As a result of some pretty funky vario behavior at the recent Bermuda High regional contest, I decided to leak test my new (to me) V2cx ship. I took as my guideline the excellent 2000 (updated in 2008) article on this subject by Mike Borgelt of Borgelt Instruments (http://www.borgeltinstruments.com/Leaks.pdf). Thanks Mike!

My ship has a Borgelt B40 vario and a SN10B vario. A single TE line comes out of the tubing channel under the instrument panel, and is T'd there to both the B40 and the SN10, with about 5" tubing runs from the T to the SN10/B40 (i.e. about 10" of tubing run between the two). Pretty much the same geometry with the Pitot and Static lines - single line coming into the instrument panel area, and short connectors to the instruments. I have read that at least the TE line should be T'd well away from the instrument (one article recommended T'in the TE line under the pilot's seat so that the instrument-to-instrument length is 10-15'), so I'm a little concerned about that part. I've also read that the SN10B is a 'flow' instrument (don't know about the B40). Any comments on this?

To conduct the tests, I first tested the ASI and verified that it was working properly. Then I used it to measure leakage rates for the Pitot, Static, and TE lines.

Pitot: I attached a long length of tubing to the tailfin-mounted pitot port, and carefully pressurized the line to 95KT indicated. Then I clamped the line with a hemostat, and watched for decreasing airspeed. It took approximately 4 minutes to go from the initial 95KT to 90Kt.

Static: I taped off all 4 static ports, and then replaced the transponder's static line with my test line, connected to a 60ml syringe. I slowly pulled negative pressure until the ASI read about 100KT, and clamped the line off with the hemostat. In this test, it took about 3 minutes to decrease 5Kt, from 100KT to 95KT.

TE: For this test, I replaced the ASI's static line with the TE line from my SN10, leaving the B40 still connected to the TE system. Then I attached a long length of tubing to the tailfin-mounted TE port, and carefully pulled negative pressure to achieve 120KTIAS. Then I clamped the hose as before with the hemostat. In this test, it only took about 30 seconds for the ASI to decrease 10KT to 110KT, and another 30 seconds to decrease to 100KT.

Leak Rates:

Pitot: 5Kt in 4 minutes = 1.25Kt/min
Static: 5Kt in 3 minutes = 1.33Kt/min
TE: 5Kt in 0.5 minutes = 10Kt/min (almost an order of magnitude higher!)

Any thoughts and/or advice on whether these leak rates are normal or excessive, and how to proceed from here would be appreciated.

TIA,

Frank (TA)