M.Hardy. Gliders & Sailplanes of the world

LET L-13 Blanik

  Arguably the most commercially successful sailplane ever to be built, the LET L-13 Blanik all-metal tandem two-seater trainer has been exported to more than 40 countries, more than 2,000 of about 2,500 sold by the summer of ДальшеMore>>> 1977 having been exported abroad, including more than 1,000 to the Soviet Union, about 200 to the USA, about 150 to the United Kingdom and more than 100 each to Australia and Canada. Production continues at the LET Narodni Podnik (Let National Corporation) and is now getting close to the 3,000 mark; like all Czechoslovak aircraft, export sales of the L-13 Blanik are handled by the Omnipol Foreign Trade Corporation. The Blanik has set up no fewer than 13 international records recognised by the FAI, as well as many other national gliding records, and in 1969 a particularly notable flight across the Andes in a Blanik by the Chilean pilot Alejo Williamson, taking 5hr 51 min, won him an FAI Gold Medal. The Blanik is intended for training in all categories from elementary to blind flying and is also suitable for high performance flight. It is fully aerobatic when flown solo, and can do basic aerobatic manoeuvres when carrying two pilots; this degree of versatility, combined with good flying qualities, sound construction, durability and ease of maintenance have helped it to become a best-seller. Design work on the Blanik, whose designer was Karel Dlouhy, started in January 1955 and construction of two prototypes began in August of that year; the first flight was made in March 1956 and 2,094 Blaniks had been built by the end of 1975. The cantilever shoulder wings are characterised by a moderate aspect ratio (13.7) and 5° forward sweep at the quarter-chord line; wing tip 'salmon' fairings are fitted. The wings are all-metal two-spar structures, the main spar forming a torsion box with the leading edge, and each wing is secured by three fuselage attachments. The metal ailerons and slotted area-increasing flaps are fabric-covered, and there are light alloy DFS-type air brakes above and below the wings. The all-metal fuselage is a semi-monocoque of oval cross-section built in two halves riveted together in the vertical plane, with riveted skin, and the cantilever all-metal tail unit has fabric-covered elevators and rudder, with a controllable trim tab in each elevator. The horizontal tail surfaces fold upwards parallel to the rudder for transport. The landing gear consists of a retractable monowheel, with an oleo-pneumatic shock absorber and mechanical brake. The two pilots sit in tandem in a partly-upholstered cockpit with heat-insulated walls, under a sideways-opening canopy hinged to starboard which is jettisonable in flight. Optional 'extras' include, amongst other things, electric gyros, navigation lights, radio, a battery and rear compartment blinds for instrument flying instruction, while more unusual 'extras' are a water ballast system to increase the wing loading for solo flight and skis for operation on snow.


Span: 53 ft 2 in
Length: 27 ft 6 1/2 in
Height: 6 ft 10 in
Wing area: 206.1 sqft
Aspect ratio: 13.7
Empty weight: 677 lb
Max weight: 1,102 lb
Max speed: 157 mph (in smooth air)
Max aero-tow speed: 87 mph (IAS)
Min sinking speed: 2.79 ft/sec at 50 mph (IAS)
Best glide ratio: 28:1 at 55 mph (IAS)



LET L-13J Blanik

  The L-13J was a powered version of the well-known L-13 Blanik tandem two-seater trainer, fitted with a newly-developed 42hp Avia Jawa (Motorlet) M-150 two-cycle three-cylinder inverted air-cooled engine, driving a V-210 two-bladed wooden tractor propeller. This auxiliary engine, which was housed in a non-retractable glassfibre cowling aft of the cockpit, could be stopped and restarted in flight to prolong periods of soaring flight. The L-13J prototype, OK9821, first flew on 26 March 1968 but only a small number were built and this variant did not go into large-scale production. The first powered version of the Blanik had been the XL-13M, a 1964 conversion with a 26hp Walter engine on a non-retractable mounting aft of the cockpit, and this was later followed by a number of other powered conversions of the Czech glider. The XL-13T was similar to the L-13J, with a 35hp Motorlet M-151 also on a non-retractable dorsal mounting; the prototype, registered OK-62, first flew in 1970. The following year a twin-engined conversion was produced by the German firm of Sigmund Flugtechnik, who also helped in the design of the Yugoslav VTC SSV-17 motor glider. Designated L-13-2M, this version of the Blanik, registered D-KACS, was fitted with two 44hp Lloyd LS-400 radials mounted in overwing nacelles in a conventional leading edge installation and driving two-blade fixed-pitch propellers; there is a small outrigger wheel under each wing to ensure ground clearance for the airscrews.
  A second foreign conversion was produced in 1975 by the Russian LAK factory (Litovskaya Aviatsionnaya Konstruktsiya), which produced the LAK-9 Lietuva sailplane. LAK fitted a 68hp Limbach SL 1700E1 'flat four' engine into the nose of a standard L-13 Blanik, the resulting aircraft being designated LAK-6 and serving as a flying test bed for a new motor glider of plastics construction, of which a prototype was being built in 1977. LAK is now the sole repair and overhaul centre in the USSR for the Blanik, more than 300 of which had been overhauled by mid-1977. Another version with the engine in the nose was the L-13SW with a 65hp Walter Mikron IIIA in-line powerplant; the prototype of this, registered OK-068, first flew on 10 May 1978. In 1976 a conversion of the L-13 with a 50hp Wankel rotating piston engine appeared; this motor was carried dorsally on a non-retractable mounting. A similar mounting is being used by Mr Pentti Alanne of Finland in his conversion of an L-13 to have a Volkswagen engine; this was expected to make its first flight in 1981.
  In Germany Blanik D-KOEB has been modified to flight test an RFB SG 85 fan pod engine, which is mounted dorsally and gives 209!/2 lb st at full throttle at sea level. This powerplant, made by Rhein-Flugzeugbau GmbH, is a fixed-geometry pod marketed as a complete unit for fitting to powered gliders or ultra light aircraft. It consists of dual rotating-combustion Wankel-type engines mounted in tandem, and driving a three-blade fan in a circular fan duct.


Data: L-13J
Span: 53 ft 2 in
Length: 27 ft 6 1/2 in
Height: 6 ft 10 in
Wing area: 206.1 sq ft
Aspect ratio: 13.7
Empty weight: 794 lb
Max weight: 1,228 lb (two pilots)
Max speed: 92 mph
Cruising speed: 80 mph
Best glide ratio: 21:1
Normal range: 112 miles