 2015 Ford F-150, 3.5-L, Super Crew dimensions, and four views of the truck, from which scale dimensions could be derived and extrapolated to full-scale, as verisimilitude provides for.
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5) I ran calculations for all airdam face sizes, from 5" - to - 9", as the OEM pickup is already fitted with a five-inch airdam.
6) From the 'rule of thumb' metric, a 6.35" airdam would have been selected.
7) On a CdA basis, the drag minimum actually occurs with a seven-inch airdam. So I missed it by 0.65"
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8) The F-150's EPA HWY, 22.00 mpg occurs at a constant 100km/h ( 62-mph ). I reported this back in 2015, after AeroStealth and I tested his F-150, out in West Texas.
9) The lowest drag, seven-inch airdam returned an estimated 22.255-mpg, with a drag force of 139.989-pounds, aerodynamic horsepower of 23.143-hp.
10) The 'rule-of-thumb' airdam returned an estimated 22.200-mpg, @ 140.447-pounds drag, 23.218- aerodynamic horsepower.
11) The eight-inch airdam returned 22.211-mpg, @ 140.341-pounds drag, 23.203-hp.
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12) Without any 'measurement', the 'rule-of-thumb' airdam happened to come in at 0.247% lower mpg than the 'optimum.' ( a quarter of one percent ).
13) The 'rule-of-thumb' airdam came in at 5/100 % lower mpg than the eight-inch airdam ( Ford's claimed minimum drag example ).
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14) Larsen & Woodiga's work is ambiguous. I'm not going to speculate as to the reasons they chose to present their data in the fashion that they did. It doesn't speak well of the Ford Motor Company.
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I have the starting assumptions, premises, and more quanta if anyone's interested.