Hi Tom,

Good guess, but it's not the fixture drag per se, as we tare and subtract that; there are probably slightly different fixture interactions though. This is another plus for us when using CFD: Just like in real life, there's no holding fixture in CFD. (Unless we want to include it.)

There are many small but significant differences between any two wind tunnels. Like Chuck Zimmer used to tell me when I was a young associate engineer at GKN Aerospace: "As usual Damon, it's more than one thing!" So far it's just been easier for us to compare results from the same tunnel.

As for CdA, point taken. But the balance actually measures the drag force, and we report the drag force; CdA would be subsequently calculated from that, so I'm not seeing how it would allow us to compare results from different tunnels any better. Drag force is just what we work in; my mind is more used to it (I hope that doesn't mean I'm getting old! LOL).

Cheers,

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Damon Rinard
Engineering Manager,
CSG Road Engineering Department
Cannondale & GT Bicycles
(ex-Cervelo, ex-Trek, ex-Velomax, ex-Kestrel)