My airspeed reads normal in takeoff roll but falls to erroneously low values during climb done at a normal angle of attack and normal GPS ground speed. In cruise it catches up and goes higher than it should be. In descent it reads much higher than it should. Both the round gauge and the G-5 are doing this. The altimeter is normal but the VSI lags level changes in a sluggish way. Before I start chasing this, who has experienced the same and where should I start? I have blown out the tube itself with no positive results.
You have a blockage in the STATIC line. Check to make sure your lines are installed properly in the tailcone area with no low spots in whcih water can collect. That is usually the primary culprit.
If that's OK. Then you have a blockage or perhaps a kinked STATIC line.
If you happened to put an alternate static port on your panel, activate it and all will be well (except airspeed will read a little high and so will altitude due to the lower pressure of the cabin area).
Here's a little primer to help you understand why you are seeing your erroneous numbers:
With a blocked static line the pressure inside the static line actually increases as you climb, so it puts HIGH PRESSURE on the static side of the airspeed, causing it to read low. ONce it equalizes in cruise (due to a slow leak usually) it will read close to normal.
On descent, the reverse is happening. The pressure inside the static line now decreases, so the airspeed reads high.
For those who might be confused about the pressure increasing in a climb, and decreasing in the descent, keep in mind that this is with a BLOCKED line.
Vic