When I get a new airplane I typically look at the systems to see how well they are calibrated. I am working my way through the systems on my new Carbon Cub SS with the G3X panel. So far I have confirmed the compass system is calibrated perfectly. Very little error.

This SS came with the relatively new static ports on the cowl. This was an addition to the SS and I think other models via an SB several years ago. I added the static ports to my 2014 SS and found that they induced a speed related error in that aircraft. Far better than sensing static pressure from the cockpit but not without error. In my 2014 CC SS the error increased linearly with TAS. An error of around 2 mph around 90 mph and up to 5 mph around a TAS of 110. These measurements were made near sea level.

I just finished several runs with the 2020 SS and see about the same airspeed related error. For those who have never calibrated TAS in their airplane it is easy to do with this on line calculator.

I know we are dealing with a cub so why does it matter if the TAS is not accurate? The G3X system is so precise in the calculations it really messes up the winds aloft calculation when the TAS is not accurate. Otherwise no big deal except it shows the airplane flying faster than it really is. The good news is the error is very small near landing speed.

Why is there an error? Cubcrafters uses a raised static port button on each side of the cowl. Most static ports are flush with the skin. Most likely a slight amount of lower pressure is caused by the edge of the static port button as air moves across the cowl. There are tricks to change the shape of the static port to even out these errors.