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Cessna Skymaster


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The Cessna Skymaster is a twin-engine civil utility aircraft built in a push-pull configuration. Its engines are mounted in the nose and rear of its pod-style fuselage. Twin booms extend aft of the wings to the vertical stabilizers, with the rear engine between them. The horizontal stabilizer is aft of the pusher propeller, mounted between and connecting the two booms. The combined tractor and pusher engines produce 'centerline' thrust and a unique sound.

Development

The first Skymaster, model 336, had fixed landing gear and first flew on February 28, 1961. It went into production in May 1963, and 195 were produced through mid 1964.

In February 1965 Cessna introduced the model 337 Super Skymaster. The model was larger, and had more powerful engines, retractable landing gear, and a dorsal air scoop for the rear engine ("Super" was subsequently dropped from the name). In 1966 the turbocharged T337 was introduced, and in 1973 the pressurized P337G entered production.

Cessna built 2993 Skymasters of all variants, including 513 military O-2 versions. Production in America ended in 1982 but continued with Reims in France with the FTB337 STOL and the military FTMA ''Milirole''. Production totalled 94 units.

Design

The Skymaster handles differently from a conventional twin-engine aircraft, primarily in that it will not yaw into the dead engine if one engine fails. Without the issue of differential thrust inherent to conventional (engine-on-wing) twins, engine failure on takeoff will not produce yaw from the runway direction. With no one-engine-out minimum controllable speed(Vmc), in-flight control at any flying speed with an engine inoperative is not as critical as it is with engines on the wing with the associated leverage. Nevertheless, the Skymaster requires a multi-engine-rating, although many countries issue a special "centerline thrust rating" for Skymaster and other like-configured aircraft.

Ground handling requires certain attention and procedures. The rear engine tends to overheat and can quit while taxiing on very hot days. There have been accidents when pilots, unaware of the shutdown, have attempted take-off on the nose engine alone, even though the single-engine take-off roll exceeded the particular runway length. FAA Airworthiness Directive 77-08-05 prohibits single engine take-offs and requires the installation of a placard with words that say "DO NOT INITIATE SINGLE ENGINE TAKEOFF".

The Skymaster produces a unique sound: a combination sound of its rear propeller slicing through turbulent air from the front prop and over the airframe, while its nose propeller addresses undisturbed air.

Maintenance

The Skymaster has something of a reputation for being maintenance intensive. Though not perhaps more so than any other twin, the Skymaster is a unique aircraft with difficult to reach systems which require attention to detail. Among issues to pay attention to is a complicated electrical-hydraulic landing gear system as well as a rear engine which can overheat if not monitored and maintained.

Selected Airworthiness Directives

97-26-17
- requires ultrasonic inspection of crankshafts
96-20-7
- requires repeated inspections of Janitrol heater combustion tubes
92-4-19
- inspection and retorquing of rocker arm shaft hold down
91-15-4
- prop inspections
78-9-5
- initial inspection of wing spar caps at 3000 hours and every 500 hours after

Operational history

From 1976 until the middle 1990s, the California Department of Forestry and Fire Protection used O-2 variants of the 337 Skymaster as tactical aircraft during firefighting operations. These were replaced with North American OV-10 Bronco s, starting in 1993.

Brothers to the Rescue

From 1991 until 2001 the Cuba n exile group ''Hermanos al Rescate '' (Brothers to the Rescue) used Skymasters, among other aircraft, to fly search and rescue missions over the Florida Straits looking for rafters attempting to cross the Straits to defect from Cuba and, when they found them, dropped life-saving supplies to them. Rescues were coordinated with the US Coast Guard, who worked closely with the group. They chose Skymasters because their high wing offered better visibility of the waters below, they were reliable and easy to fly for long-duration missions (averaging 7 hours), and they added a margin of safety with twin engine centerline thrust. In 1996, two of the Brothers to the Rescue Skymasters were shot down by the Cuban Air Force (FAC) over international waters. Both aircraft were downed by a MiG-29, while a second jet fighter, a MiG-23 orbited nearby.

