leakage through flight computer

[thomas]

I did a leak test on my instruments and plumbing because I suspect my
ASI to be indicating low. I was surprised to find a rather large
leakage through the MNAV. I understand why the MNAV leaks, but would
welcome input from others on whether my observations are normal or not
before I open the instrument. Without the MNAV, the total pressure
line holds the pressure very well. If I include the MNAV, I am losing
total pressure at a rate of about 10knots/4sec (rough estimate, at
100knots). I didn’t add an additional capacity to the pressure line to
stabilize the pressure.

I do not need input on true vs. indicated airspeed. But I would
welcome input from others who have looked at such instrument leakages
as well.

Regards,

Thomas

[John Ferguson]

Cambridge equipment leaks air from the pitot line as it uses a flow
arrangement rather than a pressure sensor. Worried me as well till I
worked it out.

Some glider makers insist on a separate pitot arrangement for such varios
in order that the asi does not under read. An LS7 I used to have have a
three way probe and a standard pitot installed for this reason.