Question about static leak and ASI

lr172 · #1 09-21-2016, 08:43 AM

I worked on my static setup in phase I and got within 2 MPH of the GPS numbers (4 leg test). Recently I noticed my IAS reading higher than expected. I ran a couple test runs and am reading about 5-7 MPH high.

At my annual I moved one the soft vynal lines attached to the rivet to be sure that I had Good drainage. I am suspecting that I disturbed the RTV seal and caused some leakage. I taped off one port and used a hose to test. I am seeing about a 100' loss of altitude in about 20 - 30 seconds. I thought the standard is 100' in one minute. Is this type of leakage enough to cause a 7 MPH error in the IAS?

Thanks,

Larry

vic syracuse · #2 09-21-2016, 10:38 AM

Yes, a static leak will cause the airspeed to read high, especially if it is in the aft fuselage where you mentioned it. Most of our cabins are at a lower pressure than the outside air due to the airflow. You can see this effect by opening your alternate static vent while in flight---both the altimeter and the airspeed will increase.
Yes, the 300 FPM leak that you have is not in spec for an IFR cert.

Vic