Beechcraft Model 18
|Instructor and pilot in a Beechcraft AT-7 doing navigation training at Kelly Field, TX.|
|Role||Trainer & Utility aircraft|
|National origin||United States|
|Manufacturer||Beech Aircraft Corporation|
|First flight||15 January 1937|
|Primary users||United States Army
United States Navy
Royal Air Force
|Number built||More than 9,000 of 32 variants built|
|Unit cost||In 1952: D18S: US$78,050.00|
The Beechcraft Model 18, or "Twin Beech", as it is better known, is a 6–11 seat, twin-engine, low-wing, conventional-gear aircraft that was manufactured by the Beech Aircraft Corporation of Wichita, Kansas. This model saw military service during and after World War II in a number of versions including the United States Army Air Forces (USAAF) C-45 Expeditor, AT-7 Navigator, AT-11 Kansan; and for the United States Navy (USN), UC-45J Navigator and the SNB-1 Kansan.
In addition to carrying passengers the aircraft's uses have included aerial spraying, sterile insect release, fish seeding, dry ice cloud seeding, aerial firefighting, airborne mail pick up and drop, ambulance service, numerous movie productions, skydiving, freight, weapon- and drug-smuggling, engine test bed, skywriting and banner towing. Many are now in private hands.
Design and development 
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 semi-monocoque construction with fabric covered control surfaces and "taildragger" undercarriage, while less common were the twin tail fins. Upon an immediate glance they can be mistaken for the larger Lockheed Electra series of airliners which closely resemble the Model 18. Early production aircraft were either powered 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 15 January 1937.
Prior to the Pearl Harbor attack, the Beech 18 was outsold by the Lockheed 12 by 2-to-1. However, war priorities forced Lockheed to concentrate on its heavier aircraft, and Beechcraft received a major boost through wartime contracts.
The aircraft has used a variety of engines and has had a number of airframe modifications to increase gross weight and speed. At least one aircraft was modified to a 600 hp (447 kW) Pratt & Whitney R-1340 powerplant configuration. With the added weight of approximately 200 lb (91 kg) per engine, the concept of a Model 18 fitted with R-1340 engines was deemed unsatisfactory due to the weakest structural area of the aircraft being the engine mounts. Nearly every airframe component has been modified.
In 1955 deliveries of the Model E18S commenced; the E18S featured a fuselage that was extended 6 inches (150 mm) higher for more headroom in the passenger cabin. All later Beech 18s (sometimes called Super 18s) featured this taller fuselage and some earlier models (including one AT-11) have been modified to this larger fuselage. The Model H18, introduced in 1963, featured optional tricycle undercarriage. Unusually, the undercarriage was developed for earlier-model aircraft under an STC by Volpar, and installed in H18s at the factory during manufacture. A total of 109 H18s were built with tricycle undercarriage, and another 240 earlier-model aircraft were modified with the undercarriage.
Construction of the Beechcraft Model 18 ended in 1970 with a final Model H18 going to Japan Airlines. Beechcraft set a record that still stands today for longest continuous production of a piston engine aircraft. Through the years, 32 variations of the basic design had flown, over 200 improvement modification kits were developed, and almost 8,000 aircraft had been built. In one case the aircraft was modified to a triple tail, tri-gear, hump backed configuration and appeared similar to a miniature Lockheed Constellation. Another distinctive conversion was carried out by PacAero as the Tradewind. This featured a lengthened nose to accommodate tricycle undercarriage, and the Model 18's twin tails replaced with a single fin.
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.
Spar Problems 
The wing spar of the Model 18 is fabricated by welding an assembly of tubular steel. The configuration of the tubes and inadequate corrosion inhibitors, along with holes from after-market STC modifications have allowed the spar to become susceptible to corrosion and cracking while in service. This prompted the FAA to issue an Airworthiness Directive in 1975, mandating the fitment of a spar strap to Model 18s. This led in turn to the retirement of a large number of Model 18s when owners determined that the aircraft were worth less than the cost of the modifications. Further requirements have been mandated by the FAA and other national airworthiness authorities, including regular removal of the spar strap to allow the strap to be checked for cracks and corrosion and the spar to be X-rayed. In Australia the airworthiness authority has placed a life limit on the airframe, beyond which aircraft are not allowed to fly.
Manufacturer Models 
Unless otherwise noted, the engines fitted are Pratt & Whitney R-985 radials.
