The Thorp T-18 is an American, two-place, all-metal, plans-built, homebuilt aircraft designed in 1963 by John Thorp. The aircraft was originally designed as an open cockpit aircraft, powered by a military surplus Lycoming O-290G ground power unit engine, but evolved into a fully bubble canopied aircraft powered by engines of up to . Design and development The T-18 was designed to be easily constructed from sheets of aluminum, and use the modified Lycoming O-290G powerplant. It was originally designed with an open cockpit and with the cylinder heads protruding through the engine cowling in the interest of simplicity. Even as originally designed, the cruising speed was quite high. The design showed great potential for higher performance and so modifications were created to install larger, cowled Lycoming engines and a bubble canopy. These modifications allow a T-18 with to cruise at and higher-powered examples to cruise in excess of . Some aircraft have been constructed with retractable landing gear. These performance improvements made the T-18 one of the most popular homebuilt designs of the 1970s and early 1980s until the Van's Aircraft RV kitplane series came on the market. The T-18 was designed to use the Lycoming O-290G Ground Power Unit. At the time the T-18 was developed these engines were inexpensive and widely available as military surplus generator motors. When converted for aircraft use they are virtually identical to the O-290D or O-290D2 aircraft engines. Other Lycoming engines can be used, including the Lycoming O-320, Lycoming O-340, Lycoming O-360 and the Lycoming IO-360. T-18 plans were available to builders from Eklund Engineering, which was also developing a laser-cut kit version and as of 2009 had aileron, flap and empennage kits. Classic Sport Aircraft at one time supplied plans, parts, and kits for the S-18 and the S-18T tricycle gear version, but went out of business in 2014. Thorp Central acquired the assets of Classic Sport Aircraft and now provides S-18 plans and parts. By 2011 over 1600 sets of plans had been sold and 400 examples were flying. Operational history One T-18, N455DT, was built by Donald Taylor of California and flown around the world from Oshkosh, Wisconsin, in 1976. This was the first successful circumnavigation of the world by a homebuilt aircraft. Taylor subsequently flew N455DT to the geographical North Pole, using a Sperry hybrid inertial navigation system. Clive Canning flew another T-18 from Australia to England earlier the