How to calibrate the ASI?

My airspeed indicator reads about 10 to 12 mph high. Such as when I stall the plane, it stalls at 62 mph indicated with just me in the plane and partial fuel. With full flaps it might drop to 60 mph. Vans advertises 54 to 48 mph so something is not right in mine. My static system is tight as my mode C is bang on with ATC.

But when I look close at my ASI, it is not centered. The needle at rest is off to the right about 10 mph. So I'm thinking that is where the problem is. Looking at the ASI there does not appear to be anything on the outside to adjust it like there is on the VSI.

Has anybody had one of these apart and made any adjustments? Or should I just take it in to an instrument shop?

Thanks

Tim

These are rather sensitive instruments, so be careful if you take it apart ...

I'm not sure that a report from ATC says that your static source is accurate - it just says your altimeter and the encoder say the same thing. How does ATC know your actual altitude? The hangar check just looks at the calibration of the instruments. If you feed it pressure X it will report altitude Y, but is that accurate, without a trailing static cone who knows? If the pressure is off so will be the reported altitude. What does the GPS say (bear in mind this relates to a 29.97 day)? Do you have a buddy in the Navy who serves on a ship with a height finding radar?

If the static is accurate fly some ASI/GPS calibration squares or triangles to figure out if the ASI is out throughout the speed range (careful at high speed).

But, does it really matter? At low speed you will know that your airplane stalls at 60 bananas, so approach at 80 bananas - these numbers may not be mph or knots, but does it matter? At the high speed end of the scale it is a little more important, you would not want to exceed Va or Vne inadvertently, but your error (if its constant through the speed range) is on the safe side.

If you are really worried you may be in for a new ASI - go for a reputable brand made in the US or Germany (ie not China).

Pete

Sounds like you may have a problem with the placement and/or installation of your static port(s). Try the search feature on these forums; there's lots of info on that subject. Getting a good static pressure from the outside of a moving airplane is fairly tricky propositon.

What Pete said

Tempting as it may be to jump to a solution, suggest you consider defining the problem first...

a) try the cal squares/triangles
b) if the ASI consistently shows the same value, under the same conditions, performing the same maneuvers... you're OK, in that you can scan the gauge and know where you are relative to those known values (kts, mph, furlongs per fortnight...)
c) your mileage will vary, compared to every other RV...

the obvious seems to be the ASI

maybe but the obvious seems to be the ASI.

The needle on my ASI does not sit pointing straight up at 0 when it's in the hanger and out of the wind.

The needle is a good 15+ degrees to the right of where Zero would be or indicating about 10 to 15+ mph...............

What % of planes out there indicate 10 to 15+ mph when parked in a hanger out of the wind?

The ASI is not rocket science, I will take it apart and look at it. Worse case is that I take it into an instrument tech to calibrate it.

Tim

Airspeed error

Had a 10 to 12 Knot high indication. Sent it to the manufacture (UMA). Was repaired with a new diaphragm, cleaned, re-calibrated, reinspected and re- certified . Cost of repair $55.00.