- Model 18A
- First production model with seating for two pilots and seven or eight passengers, fitted with Wright R-760E-2 engines of 350 horsepower (260 kW). MTOW: 6,700 lb (3,000 kg).
- Model S18A
- Version of Model 18A capable of being fitted with skis or Edo 55-7170 floats; MTOW: 7,200 lb (3,300 kg).
- Model 18B
- Improved model with increased range and useful load, fitted with 285 hp (213 kW) Jacobs L-5 engines.
- Model S18B
- Version of Model 18B capable of being fitted with skis or floats.
- Model 18D
- Variant with seating for two pilots and nine passengers, fitted with Jacobs L-6 engines of 330 horsepower (250 kW). MTOW: 7,200 lb (3,300 kg).
- Model S18D
- Version of Model 18D capable of being fitted with skis or Edo 55-7170 floats; MTOW: 7,170 lb (3,250 kg).
- Model A18D
- Variant of 18D with MTOW increased by 300 lb (140 kg) to 7,500 lb (3,400 kg), fitted with Pratt and Whitney R-985 engines with 450 hp each.
- Model SA18D
- Seaplane version of Model A18D but same MTOW as S18D, fitted with Edo 55-7170 floats.
- Model A18A
- Version fitted with Pratt and Whitney R-985 engines of 450 horsepower (340 kW). MTOW: 7,500 lb (3,400 kg).
- Model SA18A
- Seaplane version of Model A18A, fitted with Edo 55-7170 floats; MTOW: 7,170 lb (3,250 kg).
- Model 18R
- Model with Pratt and Whitney R-985-A1 engines with dual stage blower for increased power at higher operating altitudes. 450 horsepower (340 kW); seven built, one to Sweden as an air ambulance, six to Nationalist China as M18R light bombers.
- Model 18S
- Nine-passenger pre-World War II civil variant, served as basis for USAAF C-45C.
- Model B18S
- Nine-passenger pre-World War II civil variant, served as basis for USAAF F-2.
- Model C18S
- Variant of B18S with seating for eight passengers, and equipment and minor structural changes.
- Model D18S
- First post-World War II variant introduced in 1945 with seating for eight passengers and Maximum Take Off Weight (MTOW) of 8,750 lb (3,970 kg). 1,035 built.
There were 280 D Models made for the Royal Canadian Air Force (RCAF), and they were delivered between 1951 and 1952. (Their serial numbers ranged from CA-1 to CA-280.) Seating for RCAF was for 5 passengers, or two RCAF Navigator students and 1 RCAF Navigator Instructor. MTOW for RCAF was 9300 lbs.
- 3N: Fitted as a navigation trainer with astrodome and two trainee stations in the cabin; 88 built
- 3NM: Fitted primarily as a navigational trainer, and is fitted with floor lugs to accept transport seats on removal of navigation equipment; 59 built
- 3NMT: Basically a 3NM, converted to a transport aircraft; 67 built
- 3NMT(Special): Fitted as a navigation trainer personnel transport. First navigation training position retained, slightly modified ie: removal of API (Air Position Indicator) and replaced with Radio Compass and Indicator from removed second navigation position. In addition, three reclining type chairs fitted; 19 built
- 3TM: Normally fitted with transport type seats but has the necessary wiring, plumbing and fittings for conversion to a navigation trainer, including provisions for fitting an astrodome; 44 built
- 3TM(Special): Specifically modified RCAF Expeditor under Project WPB6, and it refers specifically to Overseas Expeditors; 3 built
- Model D18C
- Variant with Continental R9-A engines of 525 horsepower (391 kW) and MTOW of 9,000 lb (4,100 kg), introduced in 1947. 31 built.
- Model E18S
- Variant with redesigned wing and MTOW of 9,300 lb (4,200 kg); 403 built.
- Model E18S-9700
- Variant of E18S with MTOW of 9,700 lb (4,400 kg); 57 built.
- Model G18S
- Model H18
- Last production version, fitted with optional tricycle undercarriage developed by Volpar and MTOW of 9,900 lb (4,500 kg); 149 built, of which 109 were manufactured with tricycle undercarriage.
Military versions 
- Redesignation of all surviving F-2, F-2A and F-2B aircraft by the USAF in 1948.
- Based on C18S but with modified internal layout; 223 ordered. Re-designated UC-45B in 1943.
- Two Model 18S aircraft impressed into the USAAF. Re-designated UC-45C in January 1943.
