Jim,
There are many different ways to cut inspection holes and use Pro Seal (you
can get Pro Seal from Aircraft Spruce, MEK at any hardware) and every builder
seems to have a different method.
I used a two headed fly wheel circle cutter to cut inspection holes (bought
at Harbor Freight) because you can use it free hand with a drill. Practice on
some scrap, aluminum to gain confidence, before attempting to use it on the
under wing skin.
If you cut the holes in the tank you will need to make doubler rings that
rivet to the tank skin and over lap the hole you cut out, leaving a 1/2"
flange to attach the cover plate you will have to make. Use tank rivets and
Pro Seal to seal everything. You will most likely have to make two or three
holes in each leaking tank.
If the holes are cut in the bay aft of the wing tank (like I did) you will
only need to make cover plates to over lap the hole and attach them with
Truss screws, anchor nuts and bolts or clip nuts.
To pressurize the tank and test for leaks, keep it simple. Rubber band a
latex glove over the tank filler cap. Put a rubber hose on the tank shut off
valve, plug all other openings and blow into the hose until the glove stands
up and shut the value to trap the air. If you have a leak the glove will
visibly deflate in a short time. Be sure to maintain a constant temperature.
If you come back the next day and the temperature is colder or warmer the
glove will deflate or expand accordingly. This is not a leak. bring the room
up to the same temperature and check the glove again. Barometric pressure
changes may effect this as well but I never experienced a noticeable
difference.
MEK is not good to touch or breath so protect your hands with gloves and use
a painters mask. Pro Seal comes in thick and thin. I have never used the thin
but many builders say it works well to patch holes because it can be brushed.
I use pop sickle sticks to apply the thick type. Good luck.
Bruce G 357R
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