RB199 devel­opment: the engine that started it all

MTU had to overcome several chal­lenges to get the Tornado engine per­forming as it should—and built up invaluable know­ledge in the process.

03.2019 | Text: Denis Dilba

Denis Dilba holds a degree in mechatronics, is a graduate of the German School of Journalism, and founded the “Substanz” digital science magazine. He writes articles about a wide variety of technical and business themes.


“With­out the RB199, there would be no MTU Aero En­gines.” This one sen­tence un­der­lines the im­por­tance the de­vel­op­ment of the Tor­na­do en­gine had for MTU. But this alone does not do jus­tice to this pi­o­neer­ing achieve­ment. Be­cause no oth­er sto­ry il­lus­trates quite as ef­fec­tive­ly what MTU had been about since day one: us­ing high-cal­iber tech­ni­cal in­ge­nu­ity to push the bound­aries of what’s pos­si­ble—in short, to in­no­vate. Back at the start of RB199 de­vel­op­ment in 1969, this was known as en­gi­neer­ing in­ge­nu­ity, says en­gine de­vel­op­er Arthur Schäf­fler. This savvy was ab­solute­ly nec­es­sary in or­der to mas­ter the chal­lenges MTU en­gi­neers faced back then with the new jet en­gine, notes 81-year-old Schäf­fler, who was part of RB199 de­vel­op­ment from day one and whose ca­reer would take him all the way to the role of tech­ni­cal di­rec­tor for Eu­ro­jet.

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“The mis­sion re­quire­ments for the Tor­na­do could hard­ly have been any big­ger,” re­mem­bers Schäf­fler. “On the one hand, the mul­ti­role fight­er had to in­ter­cept en­e­my air­craft at Mach 2.2, on the oth­er mas­ter op­er­a­tions at low al­ti­tude.” And of course the jet should be able to take off and land on short run­ways. In oth­er words, the RB199 not on­ly had to gen­er­ate a great deal of thrust while be­ing as light­weight as pos­si­ble—and con­sume low amounts of kerosene and en­able peak ac­cel­er­a­tion in a short time­frame—it al­so had to have a thrust re­vers­er. The idea was to have a three-shaft en­gine with 12 com­pres­sor stages, with a com­pres­sor pres­sure ra­tio of 23:1 and a tur­bine in­let tem­per­a­ture of some 1,300 de­grees Cel­sius. “Con­sid­er­ing what was state of the art back then, this was a mas­sive leap in both of these re­spects,” Schäf­fler says.

Together with Rolls-Royce and Fiat (today Avio Aero), MTU began devel­oping and pro­ducing the RB199 in 1969 to power the Tornado multirole fighter jet.

Grown-up chal­lenge for the young MTU

Schäf­fler re­mem­bers how the Tur­bo-Union con­sor­tium, a joint ven­ture be­tween Rolls-Royce (40 per­cent), Fi­at (20 per­cent) and MTU (40 per­cent) that was found­ed specif­i­cal­ly to build the RB199, ea­ger­ly set about work. The di­vi­sion of la­bor meant that the MTU team, made up of en­gi­neers from Daim­ler-Benz and MAN Tur­bo­mo­toren GmbH, “land­ed a ma­jor deal con­sid­er­ing what they knew at the time,” says Schäf­fler. “We were re­spon­si­ble not on­ly for the medi­um- and high-pres­sure com­pres­sors, the medi­um-pres­sure tur­bine and thrust re­vers­er, but al­so for the in­ter­nal air and oil sys­tem for cool­ing and lu­bri­cat­ing the high­ly stressed cas­ing and chan­nel­ing cool­ing air to the tur­bine blades. Such tech­no­log­i­cal re­quire­ments were not the on­ly un­chart­ed ter­ri­to­ry for MTU. Up un­til that point, the Mu­nich-based com­pa­ny and its pre­de­ces­sors had main­ly man­u­fac­tured li­censed en­gine parts and had nev­er had the re­spon­si­bil­i­ty for de­vel­op­ing such ma­jor por­tions it­self. “Be­ing sole­ly ac­count­able for an as­sem­bly al­so meant we were un­der a fair amount of psy­cho­log­i­cal pres­sure,” Schäf­fler says.

At the beginning, the engineers struggled with the engine’s complexity. Hover over the image for a bigger view

At the beginning, the engineers struggled with the engine’s complexity.


At the beginning, the engineers struggled with the engine’s complexity.

Installation of the RB199 engines in the Tornado in Manching. Hover over the image for a bigger view

Installation of the RB199 engines in the Tornado in Manching.


Installation of the RB199 engines in the Tornado in Manching.

MTU engineers built a total of 2,504 RB199 engines and many are in service today. Hover over the image for a bigger view

MTU engineers built a total of 2,504 RB199 engines and many are in service today.


