With the firewall and tail ring mounting structures completed, it is time to "swiss cheese" the structures to reduce weight. The overall shape of the firewall lended itself fairly well to a number of holes of various sizes (drilled with Forstner bits) while the tail ring former had room for some substantial "windows". Forstner bits were used to cuts holes in the firewall and the corners of the windows in the tail ring former. After drilling the corners of each window, the four sides were cut using a fine tooth blade on a scroll saw. An additional function of the holes in the mounting structures is to allow cooling air to pass through the fuselage.
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