On Aug 13, 7:40*pm, Tom Nau wrote:
I fly an ASW-28. The under-surface of the wing has a nice little piece
of plastic that covers the dump valve and which is hinged by a piece
of cloth tape. When flying with water ballast my assumption is that
correct procedure is to leave the piece of plastic in place, but open
and hanging down from the cloth tape hinge. I am thinking that airflow
will keep the plastic closed and be more aerodynamic over the dump
valve but when dumping ballast it will open sufficiently to let the
ballast dump efficiently. Or should I simply remove the piece of
plastic entirely when carrying water ballast? *Thanks.
Tom

I noticed during pre-flight that my 28 had lost one so I took the
other off to save as a template. The uncovered dump ports are excited
by the airflow and "sing". Trouble is they sing at slightly different
frequencies. The beat tone is almost unbearable and I nearly
abandoned the flight. The noise stops during dumping. I don't know
if it happens with the dump valves open after all the water is gone.
I suspect they don't sing then as the port resonant frequency should
be very different with the valves open. I wanted to keep my water and
didn't try it. I keep a set of ear plugs in the glider just in case
it happens again.

I cut new ones from clear plastic sheet which I had covered with white
shelf covering. The clear plastic was available and the white shelf
covering made it look better. I attached them with 3M electrical
tape, the same as used for wing gap sealing. The home made ones have
lasted about 7 years compared to 1year for the factory ones. Perhaps
that's because I learned not to hit them when cleaning the wing. It's
also a good idea to replace the tape each year

Andy