I had my pitot tube freeze up at 15,000′ last summer in IMC. The Dynon algorithm doesn’t handle this situation very well; it’s supposed to fall back to GPS ground speed in the attitude calculation if the pitot indication is lost, but that apparently only works if the airspeed actually goes to zero. If the pitot tube is only partially frozen over and the airspeed is fluctuating, the indicated pitch attitude of the aircraft will swing widely and the autopilot will try to follow it. That’s frankly dangerous and Dynon should address this.
To reduce the likelyhood of this happening, I ordered a heated pitot tube and finally took the opportunity today to install it.
The heated pitot tube requires the installation of a heated pitot controller near the pitot tube. If I were installing this during the initial build, I would have mounted this to a nearby rib, but that was going to be rather challenging in a completed wing, so I decided to install it to the adjacent access plate. I drilled four mounting holes and dimpled them so that the screws sit flush. With the plate installed, none of the wires can rub on the controller or access plate nut plates.
I had to fish three additional wires out to the controller (power, ground, and sense wire to be routed to the EMS). Unfortunately, I ran the wing wires through a snap bushing in the fuselage and then into the wing conduit between the wing and fuselage. The additional wires wouldn’t fit through the snap bushing, so I had to cut it out and then use some RTV to prevent the wires from chafing on the edge of the hole. If I were building again, I would have drilled a larger hole in the side of the fuselage and left the wing conduit long so that it penetrated into the fuselage. It would have made running these additional wires substantially easier. The sense wire is not currently connected to the EMS as accessing it is quite difficult. I’m planning on adding the forward fuselage access panels at some point and will hook up the sense wire when I do that.
