Issue No 21 THE AVIATION HISTORIAN 115
was a better primary trainer than the standard
L-4J, and in 1960 the workshops at Bandung
began converting all of the air arm’s L-4Js into
NU-90s, fitted with a 90 h.p. Continental C-90-
12F flat-four direct-drive engine.
The USA-35B aerofoil of the L-4J’s wing was
retained but the flaps were later removed and
the aileron length extended on the NU-90A,
which was fitted with a Continental O-200 (an
uprated C-90) engine with a 6ft (1·8m)-diameter
McCauley metal fixed-pitch propeller. The
Belalang’s wing was braced by vee struts from
the top fuselage longerons and was set with 1°
37’ incidence at the root and 5° dihedral. The
wings incorporated its forerunner’s standard
spruce spars, aluminium ribs and fabric
covering, but the aluminium-alloy-frame control
surfaces were fibreglass-covered.
The welded-steel fixed surfaces on the tail
were fabric-covered but the rudder and elevators
were again fibreglass-covered. The fuselage
was fibreglass-covered welded steel, while
the cockpit canopy was in two sections; the
forward unit hinged to open to starboard and
the rear section sliding aft. The L-4J’s split-axle
mainwheels were retained but were moved
forward some 4in (10cm). The Kelsey-Hayes
wheels were fitted with Goodrich low-pressure
tyres and incorporated hydraulic expander-tube
brakes. The Belalang entered very small-scale
production in the early 1960s, and at least five
NU-90 Belalangs saw service with the AURI and
Indonesian Army.fireflies and a dragonfly
Having got the bit between its teeth, Indonesia’s
growing aircraft industry set its sights on the
civil light aircraft market, and during 1957 work
was started on an economical lightweight single-
seat low-wing aircraft for Indonesian flying
clubs. Of fabric-covered wood construction, the
NU-25 Kunang (Firefly) was powered by a 25 h.p.
Volkswagen flat-four air-cooled engine driving
a two-bladed fixed-pitch propeller of 4ft 9in
(1·45m)-diameter, although a more powerful 35
h.p. VW engine was later fitted.
The Kunang’s wing was tapered, with a mean
chord of 2ft 11in (0·9m), incorporating a NACA
2412 aerofoil and an aspect ratio of 7:1. The
spars were of box type with girder-type ribs
and the wing was fitted with fixed leading-edge
slats. An exact first-flight date remains elusive,
but after testing of the prototype the span was
increased from 22ft 11in (6·98m) to 28ft 2½in
(8·6m), giving a revised aspect ratio of 9·6:1. The
extended-span wing had a dihedral of 5°, with 3°
incidence at the root and 0° at the tip. The open-
cockpit fuselage was constructed of a spruce and
plywood framework with a fabric covering, and
the tail unit was of braced-wire monoplane typeABOVE Designed as an economical single-seat ultra-light training aircraft for pilots of very limited experience, the
NU-25 Kunang first flew circa 1957–58, and was roughly equivalent to the Druine Turbulent in terms of size and
performance. The same aircraft, “04”, was later fitted with a 35 h.p.engine and an enclosed cockpit with canopy.