for it, to the point where it is quite rare to find an original, completely stock Super Cub. Modifications include extended baggage compartments (reaching farther back into the fuselage, or even two-level baggage compartments in the top and bottom of the rear fuselage), external luggage pods, fuel pods, lumber racks for carrying construction materials into unimproved bush runways. Also the removal of header tanks, larger 24 or even 30 gallon wing fuel tanks, extended main landing gear for better ground clearance of the propeller, strengthened tailwheel springs, the addition of a small third passenger seat in the luggage area and lightweight generators and starters. Also various different mount areas for the battery (to move the weight forward, and reduce tail weight to shorten takeoff distance), various different tailfin shapes to increase surface area, lengthened flaps, various wingtip designs, vortex generators on the leading edge of the wings, movement of the electrical panel from the right wing root to the dashboard to reduce fire hazard during a crash, and even the addition of a constant-speed propeller. Above all, the most common modification is the addition of "bush wheels" (themselves said to be direct descendants of Alvin Musselman's 1920s-origin "airwheel" tires used on the original Piper J-3), large, soft, low pressure balloon-tires designed to absorb impacts from rocks and boulders, and to not sink into sand or other soft surfaces, ideal for off-runway landings. Variants PA-18 Super Cub Prototype and production variant powered by a 95 hp Continental C-90-8F piston engine, sometimes known as the PA-18-95. PA-18-105 Super Cub Production variant fitted with a 105 hp Lycoming O-235-C1 piston engine and larger tailplane. PA-18-105 Special Special variant built in 1952 and 1953 for the Civil Air Patrol as a trainer with horn-balanced elevators and provision for seat parachutes. PA-18-125 Super Cub Variant to replace the PA-18-95 with flaps and horn-balanced elevators and a 125 hp Lycoming O-290-D piston engine and either wood or metal controllable-pitch propeller. PA-18-135 Super Cub Variant with a 135 hp Lycoming O-290-D piston engine and fitted with two wing tanks as standard. PA-18-150 Super Cub 1954 variant with a 150 hp Lycoming O-320. PA-18-180 Super Cub Experimental variant with a 180 hp Lycoming O-360 engine, one built in 1980 by Piper. Other aircraft have been re-engined under a Supplemental Type Certificate. PA-18A Designation for production agricultural aircraft, including cropdusters and sprayer variants and incorporating a slightly different rear