The Tervamäki JT-5, later marketed as the VPM MT-5, is a single-seat autogyro developed in Finland[1] by Jukka Tervamäki in the early 1970s and which was marketed in kit form for amateur construction.[2] A development of his ATE-3 design of 1968, the JT-5 first flew in 1973,[2] and Tervamäki sold the prototype, its tooling, and its manufacturing rights the following year.[3]
The JT-5 features a streamlined fuselage pod that fully encloses its cockpit and a single, piston engine that drives a pusher propeller.[2] It has a two-bladed main rotor, and fixed, tricycle undercarriage.[2] The structure makes extensive use of composite materials[2] [3] around a frame of welded steel tube.[2] [4] The empennage is a triple tail that consists of a large fin and rudder plus smaller fins at the ends of the horizontal stabiliser,[2] an arrangement that Tervamäki compared to that of the Lockheed Constellation.[5] This configuration was chosen to increase the area of the tail surfaces and therefore the static and dynamic stability of the aircraft.[5] Tervamäki saw this as an important safety feature to reduce the possibility of pilot-induced oscillation, which had been implicated in fatal autogyro crashes.[5]
The cockpit is enclosed by an expansive plexiglass canopy that hinges sideways.[2] [3] The instrument panel and the firewall that separates the cockpit from the rotor mast and engine hinge together with the canopy.[2] [3] This feature was intended to facilitate inspection and maintenance of the instruments, nosegear, rudder pedals, and front side of the engine.[5] The level of access to the engine that this created was so great that most routine engine inspection tasks could be carried out without removing the cowling.[6]
Provisions for cold weather include an optional cabin heater, a ventilation system to prevent canopy fogging, and a carburettor heater.[5] [7]
The prototype was powered by a Volkswagen automotive engine modified for aero use by Limbach Motorenbau.[2] VPM specified a Limbach L1700 for the MT-5 instead.[8] The aircraft is equipped with a pre-rotation mechanism for the rotor.[2] [4]
Design work on the JT-5 began in 1969, and construction of the prototype the following year.[3] Initially, the work was shared between Tervamäki and Aulis Eerola, with whom he had collaborated on the ATE-3.[3] Eerola contributed to some of the construction work, but departed the project before its completion.[3] Some of the funding for the development work came from a grant by the Finnish Technical Foundation.[3] [9] Tervamäki estimated that around 2,000 hours' work went into the prototype[9] [10] over three years.[9] He later reflected that this level of effort was contrary to one of the main reasons he had originally been drawn to autogyros: their simplicity.[11]
The prototype first flew on 7 January 1973, carrying the registration OH-XYS.[2]
By then, however, Tervamäki's focus was on his JT-6 motorglider, and he realised that he would not have time to effectively market and support the JT-5.[9] Therefore, in 1974, he sold the prototype, together with its moulds, tooling, and manufacturing rights to Vittorio Magni.[12] [9] In 1979, Magni founded the VPM company to market components and complete kits of the aircraft under the name VPM MT-5.[2] The following year, Magni contracted Tervamäki to design an enlarged, two-seat derivative, the MT-7.
In 1986, VPM sold the rights to the MT-5 and MT-7 to Spanish firm Cenemesa.[13]
Apart from the prototype, at least four other JT-5s were built by 2009, three in Finland and one in Sweden, with a number of others under construction.[3] Tervamäki continued to sell JT-5 plans for some time,[3] with around 60 sets sold by 1979.[10] He later made them available for free download on his personal website.[14]