What other ways are there?
What I was trying to get at, is if you need to recalibrate when you change configurations, you're screwed. The sensor needs to be located in a place where the changes you are making won't affect it. If *that* is true, then calibrating by assuming the wind cancels is fine. You just need to have the same calibration for both configurations. Calibration accuracy is not so important then. Your absolute CdA value will still be off, but there won't be any bias favoring one of the setups.
If I calibrate for configuration A and it's +1% off (airspeed says 50.5km/hr when it's really 50), and I calibrate for configuration B and it's -1%, I've just introduced a 2% airspeed bias in favor of A. That's about a 5% CdA bias in favor of A! See the problem? B could actually be 4% better than A, but you'd erroneously think A was better.
What I was trying to get at, is if you need to recalibrate when you change configurations, you're screwed. The sensor needs to be located in a place where the changes you are making won't affect it. If *that* is true, then calibrating by assuming the wind cancels is fine. You just need to have the same calibration for both configurations. Calibration accuracy is not so important then. Your absolute CdA value will still be off, but there won't be any bias favoring one of the setups.
If I calibrate for configuration A and it's +1% off (airspeed says 50.5km/hr when it's really 50), and I calibrate for configuration B and it's -1%, I've just introduced a 2% airspeed bias in favor of A. That's about a 5% CdA bias in favor of A! See the problem? B could actually be 4% better than A, but you'd erroneously think A was better.