The Power to Train

From the Ivchenko AI-25 to the Wil­liams FJ44-4M

Aviation Classics - - CONTENTS -

The vast ma­jor­ity of L-39s built used the first en­gine to power the trainer, the Ivchenko AI-25. As greater per­for­mance was re­quired in the later mod­els of the air­craft, this was re­placed by other en­gines from both the Ukraine and the US.

THE IVCHENKO-PROGRESS AI-25 The de­vel­op­ment of one of the first small tur­bo­fans to be pro­duced in the Soviet Union be­gan in 1965 and was in­tended to pro­duce a suit­able pow­er­plant for a new class of rugged re­gional jet air­lin­ers. Aeroflot re­quired a new type of trans­port to re­place its age­ing fleet of pis­ton-en­gined air­lin­ers on lo­cal routes, air­craft such as the Ilyushin Il-12 and Lisunov Li-2. The new air­liner had to be rugged to op­er­ate from the many grass air­fields on the in­ter­nal routes in the Soviet Union, and pow­ered by a sim­ple, re­li­able and easy to main­tain jet en­gine. This also had to be able to op­er­ate from ba­sic airstrips with no ex­ter­nal sup­port equip­ment, so an aux­il­iary power unit to start the en­gines was also re­quired. The Yakovlev de­sign bureau set­tled on a 32 seat, three crew air­liner with a straight wing for short field per­for­mance and a three en­gined lay­out for re­dun­dancy. To power the new de­sign, given the des­ig­na­tion Yak-40, a light­weight en­gine that pro­duced around 3300lb (1497kg) thrust was needed. The Ivchenko-progress De­sign Bureau and En­gine Man­u­fac­tur­ing Plant at Za­porozhye in the Ukraine were al­ready work­ing on the AI-25, which was ini­tially de­signed with the air­liner in mind. Aero re­quired a very sim­i­lar en­gine for the new L-39 trainer, par­tic­u­larly in terms of re­li­a­bil­ity, sim­plic­ity and ease of main­te­nance. How­ever, a num­ber of mod­i­fi­ca­tions were re­quired to the civil en­gine, for ex­am­ple, to en­able it to with­stand the high G forces re­quired in mil­i­tary train­ing. The for­mer

