CNIAR / IAR IS-28 Lark / IS-28M2 Motor Lark / IAR-28 / IAR 34
The IS-28 two-seater high performance training sailplane first flew in August 1970.
The 17-meter IS 28B, which first flew in 1976, was manufactured by Intreprinderea de Constructii Aeronautice (Aircraft Construction Company) (ICA), the Romanian state aircraft company at its plant in the city of Brasov. ICA subsequently changed its name to Intreprinderea Aeronautici Romanesc (Romanian Aircraft Company) (IAR). The IS-28B was developed from the 15 m. IS-28 which appeared in 1970. The all metal structure IS-28B has performance flaps, with upper and lower surface (or optionally, upper surface only) Hutter type airbrakes for approach control, a partially retractable gear and fabric cover on all conrol surfaces. The 28B2 model incorporates detailed improvements. The IS-30 is metal skinned througout and in standard configuration has a fixed gear and no flaps, although these were available as factory options. Top surface only airbrakes are standard on the 30. The tail surface on the 28 fold, but the smaller, more aerodynamically refined, tail of the 30 does not.
Design work on the IS-28B began in the autumn of 1971 and the prototype made its first flight on 26 April 1973. The first production version was the IS-28B1 which did not have wing flaps, but this was succeeded by the IS-28B2 which has trailing edge split flaps and Schempp-Hirth air brakes instead of the DFS-type ones of the B1.
Developed from the IS-28, the IS-28B2 has a number of important differences from the earlier design which include 17m span all-metal mid wings of Wortmann section instead of the IS-28's 15m span shoulder wings of NACA section, a longer and more slender fuselage and reduced wing and tailplane dihedral.
About 100 IS-28B2s had been sold, and a high proportion of this total have gone to customers in Australia and the USA. Both versions are of all-metal construction, as was the earlier IS-28, and the forward-swept wings have L-section main spar booms and dural spar webs, a dural auxiliary spar and dural ribs. The Schempp-Hirth air brakes above and below the wings are metal, whereas the ailerons and flaps are fabric covered except for their leading edges. The wings are attached to the fuselage by two adjustable tapered bolts at the leading edge and two fixed tapered bolts at the trailing edge. The forward and centre fuselage is an all-metal semi-monocoque structure, while the rear fuselage is a duralumin monocoque. The two pilots are seated in tandem under a one-piece Plexiglas canopy which opens sideways to starboard and can be jettisoned in flight. A nose towing hook with Tost cable release isstandard, but a towing hook mounted on the eg is an optional choice for the customer. The folding cantilever all-metal T-tail is similar to the IS-28's but has a single-spar fin; the elevator trailing edges and rudder are fabric covered and there is a trim tab in each elevator. The landing gear consists of a semi-retractable monowheel with a disc brake and oleopneumatic shock absorber, and there is a sprung tailskid.
Designed by Iosif Silimon, two motor glider versions of the IS-28B2 were developed, the IS-28M1 tandem two-seater with a monowheel undercarriage, and the IS-28M2 (redesignated IAR-34) seating two side-by-side and with a conventional retractable undercarriage; both of these differed from the B2 chiefly in having the wings moved to the low-set position, and the forward fuselage, cockpit canopies and main landing gear redesigned. The M2 has two main wheels retracting backwards into the wing roots to lie semi-exposed in the centre-section, and incorporating shock absorbers and brakes; there is also a steerable tailwheel. The rear fuselage, tail unit and main wing structure were virtually unchanged from those of the IS-28B2; in both versions the wings can be folded from a point just inboard of the ailerons. Wing span is 17m (55ft 9.25n) instead of the 18m (59ft 0.75in) of the IS-28M1, which has a slightly greater length and less height. Approach control is by upper and lower surface Hutter type airbrakes.
The IS-28M2 was the first to take to the air, the prototype, registered YR-1013, making its first flight on 26 June 1976 and making its public debut at that year's Farnborough air show; the first 10 M2s were allocated to the UK, where they are distributed by Morisonics Ltd, and this version has also been exported to Canada and the USA.
Deliveries of the M1 were due to begin in 1979, and both versions are powered by a 68hp Limbach SL 1700E1 'flat four' engine, driving a Hoffman HOV-62R two-blade variable-pitch and fully-feathering propeller; there is a single fuel tank aft of the cockpit holding 7.9 Imp gallons.
Top-surface airbrakes and camber-changing flaps (+15 to -11) are provided, as are full dual controls. The 28M2A model has strengthened wings. The IS 28M2 has been developed into the Rotax powered 11.58 m. /38.0 ft. span IAR-46 light aircraft, which has a 17 m. extended wing sailplane variant.
Both versions, like the IS-28B2, are of mainly metal construction, the single-spar wings having 2° dihedral and 2° 30' forward sweep at the quarter-chord line. The wing, ribs and skin are of aluminium, the metal ailerons are fabric-covered and the trailing edge split flaps, which can be set to a negative position, are now an optional feature, instead of standard as on the B2; there are all-metal two section Mutter air brakes in the upper surfaces. Wing folding is also optional, the outer panels folding inwards. The fuselage is built in three parts; a metal front portion, built up on two longerons and cross-frames and with glassfibre fairings and engine cowling panels; a centre portion which is an aluminium alloy monocoque; and a rear portion made up of aluminium alloy frames and skin. Like the B2, the cantilever T-tail is of aluminium alloy with slight dihedral on the tailplane; the rudder and the elevator trailing edges are fabric-covered, and there is a trim tab in each elevator. Both versions have full dual controls and a rearward-sliding main portion of the canopy.
An Open Class development of the IS-28B2 known as the IS-30 was undergoing flight tests in the spring of 1978; this has 18m (59ft 0.75 in) span wings without provision for water ballast, and the redesigned tail unit of the IS-32.
Motor Lark IS-28M2
Engine: 51 kW/ 68 bhp Limbach SL 1700 E1
Wing span: 17 m / 55 ft 9.25 in
Wing area: 18.24 sq.m / 196.3 sq.ft
Aspect ratio: 15.8
Length: 24 ft 7.25 in
Height: 7 ft 0.75 in
Empty Weight: 600 kg / 1320 lb
Payload: 189 kg / 420 lb
Gross Weight: 789 kg / 1740 lb
Wing Load: 43.26 kg/sq.m / 8.86 lb/sq.ft
L/DMax: 27 at 100 kph / 54 kt / 62 mph
MinSink: 1.20 m/s / 3.94 fps / 2.33 kt at 50 mph
Max level speed: 124 mph
Economical cruising speed: 102.5 mph
Take-off run: 525 ft
Range with max fuel: 280 miles
No. of Seats: 2
No. Built: 50
Twin Lark IS-28B2
Span: 17m / 55 ft 9.25 in
Length: 27 ft 5.25 in
Height: 5 ft 10.25 in
Wing area: 18.24 sq.m / 196.3 sqft
Aspect ratio: 15.8
Airfoil: Wortmann FX-61-163,root; -126, tip
Empty Weight: 400 kg / 882 lb
Payload: 190 kg / 418 lb
Gross Weight: 590 kg / 1300 lb
Wing Load: 32.35 kg/sq.m / 6.62 lb/sq.ft
Max speed: 140 mph (in smooth air)
Min sinking speed: 2.26 ft/sec at 45 mph
L/DMax: 34 at 93 kph / 51 kt / 58 mph
Best glide ratio: 34:1 at 62mph
No. of Seats: 2
No. Built: 400