Such ships will also be built in the future more and more often in order to be able to respond to all new flight requirements and to meet, under optimal conditions, the new and increasingly demanding requirements (Aversa et al., 2016 a-o, 2017 a-e).
Many of the new special aircraft have been built so far to achieve special tasks, or at the request of the defense ministry in some highly developed countries, even with the United States of America (Mirsayar et al., 2017).
Methods and Materials
The PA-23 was the first twin-engine design from Piper and was developed from a proposed “Twin Stinson” design inherited when Piper bought the Stinson Division of the Consolidated Vultee Aircraft Corporation.
The prototype PA-23 was a four-seater low-wing all-metal monoplane with a twin tail, powered by a two 125 hp Lycoming O-290-D piston engines the prototype first flew 2 March 1952. The aircraft performed badly and it was redesigned with a single vertical stabilizer and an all-metal rear fuselage and more powerful 150 hp Lycoming O-320-A engines.
Two new prototypes of re-designed aircraft now named Apache were built in 1953 and entered production in 1954; 1,231 were built. In 1958, the Apache 160 was produced by upgrading the engines to 160 hp (119 kW), and 816 were built before being superseded by the Apache 235, which went to 235 hp (175 kW) engines and swept tail surfaces (119 built).
In 1958 an upgraded version with 250 hp (186 kW) Lycoming O-540 engines and adding a swept vertical tail was produced as the PA-23-250 and was named Aztec. These first models came in a five-seat configuration which became available in 1959.
In 1961 a longer nosed variant the Aztec B entered production. The later models of the Aztec were equipped with IO-540 fuel injected engines and six-seat capacity, and continued in production until 1982. There were also turbocharged versions of the later models, which were able to fly at higher altitudes (Petrescu and Petrescu, 2009, 2011, 2012 a-b, 2013 a-c).
The US Navy acquired 20 Aztecs, designating them UO-1, which changed to U-11A when unified designations were adopted in 1962.
In 1974, Piper produced a single experimental PA-41P Pressurized Aztec concept. This concept was short-lived, however, as the aspects of the Aztec that made it so popular for its spacious interior and ability to haul large loads did not lend themselves well to supporting the sealed pressure vessel required for a pressurized aircraft.
The project was scrapped, and the one pressurized Aztec produced, N9941P, was donated to Mississippi State University, where it was used for testing purposes. In 2000, N9941P was donated to the Piper Aviation Museum in Lock Haven, PA, on the condition that it never be flown again. It now sits there on display.
The DHC-6 Twin Otter is a Canadian 19-passenger STOL (Short Takeoff and Landing) utility aircraft developed by de Havilland Canada and currently produced by Viking Air.
The aircraft’s fixed tricycle undercarriage, STOL abilities and high rate of climb have made it a successful cargo, regional passenger airliner, and MEDEVAC aircraft. In addition, the Twin Otter has been popular with commercial skydiving operations, and it is used by the United States Army Parachute Team.
Development of the aircraft began in 1964, with the first flight on May 20, 1965.
A twin-engined replacement for the single-engined Otter had been planned by de Havilland Canada. Twin engines not only provided improved safety but also allowed for an increase in payload while retaining the renowned STOL qualities.
Design features included double slotted trailing edge flaps and ailerons that work in unison with the flaps to boost STOL performance.
The availability of the 550 shp (410 kW) Pratt and Whitney Canada PT6A-20 propeller turbine engine in the early 1960s made the concept of a twin more feasible.
To bush operators, the improved reliability of turboprop power and the improved performance of a twin-engined configuration made it an immediately popular alternative to the single engine, piston-powered Otter which had been flying since 1951.
The first six aircraft produced were designated Series 1, indicating that they were prototype aircraft.
The initial production run consisted of Series 100 aircraft, serial number seven to 115 inclusive.
In 1968, Series 200 production began with serial number 116.
Changes made at the beginning of Series 200 production included improving the STOL performance, adding a longer nose that was equipped with a larger baggage compartment (except to aircraft fitted with floats) and fitting a larger door to the rear baggage compartment.