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. ^{[3] [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. ^[12]

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. ^[13]

Data from Taylor 1986, p.564

General characteristics

• Crew: one pilot
• Length: 3.50 m (11 ft 6 in) (fuselage)
• Empty weight: 167 kg (368 lb)
• Max takeoff weight: 290 kg (639 lb)
• Powerplant: 1 × Volkswagen four-cylinder, horizontally-opposed, air-cooled automotive engine, 56 kW (75 hp)
• Main rotor diameter: 7.00 m (23 ft 0 in)
• Main rotor area: 38.50 m² (414.4 sq ft)

Performance

• Maximum speed: 170 km/h (110 mph, 92 kn)
• Cruise speed: 150 km/h (93 mph, 81 kn)
• Range: 350 km (220 mi, 190 nmi)
• Service ceiling: 4,000 m (13,000 ft)
• Rate of climb: 3 m/s (590 ft/min)

• Charnov, Bruce H. (27–29 May 2009). From Rolf von Bahr to Jukka Tervamäki: The Scandinavian Influence on European Gyroplane History. American Helicopter Society 65th Annual Forum.
• Raivio, Jyri (May 1973). "Tuo lentävä mies mainiossa koneessaan" [That flying man in his magnificent plane]. Ilmailu. Vol. 36, no. 5. Helsinki: Suomen ilmailuliitto. pp. 10–12.
• Shelbourne, Walter (October 1979). "The Jukka Tervamaki JT-5". Homebuilt Aircraft. Vol. 5, no. 8. pp. 28–29.
• "La Storia" [History]. Magni Gyro: produzione autogiri per il lavoro e per il tempo libero. Besante: Magni Gyro srl. Retrieved 23 July 2024.
• Markowski, Mark (1984). The Encyclopedia of Homebuilt Aircraft. Blue Ridge Summit, Pennsylvania: Tab Books.
• Taylor, John W.R., ed. (1986). Jane's All the World's Aircraft 1986-87 (77th ed.). London: Jane's Pub.
• Taylor, John W.R., ed. (1987). Jane's All the World's Aircraft 1987-88 (78th ed.). London: Jane's Information Group.
• Taylor, Michael J. H. (1993). Jane's Encyclopedia of Aviation. London: Studio Editions.
• Tervamäki, Jukka (n.d.). "The JT-5 Autogyro". The Home Page of Jukka Tervamaki. Retrieved 23 July 2024.
• Tervamäki, Jukka (August 1973). "New Super Sleek Autogyro From Finland". Popular Rotorcraft Flying. Vol. 11, no. 3. Raleigh, North Carolina: Popular Rotorcraft Association. p. 24.
• Tervamäki, Jukka (February 1974). "The Sleek New JT-5 From Finland". Sport Aviation. Vol. 23, no. 2. pp. 39–41, 61.

• History, photos, and plans for the JT-5 on designer Jukka Tervamäki's personal homepage