Tervamäki JT-5

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]

JT-5
Role	recreational autogyro
National origin	Finland
Manufacturer	homebuilt
Designer	Jukka Tervamäki
First flight	7 January 1973
Number built	at least 5
Developed from	Tervamäki ATE-3
Developed into	VPM MT-7

Design

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]

Development

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]

Specifications (prototype JT-5)

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)