DECAYS AND DISCOLORATIONS 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 giue. 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, 
