Leak Checking Static air lines

[Bob_H]

I'm new to the forum and impressed by the questions and answers. Perhaps you can help with a problem to leak check static air lines in my Pulsar. The VSI appears to read low by about 50% as determined by flying formation with a Bonanza and climbing. Replaced VSI gage and suspect a leak in lines. However, altimeter and airspeed appear to be correct, so maybe there is a small leak?
I was planning to disconnect the static source from A/S, VSI, and Altim, cap off fittings and apply a light positive pressure to lines and bubble solution the whole system looking for a leak. This is a real issue on a Pulsar as space is tight, especially under panel. If anyone has a better solution, I would appreciate comments.
Bob H

 

[Delta_Zulu]

Why disconnect and cap off?

Anytime we ran into excessive leak down rates all we did was to apply leak tech (or dishsoap and water solution) to all connections (when pressurized) and look for bubbles (leaks). Then correct those joints where the leaks occurr. If there are no leaks at any joints then you have to suspect the gauges themselves, and to isolate those, you have to start disconnecting and capping until the faulty gauge is isolated.

Don't forget to leak check your test equipment to port connections as well.

 

[khorton]

The VSI appears to read low by about 50% as determined by flying formation with a Bonanza and climbing. Replaced VSI gage and suspect a leak in lines. However, altimeter and airspeed appear to be correct, so maybe there is a small leak?

If you want to check the VSI accuracy, don't compare it against another aircraft, as you have no way of knowing how accurate his VSI is.  I communicated with a Debonair (lower powered Bonanza variant) pilot a few years ago who was raving about the performance after an engine upgrade to 300 hp - he loved the 5,000 ft/mn climb rate.  He had a hard time believing me that the reported performance was not consistent with the laws of physics as they were currently understood.  He eventually sent me a video of the cockpit, which did in fact show the VSI stabilized at a 5,000 ft/mn climb.  But if you timed the altimeter against a stopwatch, it only showed a 1,600 ft/mn climb rate, which was much more plausible.

So, to check VSI accuracy, use a stop watch against the altimeter.  Set up in a stabilised climb at a constant airspeed, start the stop watch at the next 1,000 ft, then stop it 1,000 ft higher.  Note the VSI during the climb, and compare against what you calculated from the altimeter and stop watch.

If you want to check for a static system leak, gently suck on the static port to increase the altimeter reading by 1,000 ft, then block the static port.  The altimeter should not decrease more than 100 ft in the next minute.  This is the allowable leak tolerance called up in Appendix E to FAR 43 which points to FAR 23.1325.  You don't want to disconnect any instruments, as the leak could be inside an instrument.

 

[dynonsupport]

If our altimeter is right, it's pretty much impossible for the VSI to be off. Our VSI is just a stopwatch hooked to our altimeter reading, and we're pretty darn sure after shipping thousands of units that we got the math right.

As mentioned, it is much more likely for the completely independent VSI gauge to be off. Since our altimeter and VSI are the same sensor, they should always match. A leak in the system would mess up the altimeter and the VSI at the same time. A leak is actually much more likely to just mess up the altimeter, since it will cause an offset but changes will still be pretty close (unless you're accelerating or decelerating).