What angle for airspeed sensor?

[Scott]

(This is relevant to my other post about figuring best glide speed.) I have one of the Flytec impeller-type airspeed sensors. I've noticed several pilots flying with these...but there doesn't seem to be any consensus on the angle at which the impeller should be mounted? (People just stick it on and sort-of-kind-of point it more-or-less forward.)

Since the angle of our downtubes changes with bar position, what's the best angle at which to mount it? And does it even matter? (Shouldn't it ideally be parallel to the airflow?) Or will the small difference in downtube angle not make a noticeable difference in the airspeed these things measure?

Yeah, I know---it's all relative, and as long as I mount it the same way every time, the relative airspeeds (whether remotely realistic or not) should be the same each time I fly, right?

For that matter, are these things even kind-of-sort-of accurate?

Thanks,
Scott

[jimrooney]

Tie a piece of yarn to your corner bracket... it will show you the airflow angle in flight.

Jim