Quote:
Originally Posted by JulianEdgar
I think it is impossible to accurately calculate Cd* by coastdown tests, without very sophisticated data gathering (including real time wind/yaw) and very good modelling (including all rotational inertias).
Given the high speeds you are using, it might be possible to measure some relative changes in drag. Do the tests again with windows up / windows down and see how much consistent difference in speeds you can record after 50 seconds.
(* let alone to three decimal places!!)
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After trying coast down testing several times this summer, I agree with all of this. It was just about impossible to get data consistent enough to show a change in drag with the windows up versus down, let alone try to calculate the cD with that spreadsheet (which I tried the first time. It came up with a radically different cR and higher cD with windows up than down!).
I wish there was anywhere here that I could do 100+ mph legally.