The Ubiq­ui­tous Dol­phin

The L-29 – Aero’s first jet trainer

Aviation Classics - - CONTENTS -

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

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