Aérospatiale SA 321 Super Frelon
The Aérospatiale 'SA 321 Super Frelon is a three-engined heavy transport helicopter produced by aerospace manufacturer Sud Aviation of France. It held the distinction of being the most powerful helicopter to be built in Europe at one point, as well as being the world's fastest helicopter.
The Super Frelon was a more powerful development of the original SE.3200 Frelon, which had failed to enter production. On 7 December 1962, the first prototype conducted the type's maiden flight. On 23 July 1963, a modified Super Frelon flew a record-breaking flight, setting the new FAI absolute helicopter world speed record with a recorded speed of. Both civilian and military versions of the Super Frelon were produced; the type was predominantly sold to military customers. In 1981, Aerospatiale, Sud Aviation's successor company, chose to terminate production due to a lack of orders.
The Super Frelon was most heavily used by naval air arms, such as the French Naval Aviation and the People's Liberation Army Naval Air Force. On 30 April 2010, the type was retired by the French Navy, having been replaced by a pair of Eurocopter EC225 helicopters as a stopgap measure pending the availability of the NHIndustries NH90 helicopter. The Super Frelon was in use for an extended period within China, where it was manufactured under license and sold by the Harbin Aircraft Industry Group as the Harbin Z-8'. A modernised derivative of the Z-8, marketed as the Avicopter AC313, performed its first flight on 18 March 2010.
Development
Background
The SA.3210 Super Frelon was developed by French aerospace company Sud Aviation from the original SE.3200 Frelon. During the type's development, Sud Aviation had risen to prominence as a major helicopter manufacturer, having exported more rotorcraft than any other European rival. Having produced the popular Aérospatiale Alouette II and Aérospatiale Alouette III, the firm was keen to establish a range of helicopters fulfilling various roles, functions, and size requirements; two of the larger models in development by the early 1960s were the Super Frelon and what would become the Aérospatiale SA 330 Puma. The Super Frelon was the largest helicopter in development by the firm, being substantially increased over the earlier Frelon, and was considered to be an ambitious design at the time.The earlier Frelon had been developed to meet the requirements of both the French Navy and the German Navy, which both had released details on its anticipated demands for a heavy helicopter; however, these requirements were revised upwards by the customer, leading to the redesign and emergence of the Super Frelon. Changes included the adoption of much more powerful engines, using three Turbomeca Turmo IIIC turboshaft engines, each capable of generating on the prototypes in place of the Frelon's Turbomeca Turmo IIIB engines; these drove a six-bladed main rotor, instead of the Frelon's four-bladed one, and a five-bladed tail rotor. Overall, the modified design provided for a greatly increased gross weight, from, whilst improving the rotorcraft's aerodynamic efficiency and handling qualities.
Additional external changes between the Frelon and Super Frelon had been made, such as the original stubby tail boom having been replaced by a more conventional one, albeit with a crank in it to raise the tail rotor clear of vehicles approaching the rear loading ramp. Taking note of American experiments with amphibious helicopters, the Super Frelon's fuselage was redesigned into a hull, featuring a bow, planing bottom and watertight bilge compartments. Various foreign manufacturers participated in the development and manufacturing of the type; American helicopter company Sikorsky was contracted to supply the design of a new six-bladed main rotor and five-bladed tail rotor, while Italian manufacturer Fiat supplied the design for a new main transmission.
Into flight
On 7 December 1962, the first prototype Super Frelon conducted the type's maiden flight. On 28 May 1963, it was followed by the second prototype. The first prototype was tailored towards meeting the needs of the French Air Force, while the second was fully navalised, including lateral stabilising floats fixed to the undercarriage. On 23 July 1963, a modified prototype Super Frelon helicopter was used to break the FAI absolute helicopter world speed record, having attained a maximum speed of during the flight. Flown by Jean Boulet and Roland Coffignot, a total of three international records were broken, these being: speed over 3 km at low altitude,; speed at any altitude over 15 and 25 km, ; and 100km closed circuit.
