A/S calibration after paint

[jjconstant]

I'll be doing this in the coming week, but I just wanted to check in and see if folks noticed any differences in airspeed calibration after paint. After all the fussing and filing I did to the static port to get things predictable the paint has definitely altered the shape of the dome on the rivet head on the static ports. Based on the amount I had to remove to get it right my initial guess is that the different shape might cause as much as a 3-5kt change in indications at some unkown airpseed. Has anyone checked to see the difference?

 

[Mel]

Sounds to me like you have waaaaaay too much paint.
Paint should NOT alter the shape of your static air fitting.
Be sure to do a new weight & balance.

 

[jjconstant]

W&B

Already done Mel. New W&B came in at 30 extra lbs and of course moved the C.G aft. 4 colors and clear coat. The static ports are in the orange color field and it seems to be the thickest paint/primer. The paint seems to have re-rounded the head where I had filed it flat. I think it is mostly a surface tension thing rather than a paint thickness thing. When the painter took a look at my scheme he recommended a specific DuPont paint product and clear coat. He has also painted other planes in the chapter with Jet Glo and other products, depending on the scheme and metalic/no metalic choices. He felt the DuPont paint and clear was the best compromise between looks and weight. Other folks' less complicated and fewer color paint jobs and no clear seem to come in between 20 and 25lbs so I'm O.K. with the extra 5lbs. I don't think it's that excessive. If there are issues I can revert to filing the dome down again, just like I did in the initial calibration.

 

[jimgreen]

Are you using Van's hi tec rivet static ports? Mine seem to give accurate airspeed readings without any filing. In any case, I don't see a need for perfect accuracy except to avoid exceeding limiting speeds. I think most people treat those speeds conservatively.

I prefer masking off the ports and leaving them naked. Much less chance of paint interfering with the air flow.
It would be easy to remove the original rivets and replace them with new. Probably could be done quite neatly without spoiling your paint if you cut the paint around the rivet first.

 

[Mel]

I am in full agreement with Jim.
Cut the paint around your port and remove all paint from the port.
Frankly, the port should have been masked off before paint anyway.

Actually paint should come in between 15-20 lbs. Even 25 lbs. is to high for my taste.
Many paint shops are putting on too much paint these days. If you look at the older painters such as "Poplaski", his paint jobs last for many decades and seldom added more than 18 lbs.

My paint job added 18 lbs and looks great after 19 years.

 

[jjconstant]

just to close out the thread...

...even though there was a visible change to the contour of the pop rivet head, there was no real difference in airspeed calibration. Quite different from the initial calibrating, where even seemingly insignificant changes yielded different results. It sure looks better now, too