Beechcraft Model 18


The Beechcraft Model 18 is a 6- 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 9,000 were built, 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 were used in military service—as light transport, light bomber, aircrew trainer, photo-reconnaissance, and "mother ship" for target drones—including United States Army Air Forces C-45 Expeditor, AT-7 Navigator, and AT-11 Kansan; and United States Navy 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 stocking, 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 240 in the U.S. still on the FAA Aircraft Registry in August 2017.

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 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 Jacobs L-6s or 350-hp Wright R-760Es. The 450-hp Pratt & Whitney R-985 became the definitive engine from the prewar C18S onwards. The Beech 18 prototype first flew on January 15, 1937.
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 Pratt & Whitney R-1340 powerplant configuration. With the added weight of about 200 lb 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 higher for more headroom in the passenger cabin. All later Beech 18s featured this taller fuselage, and some earlier models 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 was built with tricycle undercarriage, and another 240 earlier-model aircraft were modified with this.
Construction of the Beechcraft Model 18 ended in 1970 with a final Model H18 going to Japan Airlines. Through the years, 32 variations of the basic design had flown, over 200 improvement modification kits were developed, and almost 8,000 aircraft were built. In one case, the aircraft was modified to a triple tail, trigear, humpbacked configuration and appeared similar to a miniature Lockheed Constellation. Another distinctive conversion was carried out by Pacific Airmotive as the PacAero Tradewind. This featured a lengthened nose to accommodate the tricycle nosewheel, and the Model 18's twin tailfins were replaced by 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 Model 18 variants from 1946 until 1951. From 1951 to 1955, the USAF had many of its aircraft remanufactured with new fuselages, wing center sections, and undercarriages 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, and Air Force serial numbers. The USN had many of its surviving aircraft remanufactured, as well, these being redesignated as SNB-5s and SNB-5Ps. The C-45 flew in USAF service until 1963, the USN retired its last SNB in 1972, while the U.S. Army flew its C-45s until 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.
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 takeoff weight was increased to. The increase was achieved by several airframe modifications, including increased horizontal stabilizer angle-of-incidence, redesigned undercarriage doors, and aerodynamically improved wingtips. 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.

Spar problems

The wing spar of the Model 18 was fabricated by welding an assembly of tubular steel. The configuration of the tubes in combination with drilled holes from aftermarket STC modifications on some of these aircraft 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 fitting of a spar strap to some Model 18s. This led, in turn, to the retirement of a large number of STC-modified Model 18s when owners determined the aircraft were worth less than the cost of the modifications. The corrosion on unmodified spars was not a problem; it occurred due to the additional exposed surface area created through the STC hole-drilling process. 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.

Variants

Manufacturer models

Unless otherwise noted, the engines fitted are Pratt & Whitney R-985 radials.
;Model 18A
;Model 18B
;Model 18D
;Model A18D
;Model A18A
;Model 18R
;Model 18S
;Model B18S
;Model C18S
;Model D18S
;Model D18C
;Model E18S
;Model E18S-9700
;Model G18S
, England
;Model G18S-9150
;Model H18

Military versions

USAAC/USAAF Designations

;C-45
;C-45A
;RC-45A
;C-45B
;C-45C
;C-45D
, Hudson, CO, June 2007
;C-45E
;C-45F
;C-45G
;TC-45G
;C-45H
;TC-45H
;RC-45J
;TC-45J
;UC-45J
;AT-7 Navigator
;AT-7A
;AT-7B
;AT-7C
;AT-11 Kansan
;AT-11A
;CQ-3
;F-2
;F-2A
;F-2B

US Navy Designations

;JRB-1
;JRB-2
;JRB-3
;JRB-4
;JRB-6
;SNB-1
;SNB-2
;SNB-2C
;SNB-2H
;SNB-2P
;SNB-3
;SNB-3Q
;SNB-5
;SNB-5P

RAF/RCAF Lend-lease Designations

;Expeditor I: C-45Bs supplied to the RAF under Lend-Lease.
;Expeditor II: C-45Fs supplied to the RAF and Royal Navy under Lend-Lease
;Expeditor III: C-45Fs supplied to the RCAF under Lend-Lease

Post-war RCAF designations

C-45Ds delivered between 1951 and 1952.
;Expeditor 3N: navigation trainer - 88 built

;Expeditor 3NM: navigational trainer that could be converted to a transport - 59 built
;Expeditor 3NMT: 3NM converted to a transport aircraft - 67 built
;Expeditor 3NMT: navigation trainer/personnel transport - 19 built
;Expeditor 3TM: transport with fittings so it could be converted to a navigation trainer - 44 built
;Expeditor 3TM: modified RCAF Expeditors used overseas in conjunction with Project WPB6 - three built.

Conversions

;Conrad 9800
;Dumod I
;Dumod Liner
;Hamilton HA-1
;Hamilton Little Liner
;Hamilton Westwind
;Hamilton Westwind II STD: Stretched conversion powered by two 840-hp PT6As, and with accommodation for up to 17 passengers.
;Hamilton Westwind III:two 579-hp PT6A-20s or 630-hp PT6A-27s or 630-hp Lycoming LTS101s.
;Hamilton Westwind IV:two 570-hp Lycoming LTP101s or 680-hp PT6A-28s or 750-hp PT6A-34s or 1020-hp PT6A-45s
;PacAero Tradewind
;SFERMA-Beechcraft PD.18S
;Volpar Model 18:
;Volpar Super 18:
;Volpar Turbo 18:Beech Model 18s fitted with the Volpar MkIV tricycle undercarriage and powered by two 705-hp Garrett TPE331-1-101B turboprop engines, flat-rated to, driving Hartzell HC-B3TN-5 three-bladed, reversible-pitch, constant-speed feathering propellers
;Volpar Super Turbo 18
;Volpar C-45G
;Volpar Turboliner
;Volpar Turboliner II

Operators

Civil

, the Beechcraft Model 18 remains popular with air charter companies and small feeder airlines worldwide.

Military

;

Argentina

Notable appearances in media