LET L-13
Encyclopedia
The L-13 Blaník is a two seater trainer glider
produced by Let Kunovice
since 1956. It is the most numerous and widely used glider in the world. In United States Air Force Academy
service, it is designated TG-10C and is used for basic flight training.
wing profiles. The L-13 was developed as a practical glider suitable for basic flight instruction, aerobatic instruction and cross-country training. This design concept was combined with true and tested technology: metal construction, NACA
laminar profiles and many standard-issue components of the Soviet aerospace industry.
The Blaník entered production in 1958 and quickly gained popularity as an inexpensive, rugged and durable type, which was easy to fly and operate. It was widely adopted in the Soviet bloc and was exported in large numbers to Western Europe and North America. Total production was in excess of 2650, or more than 3000 if variants are included. More than half a century after its first flight it is still the most common glider in the World.
In the cross-country role the Blaník achieved many two-seater World distance records during the 1960s in spite of having only fair performance.
The Blaník inspired other designs, notably the Démant and L-21 Spartak single-seaters developed to equip the Czechoslovak team in the 1956 and 1958 World Championships.
For this reason, some pilots trained in the Blaník benefit from differences training in a modern two-seater (such as Lark IS-28B2) before transitioning to high performance plastic single seaters.
The Blaník was originally stressed for simple aerobatics, including inverted flight where the aircraft has a single occupant. As a result of this latter requirement, intermediate level
aerobatic training in the Blaník was done in solo flight with the instructor on the ground or in another aircraft. Following a manufacturer airworthiness directive in June 2010, all aerobatic manoevres were forbidden.
and the FAA
.
According to Let company, the current situation may change in spring 2011 when new processes of control will be developed - http://www.let.cz/files//File/AI_opinion_gliders_092010_ENG.pdf
Initially, the directives mandated the aircraft be grounded unless logbook records show that dual flying hours comprise less than 50% of the aircraft's total flying time. Further investigation into the original accident has shown that these limits and analysis of flight records (such data also not being guaranteed to exist) will not be sufficient to guarantee safe operation of the type.
recognized the potential fatigue-life limitations of the Blaník and in conjunction with the Ansett Airlines NDT laboratory and the Civil Aviation Authority
of Australia developed an inspection programme culminating in the issue of GFA AD-369, designed to monitor the condition of the fatigue-critical components. Most of these fatigue-critical components are called into question by the accident on 12 June 2010.
GFA AD-369 gave 3 options for continued operation beyond 5000 hours or 18,000 launches.
In 1984 Dafydd LLewellyn and Riley Aeronautics received Department of Aviation certification for a modification of the wing to extend its fatigue life. Nine Blaníks in Australia were modified and re-certificated as L-13A1 (option B in AD-369)..
GFA AD 663 was issued on 25 June 2010 imposing the operational limitations specified by the Type Certificate holder. GFA AD 663 does not apply to Blaníks which have been modified to L-13 A1 (Llewellyn Modification)..
Regaining airworthiness of Blanik L-13: STC ADxC-DC-39-001
STC has been approved by EASA on 14-june-2011. http://www.aircraftdc.de/ENG/images/Blanik/stc%2010035295%20a.024.pdf
Glider (sailplane)
A glider or sailplane is a type of glider aircraft used in the sport of gliding. Some gliders, known as motor gliders are used for gliding and soaring as well, but have engines which can, in some cases, be used for take-off or for extending a flight...
produced by Let Kunovice
Let Kunovice
Aircraft Industries, a.s., operating as Let Kunovice, is a Czech civil aircraft manufacturer. Its most successful design has been the L-410 Turbolet, of which more than 1000 units have been built...
since 1956. It is the most numerous and widely used glider in the world. In United States Air Force Academy
United States Air Force Academy
The United States Air Force Academy is an accredited college for the undergraduate education of officer candidates for the United States Air Force. Its campus is located immediately north of Colorado Springs in El Paso County, Colorado, United States...
service, it is designated TG-10C and is used for basic flight training.
Development
The L-13 Blaník was designed by Karel Dlouhý of VZLÚ Letňany ca. 1956, building upon the experience gained with the Letov XLF-207 Laminar, the first Czech glider to employ laminar flowLaminar flow
Laminar flow, sometimes known as streamline flow, occurs when a fluid flows in parallel layers, with no disruption between the layers. At low velocities the fluid tends to flow without lateral mixing, and adjacent layers slide past one another like playing cards. There are no cross currents...
wing profiles. The L-13 was developed as a practical glider suitable for basic flight instruction, aerobatic instruction and cross-country training. This design concept was combined with true and tested technology: metal construction, NACA
NACA
- Organizations :* National Advisory Committee for Aeronautics, the forerunner of the U.S. federal agency NASA* National Association for Campus Activities, an organization for programmers of university and college activities...
laminar profiles and many standard-issue components of the Soviet aerospace industry.
