Finally got some hard data on the factory Beech floorboard material. The
Model 76 Duchess shares most of the same floorboard part numbers with the
Models 19/23/24. I have updated the BAC FAQ with this data. Apparently the
original floorboards, which I had measured at a quarter-inch thick, had
swollen somewhat from oil or moisture or both. Or perhaps they were not
really original after all, as they were at least four-ply (though it was
hard to tell on such thin wood). Pay attention to the grade (A-B), as this
will be important in such thin plywood. Any knots or voids would
significantly affect the strength and puncture resistance. Each ply of the
wood will only be 1/16" thick.

***
Floorboards P/N 169-530004-205, -211, -223, -565, -571 are manufactured from
commercial fir plywood sheet, grade A-B, 3 ply, 0.187 thick (nominal 3/16"
thick). Then the floorboards are treated with a fire retardant to meet FAA
requirements.
***

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