- Designation given to two AT-7 aircraft converted as passenger transports during manufacture. Re-designated UC-45D in January 1943.
- Designation given to two AT-7 and four AT-7B aircraft converted as passenger transports during manufacture. Re-designated UC-45E in January 1943.
- Standardised seven-seat version based on C18S, with longer nose than preceding models; 1,137 ordered. Redesignated UC-45F.
- AT-7s and AT-11s remanufactured in early 1950s for the United States Air Force (USAF) to similar standard as civil D18S with autopilot and R-985-AN-3 engines; 372 aircraft rebuilt.
- Multi-engine crew trainer variant of C-45G; AT-7s and AT-11s remanufactured in early 1950s for the USAF to similar standard as civil D18S. 96 aircraft rebuilt.
- AT-7s and AT-11s remanufactured in early 1950s for the USAF to similar standard as civil D18S, with no autopilot and R-985-AN-14B engines; 432 aircraft rebuilt.
- TC-45H 
- RC-45J 
- In 1962 all surviving U.S. Navy SNB-5Ps were redesignated RC-45J.
- TC-45J 
- In 1962 all surviving U.S. Navy SNB-5s were redesignated TC-45J.
- UC-45J 
- AT-7 Navigator
- Navigation trainer based on C18S, with an astrodome and positions for three students. Powered by 450 hp (336 kW) R-985-25 engines; 577 built.
- Floatplane version of AT-7; six built.
- Winterised AT-7; nine built.
- AT-11 Kansan
- Bombing and gunnery trainer for USAAF derived from AT-7. Fuselage had small circular cabin windows, bombardier position in nose, and bomb bay; Gunnery trainers were also fitted with two or three .30 caliber machine guns. Early models, (the first 150 built), had a single .30 AN-M2 in a Beechcraft-manufactured top turret, Later models utilized a Crocker Wheeler twin .30 caliber top turret. A bottom tunnel gun was used for tail gunner training. 1,582 built for USAAF orders, with 24 ordered by Netherlands repossessed by USAAF and used by the Royal Netherlands Military Flying School at Jackson, Mississippi.
- Conversion of AT-11 as navigation trainer; 36 converted.
- Conversion of UC-45F, modified to act as drone control aircraft. Re-designated as DC-45F in June 1948.
- Photo-reconnaissance version based on B18.
- Improved version.
- Photographic aircraft for the U.S. Navy, based on the C18S, fitted with fairing over cockpit for improved visibility. 11 built.
- Photographic version, similar to C-45B; 23 built.
- Utility transport version, equivalent to UC-45F; 328 built.
- JRB-6 
- Navigation trainer for the U.S. Navy. Similar to AT-7; 299 built.
- Variant for the U.S. Navy, similar to AT-7C.
- Ambulance conversion for the U.S. Navy.
- Photo reconnaissance trainer for the U.S. Navy.
- Variant for the U.S. Navy, similar to AT-7C.
- Electronic counter-measures trainer for the U.S. Navy.
- SNB-5 
- SNB-2s and SNB-2Cs were remanufactured, and designated SNB-5 by the U.S. Navy.
- SNB-5P 
- Photographic-reconnaissance trainer for the U.S. Navy.
- PAC Super 18S Tradewind
- Custom conversion of Beech D-18S/C-45 to 5–11 seat executive transport by Pacific Airmotive
- Hamilton HA-1
- conversion of a TC-45J aircraft.
- Hamilton Little Liner
- Modification of D.18S with aerodynamic improvements and new, retractable tailwheel, capable of carrying 11 seats.
- Hamilton Westwind
- Turboprop conversions with various engines
- Volpar (Beechcraft) Model 18
- Conversion of Model 18 with nosewheel undercarriage.
- Volpar Super Turbo 18
- 2x 705hp Garrett TPE331
- Volpar C-45G
- C-45G aircraft modified with tricycle undercarriage.
- Volpar Turboliner
- Turboprop conversions of Beechcraft 18, 2x 705hp Garrett TPE331-1-101B
As of 2012[update], the Beechcraft Model 18 remains popular with air charter companies and small feeder airlines worldwide.
