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Beechcraft SNB-5 Navigator Twin-engine
light utility cabin monoplane
Archive Photos Ή
Beech SNB-5 Navigator (BuNo 44588,
ex AF 52-10588) on display (c.1998) at the March Field Air Museum,
Riverside, California (Photo by John Shupek copyright © 1998 Skytamer
Images)
Overview ²
The Beechcraft Model 18, or "Twin Beech", as it was
better known, is a 6-11 place, 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. An estimated
aggregate total time in service for the aircraft is in excess of
20,000,000 hours.
- Role: Trainer & Utility aircraft
- National origin: United States
- Manufacturer: Beech Aircraft Corporation
- First flight: 15 January 1937
- Introduced: 1937
- Primary users: United States Army, United States Navy, Royal Air
Force
- Produced: 1937-1970
- Number built: More than 9,000 of 32 variants built
- Unit cost 1952: D18S $78,050.00 USD
The Beech 18 is the most modified U.S.-certified
aircraft design, with over 200 Federal Aviation Administration (FAA)
approved Supplemental Type Certificates (STC's) on record for the
aircraft.
The aircraft's uses have included aerial spraying,
sterile bug release, fish seeding, dry ice cloud seeding, aerial
fire-fighting, airborne mail pick up and drop, ambulance service, numerous
movie productions, skydiving, freight, gun- and drug-smuggling, engine
test bed, skywriting and banner towing. A number of Model 18's were
operated as passenger aircraft; the Model 18 was the first aircraft flown
by Philippine Airlines, Asia's first and oldest airline. Many are now in
private hands as prized collectibles.
Design and Development ²
By the late 1930's, 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 "tail-dragger" 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-6's or 350 hp (260 kW) Wright R-760E's. The 450 hp (295 kW) Pratt
& Whitney R-985 became the definitive engine from the prewar C-18's
onwards. The Beech 18 prototype first flew on 15 January 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 450 kW (600 hp) 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. With the exception of the center
truss (the central component around which the entire aircraft is built),
nearly every airframe component has been modified at one time or
another.
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 18's (sometimes
called Super 18's) 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 H18's 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 the last, a 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. Some aircraft were almost
unrecognizable as having originated as a Beech 18. 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 ²
Production got an early boost when Nationalist China
paid the company US$750,000 for six M18R light bombers,[6] but by the time
of the U.S. entry into World War II, only 39 Model 18's 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/n) and Air Force serial Numbers
(s/n). The USN had many of its surviving aircraft remanufactured as well,
these being re-designated as SNB-5's and SNB-5P's. The C-45 flew in US Air
Force service until 1963, the USN retired their last SNB in 1972 while the
U.S. Army flew their C-45's 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 1960's and 1970's.
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 18's 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 1960's and 1970's 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 ²
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 18's.
This led in turn to the retirement of a large number of Model 18's 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.
Mfg. Models and Military Versions ²
Note:Unless otherwise noted, the engines fitted are
Pratt & Whitney R-985 radials.
Civil Versions
- 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 nd 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 Jacobs L-6 engines.
- Model SA18D Seaplane version of Model A18D but same MTOW as
S18D, fitted with Edo 55-7170 floats.
- Model A18A Version fitted with Wright R-760 engines of 350
horsepower (260 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 Wright R-975 engines of 420 horsepower
(310 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 MTOW of 8,750 lb (3,970 kg).
1,035 built (c/n A-1 to A-1035).
- Model D18S-3N Version of D18S delivered to the Royal
Canadian Air Force (RCAF); 100 built (c/n A-601 to A-700, re-serialed as
CA-1 to CA-100).
- Model D18S-3NM Version of D18S delivered to the RCAF; 133
built (c/n A-702 to A-715, A-736 to A-755, A-767 to A-769, A-780, A-782,
A-784, A-786, A-788, A-790 to A-800, A-851 to A-930; re-serialed as
CA-102 to CA-115, CA-136 to CA-155, CA-176 to CA-194, CA-201 to
CA-280).
- Model D18S-3TM Version of D18S delivered to the RCAF; 48
built (c/n A-701, A-716 to A-735, A-756 to A-766, A-770 to A-779, A-781,
A-783, A-785, A-787, A-789 and A-931; re-serialed as CA-101, CA-116 to
CA-135, CA-156 to CA-175, CA-195 to CA-200 and CA-281).
- 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 (c/n AA-1 to AA-31).
- Model E18S Variant with redesigned wing and MTOW of 9,300
lb (4,200 kg); 403 built (c/n BA-1 to BA-402 and BA-497).
- Model E18S-9700 Variant of E18S with MTOW of 9,700 lb
(4,400 kg); 57 built (c/n BA-403 to BA-433, BA-435 to BA-460).
- Model G18S Superseded E18S, MTOW of 9,700 lb (4,400 kg);
155 built (c/n BA-434, BA-461 to BA-496, BA-498 to BA-562, BA-564 to
BA-579, BA-581 to BA-617).
- Model G18S-9150 Lightweight version of G18, MTOW of 9,150
lb (4,150 kg); 1 built (c/no. BA-563).
- Model H18 Last production version, fitted with optional
tricycle undercarriage developed by Volpar and MTOW of 9,900 lb (4,500
kg); 149 built (c/n BA-580, BA-618 to BA-765), of which 109 were
manufactured with tricycle undercarriage.
