During the interruption caused by computer problems last month, the Chukka project reached its final stages. With the fuselage top and the wing root planked and the wing ready for covering, it was time for tissue, nylon, and dope. First the sheeted areas had to be treated ready for the covering, treatment that is initially the same whether tissue is to be used, or nylon. Tissue covering over sheet balsa is an old traditional practice and gives a fine surface with a modest amount of filling and rubbing down. Nylon is stronger but the weave takes more filling, and there is a danger, when rubbing it, of bringing up the nap of the fabric - a hairy surface, which then can be difficult to subdue. The first stage is a coat of clear gloss dope directly on to the sheet areas, to begin to seal the wood. Next it has to be sanded lightly to remove the roughness of the surface caused by fine wood fibres that are raised and hardened by the dope. Then it is ready for a coat of sanding sealer, after which the layer of tissue or nylon can be applied. Without this first layer of sanding sealer, or perhaps two coats, the texture of the wood grain tends to show through the covering. When clear dope is applied to nylon over sheeting, small bubbles can develop in the surface if the wood has not been sealed, leaving marks that are tricky to remove, calling for extra sanding and more coats of dope. These are rarely necessary if enough sanding sealer is applied before the fabric.
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