﻿DECAYS AND DISCOLO RATIONS IN AIRPLANE WOODS. 41 



place when not in use will suffice in most climates. There is more 

 danger in humid tropical or semitropical regions, particularly to 

 seaplanes. 



Serious loss can easily result to machines through improper han- 

 dling while being stored or shipped. Airplanes are usually knocked 

 down for storing and shipping; that is, the machine is taken apart, 

 and the individual assemblies, such as the wings, tail surfaces, and 

 fuselage, are handled separately. When shipped, these parts are 

 carefully wrapped in heavy paper and packed in solid crates. If 

 these crates are left out in the air, cracks open up between the boards, 

 water may get in, and then the trouble commences. Once damp, it 

 is almost impossible for the mass of paper wrappings to dry out un- 

 less the crate is completely unpacked. Varnish or dope does not 

 prevent the taking up of moisture, so that the wood soon attains a 

 moisture content sufficient for the growth of molds and wood-destroy- 

 ing fungi, while the other conditions within the crate, such as lack 

 of air circulation with the resulting high humidity and the higher 

 temperatures, are ideal for the development of these organisms. 

 Even before the wood is decayed the elements of the ply wood are 

 very likely to separate, owing to the action of moisture and molds on 

 the glue. Even water-resistant glues can not permanently withstand 

 such conditions. 



There is no cure for decay, once it has started. The damaged 

 part can be replaced and further destruction prevented, but the con- 

 stant aim should be not to let decay begin. Material should not be 

 kept in packing cases any longer than is necessary. The practice 

 of leaving packing cases containing airplanes or spare parts in the 

 open for several months can not be too severely condemned. 



When put in storage, the parts should be removed from the cases 

 and placed on racks, so that a complete circulation of air is possible 

 around each unit or piece. The storage houses should be equipped 

 with a forced- ventilation system, so that air of the proper humidity 

 can be constantly circulated through the piles of material. The 

 relative humidity should be maintained at 60 which will keep the 

 wood at a moisture content of about 11 per cent, low enough to pre- 

 vent decay, mold, or sap-stain. 



Circumstances will arise where planes are in use or while being 

 shipped when it will be impossible to maintain proper conditions to 

 prevent deterioration. In the warm climate and high humidity of 

 tropical or semitropical regions in particular this will be true. It 

 is advisable to have planes for use under such conditions constructed 

 from a durable wood such as Port Orford cedar. Where this can 

 not be done, methods should be employed to make the other species 

 more durable. 



Wood may be moisture-proofed by the application of aluminum 

 leaf. This not only prevents decay, since the wood is kept dry, but 

 protects the glue joints from the action of moisture and mold. 



As a last resort, the wood could be treated with preservatives to 

 prevent decay. These liquids are most effective when forced into 

 the wood under pressure. Consequently the completed individual 

 wood parts would have to be treated before assembly. Sodium 

 fluorid could be used on parts to be glued, while coal-tar creosote 

 could be applied to the others. The most highly efficient of all, 



