Quick overview
Just after WWII the Zlin Trener, was produced in Moravan Otrokovice. Czech pilots won the first FAI world aerobatics championship in 1960 in Treners, which became known as the best aerobatic airplane in the world for a decade. Many Treners are still flying after more than thirty years. The Zlin Z-50 aerobatic aircraft was to become the accepted aerobatic world leader from 1976 through the end of the 1980’s.  The Zlin Z-50 has seen four world championship titles since beginning production.

The story of success
In the post Second World War history of the Czechoslovakian aircraft industry the most successful series of aeroplanes was the Zlin Tréner family, which has been produced and constantly enhanced by the Moravan factory for over three decades. The Moravan (Zlin) factory has been established in 1934, and shortly afterwards it had produced successful types of airplanes. The factory is located in the vicinity of the town “Zlin” on the Morava riverbank. For a period of time the town was called Gottvaldov.
The best known types - produced here - were: Z-XII, Z-XIII, Z-22 Junak, Z-25 Sohaj and HC helicopters.
The base concept of the Zlin family was the Z-26 Tréner, which was designed by a team of the factory employed airplane constructors led by Tomas Karel in 1946. The design was inspired by a multi purpose military trainer and sport plane tender invited by the Czeh MoD in 1946. The original concept was not accepted by the MoD officials because it was not powered by the Czeh made Walter-Minor 4-III engine, therefore the original plan had to be modified. Karel and his team from the National Airplane Factory have won the tender and the first plane maiden flight was made on the 20th of October 1947. The mass production has started in May 1948, and all together 163 pieces have been built mainly for the Air Force (C-105).
The prototype – and its successors as well – was a typical single engine, two seater, low wing, tail dragger inspired by the pre WW II German Bü-131 "Jungmann", the Bü-181 "Bestmann" and the Arado Ar-96, but it was lighter than the latter and faster and more manouverable than the former.
The wings were entirely made of wood, welded steel tube fuselage, with control surfaces covered by aircraft canvas. She had fixed undercarriage with air foiled strut, and she has a main distinguishing feature a - later abandoned - rounded fin.

The WM-4 III 77 kW engine drove a hard wood, two blade propeller.

The modernisation of the technology made it possible to change the wooden parts (wings, tail control surfaces) for a stronger aluminium structure. The shape of the fin and the rudder had also been changed, the curves were straightened and the tail planes become squarer in appearance. The changes were so fundamental, that a renewed design was given a new “name” in 1953, the Z-126 or tréner 2 variant
Through the development of the Walter Minor 4-III engine, the 120 kW (160hp) Walter Minor 6-III inverted, inline, six cylinder, piston engine has been introduced. The engine was driving a two blade fixed pitch propeller. The new engine enhanced the plane’s performance significantly, and since that it become suitable for glider towing. An extra fuel tank was placed right behind the rear seat and the glider tug was ready in 1954. She was named Z-226B “Bohatyr”.
During the Z-226 test flights it was discovered and proved, that the type – beside being a good tug plane – has excelent aerobatic characteristics too. In order to further improve „akrobat” aerobatics performance, the extra fuel tank from the fuselage was removed, the towing propeller was changed and the fuselage was reinforced. The Z 226 Tréner 6 – introduced in 1955 - was built in different sub types as the, single seat Z 226A Akrobat, the already mentioned glider tug Z 226B and the Z 226T trainer. When the type has won the Lockheed Trophy, the first ever Czechoslovakian aerobatics victory was born. In 1957 the single seater Z-226A Akrobat won the Lockheed Trophy again.
The name of Czechoslovakian aircraft manufacturer Zlin has been associated with excellence in aerobatic aircraft since the firm was founded in 1934. The first airplane to win a modern World Aerobatic championship was the two seat Zlin 226T Trener, at the hands of Ladislav Bezák, who flew one at the 1960 World Championships at Bratislava, Czechoslovakia in 1960. Hungarian József Tóth became the second World Champion two years later at Budapest also flying a Zlin 226. So able was the 226 series that 33 of 61 contestants in the first two World Championships flew Zlin 226 models.

From 1963 the Z-226 AS Akrobat Special was equiped with a newly developed - manual hydarulic pitch control - V-500 propeller, which made the use of the engine power more efficient.
With the increasing demand on the performance of the trainer airplanes in general, the Z-226T had undergone some modification from 1957. She has received a semi retractable undercarriage and the “V” setting of the wings was modified. The new successful version was named Z-326 Tréner Master, and was produced in large series, and exported to many countries over the years. The Tréner Master also had a single seater aerobatics version, the Z-326A Akrobat.

In order to eliminate the weak points of the design of the 326 series, the Z-326 S Special was built. The “Special” was used to test the different modifications on the way of the formation of a new type of the Z-x26 series. During the test flights it was proved that the changes in the design was made in the right direction, and the new member of the Tréner family was borne in 1956 with the start of the serial production of Z-526 Tréner Master. The new type won the Lockheed Trophy for the third time.
To continuo the tradition, the Z-526 also had an aerobatics version, the Z-526A Akrobat. The front seat was removed, and the fuel tanks were shrinked to a capacity of two times 35 litres. Later she was also modified. It received a new bubble shaped canopy and its constant speed V-503A propeller was driven by the more powerful M-137A engine with its 132 kW (160 HP).

With the start of the mass production of the M-137A turbo engine and the constant speed two blade aluminium propeller, both became the standard equipment of the Zlin series. The two seater version became the Z-526F.

The aerobatics - single seater - version of this type was the Z-526 AF Akrobat. The competition on the aerobatics plane market becomes very tight, resulting in the dramatically increased performance of the planes. The designers in Otrokovice came to the conclusion, that the Zlin airplane needs fundamental reconstruction in order to keep up with its increasing number of competitors and demands. They took the Z-526AF as the base and cut the length of the fuselage (removed the part between the leading edge and the firewall) reduced the wingspan, removed the flaps, made the wing-fuselage transition aerofoil and increased the surfaces of the ailerons. The rebuilt new model became the Z-526 AFS Akrobat Special (1971).

Due to the pressure from customers of the western countries a Lycoming engine (146 kW) was built in the Z-526. The four cylinder boxer engine version became the Z-526L.

As the result of the modernisation of the two seater versions, and the extended use of the Tréner family as touring plane, the canvas covered parts were minimised. The control surfaces and the front end of the fuselage received aluminium skin. The wingspan was reduced and she received a modified M-137AZ engine. The new type is known as Z-726 Universal. She became heavier and the aerobatics performance was also far from the previous models. The constructors tried to match the power needs of the “universal” by employing the M-337 AK (Compressor) engine and the V-500A manual pitch controlled propeller.
The modifications resulted in some unwanted consequences. The new propeller prevented the plane to execute an aileron roll and other high speed aerobatics figures, and the compressor has to be switched off during aerobatics. As a result of these, the plane’s performance was limited back to the original Z-26, towing, touring and basic training.
After this it comes with no surprise that Z-726 K became the last member of the famous Tréner family.

During the seventies, the WM-4 III engines of the Z-126 were changed for the WM-6 III, and the more powerful planes (Z-126T) were used for pilot’s training and glider towing.
During the early eighties it became more and more difficult to maintain the WM-6 III engines airworthiness, (lack of spare parts) therefore the still flying Z-226 and Z-326 series were equipped with M-137A engines. These planes (Z-226M and Z-326M) were mainly used for pilot’s training and glider towing.

All together 1450 pieces has been built from the Zlin Tréner series, and they were exported into 37 countries.


Source: Takács Miklós

Translated and edited/amended by Ferenc Pállai