The Beechcraft Model 18 (or "Twin Beech", as it is also known) is a 6- to 11-seat, twin-engined, low-wing, tailwheellight aircraft manufactured by the Beech Aircraft Corporation of Wichita, Kansas. Continuously produced from 1937 to November 1969 (over 32 years, a world record at the time), 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.
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.
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 about 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 in (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 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.
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 United States Army Air Forces (USAAF) military pilots, bombardiers, and navigators. The effort resulted in the Army AT-7. Further development led to the AT-11 navigation trainer, C-45 military transport, and F-2 (the "F" standing for "Fotorecon", short for "photographic reconnaissance"). The United States Navy first adopted the Beech 18 as the JRB-1, equivalent to the F-2, followed by the JRB-2 transport; the JRB was initially named the Voyager, but this name did not enter common use, and JRBs were generally called Expeditors like their USAAF counterparts. The first JRB-1 obtained by the Navy, bureau number (BuNo) 09771, was converted from the last civil Model 18 built before production was earmarked solely for the military for the duration of the war. The Navy subsequently obtained more Model 18s as the JRB-3 (C-45B), JRB-4 (UC-45F), SNB-1 Kansan (AT-11), SNB-2 (AT-7), and SNB-2C (AT-7C). Existing naval Twin Beeches were subsequently modified into the SNB-2H air ambulance, SNB-2P reconnaissance trainer, and SNB-3Q electronic countermeasures trainer. The United States Coast Guard acquired seven JRB-4 and JRB-5 aircraft from the Navy between 1943 and 1947; they were primarily used as utility transports, with one aircraft later converted for aerial mapping, and another used for proficiency flying.
After the war, the USAAF became the United States Air Force (USAF), and the USAF Strategic Air Command had Model 18 variants (AT-11 Kansans, C-45 Expeditors, F-2 Expeditors, and UC-45 Expeditors) from 1946 until 1951. In 1950, the Navy still had around 1,200 JRB and SNB aircraft in inventory. 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, resulting in the JRB-6, the SNB-5, and SNB-5P. The Coast Guard retired its JRBs in 1956 and sold most of them as surplus in 1959, but one was retained by the United States Coast Guard Reserve until at least 1972. With the adoption of the 1962 United States Tri-Service aircraft designation system, the Navy's SNB-5 and SNB-5P became the TC-45J and RC-45J respectively, later becoming the UC-45J as their primary mission shifted from aircrew training to utility transport work. The C-45 flew in USAF service until 1963, the USN retired its last UC-45J 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 (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 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 10,286 lb (4,666 kg).
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.
Nine-passenger pre-World War II civil variant, powered by 450 hp (340 kW) served as basis for USAAF C-45C
Nine-passenger pre-World War II civil variant, served as basis for USAAF F-2
Variant of B18S with seating for eight passengers, and equipment and minor structural changes
First post-World War II variant introduced in 1945, with seating for eight passengers and MTOW of 8,750 lb (3,970 kg), 1,035 built
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.
Variant with redesigned wing and MTOW of 9,300 lb (4,200 kg); 403 built
Variant of E18S with MTOW of 9,700 lb (4,400 kg); 57 built
Superseded E18S, MTOW of 9,700 lb (4,400 kg); 155 built
Lightweight version of G18, MTOW of 9,150 lb (4,150 kg); one built
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
Six-seat staff transport based on C18S; 11 built
Eight-seat utility transport based on C18S; 20 built
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, redesignated UC-45B in 1943 Equipped with a hatch in the cabin door for aerial photography.
Two Model 18S aircraft impressed into the USAAF, redesignated UC-45C in January 1943
Designation given to two AT-7 aircraft converted as passenger transports during manufacture, redesignated UC-45D in January 1943
Designation given to two AT-7 and four AT-7B aircraft converted as passenger transports during manufacture, redesignated UC-45E in January 1943
Standardized 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 the early 1950s for the USAF to similar standard as civil D18S with autopilot and R-985-AN-3 engines; 372 aircraft rebuilt
Multiengine crew trainer variant of C-45G; AT-7s and AT-11s remanufactured in the early 1950s for the USAF to similar standard as civil D18S, 96 aircraft rebuilt
AT-7s and AT-11s remanufactured in the early 1950s for the USAF to similar standard as civil D18S, with no autopilot and R-985-AN-14B engines; 432 aircraft rebuilt
Based on C18S with R-985-AN3 engines; 549 built
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-cal AN-M2 in a Beechcraft-manufactured top turret, later models used a Crocker Wheeler twin .30-cal 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, redesignated as DC-45F in June 1948
Conversion of Beech D18S/C-45 to five- to 11-seat executive transport with single fin by Pacific Airmotive
Rausch Star 250
Built as C-45F 44-47231, this aircraft was re-manufactured at Wichita by Beech in 1952, to become TC-45G 51-11544. From 1959 Rausch Engineering Inc. of South San Francisco, California, converted N8186H to tricycle undercarriage, using forward retracting main gear from a P-51 and rearward-retracting nose-leg from a T-28, adding a 3 ft (0.91 m) nose extension, 4 ft (1.22 m) rear fuselage extension, re-roofed fuselage for increased headroom and enlarged cabin windows. The modifications did not obtain FAA certification despite 58 hours of flight testing, with the aircraft eventually being broken up at Antioch, CA, in 1978.