Wal­ter en­gine fac­tory at Ji­inon­ice in Cze­choslo­vakia, now kn­nown as Mo­tor­let, was given the task of pro­duc­ing the AI-25W, a mod­i­fied ver­sion of the en­gine to power the pro­to­type L-39s and al­low flight test­ing to be­gin. The AI-25 was the firstt tur­bo­fan to be con­sid­ered forf a mil­i­tary trainer, and con­sis­sted of three fan or low pres­sure sttages fol­lowed by nine high press­sure com­pres­sor stages then a ringr of an­nu­lar com­bus­tion chamb­bers. The last el­e­ment of the en­gine was the tur­bine that con­sisted of twwo high and one low pres­sure stages. Fit­ted witth the AI-25W, the sec­ond pro­to­type L-39, X-02,2 was theh fi­first to flyfl on Novem­ber 4, 1968, when test pi­lot Ru­dolf Du­chon took off from the Aero fac­tory air­field at Vodochody. The pro­to­type and pre-pro­duc­tion ver­sions of the L-39 were all pow­ered by the AI-25W, but prob­lems with the en­gine were to de­lay the de­liv­ery of the first 15 pro­duc­tion stan­dard air­craft. The test pro­gramme had al­ready proved that the en­gine was oth­er­wise ideal for the trainer, so Ivchenko-progress, who had been kept in­formed through­out the pro­ject, had de­vel­oped a ver­sion of the tur­bo­fan specif­i­cally tai­lored to the per­for­mance re­quire­ments of the trainer, the AI-25TL. The clear­ances be­tween the tur­bines and en­gine casing were in­creased and a spe­cial lu­bri­ca­tion sys­tem was fit­ted to en­able nor­mal op­er­a­tion un­der zero and neg­a­tive G forces. The new ver­sion was fit­ted to the X-02 and X-07 pro­to­types to be­gin flight test­ing in 1971, pass­ing Aero’s and the Czech Air Force’s tri­als in 1972 and the Soviet Air Force’s state ver­i­fi­ca­tion tri­als in 1973. The AI-25TL be­came the stan­dard en­gine for the L-39, and a smaller ver­sion, the AI25TLK was later pro­duced for the Chi­nese K-8 trainer. Both ver­sions pro­duce 3792lb (1720kg) of thrust, achiev­ing this in­crease over the ear­lier AI-25 through higher com­pres­sor pres­sure ra­tios and in­creased tur­bine in­let tem­per­a­tures. Af­ter the dis­so­lu­tion of the Soviet Union, in the 1990s Ivchenko-progress and the en­gine man­u­fac­turer Mo­tor Sich had de­vel­oped an im­proved ver­sion of the en­gine, the AI-25TLSH. This was in­tended for up­graded ver­sions of the L-39 de­vel­oped in the Ukraine and flight tested in 2002. The new ver­sion could be pro­duced by up­grad­ing ex­ist­ing AI-25TL en­gines at the fac­tory with a new com­pres­sor, high pres­sure tur­bine stage, fuel con­trol and elec­tri­cal sys­tems among many other de­tail changes. The changes saw the thrust in­crease to 4078lb (1850kg), with a re­duced throt­tle re­sponse time and im­proved fuel con­sump­tion. The com­pa­nies are cur­rently mar­ket­ing the im­proved en­gine to L-39 op­er­a­tors around the world. Al­to­gether over 9500 of all vari­ants of this in­cred­i­bly suc­cess­ful en­gine have been pro­duced and are still in ser­vice to­day all over the globe. LOTAREV DV-2 The de­vel­op­ment of the L-39MS and L-59 vari­ants of the Al­ba­tros gave rise to the need for a more pow­er­ful en­gine to pro­vide the per­for­mance re­quired of the im­proved trainer. In­ter­est from the Soviet Air Force in the pro­ject saw the sign­ing of a bi-lat­eral agree­ment be­twween the Soviet U Cze­choslo­vakian­ion and nc to de­velop and pro­duce the new tur­bo­fan. De­vel­op­ment would be the re­spon­si­bil­ity of the IvchenkoPprogress De­sign Bu­ureau and En­gine Manu­u­fac­tur­ing Plant in the Ukrainee un­der their new de­sign leader, Volood­ymyr Lotarev, the en­gines he de­signed bee­ing known by his sur­name rather than thaat of the pre­vi­ous chief de­signer, Alekksandr Ivchenko. Pre-pro­duc­tion and pro­duc­tioon of the new en­gine would take place at thhe new Slovak Ppo­vazskéké Stro­jár­nesjá Lleteck­éké Mo­tory (PSLM) en­gine fac­tory which had been built at Povázská Bys­trica. Ini­tially bas­ing his con­cept on the AI-25, Lotarev de­cided on a new ap­proach to the mil­i­tary en­gine by tak­ing his de­sign phi­los­o­phy from civil tur­bo­fans of the type com­monly pro­duced for trans­port air­craft. Usu­ally in mil­i­tary en­gines, a mul­ti­stage fan had been the com­mon prac­tice, whereas in larger civil tur­bo­fans, a sin­gle stage fan suf­ficed to pro­vide the nec­es­sary pres­sure ra­tio. Lotarev elected to fit a sin­gle stage fan as he de­sired a low spe­cific thrust cy­cle for the new en­gine, so an ef­fi­cient sin­gle stage fan that could pro­duce a higher than nor­mal pres­sure ra­tio would be suf­fi­cient, only with a higher air­flow by­pass ra­tio than was com­mon in mil­i­tary en­gines at that time. The DV-2, as it was now known, also dif­fered from the AI-25 in be­ing a twin spool de­sign con­sist­ing of a sin­gle stage fan, two stage low pres­sure com­pres­sor, seven stage high pres­sure com­pres­sor, an an­nu­lar com­bus­tion cham­ber with 16 fuel in­jec­tors, then a sin­gle stage high pres­sure and two stage low pres­sure tur­bine. In this form, the DV-2 pro­duced one third more thrust than the AI-25, de­vel­op­ing 4850lb (2200kg) as op­posed to the 3800lb (1724kg) of

ABOVE: The an­cil­lary drives and sys­tems were largely mounted be­low the AI-25TL for ease of ac­cess when mounted in the air­craft. Jakub Fo­jtík BE­LOW: The Ivchenko-progress AI-25TL was an in­cred­i­bly suc­cess­ful en­gine with more than 9500 built. Jakub Fo­jtík

ABOVE: The Lotarev DV-2 pow­ered both the Aero L-39MS and L-59. Jakub Fo­jtík RIGHT: The Lotarev DV-2 was based on the AI-25 but fea­tured a new sin­gle stage fan among other changes. Jakub Fo­jtík BE­LOW RIGHT: A cut­away of the Gar­rett, now Honey­well, TFE 731, the en­gine that pow­ered the sole L-139. In­ter­est­ingly it was ex­actly the same di­am­e­ter as the AI-25. Honey­well

Newspapers in English

Newspapers from UK

© PressReader. All rights reserved.