LET L-13 Blaník

L-13 Blaník
Penn State Soaring Club L-13 flying over State College, Pennsylvania, showing forward-swept wing
Role Two Seater class sailplane
National origin Czechoslovakia, later Czech Republic
Manufacturer Let Kunovice
Designer Karel Dlouhý
Number built 2649[1]
Variants Blanik TG-10

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.

Development L-13

The L-13 Blaník was designed by Karel Dlouhý of VZLÚ Letňany c. 1956, building upon the experience gained with the Letov XLF-207 Laminar, the first Czech glider to employ laminar flow 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.

L-13AC( Airworthy with Shorter L-23 Wing)

As taken from the web side at Blanik America, "the two-seat all-metal L13AC Blaník is an aerobatic version of the L13 Blanik, primarily intended for dual aerobatic training while also used for elementary glider training. It has the same cockpit as the L23 Super Blanik with one piece canopy, the tail of an L13, and shortened L23 wings. The intended users of the L13AC Blaník are clubs, commercial, and military schools where instructors and other pilots are trained in mastering basic aerobatic maneuvers."

As Claimed by Blanik america, "the aim of the L13AC Blanik is to promote instruction in aerobatics, including recoveries from unusual glider attitudes. The availability of this kind of glider, similar to the original Blanik, the most widely used trainer in the world, makes it possible for instructors to refresh their aerobatic skills, and to pass the confidence gained on to their students. The advent of the L13AC Blanik heralds more participation in glider aerobatics, and brings a boost to the sport of soaring."

In addition the L13AC Blanik has received the FAA Type Certificate G24EU, Rev. 5 Section II, in the Aerobatic Standard U.S. Airworthiness Category, on August 25, 1999.[2] It is found in the type certificate data sheet NO. G24EU section II, that the Blanik L-13AC, maximum weight acrobatic category with 1 occupant is 880 lb and a limited acrobatic category with 2 occupants 1100 lb and limited cloud flying with 2 occupants 1100 lb.

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 an IS-28B2 Lark) before transitioning to high-performance, composite-materials 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 manoeuvres were prohibited.[3]

Construction

Flaps deployed for landing - torpedo tips clearly visible, and air brakes partially open
Motorglider LET L-13M Blanik over Vecaki, Riga - Latvia

L-13 Main spar failure [L-13 and L-13A grounded until found in conformity ]

A Blaník L-13 [not an L-13 AC which has a different wing and type certificate] was involved in a fatal accident in Austria on 12 June 2010[4] when a wing spar failed at height, leading to separation of the wing and loss of control of the aircraft. I newspaper report reported the cause of the failure was attributed to fatigue.,[5] however the preliminary investigation has revealed that the fracture may have been due to fatigue, and consequently remains found "un-rebutted" that the aircraft may have been over stressed. As a result, in an abundance for safety, and as a precaution, 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.[3] Following further discoveries from the accident investigation, this method of investigating for fatigue has not proved conclusive[6] and so the type remains grounded by the EASA and the FAA.

According to Let company, the current situation may change in spring 2011 when new processes of control will be developed.[7] However, and in year 2016, follow on STC's are found issued in:

for regaining airworthiness of this Type[8]

Blanik L-13AC not affected by AD 2011-0135 (Uses shorter L-23 Wing)

The Blanik L-13AC that uses a shorter wing similar to the L-23, is a two-seat all-metal L13AC Blaník is an aerobatic version of the L13 Blanik, primarily intended for dual aerobatic training while also used for elementary glider training. It has the same cockpit as the L23 Super Blanik with one piece canopy, the tail of an L13, and shortened L23 wings. The intended users of the L13AC Blaník are clubs, commercial, and military schools where instructors and other pilots are trained in mastering basic aerobatic maneuvers, where it can take two pilots for aerobatic training.[2] It has the same cockpit as the L23 Super Blanik with one piece canopy and shortened L-23 wings. Since it uses sorted L-23 wings, it was not effected by the emergency bulletin on 18 June 2010 and Blanik model L-13AC and Blanik model L-23 both continue operations as of 2016.

Europe

European Aviation Safety Agency AD No.: 2011-0135, is found to only affect the L13 and L13A. According to AD requirements, there is a restatement of requirement of AD 2010-0185-E:[9] which is found to read From 5 September 2010 [the effective date of AD 2010-0185-E], all flights are prohibited. In part, the new requirements of the AD are to inspect the sailplane to determine whether the wing structure is in conformity to the L-13 A BLANÍK design specification, or in conformity to the L-13 BLANÍK ‘reinforced’ design specification, in accordance with the instructions of Aircraft Industries a.s.(AI) Mandatory Bulletin (MB) No. L13/112a.

