The name "Super Skymaster" was used in all retractable gear tandem-twins from 1965 through 1971. From 1972 until the end of production in 1980 the airplanes were all called Skymasters. Except for the pressurized versions, the serial numbers did not identify normally-aspirated versus turbocharged airplanes. Therefore, the production quantities that follow represent a mixture of both types. Starting out with 238 units in 1965, the production peaked at 285 units in 1966. Then it dipped to around 225 units delivered in 1970. The production in that decade varied between 81 units in 1971 to 29 units in 1980. No turbocharged C-T337 were manufactured in 1972 through 1977. However, production was resumed in 1978. Augmenting the 1967-70 production were 144 O-2A's and 30 O-2B's (M337's) for the USAF as will be described in a following section of this chapter.

Standard prices for the normally aspirated C337's ranged from $39,950 in 1965 to $124,090 for the C-337H II in 1980. Similarly, prices for the turbocharged versions varied from $49,500 in 1967 to $140,890 for the C-T337H II in 1980. The -II designation refers to a popular combination of optional equipment sold as a package.

The Pressurized C-P337 Super Skymaster Story

The success of the C-T337 prompted the next expensive development step-a pressurized cabin. With essentially a rectangular cabin cross-section, our project and structural engineers elected to simply beef up the existing structure with heavier gauge (and more numerous) bulkheads and limit the cabin pressure differential to 3.35 pounds-per-square-inch. This provided a 10,000 feet cabin altitude at a 20,000 feet aircraft altitude. By far the biggest challenge was replacing the large existing cabin door with a new high-strength door hinged along both the top edge and the bottom edge. When opened on the ground, the top half was raised by pneumatic springs, and the lower half would drop downward to serve as a stair step. Numerous locking pins were placed in an array in the forward and aft door jambs. This meant that there had to be no possibility of door unlatching in flight, and a very ingenious door latching device had to be invented. I recall many iterations of that design and, also, many design suggestions by those top management people who were engineers. It was obvious to all that an explosive door opening in flight (with the cabin pressurized) could possibly eject the co-pilot. To our great satisfaction, the latch proved to be "fail safe," and the author is unaware of any incidents of door unlatching in flight.

Other design challenges were beefing up the front and rear ends of this pressure vessel. The monstrous rear firewall/bulkhead, in particular, had to withstand very high cabin pressuration loads. In addition, all penetrations of this pressure vessel such as engine and flight control cables and flex shafts had to be treated with air-tight grommets, special mastic putty, or bellows. The last item added undesired points of friction for the control cables, giving the airplane the control feel of a much larger airplane.

The TSIO-360-C engine's horsepower was increased to 225 hp at 37 in. manifold pressure Hg and 2800 rpm. Pressurized air from the compressor sections of the front and rear-engine turbochargers flows to the engine air induction systems and also through sonic venturis (flow limiters) and then into heat exchangers. Outflow and safety/dump valves, located in the rear cabin bulkhead, would work automatically to maintain the selected cabin pressure differential using a pilot-controlled pressurization console in the instrument panel. Typically, the pilot would simply set the knob at 1,000 feet above the elevation of the destination airport. Then, after takeoff, the cabin pressurization schedule would be performed automatically. Any intervening readjustments were not recommended because of sudden sharp cabin pressure changes that could be extremely painful to one's eardrums.