The Ubiquitous Dolphin
The L-29 – Aero’s first jet trainer
By the mid-1950s military training aircraft were predominantly piston engined, yet the air forces of the world were largely equipped or steadily re-equipping with jet aircraft. It became apparent that an efficient jet powered trainer was both a priority and a necessity, one Aero was ideally placed to fill.
In July 1953, the Czechoslovak aircraft industry had changed in organisation, capacity and make up, almost beyond recognition to its prewar form. The Motorlet factory, formerly Walter Aero Engines, at Jinonice in Prague, was mass producing jet engines and both the Letov plant at Letnany and the brand new Aero factory at Vodochody were building Mig-15s, Let supplying sub assemblies and Aero mating these with its own parts on its final assembly line. Production of these machines taught a number of Czech companies a great deal about the complex systems and very high standards of engineering and finishing that such aircraft and engines require, giving the industry tremendous experience, a great advantage in the early evolution of jet propulsion. For military operators, these aircraft also brought with them a new set of operational problems, one of which was in the training of pilots. At the time, pilots began flying simple piston engined aircraft as had always been the case, this basic flying stage eliminating those students who lacked the aptitude for flight. From here, more complex aircraft would be used for advanced training, many of these being powerful piston engined tailwheel aircraft similar to those that had been used in the Second World War, such as the T-6 in the US, Balliol in the UK and Yak-11 in the Soviet Union, the latter also being built under licence by Let in Czechoslovakia. Then, those students with the aptitude for fighters would begin training on the few two seat jet aircraft that existed at the time, all of which were converted fighters such as the T-33, the Meteor T Mk.7 and the MIG-15UTI. That last transition was the problem, moving from tailwheel piston aircraft to nosewheel jet types was a tremendous jump requiring additional hours of flying just to introduce the basic handling of the new aircraft. The tailwheel piston trainers required a very different set of flying skills to those needed by the jets and those tailwheel skills would never be needed by the students again, making them an anachronism in a modern air force, and a costly one at that, in terms of both time and money. It was quickly realised that what was needed was a simple, reliable jet trainer, one that was cheap to operate and maintain, to replace the more advanced piston engined trainers. If this new trainer could also carry out more advanced tasks, such as weapons training and other military requirements, then so much the better
as this would also reduce the cost of this stage of pilot training. The two seat versions of the fighters could then be used only for operational conversion training onto those or similar types. A basic jet trainer with intermediate capabilities would therefore make pilot training a much more efficient process, reducing the flying hours required and the cost, not to mention the workload on the students themselves. This realisation was to lead to the development of basic jet trainers worldwide. In the US, the Cessna T-37 would emerge toward the end of the 1950s, whereas in the UK, a piston engined trainer was re-engined and given a tricycle undercarriage to become the Jet Provost. The Soviet Union was also interested in the development of such a type and three companies would produce prototypes for a competition held in 1961. One of these was Aero’s first jet design, but the story of the aircraft was to begin much earlier. In 1950, the MNO was looking to replace the Arado Ar 96 piston engined trainer, known as the C-2 in Czechoslovakia, with a more modern version. The design teams of Avia and Letov responded to this requirement with two similar aircraft, the XLE-10 and the XLA-54, both powered by the 580hp M-411R, a licence built version of the Argus As 411. The centralised design agency also included a common prototype workshop which was to build both aircraft, neither of which was selected for production due to performance issues. Both design teams attempted to resolve these issues in 1951 by re-engining their aircraft with the 700hp Walter M-446 V12 engine to produce the Avia XLE-110 and Letov XLA-154, but to no avail and the projects were dropped. One of Aero’s test pilots during the Second World War, Karel Vanek, was killed in a forced landing while testing the XLE-110 on December 12, 1951, when the crankshaft in the relatively untested M-446 broke. In order to fulfil the training requirement, the Let factory at Kunovice built the Yak-11 under licence as the C-11, over 700 being built for the Czechoslovak Air Force and for export beginning in 1953. In 1956, another attempt to produce an indigenous trainer was made when the TOM-8 was produced by the Výzkumný a zkusební letecký ústav, VZLÚ or Aeronautical Research and Test Institute, the management body for the central design agency. The TOM-8 was powered by the 230hp Praga Doris M-208C flat six piston engine which proved unreliable and again the project was dropped. By this time however, the need for a jet trainer had been realised and preliminary studies resulted in the MNO issuing a specification for such an aircraft in the second half of 1955. The united design team under chief designer Zdenek Rublic and Karel Tomás began
ABOVE RIGHT: One of the L-29 prototypes seen during flight testing at the VZLÚ, fitted with additional probes and air data sensors to fully evaluate the aircraft and its systems. Pavel Kucˇera RIGHT: The first L-29 powered by the Motorlet M-701 turbojet was 00031, now with the production standard canopy, fin and rear fuselage. Pavel Kucˇera
ABOVE: The third prototype was the first to fly, but powered by a Bristol Siddleley ASV-8 Viper. Note the early windscreen and the greater sweep to the leading edge of the fin as well as the rounded rear fuselage, all of which would change in the production aircraft. Pavel Kucˇera LEFT: The Avia XLE-10 trainer prototype. Editor’s collection ABOVE: The TOM-8 was produced by the Výzkumný a zkušební letecký ústav, VZLÚ or Aeronautical Research and Test Institute in 1956. Editor’s collection
ABOVE: The Aero L-29 on display in the Prague Aeronautical Museum is a very early production aircraft with the nose mounted landing light and the pitot static tube fitted to the fairing at the top of the fin. Editor