By April 1964, the two prototypes had accumulated 388 flying hours, which included 30 hours of seaworthiness trials performed with the second prototype. In January 1964, the third Super Frelon prototype made its first flight, the fourth first flew during May 1964, and a pair of pre-production models were completed during the latter half of 1964. The third prototype participated in a series of accelerated wear trials to establish component endurance and overhaul lifespan, while the fourth prototype was assigned to further tests of equipment for the naval environment.
By July 1964, the French Government had placed an initial order for the Super Frelon, intended to perform logistic support duties at the Centre Experimental du Pacifique; negotiations for a further order was already being negotiated for the naval version, which were to be equipped for anti-submarine duties. However, West German support for the Super Frelon programme had already declined by this point, partially due to interest in the rival Sikorsky SH-3 Sea King, which was evaluated against the type.
Both civilian and military versions of the Super Frelon were built, with the military variants being the most numerous by far, entering service with the French military as well as being exported to Israel, South Africa, Libya, China and Iraq. Three military variants were produced: military transport, anti-submarine and anti-ship. The transport version is able to carry 27 equipped troops, or alternatively 15 stretchers for casualty evacuation tasks.
Design
The Aérospatiale SA 321 Super Frelon is a large, heavy-lift single-rotor helicopter, furnished with a relatively atypical three-engine configuration; these are Turboméca Turmo IIIC turboshaft engines set on top of the fuselage, a pair of turbines positioned side by side at the front and one located aft of the main rotor. The naval anti-submarine and anti-ship variants are usually equipped with navigation and search radar, and a 50-metre rescue cable. They are most often fitted with a 20 mm cannon, countermeasures, night vision, a laser designator and a Personal Locator System. The Super Frelon can also be fitted for inflight refueling.The front engines have simple individual ram intakes, while the rear one is fitted with a semi-circular scoop to provide air; all three bifurcated exhausts are near to the rotor head. The three engines and the reduction gearbox are mounted on a horizontal bulkhead and firewall which forms the roof of the cabin and upper structural member of the fuselage. The engines are isolated by multiple firewalls, including transverse firewalls separating front and rear engines from the rotor gearbox, and zonal engine firewalls. Eight sturdy hinged doors provide access to the compact Turmo engines, which have ample space around them to enable ground crew to service them without using external platforms.
The fuselage is actually a hull, which makes use of a semi-monocoque light alloy construction; according to aerospace publication Flight International, the hull design was "reminiscent of flying-boat engineering". The main cabin lacks any transverse bracing, except for a single bulkhead between the cockpit and cabin. Substantial built-up frames connect the strengthened roof structure with the floor/planing-bottom of transverse under-floor bulkheads and outer skin. A conventional exterior skin is used, employing longitudinal stiffeners as well as two lines of deep channel members, while the under-floor cross members are reinforced with vertical stiffeners. There is no keel, at the floor level there are horizontal members between frames which are stiffened by transverse shear angles. Flexible fuel cells are stored in four watertight under-floor compartments lying fore and aft of the rotor axis, while the floor itself is fitted with removable panels. A hatch set into the floor, positioned approximately underneath the rotor axis, is used for sling-load operations.
At the rear of the cabin is a tapered section of simple semi-monocoque construction, which is closed by a robust hinged rear loading ramp, which serves as the main entrance for bulky loads or equipment. The loading ramp is jettisonable in emergency situations. Additionally, there is a sliding door located on the forward starboard side, while a small hinged emergency door is set on the aft port side. The tail boom uses conventional semi-monocoque construction, supported by closely spaced notched channel-section frames and continuous stringers, absent of any major longitudinal sections or longerons. The cranked section carrying the tail rotor and trim plane is more robust, strengthened by a solid-web spar, frames, and stiffeners. The juncture of the main boom and cranked section is hinged in order to reduce the rotorcraft's folded length to. Along the top of the boom, the shaft for the tail rotor is covered by a fairing.
The fixed landing gear has twin wheels on each of the three vertical shock absorber-equipped struts. The main leading gear units are mounted on triangulated tubular structures, while the nose gear is bracketed to the cockpit bulkhead via a watertight seal in the planing bottom. The main wheels have hydraulic brakes operated from the pedals, complete with a parking hand brake, while the nose unit is fully castoring. The nose, which is covered by large glazed panels, has a bow chine and planing bottom built as a unit with the flight deck, which is higher than the main cabin floor.