Erratic airspeed indication

[60av8tor]

Having fits with my airspeed indication - constantly moving several knots.  Obviously worse the more turbulent it is, but even in calm air the indicator is always moving up a knot down a knot, etc.

It's one of those things that I cannot remember if it was rock steady before or not.  I look at old EMS data, but still hard to tell if/how much worse it has gotten over time.

I upgraded my pitot tube to the  replacement (heated AoA), but again cannot remember the difference pre/post change out.  Shortly after, I went for an IFR pitot-static check and failed for static leaks.  I have since replumbed, but have not gone back for another check yet. 

So, how about the others - airspeed rock steady in relatively calm air?  It's like mine has become super-sensitive constantly in motion.  Even on final with a steady glide slope - 70-68-71-70-69-65-70...  Any chance the check could have affected my ASI? 

Wish I had more specific info, but I've just lived with it for so long now that I cannot remember how long it has been like this, if it has gradually gotten worse, etc.

 

[thibault]

While in the hangar, get a balloon, blow it up, and put it on the pitot tube far enough so that it covers the drain hole.

If there are no leaks between the tube and the ADAHRS box, then the reading should be rock steady.  If it isn't, then there is something electronic going on.

 

[S5_aero]

I also had the same thing. try opening and closing the window or anithing else that changes pressure inside your cabin, you will see dramatic changes on gauges that uses static pressure (altimeter, vario and airspeed). This indicates you have static leakage. If this is not the case and you have only airspeed gauge problem. then it is probably dinamic pressure from pitot.
Also try if you use rudder pedals if your static gauges are stable. Perhaps you have static port cloged on one side.

 

[60av8tor]

Thank you both for the info - no issue with vs/alt (however I'll double check next flight). Good idea for the pitot leak check. This will be my next trouble shooting step.

 

[Carl_Froehlich]

A fail proof way to test the pitot plumbing for leaks and airspeed indication accuracy on the ground is to make a simple manometer out of some 3/8" clear tubing, a vertical piece of plywood for a mount and water column height chart calibrated in knots. Attached PDF file provides instructions.
Carl
RV-10

 

[60av8tor]

A fail proof way to test the pitot plumbing for leaks and airspeed indication accuracy on the ground is to make a simple manometer out of some 3/8" clear tubing, a vertical piece of plywood for a mount and water column height chart calibrated in knots.  Attached PDF file provides instructions.
Carl
RV-10

Thanks, Carl.  That was my plan eventually - to make a manometer.  But I've been lazy :-[.  The balloon idea was a good stand in for my laziness, however.  Removed the tube and using the balloon, I found the culprit (we'll see if this is the only leak).  Yes, that says China :-/

 

[Carl_Froehlich]

Jon,

I know of many people regretting use of such quick connect unions for the same reason - leaks.

BTW - the same rig can be used to check for static system leaks before you have a guy on the clock doing your pitot/static biannual check. For static you tape over the static ports, connect into the static system and suck a few inches of water and see if the altimeter stays put.

 

[60av8tor]

Jon,

I know of many people regretting use of such quick connect unions for the same reason - leaks.

BTW - the same rig can be used to check for static system leaks before you have a guy on the clock doing your pitot/static biannual check.  For static you tape over the static ports, connect into the static system and suck a few inches of water and see if the altimeter stays put.

Thanks a lot for the help, Carl. Still on the to-do list for the reason you state