- China/ Taiwan
- Costa Rica
- Côte d'Ivoire
- Dominican Republic
- El Salvador
- South Africa
- Sri Lanka
- United Kingdom
- United States
- United States Army
- United States Air Force
- United States Marine Corps
- United States Navy
Aircraft on display 
- 1941 Historical Aircraft Group Museum, Geneseo, New York, UC-45H
- Air Mobility Command Museum, Dover, Delaware, C-45G, ser. no. 51-11795
- Alaska Aviation Heritage Museum, Anchorage, Alaska, UC-45F, FAA no. N1047B, Air Force ser. no. 44-4734
- Alberta Aviation Museum, Edmonton, Alberta, Beech D18S-3NM
- Aviodrome, Netherlands, Beech D.18, tail code G-BKRG from Bond movie Octopussy
- Beechcraft Heritage Museum, Tullahoma, Tennessee
- -1938 S18D, c/n 178, CF-BKO – Prairie Airways Twin Beech
- -1952 D18S, c/n A-935, N4477 – Parish Twin Beech
- -1954 C-45H, c/n AF-824, N7916A – Morton Lester Twin Beech
- -1959 Super E18S, c/n BA-453, N712JS – "Miss Maine" – Cianchette Twin Beech 
- Canadian Air Sea Land Museum, Toronto/Markham Airport
- Canadian Bushplane Heritage Centre, Sault Ste. Marie, Ontario, UC-45A, tail code CF-MJY
- Canadian Museum of Flight, Langley, British Columbia, civil registration: CF-CKT
- Canadian Warplane Heritage Museum, Hamilton, Ontario, model D18S
- Castle Air Museum, Atwater, California, model C-45G, ser. no. 51-11897
- Fundación Infante de Orleans, Spain 
- Hotel Mayfair Lagoon, Bhubaneswar, Orissa, India 
- Jimmy Doolittle Air & Space Museum, Travis AFB, California, modle C-45H
- Laughlin AFB, Del Rio, Texas, C-45, ser. no. 23774
- Lone Star Flight Museum, Galveston, Texas
- Malta Aviation Museum, Ta' Qali, Malta
- Museo Aeronautico y del Espacio, Chile
- Museo Nacional de Aerónautica, Argentina
- Museu Aeroespacial, Rio de Janeiro, Brazil
- Museu do Ar, Sintra, Portugal
- Museum of Flight, Seattle, Washington
- Museum of Transport and Technology, Auckland, New Zealand
- National Museum of Flight, East Lothian, Scotland
- National Museum of the USAF, Dayton, Ohio
- North Atlantic Aviation Museum, Gander, Newfoundland
- North Carolina Aviation Museum, Asheboro, North Carolina
- Olbia – Costa Smeralda Airport, Sardinia
- Tennessee Museum of Aviation, Sevierville, Tennessee
- TransCanada Highway, Ignace, Ontario
- Vintage Flying Museum, Fort Worth, Texas
- Western Canada Aviation Museum, Winnipeg, Manitoba
- Wings Over the Rockies Air and Space Museum, Denver, Colorado, UC-45 version, ser. no. 42-37496 (originally an AT-11)
Specifications (UC-45 Expeditor) 
Data from Jane's Fighting Aircraft of World War II
- Crew: 2 pilots
- Capacity: 6 passengers
- Length: 34 ft 2 in (10.41 m)
- Wingspan: 47 ft 8 in (14.53 m)
- Height: 9 ft 8 in (2.95 m)
- Wing area: 349 ft² (32.4 m²)
- Empty weight: 6,175 lb (2,800 kg)
- Loaded weight: 7,500 lb (3,400 kg)
- Max. takeoff weight: 8,727 lb (3,959 kg)
- Powerplant: 2 × Pratt & Whitney R-985-AN-1 "Wasp Junior" radial engines, 450 hp (336 kW) each
- Maximum speed: 225 mph (195 knots, 360 km/h)
- Range: 1,200 mi (1,000 NM, 1,900 km) at 160 mph (260 km/h)
- Service ceiling: 26,000 ft (7,930 m)
- Rate of climb: 1,850 ft/min (9.4 m/s)
See also 
- Aircraft of comparable role, configuration and era
- Airspeed Oxford
- Avro Anson
- Barkley-Grow T8P-1
- Bristol Blenheim
- Cessna AT-17/Cessna T-50 Bobcat
- De Havilland Dove
- Evangel 4500
- Fairchild AT-21 Gunner
- Lockheed Model 10 Electra
- Lockheed Model 12 Electra Junior
- Siebel Si 204
- Related lists
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- For the particular breakdown of each model for the RCAF, Refer to RCAF Data Record Cards CA-1 to CA-280
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- Taylor 1965, p. 316.
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