Beechcraft Model 18 - Operational History

Operational History

Production got an early boost when Nationalist China paid the company US$750,000 for six M18R light bombers, but by the time of the U.S. entry into World War II, only 39 Model 18s had been sold, of which 29 were for civilian customers. Work began in earnest on a variant specifically for training military pilots, bombardiers and navigators. The effort resulted in the Army AT-7 and Navy SNB. Further development led to the AT-11 and SNB-2 navigation trainers and the C-45 military transport. The United States Air Force Strategic Air Command had Beechcraft Model 18 (AT-11 Kansans, C-45 Expeditors, F-2 Expeditors (the "F" standing for "Fotorecon"), and UC-45 Expeditors) from 1946 until 1951. From 1951 to 1955 the USAF had many of its aircraft remanufactured with new fuselages, wing center sections and landing gear to take advantage of the improvements to the civil models since the end of World War II. Eventually 900 aircraft were remanufactured to be similar to the then-current Model D18S and given new designations, constructor's numbers (c/nos.) and Air Force serial Numbers (s/nos). The USN had many of its surviving aircraft remanufactured as well, these being re-designated as SNB-5s and SNB-5Ps. The C-45 flew in U.S. Air Force service until 1963, the USN retired their last SNB in 1972 while the U.S. Army flew their C-45s through 1976. In later years the military called these aircraft "bug smashers" in reference to their extensive use supplying mandatory flight hours for desk-bound aviators in the Pentagon.

Some of the modifications created by independent engineering entrepreneurs were adopted in concept by the factory in later production versions in similar fashion to the current practice Harley Davidson copying of custom motorcycles built in the 1960s and 1970s.

Among the most notable cooling air and exhaust modifications were those engineered by Benjamin Israel while employed by Conrad Conversions. His modifications were based largely on creating a more efficient use of cooling air to reduce drag, a major detriment to cruise performance. Cruise performance was improved 10% or more at the same power settings as before the modifications. These modifications were largely copied on the factory produced G and H models. Beech 18s were used extensively by Air America during the Vietnam War; initially more-or-less standard ex-military C-45 examples were used, but then the airline had 12 aircraft modified by Conrad Conversions in 1963 and 1964 to increase performance and load-carrying capacity. The modified aircraft were known as Conrad Ten-Twos, as the maximum take-off weight (MTOW) was increased to 10,200 lb (4,600 kg). The increase was achieved by several airframe modifications, including increased horizontal stabilizer angle-of-incidence, redesigned landing gear doors, and aerodynamically-improved wing tips. Air America then had Volpar convert 14 aircraft to turboprop power, fitted with Garrett AiResearch TPE-331 engines; modified aircraft were called Volpar Turbo Beeches and also had a further increase in MTOW to 10,286 lb (4,666 kg).

A factory option at one point was the addition of JATO bottles on each engine nacelle which added the equivalent of 200 horsepower (150 kW) per engine for about 12 seconds. The most successful powerplant upgrade was that of the Pratt & Whitney Canada PT6 turbine engine and Hartzell propeller. This conversion was carried out by Hamilton Aircraft in the 1960s and 70s as the Hamilton Westwind, successfully extending the commercial life of the aging aircraft. The Westwind II added a fuselage stretch to provide seating for 17 passengers, the Westwind III seated eight and used the remainder of the extra room for cargo, and the Westwind IV added an extra stretch and a large cargo door.