[MSFT-1]

I am early in Phase I with my RV-10 and most of the squawks are being cleared (and the early numbers look very good on temps/pressures etc.).

One strange problem is that the indicated airspeed on both the GRT and the backup airspeed indicator are too high by more than ten knots. I have heard of several instances where the airspeed reads too low but not too high. Anyone have any thoughts on where to investigate a problem like this?

thanks!

 

[Kevin Horton]

Four possible sources, off the top of my head:

1. Check for a static system leak. If you have the vents closed, the air in the cockpit may very well be at lower pressure than the free stream ambient pressure, as the air is sucked out around leaks at doors, canopy seals, etc. A static leak in the cockpit could cause the static pressure at the ASI to be too low, leading to a too high IAS, and a too high altimeter.

2. Do you have a completely standard static port? I.e. as designed by Van, in every respect - same location, same part number rivets, etc?

3. What are you using as your truth data to say what the IAS really should be? How are you calculating the correct IAS? Maybe, just maybe, there is a problem with the test technique, or the data analysis.

4. Is it possible that both the GRT and backup ASI have significant instrument error? It would seem unlikely that both instruments would have a similar problem, but stranger things have happened.

 

[Ironflight]

I had a flight where my IAS suddenly started reading about 10 knots high. Assuming that I had not suddenly shed drag or gained horsepower, I checked behind the panel, and sure enough, I had a loose static line that caused a system leak....drat!