United States

Emergency airworthiness directives were published by the FAA.[10] 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 L-13 and L-13A without regard to serial number or category.[11] The L-13 AC does not use the same wing as the L-13. The FAA type certificate for the L-13 AC is specific to "G24EU Section II(1999)" and not specific to "G24EU Section I, (1971)".

Australia

During the 1970s and 1980s, the Gliding Federation of Australia 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).[12]

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).[13]

Regaining airworthiness of Blanik L-13: STC ADxC-DC-39-001 This STC was approved by EASA on 14-June-2011.[14]

On Display

A Blanik L-13 is on display at Yankee Air Museum in Belleville, Michigan

Variants

L-13 AC Blaník(Not affected by AD No.: 2011-0135)
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, L-13/AC uses a shorter L-23 wing and is not to be affected by the FAA grounding.[15]
L-13 J
An auxiliary-powered Blaník was also developed, with an external Jawa engine permanently mounted on a pylon above the rear fuselage.
Sportinë Aviacija SL-2P
aka Kensgaila VK-7 twin-fuselage Blaník was developed by Sportinë Aviacija in Lithuania 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 Janus once operated by the DFVLR (today the DLR, or German Aerospace Center) for the same purpose.
L-13 TJ
(OK-3801) single-seat experimental motor glider fitted with a jet engine TJ100C with take-off thrust 1,0 kN from První brněnská strojírna Velká Bíteš.[16]
L-13 B Bačostroj
(OK-8902) single-seat experimental motor glider with Walter Mikron IIIA, 48 kW
L-13 A1
(Llewellyn Modification) to extend the fatigue life to nominally three times the basic Blanik L-13 life.
TG-10 Blanik
United States Air Force Academy, gliding school.
Aerotechnik L-13 Vivat
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 firewall-forward engine installation with either a Walter Mikron IIIAE four-cylinder inverted inline engine or a Limbach L2000.
Aerotechnik L-13 SE Vivat
Aerotechnik L-13 SW Vivat
Aerotechnik L 13 SEH Vivat
Aerotechnik L-13 SDM Vivat
Aerotechnik L 13 SL Vivat
Aerotechnik L-13 SDL Vivat

Operators

 Italy

Specifications (L-13 Blaník)

Data from The World's Sailplanes:Die Segelflugzeuge der Welt:Les Planeurs du Monde Volume II[18]

General characteristics

Performance

See also

Related development


Related lists

Notes

  1. ↑ Simons (2005) p.30
  2. 1 2 "L13AC acrobatic Blaník". home.nwi.net. Retrieved 2016-01-02.
  3. 1 2 LET Mandatory Bulletin L13/109A
  4. ↑ German-language news article on the crash
  5. ↑ EASA EAD 2010-0160-E
  6. ↑ EASA EAD 2010-0185-E
  7. ↑ http://www.let.cz/files//File/AI_opinion_gliders_092010_ENG.pdf
  8. ↑ "Blaník L13". www.aircraftdc.de. Retrieved 2016-01-07.
  9. ↑ "EASA Airworthiness Directives Publishing Tool". ad.easa.europa.eu. Retrieved 2016-01-02.
  10. ↑ FAA EAD 2010-14-15
  11. ↑ AD 2010-18-05
  12. ↑
  13. ↑
  14. ↑ EASA STC Retrieved 2012-12-13
  15. ↑ Letter, FAA to SSA, September 14, 2010
  16. ↑ Turbojet engine TJ 100, PBS Velká Bíteš, a.s.
  17. ↑ aeroflight
  18. ↑ Shenstone, B.S.; K.G. Wilkinson (1963). The World's Sailplanes:Die Segelflugzeuge der Welt:Les Planeurs du Monde Volume II (in English, French, and German) (1st ed.). Zurich: Organisation Scientifique et Technique Internationale du Vol a Voile (OSTIV) and Schweizer Aero-Revue. pp. 58–59.

References

  • Shenstone, B.S.; K.G. Wilkinson (1963). The World's Sailplanes:Die Segelflugzeuge der Welt:Les Planeurs du Monde Volume II (in English, French, and German) (1st ed.). Zurich: Organisation Scientifique et Technique Internationale du Vol a Voile (OSTIV) and Schweizer Aero-Revue. pp. 34–36. 
  • Simons, Martin (2005). Sailplanes 1965-2000 (2nd revised ed.). Königswinter: EQIP Werbung & Verlag GmbH. pp. 51–3. ISBN 3 9808838 1 7. 

External links

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