Prevention of Corrosion in Duralumin Airplane Structures 290066
AT first believed immune, aluminum alloys have been found extremely susceptible to both surface corrosion and intercrystalline corrosion. The latter goes on under paint that has been applied to imperfectly cleaned surfaces, and shows only as blisters. Because of this, it has become commonplace to break with the fingers the ribs and the trailing edges of duralumin lower wings and tail-surfaces.
Contact of duralumin with brass or steel hastens corrosion, and protective paint coverings are dissolved by dope where fabric surfaces meet metal parts.
All-duralumin structures are not considered suitable for sea-going aircraft unless all joints and seams are of water-tight construction, not only in hulls but in other members of the structure. Corrosion over the land is much less severe.
Few manufacturers seem awake to the importance of corrosion. The fight to avoid it should begin with avoiding seams that are difficult to protect and hollow members that cannot be sealed hermetically.
Service precautions recommended include greasing at points that are hard to clean, a thorough washing with fresh water after each flight, and the same precautions in making repairs as in the original building of the airplane.
In the discussion mention is made of C. W. Hall's seaplane, protected only by grease, and various reports are given of European experience with corrosion. It is stated that the duralumin hulls of the flying-boats that received such severe treatment durirg the attempted Rogers flight to Hawaii emerged virtually uninjured, while the all-metal planes used in a recent flight from England to Australia stopped for extensive overhauling necessitated by corrosion.
A thrilling experience with fire in the air, which demonstrated the increased safety secured by metal construction, is related by one discusser.