"Matched Hole" assembly
"Matched Hole" assembly techniques, pioneered in earlier Thorp designs, make it easier to build the all-metal T-18 than airplanes of less sophisticated performance, made from less desirable structural materials. It is hoped that the T-18 will prove to be the simplest airplane to build yet designed. The numbers of parts have been held to a minimum.
Parts are designed to be made with minimum tooling and minimum shop equipment. Arrangements are being made with specialists to fabricate a relatively few components which require equipment and skills not normally available to amateur constructors. Even in these cases, alternatives are offered so that the entire airplane can be built by the amateur builder, if he so desires.
All rivet holes are put in detail parts before assembly by "hole coordination template techniques". Assembly is accomplished without jigs, "Erector set" fashion. External skins are predominantly .025 or .032 thick 2024 T3 Alclad aluminum. Wing skins are all four feet wide and wrap from trailing edge around to trailing edge without skin laps. They are cut from standard 4 ft. x 12 ft. sheets. The fuselage side skins are cut from one 5 ft. x 15 ft. sheet. The sheet is split down the middle and the two side skins are cut and drilled in one operation, minimizing labor and assuring symmetry. In localities where only 4 ft. x 12 ft. sheets are available, a flush splice is made just behind the fuselage station 179.2.
The main landing gear is an "A" frame structure welded up from heavy wall 4130 steel tubing. It attaches to the fuselage at 3 points. In the event that proper welding and heat treating skills and equipment are not available to the amateur builder, a professional tubing fabrication source has been developed from which the main landing gear structure may be purchased.
Where sheet metal forming and aluminum welding skills are minimal, alternate materials and methods are provided. The fuel tank, seats, wing and tail tips, and certain cowling parts may be fabricated of fiber glass.