Military Versions
- C-45 Six seat staff transport based on C18S.
- C-45A Eight seat utility transport based on C18S. 20
built.
- RC-45A Redesignation of all surviving F-2, F-2A and F-2B
aircraft by the USAF in 1948.
- C-45B Based on C18S but with modified internal layout, 223
ordered. Re-designated UC-45B in 1943.
- Expeditor I: Some C-45B's were supplied to the RAF under
Lend-Lease.
- C-45C Two Model 18S aircraft impressed into the USAAF.
Re-designated UC-45C in January 1943.
- C-45D Designation given to two AT-7 aircraft converted as
passenger transports during manufacture (USAAF s/n 42-56785 and
43-33281). Re-designated UC-45D in January 1943.
- C-45E Designation given to two AT-7 and four AT-7B aircraft
converted as passenger transports during manufacture (USAAF s/n
42-43484, 42-43486, 43-33282 to 43-33285). Re-designated UC-45E in
January 1943.
- C-45F Standardized seven-seat version based on C18S, with
longer nose than preceding models; 1,137 ordered. Redesignated
UC-45F.
- Expeditor II C-45F's supplied to the RAF and Royal Navy
under Lend-Lease.
- Expeditor III C-45F's supplied to the RCAF under
Lend-Lease.
- C-45G AT-7's 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 (c/n AF-61
to AF-60, AF-157 to AF-468; USAF s/n 51-11444 to 51-11503, 51-11600 to
51-11911).
- TC-45G Multi-engine crew trainer variant of C-45G; AT-7's
and AT-11s remanufactured in early 1950s for the USAF to similar
standard as civil D18S. 96 aircraft rebuilt (c/n AF-61 to AF-156, USAF
s/n 51-11504 to 51-11599).
- C-45H AT-7's 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 (c/n AF-469 to AF-900; USAF
s/n 52-10539 to 52-10970).
- TC-45H
- RC-45J In 1962 all surviving US Navy SNB-5P's were
redesignated RC-45J.
- TC-45J In 1962 all surviving US 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.
- AT-7A Floatplane version of AT-7. Six built.
- AT-7B Winterized AT-7. Nine built.
- AT-7C Based on C18S with R-985-AN3 engines. 549 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; fitted with two machine guns, one in
nose and one in a dorsal gun turret. 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.
- AT-11A Conversion of AT-11 as navigation trainer. 36
converted.
- CQ-3 Conversion of UC-45F, modified to act as drone control
aircraft. Re-designated as DC-45F in June 1948.
- F-2 Photo-reconnaissance version based on B18.
- F-2A Improved version F-2B.
- JRB-1 Photographic aircraft for the US Navy, based on the
C18S, fitted with fairing over cockpit for improved visibility. 11
built.
- JRB-2 Light transport for the US Navy, based on the C18S.
15 built.
- JRB-3 Photographic version, similar to C-45B, 23
built.
- JRB-4 Utility transport version, equivalent to UC-45F, 328
built.
- JRB-6
- SNB-1 Variant for the US Navy, similar to AT-11. 110
built.
- SNB-2 Navigation trainer for the US Navy. Similar to AT-7.
299 built.
- SNB-2C Variant for the US Navy, similar to AT-7C.
- SNB-2H Ambulance conversion for the US Navy.
- SNB-2P Photo reconnaissance trainer for the US Navy.
- SNB-3 Variant for the US Navy, similar to AT-7C.
- SNB-3Q Electronic counter-measures trainer for the US
Navy.
- SNB-5 SNB-2's and SNB-2C's were remanufactured, and
designated SNB-5 by the US Navy.
- SNB-5P Photographic-reconnaissance trainer for the US
Navy.
Military Operators ²
- Argentina
- Bolivia
- Brazil: Brazilian Air Force
- Canada: Royal Canadian Air Force
- Chile: Air Force, Army and Navy
- China
- Colombia
- Costa Rica
- Cτte d'Ivoire
- Dominican Republic
- Ecuador
- El Salvador
- France
- Guatemala
- Honduras
- Indonesia
- Iran
- Italy
- Mexico
- Netherlands
- Nicaragua
- Niger
- Nigeria
- Peru
- Philippines
- Portugal
- Somalia
- South Africa
- Spain
- Sri Lanka: Department of Survey, Sri Lanka Air Force
- Sweden
- Switzerland
- Thailand
- Turkey
- United Kingdom: Royal Air Force, Royal Navy
- United States: United States Army, United States Army Air Corps,
United States Army Air Force, United States Air Force, United States
Marine Corps, United States Navy
- Uruguay
- Venezuela
- Zaire
Specifications (UC-45 Expeditor) ²
General Characteristics
- 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: 2Χ Pratt & Whitney R-985-AN-1 "Wasp Junior" radial
engines, 450 hp (336 kW) each
Performance
- 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)
References
- Photos: John Shupek, Copyright © 1998 Skytamer Images. All Rights
Reserved
- Wikipedia, the free encyclopedia, Beechcraft
Model 18
Copyright © 1998-2016 Skytamer Images,
Whittier, California ALL RIGHTS RESERVED
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