Quote:
Originally Posted by Nerys
...I don't even think a 10mph change in wind would have more than a few % impact on the results....
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I've been mulling this over for the last two days, and have to say that a 10 mph difference is a big deal.
For example, we know that air drag is affected by (velocity)^2, so if Metro were driving at 56 mph as he indicated and going into a 10 mph head wind, the effective wind forces would be:
(66)^2 / (56)^2 = 1.38 or a
38% increase in drag.
Likewise if Metro were going with the wind, then it work out to:
(56)^2 / (46)^2 = 1.48 or a
48% reduction in drag.
Both numbers are nothing to sneeze at...
Metro was very wise to maintain his speed through the test within 1 mph or so. A 1 mph change amounts to...
(56)^2 / (55)^2 = 3.7%
If his speed varied by ± 1 mph then our measurement uncertainty for the gas mileage difference for the boat tail addition would be ± (3.7%/2) according to AeroHead, where the air drag forces affects the ultimate gas mileage by half.
Just my .02.
Jim.