The Swearingen Merlin or the Fairchild Aerospace Merlin is a pressurised, twin turboprop business aircraft first produced by Swearingen Aircraft, and later by Fairchild at a plant in San Antonio, Texas.
Design and development
The Merlin was an evolution of earlier modification programmes performed by Swearingen Aircraft. Ed Swearingen started the developments that led to the Merlin through gradual modifications to the Beechcraft Twin Bonanza and Queen Air business aircraft, aircraft he dubbed Excalibur. Then hybrid aircraft was developed, with a new fuselage and vertical fin, mated to salvaged and modified (wet) Queen Air wings and horizontal tails, and Twin Bonanza landing gear. This was the SA26 Merlin, more-or-less a pressurized Excalibur but fitted with a different model engine, the Lycoming TIGO-540 6-cylinder geared piston engine. The TIGO 540 was used despite the fact that one of the reasons the IO-720 was used in the Excalibur was that the Queen Air series' IGSO-480 and IGSO-540 engines from the same manufacturer were so troublesome. The decision was soon made to offer increased engine power, this was achieved through installing two Pratt & Whitney Canada PT6A-20 turboprop engines, resulting in the SA26-T Merlin IIA.
The prototype IIA took to the air for the first time on 13 April 1965, about fifteen months after the competing Beech Model 65-90 King Air (which was also derived from the Model 65 Queen Air). 36 Merlin IIA models were built before a follow-on model with Garrett AiResearch TPE-331-1 engines called the SA26-AT Merlin IIB entered production after AiResearch was appointed as distributor for the type. The TPE-331 became the definitive engine of all subsequent production Merlins and the longer-fuselage Metros that were to follow. The Australian Department of Civil Aviation (now the Civil Aviation Safety Authority) took delivery of four Merlin IIBs in 1969 and operated them for almost fifteen years. The Merlin IIAs and IIBs were visually still obviously derivatives of the Queen Air; featuring as they did Queen Air tailplanes and wings with the same flat-top engine nacelles as the Excalibur Queen Airs; the airstair in the same place and of the same general design as the Queen Air; and the nose being especially similar, it was the same general shape with access panels the same size, shape and location as those of the Queen Air.
These visual similarities ended with the next model, the SA226-T Merlin III, which was placed in production in February 1972 after 87 Merlin IIBs were built. This had new wings and engine nacelles with inverted inlet Garrett engines (this again becoming a defining feature of all subsequent production models), new landing gear with two wheels on each leg, a redesigned horizontal tail mounted on the vertical fin instead of on the fuselage as in earlier models and a redesigned longer nose with room for a baggage compartment as well as the avionics found in the noses of Merlin II series aircraft. All of these design changes came from the Metro design, which was undergoing development in the late 1960s.
The SA226-TC Metro was more-or-less a new design, conceptually a stretch of the Merlin II (which it superficially resembled) sized to seat 22 passengers. Prototype construction of the Metro began in 1968 and first flight was on 26 August 1969. The standard engines offered were two TPE331-3UW turboprops driving three-bladed propellers. A corporate version called the SA226-AT Merlin IV was also marketed and initially sales of this version were roughly double that of the Metro. These sales were not immediately forthcoming however, as the company was financially-stretched by the development of the Metro prototype and lacked the funds to gear up for production. This situation was rectified in late 1971 when Ed Swearingen agreed to sell 90% of the company to Fairchild; the company was then renamed Swearingen Aviation Corporation.
By the end of 1972 six Merlin IVs had been built and production gradually built up alongside the concurrently-produced short-fuselage Merlin III. In 1974, the original Merlin IV and Metro models were replaced by the SA226-AT Merlin IVA and the SA226-TC Metro II after about 30 Merlin IVs and about 20 Metros had been built. Among the changes made were larger, ovalised rectangular windows replacing the circular porthole-style windows of the early aircraft, and optional provision for a small Rocket-Assisted Take Off (RATO) rocket in the tail cone, this being offered to improve takeoff performance out of "hot & high" airfields. The same year the Merlin III was replaced by the SA226-T Merlin IIIA, with an extra window on the right side of the cabin and a small window aft of the airstair on each side of the fuselage. Customers for the Merlin IIIA included the Argentinian Air Force, the Argentine Army and the Belgian Air Force.
In January 1979 production of the Merlin IIIA ended in favour of the SA226-T(B) Merlin IIIB. The IIIB differed mainly by TPE331-10U engines of increased power driving four-bladed propellers turning in the opposite direction to those of earlier models. The SA227-TT Merlin IIIC was next, introduced concurrently with the SA227-AC Metro III (the first Metro III was Fairchild c/n AC-420 and the first Merlin IIIC was c/n TT-421, Metro and Merlin aircraft at this stage being numbered consecutively with different prefixes to denote the different types), and the SA227-AT Merlin IVC version of the Metro III followed shortly after (the first Merlin IVC was c/n AT-423). The Merlin IIIC was a redesign to incorporate structural and other changes but was visually the same as the Merlin IIIB, the redesign taking place to make the aircraft compliant with Special Federal Aviation Regulation 41 (SFAR-41). The Merlin IVC version was initially certified in 1980 at up to 14,000 pounds (6,350 kg) this increasing to 14,500 pounds (6,577 kg) as engines and structures were upgraded. An option to go as high as 16,000 pounds (7,257 kg) was offered. Other improvements incorporated into the Merlin IVC were a 10 ft (3.05 m) increase in wing span (achieved by the simple expedient of removing the wingtips from the Metro II wing, bolting an extension to the end of each wing, and fitting a new wingtip, redesigned to reduce drag), TPE331-11U engines with redesigned "quick-access" engine cowlings and driving four-bladed propellers as on the Merlin IIIB, and other drag-reducing airframe modifications including landing gear doors that close after the gear is extended. The US Army bought a second-hand Merlin IVC and operated it as the solitary UC-26C.
Towards the end of production of the short-fuselage variants of the Merlin, optional winglets were offered. Ten of the last 25 SA227-TTs were built with the winglets as Merlin 300s. Production of short-fuselage Merlins ended in 1983 with the building of Merlin IIIC c/n TT-541. The last Merlin IVC (c/n AT-695B) was built in 1987 and Metro production ended in 1998.
Published in July 2009.
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