MTU engineers built a total of 2,504 RB199 engines and many are in service today.

The jet achieves a top speed of Mach 2.2. Hover over the image for a bigger view

The jet achieves a top speed of Mach 2.2.


The jet achieves a top speed of Mach 2.2.

The mod­est per­for­mance of the first RB199 test run met with long faces among Schäf­fler and his col­leagues. “The ef­fi­cien­cy was con­sid­er­ably be­low par,” he says. While the medi­um-pres­sure com­pres­sor quick­ly at­tained “very sat­is­fac­to­ry” per­for­mance, the high-pres­sure com­pres­sor ran in­to com­plex prob­lems. These in­clud­ed the rel­a­tive­ly thick ro­tor blades of the rear stages—which were made from heavy nick­el al­loys—ex­pand­ing sig­nif­i­cant­ly slow­er than the cas­ing un­der fast-chang­ing op­er­at­ing con­di­tions such as ac­cel­er­a­tion and de­cel­er­a­tion. This meant that over long phas­es, the ra­di­al clear­ance be­came too large. The re­sult was re­duced per­for­mance pa­ra­me­ters for the high-pres­sure com­pres­sor and an im­per­mis­si­ble low­er­ing for the aero­dy­nam­ic sta­bil­i­ty thresh­old. “It was a long time be­fore we found a de­sign that suc­cess­ful­ly slowed the ex­pan­sion of the cas­ing,” Schäf­fler says. At least all the en­gine man­u­fac­tur­ers were in the same boat at that stage, says the en­gi­neer. “The clear­ance prob­lem was not well known—we just had to ac­cept the long time it took to find a so­lu­tion.”

Fail­ing the bird strike test

Just as sur­pris­ing was the dis­cov­ery that the sur­face of the blades for all rear stages of the high-pres­sure sec­tion was much too rough. “This meant that the sys­tem wasn’t achiev­ing its full aero­dy­nam­ic po­ten­tial,” Schäf­fler says. Here too, it would be years be­fore they suc­ceed­ed in man­u­fac­tur­ing the thumb­nail-sized blades in a suit­able qual­i­ty. An­oth­er thing Schäf­fler re­mem­bers very well is how the blades had to be re­designed af­ter the first bird strike test: “The bird passed through the low- and medi­um-pres­sure com­pres­sors with­out do­ing much dam­age be­fore com­plete­ly de­stroy­ing the high-pres­sure com­pres­sor.” Com­pared to the oth­er is­sues with the RB199, Schäf­fler says this was easy to fix: “When we made the blades for the high-pres­sure com­pres­sor’s first ro­tor stage, we sim­ply ex­tend­ed the chord length by some 30 per­cent. The strength­ened blades sub­se­quent­ly with­stood the strike, as did the down­stream stages,” Schäf­fler says. Step by step, MTU de­vel­oped valu­able knowl­edge in all ar­eas.

Video: RB199: a multi-purpose engine for a multirole fighter Article with video

RB199: a multi-purpose engine for a multirole fighter

Originally developed with multiple new opera­tional character­istics, the Tornado was a chal­lenging build. The only way to fulfill the exacting mission require­ments was a collabo­ration between Rolls-Royce, Fiat and MTU to form the Turbo-Union consortium. To the video

“Even though the jour­ney was some­times ar­du­ous and caused us to curse reg­u­lar­ly, the grasp of the over­all sys­tem that we gained over this time proved ex­treme­ly use­ful to MTU,” Schäf­fler says. Schäf­fler’s time al­so saw an in­no­v­a­tive leap in en­gine con­trol tech­nol­o­gy. In the fall of 1987, the ana­log reg­u­la­tor first used for the RB199 was re­placed with a much more re­li­able, flex­i­ble and amenable dig­i­tal con­trol unit, the DE­CU 2000. The mod­el was su­per­seded in 1995 by the DE­CU 2020 fea­tur­ing im­proved proces­sors. “This con­trol unit was in pro­duc­tion un­til 2003 and suc­cess­ful­ly em­ployed by the Ger­man and Ital­ian air forces,” Schäf­fler says. Around 700 were made, “but I couldn’t tell you the ex­act num­ber,” he laughs. But this is not the case when it comes to the num­ber of RB199 en­gines built. “There were 2,504,” Schäf­fler says. “And many are still in ser­vice.” Schäf­fler says he is of course proud of the RB199, which de­spite all its chal­lenges did ul­ti­mate­ly be­came one of MTU’s ma­jor suc­cess­es.

The 81-year-old, who un­til a few years ago still gave in­tro­duc­to­ry cours­es to MTU em­ploy­ees on how jet en­gines work, says he was lucky to be em­ployed at MTU. “It was the ide­al life for an en­gi­neer.”

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