"WET WINGS" answer s.v.p.?

Question

How are wet wings sealed? if there is no 'bladder' what keeps the fuel from leaking through the rivets and seams in the wing?

Answer 1

This is a very good question to ask and to answer your question correctly I need to provide a little back information so bare with me.

Various areas of airframe structures are sealed compartments where fuels or air must be confined.  Some of these areas contain fuel tanks; others consist of pressurized compartments such as the cabin.  Because it is impossible to seal these areas completely airtight with a riveted joint alone, a sealing compound or sealant must be used.  Sealants are also used to add aerodynamic smoothness to exposed surfaces such as seams and joints in the wings and fuselage.

Three types of seals are ordinarily used. Rubber seals are installed at all points where frequent breaking of the seal is necessary, such as emergency exits and entrance doors. Sealing compounds are used at points where the seal is seldom broken except for structural maintenance or part replacement, as with riveted lap and butt seams. Special seals are required for passing cables, tubing, mechanical linkages, or wires out of the pressurized or sealed areas.

Certain areas of all aircraft are sealed to withstand pressurization by air, to prevent leakage of fuel, to prevent passage of fumes, or to prevent corrosion by sealing against the weather.  Most sealants consist of two or more ingredients properly proportioned and compounded to obtain the best results.  Some materials are ready for use as packaged, but others will require mixing before application.

Inside fuel tanks such as the wings on large aircraft the fuel tank seams are sealed with the sealant.  This is usually a two step process using MIL-8802-A2 and when it has cured a second coat of MIL-8802B2 is applied over it.  Only the seams, rivet shop heads, nuts and fasteners that protrude into the fuel tanks are sealed.

NOTE the whole fuel tank is not sprayed with sealant, just as noted above.

Pressure tightness of an area or section is checked before and after a repair is made.  Ground pressurization is accomplished by filling the section with air from an external source through ground pressure test fittings.

With the sections pressurized to a given pressure, locate leaks on the outside of the aircraft by applying a soapless bubble solution to all seams and joints in the suspected area. Air bubbles will locate the general area of leakage.  A specific leak is then isolated on the inside of the aircraft by passing the free end of a stethoscope or similar listening device along the seams in the leakage area. The leak can be detected by the change in sound when the instrument passes over it. After completing the test, remove the soapless bubble solution from the outside of the aircraft by washing with clear water to prevent corrosion.

Any sizeable fuel leak is an indication that an area may have received overloads which have broken the sealant and opened the seams

Answer 2

Sealant is sprayed on the inside surfaces of the fuel tank, coating them and making them leak proof.

Answer 3

And alot leak anyway, SNJ-2s and BT-13s are notorious for this.