"Larry Dighera" wrote:
I've been parking
my airplane under a shelter within a mile of Mobile Bay for five years.
I never top up the tanks after a flight. In that time, I don't recall
ever sumping a drop of water out of any of the drains.

That doesn't mean there is no water in your C-172RG's fuel system.

If there has been, I haven't seen--or felt--any evidence of it. While small
amounts might get stuck behind the fuel tank baffles, at least a *little*
should have shown up in the samples in all that time, don't you think? After
all, the airplane is parked in one of the most persistently humid locations
in the U. S. Day after day, warm, wet afternoons are followed by mornings
where the OAT falls to the dewpoint; you literally could wash my airplane
many mornings without using a hose. Those are perfect conditions for the
respiration/condensation scenario you fear, but they just don't seem to put
any detectable amount of water in my tanks. Why is that?

Are there rubber bladders in its fuel tanks?

No.

Now, how about some calculations showing that fuel tank respiration caused by
daily temperature fluctuations can cause enough air changes to produce
significant added condensation?

[snip]
--
Dan
C-172RG at BFM