History of the SkymasterThe first prototype Skymaster was a basic 4-seat, all-metal, high wing push-pull twin aircraft. The tricycle undercarriage was fixed and had two 175hp Continental GO-300-C geared engines. The prototype was registered N34273 and was given the construction number of 633 (Cessna Experimental Series) and first flew on 28 February 1961. It wasn't until August 1962 that the first production aircraft flew and mid-1963 before deliveries began. Production models of the 336 were different from the prototype by having IO-360 engines, an enlarged cabin to take 6 people, inboard wing sections were redesigned and the vertical tail surfaces were enlarged. TOGW was 3,900lbs. 195 production 336's were built and were given construction numbers of 336-0001 to 336-0195.
On 30th March 1964 the prototype of the 337 first flew, piloted by Dick Kember. Despite it looks being similar to the 336 it was a largely redesigned aircraft. The wing incidence angle was increased, the nose cowling was redesigned, the tail boom angle increased, a new dorsal air intake for the rear engine was added and the 337 had retractable undercarriage. This was the first model called the Super Skymaster. The word Super was dropped in 1972. The prototype was registered N5422E and had the construction number of 647. Production on the 337 started in February 1965. This model has a TOGW of 4200lbs and IO-360C engines. The cost of a new 337 would be around $39,950. A new construction number series was started for the 337. These basic models had construction numbers between 337-0001 and 337-0239.
In 1965, the USAF at Eglin AFB, FL, modified a 336 with four sets of hard points on the wings, and had a one time STC approved by the FAA. The serial number on that plane is 336-0026. It was used a proof of concept to see if the idea was feasable for the 337's to be used as FAC aircraft. The Cessna model 305's (Birdogs) were getting hammered in South East Asia and North American Aviation Bronco's were late in getting into production, so the Air Force was scrambling to find a stop gap aircraft that had the range, load carrying and had multiengine reliability to supersede the birdogs. This 336 eventually became N331KW. At one time it was owned by a Belize national who is now living in the USA. He repainted the aircraft in false Belize Air Force markings and pained on a false registration of V3-1KW. Someone from the British magazine 'Airforces Monthly' saw this aircraft and it was announced in the magazine that the Belize Air Force had an ex-USAF O-2! Even today there is a mention of this aircraft under the Belize Air Force heading in 'Air Forces of the World' and other military reference guides, despite the fact that he has now sold the aircraft and it is now back carrying its true identity (ie N331KW).
In 1966 the 337A was produced. This had minor changes to the standard 337 and construction numbers in the range 337-0240 and 337-0525. There were 286 of them built.
1967 saw the 337B. TOGW was increased to 4,300lbs and there was an optional belly cargo pack. A further option on this aircraft was a turbocharged 210hp TSIO-360-A engines. The price for a T337B in 1967 was $49,500. Construction numbers for the 337B and T337B went from 337-0526 to 337-0755 and there were 230 of them built.
1967 also saw the building of a reduced scale version of the 337. This was known as the 327. Only one aircraft was built and first flew on 4 December 1967. It was registered N3769C and had a construction number of 663 (Cessna Experimental Series). This aircraft later went to NASA as a 'full scale wind tunnel research unit'.
In 1967 the USAF placed an order for Skymasters. The military designation for theses aircraft was O-2A. They had their own construction number sequence starting at M0001. The USAF also took 32 aircraft from the civil production lines. These retained their civil construction numbers and were fitted with loud-speakers and leaflet dispensers for psychological warfare duties. They were also different from the O-2A's by not having hard-points under the wings.
The main differences between the 337 and the O-2 included the removal of the cabin step and spinners on the propellers, addition of observation windows in the cabin door and roof of the cabin. Engine fire detection equipment were added together with smoke generator equipment added to the rear exhaust system. The instrument panels were also different and they had an armament switches panel installed. Four underwing pylons for rockets, flares and cluster bombs. Amour plates were installed under the seats and porous foam slabs were place in the fuel tanks during assembly to make them explosion-resister after being hit by small arms fire. This resulted in about a 5% loss in fuel capacity.
The 337C came in 1968 with a new instrument panel and 4,400lb TOGW (4,500lb on T337C)
Minor changes were made in 1969 to produce the 337D. Construction numbers in the range 337-0979 to 337-01193 with a total of 215 built.
Cambered wing tips plus other minor changes came on the 1970 337E. T337E's has a TOGW of 4,600lbs, construction numbers between 337-01194 and 337-01316 and a total of 123 built.
The 337E was the first Skymaster model to be re-built in France by Reims Aviation. Reims Aviation started life as Avions Max Holste in 1933. Due to financial stresses Cessna acquired a 49% shareholding on 16th February 1960. Reims started building Cessna aircraft from kits supplied from the USA for the European and Middle Eastern markets. Skymasters re-built by Reims have both Cessna and Reims Construction numbers.
The 1971/2 337F model had 4,630lbs TOGW for both non-turbo and Turbo models. Construction numbers of 337-01317 to 337-01462 were on these 146 aircraft.
In 1973 the 337G emerged. This had split airstair entry door, smaller rear side windows, improved flaps, larger front propeller, modified wing struts and Cont. IO-360-G engines. Production of this model continued until 1977 by which time 353 had been built with construction numbers in the range 337-01463 to 337-01815.
A Turbo charged version of the 337G was produced in 1974. This model also had a pressurised cabin and redesigned windshield. A new construction number sequence was started for these aircraft.
Between 1978 and 1980 the 337H models were produced in three forms ie 337H (normal) T337H (Turbo) and P337H (Pressurised cabin). Cost for these aircraft were $124,090 for the standard model and $140,890 for the turbo model.
Production of the Skymaster by Cessna finished in 1980. However Reims Aviation of France was assigned world-wide marketing rights to the aircraft, and as a result they built (from scratch) a further 61 aircraft, which it called the Reims FTB337 Minirole. Most of these aircraft went to military operator in Europe and Africa. The Portuguese Air Force taking the most.
Even with production of the Skymaster finished that is not the end of the story. A modification to the pressurised 337's was first undertaken by Riley. This modification consisted of adding a Riley intercooler to pump cooler air from the turbochargers into the aircraft's engines that greatly improved the aircraft's performance. STOL modifications to the wings, air conditioning, comprehensive avionics package, new paint scheme and a custom interior were also part of the deal. This 'new' aircraft was dubbed the Riley Skyrocket. Riley also tried to launch the Super Skyrocket but unfortunately, went out of business before FAA approval came forth for this new modification. However, LLC of Carlsbad, California has now obtained the necessary approval and is now modifying P337's. This modification consists on installing two turbocharged 310hp Continental TSIO 520 engines, with intercoolers.
Additional information from:
General Aviation by R.W.Simpson (published by Airlife)
The Light Aircraft Guide by Stewart Wilson (published by DYLOWL Pty Ltd)
Cessna - Wings for the World by William D. Thompson.