Quote:
Originally Posted by 3-Wheeler
So if Metro had a fuel mileage efficiency gain of 15% with the boat tail, then according to what Aerohead has mentioned...
Metro would also have had a CdA reduction of 15% * 2 = 30%
So if Metro were to do a coast down test, his distance should improve by roughly 30% since he now has that much less aero drag (ignoring Crr for a moment).
Again I can't vouch for what Aerohead is saying, but if true, then above is accurate.
Not to belabor the point, but Metro would certainly want to do his mileage test on an almost calm day to make deciphering the data easier.
Fortunately he measured his fuel consumption going both directions on the road for A..B..A, so any change in air drag (wind speed and resultant fuel consumption) would show up.
Jim.
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Darin is very careful about selecting days to test when wind is as small of a variable as possible. If its windy, he cancels the test and waits for another day.
What Aerohead said is true, but much more of a general rule. I assume you are talking about the rule that says something to the effect of 'A 20% reduction in Cd gives a 10% improvement in FE'. That is not going to the case at 55 mph
and at 20 mph. Its just a general rule.