Conversion of Model 18 with nosewheel undercarriage
Volpar (Beechcraft) Super 18
Volpar (Beechcraft) 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 605 hp (451 kW), driving Hartzell HC-B3TN-5 three-bladed, reversible-pitch, constant-speed feathering propellers
The Beechcraft Model 18 family has been involved in the following notable accidents and incidents:
April 25, 1951: Cubana de Aviación Flight 493, a Douglas DC-4 bound from Miami to Havana, registration CU-T188, collided with a U.S. Navy SNB-1, bureau number39939, on a practice instrument approach to Naval Air Station Key West. The collision and ensuing crashes killed all 34 passengers and five crew aboard the DC-4 and all five crew aboard the SNB. The accident occurred at midday, weather was clear with unlimited visibility, and both flight crews had been cleared to fly under visual flight rules, being expected to "see and avoid" other aircraft; the student flying the SNB was wearing view-limiting goggles, but the other SNB crew were not, and were expected to keep watch. Ground witnesses said that neither aircraft took evasive action prior to the collision, and the Civil Aeronautics Board attributed the accident to the failure of both flight crews to see and avoid conflicting air traffic.
December 10, 1967: American soul music singer Otis Redding, four members of his backing band the Bar-Kays, the pilot, and another member of Redding's entourage were killed in the crash of Redding's H18, registration N390R, into Lake Monona on approach to Truax Field in Wisconsin. The National Transportation Safety Board (NTSB) was unable to determine the cause of the crash, noting that the left engine and propeller were not recovered. Trumpet player Ben Cauley, the sole survivor of the crash, subsequently revived the Bar-Kays together with another band member who was aboard a different aircraft.
September 20, 1973: American folk music singer-songwriter Jim Croce, four members of his entourage, and the pilot were killed when their chartered E18S, registration N50JR, crashed into a tree on takeoff from Natchitoches Regional Airport in Louisiana. The NTSB attributed the accident to reduced visibility due to fog, and to physical impairment of the pilot, who had severe coronary artery disease and had run 3 mi (4.8 km) to the airport. An investigation conducted for a lawsuit against the charter company attributed the accident solely to pilot error, citing his downwind takeoff into a "black hole" of severe darkness, causing him to experience spatial disorientation.
September 26, 1978: Air Caribbean Flight 309, an air taxi flight by a D18S, registration N500L, crashed on approach to Isla Verde International Airport in Puerto Rico, killing the pilot and the five passengers aboard the aircraft and causing substantial property damage and injuries to bystanders on the ground. The pilot could not communicate with approach control and was following directions relayed by local tower controllers, who told the pilot to make a turn and maintain separation from a Lockheed L-1011 that was overtaking the flight, but the pilot did not turn, and the D18S passed underneath and very close to the L-1011. Both the NTSB and a U.S. District Court ruling attributed the crash to the D18S pilot's failure to correctly follow visual flight rules and air traffic control instructions to maintain separation from the much larger L-1011, causing a loss of aircraft control due to wake turbulence. A contributing factor was the pilot's difficulties in communication with controllers.
July 4, 1987: Ten people, including all then-current members of The Montana Band, were killed when the pilot of their chartered D18S, N132E, failed to clear a hillside near Lakeside, Montana, while performing a flypast of the venue where the band had performed earlier. The pilot performed an "abrupt" climb and performed a "hammerhead stall" maneuver, reversing direction and entering a dive. The accident was attributed to the pilot's poor judgment and failure to maintain altitude during unauthorized attempted aerobatics.
^Bauschspies, James S. and William E. Simpson, "Research and Technology Program Perspectives for General Aviation and Commuter Aircraft", NASA Contract NASW-3554 for NASA, Sept. 1982, N83-17454#. Retrieved: Dec. 18, 2014. (In particular, see: Table 2.4 "COMMUTER CARGO FLEET IN 1981 - TOP TEN AIRCRAFT MODELS - NUMBER IN FLEET," which notes Beech 18 units are more than the next two aircraft combined (Convair 500/680 and Douglas DC-3), and more than the next three general aviation aircraft combined.
^Croce v. Bromley Corporation, 623 F.2d 1084 (5th Cir. 1980) ("The plaintiffs' expert medical witness testified at length that spatial disorientation resulting from the pilot's taking off into a "black hole" was the cause of the crash. See n.12, supra. This theory was buttressed by the testimony of Asher Vandenberg, a commercial, multiengine pilot with instrument ratings.").
^In Re N-500L Cases, 517 F. Supp. 825 (D.P.R. 1981) ("The Court finds that the pilot of N-500L was responsible, in the VFR flight conditions which existed on the night of the accident, to visualize and to avoid wake turbulence of EAL 75. By continuing into the flight path of EAL 75 the pilot of N-500L was negligent and this negligence was a proximate cause of the crash.").
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