ASI over reading on my Garmin G3X touch

[utawl]

HI,

I test flew my RV8 after a professionally installed avionics and EFIS system by a certified shop. I had a Pitot static done via a digital machine and it showed zero leaks and very accurate to 230kts.

On the test flight I stalled the AC and determined the over read on IAS. I added the 1.3 VSO and had a approach speed of 100 MPH.

I have the standard Pitot tube as supplied, the simple angled into the airstream bent stainless pipe?

Has anybody else had this issue with the G3X IAS scenario? If so I would love to know how you solved it as the install shop don't seem to know? We have emailed Garmin requesting info from them?

Static comes to mind, perhaps a fence in font of the static port either side on the fuselage?

Thank you?

[Carl Froehlich]

Build a simple manometer and verify your ASI is correct. It might be simple but it is very accurate. PM me your email and I’ll provide the PDF file for the scale to convert inches to knots.

If the ASI in correct, then placement and/or shape of the static port is the leading suspect.

Note - for the manometer a big syringe or blood pressure bulb work well for the pressure source. Add a few drops of food color to the water to make it look pretty.

Carl

[Richard Connell]

Respectfully, I would say testing the ASI again is unlikely to solve this problem.
99% of these issues are system leaks or static position errors. I have never heard of a faulty EFIS new out of the box. I’m not saying it hasn’t happened but it’s vanishingly rare.
Given the OP has has his equipment tested professionally already I’d focus on static position error as a priority.
This has been covered extensively here so it’s worth doing a search.

Good luck

[Thermos]

Are you using the hollow rivets (or something shaped like them) and locations for static source as specified by Van's? If not, there's a good chance that this is part or all of the problem. The plans rivet shape and static source location are known provide a good static pressure reference; some builders have tried commercially-available flush ports or ones with sharp edges and ended up with large airspeed/altitude errors. You shouldn't need a fence or other gadgets.

HTH

Dave