A Glass Autogyro From Start To Finnish
THE JUKKA TERVAMAKI JT-5
By Walter Shelbourne
MAYBE
IT'S THE weather in Finland, country with no coal or oil and long,
severe winters, Finland is a nation of beautiful forests and lakes,
abounding in wild game and fish. It's a place to fly low and slow in a
comfy rotorcraft fitted with a warm, streamlined cockpit from which to
view the beautiful countryside. At any rate, when Jukka Tervamaki
designed his JT-5 autogyro, that's what emerged - a thoroughly
beautiful machine of glass, well adapted to flight over a land where
reindeer, swans, geese, bear, wolves and Lynx play.
Tervamaki
already was deeply interested in gyroplanes when he worked briefly for
Dr. Igor Bensen in the United States 20 years ago and later obtained
his diploma in Aeronautical Engineering from the Helsinki Institute of
Technology in 1963, before serving with the helicopter section of the
Finnish Air Force. Later on, he went into design and production of
powered sailplanes and designed the engine installation for his JT-6,
now in production as the PIK-20E Motorglider.
It's
no secret that European sailplane makers were far ahead of fiberglass
homebuilt makers in the United States, where composite craft like the
KR-1 and KR-2 and the VariEze and the Quickie have adapted the
glass-reinforced epoxy resin techniques. While the framework of the
load carrying structure of the JT-5 is made of welded 4130 steel
tubing, the cockpit area, canopy and tail feathers are all glass.
A
large horizontal stabilizer and triple vertical surfaces were designed
to eliminate the danger of porpoising by providing dynamic and static
stability. The fin and rudder are of fiberglass-reinforced epoxy resin
with rigid PVC-foam ribs and Courtalds carbon fiber stiffeners, the
stabilizer and tip fins of fiberglass/foam sandwich construction. A
steel tube connects the empennage to the fuselage with a small
tailwheel under the fin.
Tervamaki
designed the cockpit and, pilot seat to the same comfort standards
found in the best glass sailplanes today, with all controls located for
easy handling. Rudder pedals are adjustable and engine noise is
suppressed by a large muffler, a soundproofed firewall behind the pilot
and a propeller with a low tip speed. The engine exhaust is direct
upward, further to prevent noise pollution below the aircraft.
The
engine is a Limbach Motorenbau converted 1 700cc VW engine with a
Scintilla Vertex magneto, delivering 75 to 80 hp at 3800 rpm.
Inspection of the front of the engine is made easy by making the pilot
seat back removable. This unit forms the firewall, which also slips out
to allow easy routine inspection of the rotor prerotator, as well as to
fill the gas tank. The rear of the engine is open for other required
inspection and/or maintenance such as adding oil, adjusting magneto
timing and carburetor, and valve clearances.
The
JT-5 is an improvement of an earlier design, Tervamaki's ATE-3, which
did not have the "Constellation" tail, enclosed cockpit, or other
composite components. The prototype JT-5 first flew on January 7,1973;
later Tervamaki sold it, along with productionrights, to Sr. Vittorio
Magni in Italy, and while there has been no news of Magni's marketing
the JT-5, plans are available for $200 (New CAD-drawn plans) from
Tervamaki in Finland. At least two other JT-5s are flying in Finland,
and some 60 sets of plans have been sold.
The
rotor system for Tervamaki's pretty little single-seate! JT-5 consists
of a two-bladed semirigid rotor of fiberglass reinforced epoxy resin
over a polyurethane plastic foam core. The blades, of constant 7.1 inch
chord and NACA 8-H-12 airfoil, are each attached to the hub with two 10
mm bolts. A 3-meter long lead bar in each blade's leading edge forms
the chordwise balancing weight.
The
rotor mast is made from streamlined metal tubing of SAE 4130 quality.
The rotor tachometer was built up from a German VDO automotive
speedometer, mechanically driven by a flexible shaft from the rotor
head. The rotorhead is a compact offset-gimbal type, with centrifugal
teeter stops and a rotorbrake. Two spiral springs for adjustment are
operated by the control stick's twist handle. Normal rotor speed is 400
rpm with a Vmax of 600 rpm, and the blades have been tested up to 16-20
tons static tensile strength, with a maximum centrifugal load of five
tons at 300 rpm in a 3-G pull-up maneuver.
The
rotor prerotation system consists of a Vee-belt clutch, 90-degree gear
box, sliding universal shaft and an inertia-operated Bendix drive, the
re- duction ratio 8:1. A rotor spin-up of 300 rpm can be achieved, the
prerotation control lever pivoted to the throttle lever for
simultaneous use by the pilot's left hand.
The
JT-5's landing gear is non retractable, the main gear legs built up of
reinforced fiberglass covered with fiberglass fairings, inside which
cables run to the brake system. Main wheels have 300 x 100 tires; the
nose gear has compression-rubber shocks, a 260 x 80 tire and is
steerable through the rudder pedals.
Tervamaki
also provided for the instrument panel cover to open together with the
hinged canopy to expose its backside for inspection of instruments and
provide a look at the nosewheel steering unit, an idea he says he stole
form the German Cirrus sailplane.
He
added a simple carburetor heating unit for cold weather flying, along
with provisions for a cabin heater if required. An efficient
ventilating system prevents canopy frosting in below-zero weather.
Tervamaki
says he spent about 2000 man hours, spread over three years, to
complete the JT-5. He received assistance in funding from the Finnish
Technical Foundation and machine shop help on the rotor head components
from the company he works for as technical manager - Finland's largest
private aviation firm, Wihuri-Yhtyma OY Lentohuolto.
TERVAMAKI JT-5 AUTOGYRO
Rotor Diameter: 7 m (22 ft 11.5 in)
Rotorblade Chord:180 mm (7 in)
Fuselage Length: 3.5 m (11 ft 6 in)
Height: 2.0 m 6 ft 7 in
Wheel Track: 1.7 m (5 ft 7 in)
Propeller Diameter: 1.2 m (4 ft)
Rotor Disk Area: 38.5 sqm (414 sq.ft)
Empty Weight: 167 kg (368 lbs)
Gross Weight: 290 kg (639 lbs)
Max Disc Loading: 7.5 kg/sqm (1.54 lbs/sq.ft)
Max Power Loading: 3.9 kg/hp (8.5 lb/hp)
Vne: 170 kmh (110 mph)
Max Cruise: 140 kmh (93 mph)
Economy Cruise: 120 kmh (81 mph)
Minimum Speed: 40 kmh (22 mph)
Max ROC: 3 m/s (590 fpm)
Service Ceiling (estimated): 4000 m (13000 ft)
Takeoff Run 80 m (230 ft)
Landing Run: 5 m (16 ft)
Range: 250 km (150 miles)