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"Fokker used various tube diameters, but for their famous WWI fighter fuselages (like the Dr.I & D.VII), they used 20mm diameter steel tubing for main longerons, with smaller tubes for other structural parts, while modern RC models use metric sizes like 5mm, 6mm, or 1/16-inch tubing, depending on the scale and component. The actual diameter depended heavily on the specific aircraft model (e.g., Dr.I triplane vs. D.VII), part (longerons, struts, control cables), and era. .."
Fokker Dr.I (Triplane): Main longerons (fuselage frame) were typically 20mm diameter steel tubing.
Fokker D.VII: Also used steel tube frameworks, with diameters varying by component.
Fokker FG-2 (RC Glider): Used smaller tubes like 6x0.25mm for central spars and 5mm tubes soldered in.