The Blaník entered production in 1958 and quickly gained popularity as an inexpensive, rugged and durable type, which was easy to fly and operate. It was widely adopted in the Soviet bloc and was exported in large numbers to Western Europe and North America. Total production was in excess of 2650, or more than 3000 if variants are included. More than half a century after its first flight it is still the most common glider in the World.
In the cross-country role the Blaník achieved many two-seater World distance records during the 1960s in spite of having only fair performance.
The Blaník inspired other designs, notably the Démant and L-21 Spartak single-seaters developed to equip the Czechoslovak team in the 1956 and 1958 World Championships.
Characteristics
The effectiveness of the Blaník as a primary trainer is due to a blend of characteristics that facilitate progress of ab initio students towards solo flight, namely: slow landing speed, ample control deflections and an effective rudder. These are in effect typical of wood-and-fabric primary trainers such as the ASK 13, which the Blaník resembles in handling, though not in materials, construction and aerodynamics.For this reason, some pilots trained in the Blaník benefit from differences training in a modern two-seater (such as Lark IS-28B2) before transitioning to high performance plastic single seaters.
The Blaník was originally stressed for simple aerobatics, including inverted flight where the aircraft has a single occupant. As a result of this latter requirement, intermediate level
Aerobatics
Aerobatics is the practice of flying maneuvers involving aircraft attitudes that are not used in normal flight. Aerobatics are performed in airplanes and gliders for training, recreation, entertainment and sport...
aerobatic training in the Blaník was done in solo flight with the instructor on the ground or in another aircraft. Following a manufacturer airworthiness directive in June 2010, all aerobatic manoevres were forbidden.
Construction
- Fuselage of semi-monocoque construction employing longerons and bulkheads, with an ovoid cross-section. The cockpit is covered with a two-part acrylic glassAcrylic glassPoly is a transparent thermoplastic, often used as a light or shatter-resistant alternative to glass. It is sometimes called acrylic glass. Chemically, it is the synthetic polymer of methyl methacrylate...
canopy. - Trapezoidal single-taper wings with forward (negative) sweep, single-spar, all-metal construction. Metal ‘torpedo’ tips. Flaps and ailerons have a metal frame and are covered in fabric. Metal DFS type spoilersSpoiler (aeronautics)In aeronautics, a spoiler is a device intended to reduce lift in an aircraft. Spoilers are plates on the top surface of a wing which can be extended upward into the airflow and spoil it. By doing so, the spoiler creates a carefully controlled stall over the portion of the wing behind it, greatly...
on the upper and lower wing surfaces. - The horizontal tail surfaces fold up parallel to the fin for transportation and storage.
- The elevator and rudder are metal frames covered in fabric.
- The landing gear is semi-retractable and sprung with an effective oleo-pneumatic shock absorber, excellent features which assure landings with little or no damage even if the wheel is left (forgotten) in the raised position.
Main spar fatigue
A Blaník was involved in a fatal accident in Austria on 12 June 2010 when a wing spar failed at height, leading to separation of the wing and loss of control of the aircraft. The cause of the failure was attributed to fatigue. As a result, the manufacturer issued an emergency bulletin on 18 June 2010 mandating that each aircraft was to be grounded pending a full inspection of wing spars and compilation of usage patterns from logbook records. Following inspection, the aircraft was permitted to fly on a non-aerobatic basis only. Following further discoveries from the accident investigation, this method of investigating for fatigue has not proved conclusive and so the type remains grounded by the EASAEuropean Aviation Safety Agency
The European Aviation Safety Agency is an agency of the European Union with offices in Cologne, Germany, which has been given regulatory and executive tasks in the field of civilian aviation safety. It was created on 15 July 2002, and it reached full functionality in 2008, taking over functions...
and the FAA
Federal Aviation Administration
The Federal Aviation Administration is the national aviation authority of the United States. An agency of the United States Department of Transportation, it has authority to regulate and oversee all aspects of civil aviation in the U.S...
.
According to Let company, the current situation may change in spring 2011 when new processes of control will be developed - http://www.let.cz/files//File/AI_opinion_gliders_092010_ENG.pdf
Europe
Following the accident, EASA released a number of directives regarding all Blaník variants.Initially, the directives mandated the aircraft be grounded unless logbook records show that dual flying hours comprise less than 50% of the aircraft's total flying time. Further investigation into the original accident has shown that these limits and analysis of flight records (such data also not being guaranteed to exist) will not be sufficient to guarantee safe operation of the type.