Variants

Cessna

*327 Baby Skymaster - reduced scale four-seat version of the 337, with cantilever wings replacing the 336/337strut-braced configuration. It first flew in December 1967. One prototype was built before the project was cancelled in 1968 due to lack of commercial interest in the design. The prototype was delivered to NASA to serve as a full-scale model for wind tunnel testing. It was used in a joint Langley Research Center and Cessna project on noise reduction and the use of ducted versus free propellers.

*336 Skymaster - production version powered by two Continental IO-360-A engines, 195 built.

*337 Super Skymaster - 336; retractable undercarriage, redesigned nose cowling and new rear engine intake, and greater wing angle of incidence, powered by two Continental IO-360-C engines, 239 built.

*337A Super Skymaster - 337; minor detail changes, 255 built.

*337B Super Skymaster - 337A; increased take-off gross weight, optional belly cargo pack, 230 built.

*T337B (1967) Turbo Super Skymaster - 337B; two Continental turbocharged fuel injected engines which boosted service ceiling to, cruise speed to, and range to

*337C Super Skymaster - 337B; new instrument panel and increased take-off gross-weight, 223 built.

*337D Super Skymaster - 337C; minor detail changes, 215 built.

*337E Super Skymaster - 337D; cambered wingtips and minor changes, 100 built.

*337F Super Skymaster - 337E; increased take-off gross weight, 114 built.

*337G Super Skymaster - 337F; split airstair entry door, smaller rear side windows, improved flaps, larger front propeller, powered by Continental IO-360-G engines, 352 built.

*P337G Super Skymaster - 337G; pressurized cabin and turbocharged engines, 292 built.

*337H Skymaster - 337G; minor changes and optional turbocharged engines, 136 built.

*P337H Pressurized Skymaster - T337G; minor changes, 64 built.

*337M - US military version designated O-2 Skymaster in service, 513 built.

*Cessna O-2A Skymaster - US military designation of the 337M Forward air control, observation aircraft for the US Air Force. 501 delivered to the USAF and 12 to the Imperial Iranian Air Force

*Cessna O-2B Skymaster: Psychological warfare version for the US Air Force (31 former civil aircraft were converted to O-2B).

*O-2TT: Twin turboprop-powered version of the O-2.

*Summit Sentry O2-337 : Military version.

*Lynx: Armed military version for the Rhodesian Air Force.

*T337H-SP

Reims Cessna

*F337E Super Skymaster, 24 built.

*F337F Super Skymaster, 31 built.

*F337G Super Skymaster, 29 built.

*FT337G Super Skymaster, 22 built.

*F337H Super Skymaster, 1 built.

*FP337H Pressurized Skymaster, 1 built.

*FTB337G Milirole; military F337G with Sierra Industries Robertson STOL modifications and underwing hardpoint s, 61 built.

*Lynx : Rhodesia n designation for 21 FTB337Gs delivered to the Rhodesian Air Force.

Conversions/modifications

* Conroy Stolifter is an extensive single-turboprop engine STOL cargo plane conversion of the Skymaster. Front engine was replaced with a Garrett AiResearch TPE-331 turboprop ; rear engine was deleted, and its space filled with an extended cargo pod.

* The AVE Mizar flying car, created by Advanced Vehicle Engineers, was an attachment of Skymaster wings, tail, and rear engine to a Ford Pinto outfitted with aircraft controls and instruments.

* Summit Sentry - Summit Aviation built a militarized Skymaster as the O2-337 in 1980, and sold a few examples to the Haitian Air Force and the Thai Navy.

* Spectrum Aircraft Corporation of Van Nuys, California made an extensive single-turboprop engine conversion of a Reims FTB337G in the mid 1980s: the Spectrum SA-550. They removed the nose engine, lengthened the nose, and replaced the rear engine with a turboprop.

More 337 Information

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