"Dave Saylor" <Dave@AirCraftersLLC.com> wrote:

" [Re: Dynon pitot tube]  It has a port for the AOA which we will plumb to the panel for future use.  It's a little longer and much lighter (heated may weigh more?) than the AN pitot.
"

The Dynon pitot tube is designed as a multi-functional unit, to be used for both pitot and AOA data.  Pitot tubes that mount under the wing are fairly close to the lower wing skin in order to take advantage of the airflow's following the shape of that skin... this keeps the air flowing pretty much straight into the end of the pitot, giving you accurate airspeed pressure most of the time.  Unfortunately, in that configuration it's doing the wrong thing to accurately measure AOA, especially at high angles of attack.  In order to accurately sense the AOA on the tube (ie, become an alpha probe) it needs to be further out from the edge of the boundary layer.  This is why they came up with their mount extension... to distance the AOA port from the boundary layer wind and get it more into the relative wind.  Unfortunately, with the pickup out of the edges of the boundary layer, the airpeed pressure will be incorrect because the relative wind isn't hitting the hole in the end of the pitot straight on.  This is why, at high angles of attack, most airspeed indicators become very unreliable.

What this boils down to is another decision.  Do you want the pitot tube to provide accurate pressure over the greatest range of airspeeds?  If so, use the one with the short mount to keep the pitot port closer to the boundary layer.  If you don't care about the airspeed accuracy so much but would rather get accurate AOA info, use the entended mount so the AOA ports are actually out in the relative (not boundary layer) wind.  Point in fact, there is no free lunch.

   Marv