United States
Emergency airworthiness directives were published by the FAA. A subsequent Airworthiness Directive disallowed use of inspection solely by 10X magnification because of the possibility of metal fatigue that might not be observed by this method. As a result, on August 30, 2010, so inspected L-13 Blaníks were again grounded pending further consideration. This AD covered all L-13s without regard to serial number or category..Australia
During the 1970s & 1980s, the Gliding Federation of AustraliaGliding Federation of Australia
The Gliding Federation of Australia is the governing body for the sport of gliding in Australia. It was founded in 1949. The GFA is responsible to Civil Aviation Safety Authority for the conduct of safe gliding operations in Australia. This includes the setting and maintenance of flying...
recognized the potential fatigue-life limitations of the Blaník and in conjunction with the Ansett Airlines NDT laboratory and the Civil Aviation Authority
Civil Aviation Authority
This is a list of national and supra-national civil aviation authorities.-See also:* Air route authority between the United States and the People's Republic of China* National Transportation Safety Board -External links:****...
of Australia developed an inspection programme culminating in the issue of GFA AD-369, designed to monitor the condition of the fatigue-critical components. Most of these fatigue-critical components are called into question by the accident on 12 June 2010.
GFA AD-369 gave 3 options for continued operation beyond 5000 hours or 18,000 launches.
- Option A. total wing replacement
- Option B. major spar modification
- Option C. periodic eddy-current inspection.
In 1984 Dafydd LLewellyn and Riley Aeronautics received Department of Aviation certification for a modification of the wing to extend its fatigue life. Nine Blaníks in Australia were modified and re-certificated as L-13A1 (option B in AD-369)..
GFA AD 663 was issued on 25 June 2010 imposing the operational limitations specified by the Type Certificate holder. GFA AD 663 does not apply to Blaníks which have been modified to L-13 A1 (Llewellyn Modification)..
Regaining airworthiness of Blanik L-13: STC ADxC-DC-39-001
STC has been approved by EASA on 14-june-2011. http://www.aircraftdc.de/ENG/images/Blanik/stc%2010035295%20a.024.pdf
Variants
- The L-13 AC Blaník is primarily intended for aerobatic training with a wider flight envelope enabling dual training up to intermediate-level. It combines the wings and cockpit of the L-23 Super Blaník with the single-piece canopy and conventional empennage of the L-13. This model is considered stronger and different enough from a conventional L-13 not to be affected by the FAA grounding.
- The Vivat is a touring motorglider derivative. The wings, fuselage and tail surfaces of the L-13 are mated to a cockpit featuring side-by-side seats and a conventional firewallFirewall (construction)A firewall is a fireproof barrier used to prevent the spread of fire between or through buildings, structures, electrical substation transformers, or within an aircraft or vehicle.- Applications :...
-forward engine installation with either a Mikron M III AE four-cylinder inverted inline engine or a Limbach L 2000.
- An auxiliary-powered Blaník was also developed, with an external engine permanently mounted on a pylon above the rear fuselage. The L-13 J was Blaník with JawaJawa-Places:*Jawa , "Lost City of the Black Desert", a fourth millennium BC archaeological site in north-east Jordan*Java, also called Jawa, the most populous and fifth-largest island in Indonesia and the site of its capital, Jakarta...
motor.
- The SL-2P twin fuselage Blaník was developed by Sportinë Aviacija in LithuaniaLithuaniaLithuania , officially the Republic of Lithuania is a country in Northern Europe, the biggest of the three Baltic states. It is situated along the southeastern shore of the Baltic Sea, whereby to the west lie Sweden and Denmark...
as a flying laboratory for testing of laminar airfoils. The specimen profiles are fixed to a supporting frame erected between the fuselages. This variant is similar in concept to the modified JanusSchempp-Hirth Janus|-See also:...
once operated by the DFVLR (today the DLR, or German Aerospace CenterGerman Aerospace CenterThe German Aerospace Center is the national centre for aerospace, energy and transportation research of the Federal Republic of Germany. It has multiple locations throughout Germany. Its headquarters are located in Cologne. It is engaged in a wide range of research and development projects in...
) for the same purpose.
- The L-13 TJ (OK-3801) single-seat experimental motor gliderMotor gliderA motor glider is a fixed-wing aircraft that can be flown with or without engine power. The FAI Gliding Commission Sporting Code definition is: A fixed wing aerodyne equipped with a means of propulsion ,...
fitted with a jet engineJet engineA jet engine is a reaction engine that discharges a fast moving jet to generate thrust by jet propulsion and in accordance with Newton's laws of motion. This broad definition of jet engines includes turbojets, turbofans, rockets, ramjets, pulse jets...
TJ100C with take-off thrust 1,0 kN from První brněnská strojírna Velká Bíteš.
- The L-13 B Bačostroj (OK-8902) single-seat experimental motor glider with Walter Mikron IIIA, 48 kW
- The L-13 A1 (Llewellyn Modification) to extend the fatigue life to nominally three times the basic Blanik L-13 life.
Specifications
See also
- L-23 Super BlanikLET L-23-See also:-References:*...
- L-33 SoloLET L-33The Let L-33 Solo is a single-seat glider built by Let Kunovice. The L-33 is designed by Marian Meciar and Vaclav Zajic and is a further development of the L-13 and L-23. The L-33 Solo first flew in 1992 and is built entirely of metal . Its docile flying characteristics make the L-33 a good machine...
- LET TG-10