AT-11 Kansan

Model 18
Instructor and pilot in an AT-7 doing navigation training at Kelly Field, Texas.
Role	Trainer and utility aircraft
National origin	United States
Manufacturer	Beech Aircraft Corporation
First flight	January 15, 1937
Introduction	1937
Primary users	United States Army Air Forces United States Navy Royal Air Force Royal Canadian Air Force
Produced	1937–1970
Number built	9,000+
Unit cost	D18S: US$78,050 in 1952

The Beechcraft Model 18 (or "Twin Beech", as it is also known) is a six to 11-seat, twin-engined, low-wing, tailwheel light aircraft manufactured by the Beech Aircraft Corporation of Wichita, Kansas. Continuously produced from 1937 to November 1969 (over 32 years, the world record at the time), over 9,000 were produced, making it one of the world's most widely used light aircraft. Sold worldwide as a civilian executive, utility, cargo aircraft, and passenger airliner on tailwheels, nosewheels, skis or floats, it was also used as a military aircraft.

During and after World War II, over 4,500 Beech 18s saw military service—as light transport, light bomber (for China), aircrew trainer (for bombing, navigation and gunnery), photo-reconnaisance, and "mother ship" for target drones—including United States Army Air Forces (USAAF) C-45 Expeditor, AT-7 Navigator, AT-11 Kansan; and United States Navy (USN) UC-45J Navigator, SNB-1 Kansan, and others. In World War II, over 90% of USAAF bombardiers and navigators trained in these aircraft.

In the early postwar era, the Beech 18 was the pre-eminent "business aircraft" and "feeder airliner." Besides carrying passengers, its civilian uses have included aerial spraying, sterile insect release, fish seeding, dry ice cloud seeding, aerial firefighting, air mail delivery, ambulance service, numerous movie productions, skydiving, freight, weapon- and drug-smuggling, engine testbed, skywriting, banner towing, and stunt aircraft. Many are now privately owned, around the world, with over 300 in the U.S. still on the FAA Aircraft Registry in December 2014.

By the late 1930s, Beechcraft management speculated that a demand would exist for a new design dubbed the Model 18, which would have a military application, and increased the main production facilities. The design was mainly conventional for the time, including twin radial engines, all-metal semimonocoque construction with fabric-covered control surfaces and tailwheel undercarriage. Less conventional was the twin-tailfin configuration. The Model 18 can be mistaken for the larger Lockheed Electra series of airliners which closely resemble it. Early production aircraft were powered either by two 330-hp (250-kW) Jacobs L-6s or 350-hp (260-kW) Wright R-760Es. The 450-hp (336-kW) Pratt & Whitney R-985 became the definitive engine from the prewar C18S onwards. The Beech 18 prototype first flew on January 15, 1937.