Draft:SIAI-Marchetti SV-20

The SIAI-Marchetti SV-20 was a prototype helicopter project developed by SIAI-Marchetti in 1968. It was produced as the SV-20A and the SV-20C, both of which were abandoned in mid-1970.

History
In 1968, the Italian aircraft manufacturer SIAI-Marchetti, headquartered near Varese, established its “Sezione Volo Verticale” under the leadership of Dr. Emilio Bianchi. This new division initiated the development of the SV-20A (A = Alato, "winged" in French) and the SV-20C (C = Convertibile, "convertible") with a pusher propeller, in July of the same year.

The goal was to create a helicopter capable of transporting twelve passengers at a speed of 390 km/h. By December 1968, the manufacturing of the dynamic components and a portion of the airframe commenced. To enhance the aerodynamics of the aircraft, wind tunnel tests were conducted at the universities of Turin, Milan, and Pisa. A full-scale model of the SV-20A was unveiled during the 1969 Paris Air Show.

In 1970, multiple projects were in the development phase, including a device featuring a fenestron tail rotor and another variant equipped with two propulsive propellers, capable of achieving speeds around 460 km/h. By January 1972, three prototypes were in the process of assembly, and SIAI-Marchetti was engaged in negotiations with the FAA and the Registro Aeronautico Italiano to secure international certifications by 1975, subsequent to flight tests.

Market projections by the manufacturer indicated a demand for 500 units, with a substantial portion, several dozen, earmarked for the Italian military for various purposes such as transport, medical evacuation, electronic warfare, and search and rescue missions. At that juncture, the manufacturer sought financial assistance from the Italian government to expedite the development of the device.

In 1973, Agusta, which had already held a 30% share of SIAI-Marchetti's market since 1970, increased its stake in the company, becoming the majority shareholder. Consequently, the SV-20 program was abandoned that year.

SV-20A
The SV-20A has a relatively spacious cockpit with large windows, intended to give good visibility for the pilot and co-pilot occupying two side-by-side seats. The extended, square-section cabin has the capacity to carry up to twelve passengers or 1,250kg of cargo. Its tail boom is fitted with horizontal stabilizers and terminates with a fin that includes a two-blade anti-torque propeller. The landing gear comprises a pair of skids. Positioned above the cabin is a high-profiled fairing that shields the lift rotor transmission shaft.

This shaft is equipped with two large blades. Additionally, two small wings are affixed to the base of this fairing, which aids in partially unloading the lift rotor during horizontal flight. These wings support the two United Aircraft of Canada PT6C turbines housed in nacelles, with a maximum power of 912hp and manufactured by the Motoren-und-Turbinen-Union in Germany, the successor to MAN. There were also plans to offer alternative turbine options such as the Turbomeca Astazou XIVA or Rolls-Royce RS.360 turbines based on customer preferences.

SV-20C
In the SV-20C variant, the right turbine is outfitted with a three-blade pusher propeller featuring variable pitch. This modification, increasing the empty mass by only 80kg, results in a speed boost of 110 km/h, reaching a total speed of 390 km/h. At this velocity, the wings relieve the lift rotor to an extent that prevents it from rotating too rapidly, thereby avoiding excessively high speeds. Subsequently, the anti-torque rotor is no longer necessary, as the asymmetric propulsion from the pusher propeller and the drift adequately provide control. Furthermore, control is also facilitated by the ailerons installed on the wings.

Technical statistics
=== SV-20A ===


 * Crew: 2
 * Passengers: 12
 * Total length: 15.63 m
 * Height: 3.55 m
 * Main rotor diameter: 12.86 m
 * Main rotor area: 129.82 m²
 * Tail rotor diameter: 2.50 m
 * Tail rotor area: 4.91 m²
 * Wing span: 6.0 m
 * Empty mass: 1,950 kg
 * Maximum take-off weight: 4,000 kg

=== SV-20C ===


 * Tail rotor diameter: 2.5 m (8,202 ft)
 * Tail rotor area: 4.91 m² (52,851 sq. ft)
 * Maximum takeoff weight: 4,000 kg (8,818 lbs)
 * Empty mass: 1,950 kg (4,299 lbs)
 * Rotor area: 129.82 m² (1,397.371 sq. ft)
 * Main rotor diameter: 12.68 m (41.601 ft)
 * Height: 3.55 m (11,647 ft)
 * Wingspan: 6 m (20 ft)
 * Length: 15.63 m (51.28 ft)