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Bell 47 H-1 |
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Bell 47 H-1 |
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Tail pattern |
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This section illustrates the process required to fabricate the tail section. In the interests of saving weight the tail section will be two vacuum formed plastic parts glued together. To get an initial outline of the shape long pieces of wood are cut to length and glued. These are glued to symmetrical plastic card formers . |
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Care was taken to ensure that the shape of the tail section did not interfere with the mechanics; in this case there was ample room for the tail servo to operate. |
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Having established the profile for one side the second symmetrical half can then be made. The shape of the front former is based upon the back of the fuselage pattern built in an earlier stage. |
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The remaining air space is then filled with soft balsa and sanded down to the original formers. Consideration is given to the vac forming process; i.e. 1.5mm styrene will be wrapped around the tail pattern and the actual item will effectively ‘grow’ by 1.5mm in all directions. In contrast to the fuselage pattern where an exact fibreglass replica will be made. Again, when the sanding has been completed the balsa wood is treated with strong epoxy in preparation for the hostile environment of the vac forming machine. |
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At this stage the two halves are hollow, much like two hulls of a boat, and could deform under the pressure and heat of the vac forming machine. To prevent any warping of the pattern the inside is filled with epoxy. |
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To ensure that the plastic faithfully follows the shape of the pattern several holes are drilled close to recesses to ensure that no air remains trapped between the plastic and the pattern that would otherwise distort reproduction. |
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Webmaster: John Neasham |
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