Quote:
Originally Posted by Ecky
Finally summer in the southern hemisphere, so we get some more hard data posts from Julian!
Approximately what does this add up to in Cd? Any chance of a coast down test?
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I've been doing a lot of aero testing over the last 6 months, so posting quite a lot of hard data.
I am confident that amateurs doing coastdown testing, unless perhaps done only between two very high speeds, does not give valid results.
Refer to SAE papers 950626 -
ABCD –An Improved Coast Down Test and Analysis Method and 940420 -
A Detailed Drag Study Using the Coastdown Method to see the level of complexity required to get valid coastdown results.
Or just do a series of tests, windows up / windows down in both directions - you should of course see a marked increase in drag with the windows down. I have never been able to detect this via coastdowns. On the other hand, throttle-stop testing sees this change every time.
The throttle-stop testing showed a change in drag with the air curtains of about 5 per cent. I never work from those figure to a proposed change in Cd, as I think such an extrapolation is too unreliable.