Nature’s way: Bionics make engines quieter and more efficient

Na­ture had sev­er­al bil­lion years to evolve and de­vel­op the per­fect so­lu­tions for its needs. Wood, for ex­am­ple, gets its rigid­i­ty and strength from its cell walls. Bones have a light­weight struc­ture and yet are in­cred­i­bly strong. Reeds have dif­fer­ent lay­ers of cells that make them tough as well as flex­i­ble. And thanks to their struc­tured sur­face, the leaves of the lo­tus flower can re­pel wa­ter and dirt, while shark scales have den­ti­cles that help re­duce drag in the wa­ter.

Ex­am­ples from na­ture such as these have been spark­ing cre­ativ­i­ty and in­spi­ra­tion for hu­man in­ven­tions for years. Even Leonar­do da Vin­ci stud­ied the flight of birds pri­or to build­ing his fly­ing ma­chines—even if his first at­tempts at fly­ing failed be­cause they re­lied on hu­man strength alone to gen­er­ate the nec­es­sary lift. But the con­cept of cre­at­ing lift through propul­sion is still found on­board all air­craft to this day. Fol­low­ing in da Vin­ci’s foot­steps, en­gi­neers to­day al­so take in­spi­ra­tion and ap­ply prin­ci­ples from na­ture when they de­vel­op ma­te­ri­als and com­po­nents.

Huge innovation potential

Bion­ics, a port­man­teau of “bi­ol­o­gy” and “elec­tron­ics,” has be­come a field of re­search in its own right. As the founder and CEO of Ger­man com­pa­ny die Bioniker GbR and a con­sul­tant at Al­tran Deutsch­land, Markus Holler­mann is a firm be­liev­er in the huge in­no­va­tion po­ten­tial that bion­ics of­fers. “Bion­ics isn’t about copy­ing na­ture but about learn­ing from it—ap­ply­ing its prin­ci­ples to elec­tron­ic prod­ucts and process­es and de­vel­op­ing new func­tion­al­i­ties. Us­ing ex­am­ples from na­ture, we can cre­ate com­po­nents for avi­a­tion ap­pli­ca­tions that are light­weight, ex­cep­tion­al­ly strong and that ab­sorb sound.”

Bion­ic struc­tures can be used as a ba­sis for lighter, qui­eter and more ef­fi­cient en­gine de­signs—at least the­o­ret­i­cal­ly. For a long time, how­ev­er, this ap­peared im­pos­si­ble to trans­late in­to prac­tice. That’s be­cause con­ven­tion­al com­po­nents are forged or cast, which makes it dif­fi­cult to in­te­grate cav­i­ties or de­signs based on na­ture. But now, ad­di­tive man­u­fac­tur­ing process­es are open­ing up a world of new op­por­tu­ni­ties for de­sign en­gi­neers. A year ago, MTU Aero En­gines formed its own bion­ic de­sign team as part of its Cen­ter of Ex­cel­lence for ad­di­tive man­u­fac­tur­ing.

Head­ed by Dr. Mark Welling, the team has now de­vel­oped a bion­ic com­po­nent: a brack­et for oil lines. Giv­en that the com­po­nent is crit­i­cal to safe en­gine op­er­a­tion, it must meet strin­gent re­quire­ments to ob­tain ap­proval from the avi­a­tion au­thor­i­ties. Un­like the con­ven­tion­al, straight-edged brack­ets that are milled, this new brack­et is curved and takes a shape not dis­sim­i­lar to a bone. “The new de­sign en­abled us to cut the weight of the com­po­nent in half, with­out in­ter­fer­ing with the strength or damp­ing char­ac­ter­is­tics,” says Welling. It’s no co­in­ci­dence that the de­sign re­sem­bles a bone: “Na­ture is ex­treme­ly eco­nom­i­cal; it doesn’t in­vest any more than what is re­quired. If you look at bones, ex­tra ma­te­r­i­al is present on­ly in places where it’s ab­solute­ly nec­es­sary for sta­bil­i­ty. We used a sim­i­lar prin­ci­ple to op­ti­mize our brack­ets—you could say that they’re the re­sult of ac­cel­er­at­ed evo­lu­tion.”

Development by numerical simulation

Nu­mer­i­cal sim­u­la­tion be­gins with a hexa­he­dral mod­el, a fi­nite el­e­ment mod­el that is sub­ject­ed to spe­cif­ic loads and tem­per­a­tures. A com­put­er pro­gram then iden­ti­fies which of the hexa­he­drons are crit­i­cal for with­stand­ing the stress­es and which ones are not. The non-crit­i­cal ones are re­moved one by one un­til on­ly the es­sen­tial struc­tures re­main. Next, the com­put­er sim­u­lates dy­nam­ic stress­es and their im­pact over thou­sands of take­offs and land­ings. The mod­el ex­pos­es any weak points where the hexa­he­dral mesh needs to be mod­i­fied.

In the next step, the de­sign is op­ti­mized for ad­di­tive man­u­fac­tur­ing. Se­lec­tive laser melt­ing. In this process, thin lay­ers of the high-tem­per­a­ture iron-nick­el al­loy In­conel 718 are ap­plied to the sub­strate in pow­der form. A laser then melts the pow­der, fus­ing the lay­ers to­geth­er to cre­ate sol­id struc­tures. In prin­ci­ple, this method is suit­able for pro­duc­ing any geom­e­try, but it does re­quire any sup­port struc­tures and over­hangs to be re­moved or re­worked af­ter­wards. Op­ti­miz­ing the mod­el min­i­mizes the amount of work in­volved.

The CAD da­ta from the sim­u­la­tion can now be used for ad­di­tive man­u­fac­tur­ing with­out fur­ther pro­cess­ing. For qual­i­ty as­sur­ance pur­pos­es, MTU’s en­gi­neers de­vel­oped their own method for iden­ti­fy­ing any struc­tur­al weak points as ear­ly as pos­si­ble. Dur­ing the weld­ing process, a sen­sor records the time it takes for the pow­der melt­ed by the laser to reso­lid­i­fy and cool down. If this is un­usu­al­ly long, it’s a sign that the pow­der has not fused prop­er­ly with the lay­er be­low.

Pro­duc­tion of the blank for the brack­et takes on­ly a few hours. Be­fore the brack­et is mount­ed, it un­der­goes fur­ther qual­i­ty in­spec­tions to en­sure it is safe to use in the en­gine.

The new bion­ic brack­ets are now be­ing in­stalled in a test en­gine. Once they have passed en­durance test­ing and demon­strat­ed they meet the re­quire­ments for ap­proval, they can be rolled out in­to large-scale pro­duc­tion. “Then we’ll have an­oth­er im­por­tant mile­stone un­der our belt, paving the way for more de­vel­op­ments of this kind in the fu­ture,” Welling says. “Our plan is to pro­duce 15 to 30 per­cent of our en­gine com­po­nents us­ing ad­di­tive tech­nolo­gies by 2030. That’s no mean feat, and we know we’ve still got some chal­lenges to over­come. But we’re work­ing through them sys­tem­at­i­cal­ly to find so­lu­tions.”

There is a long list of com­po­nents that would be suit­able for ad­di­tive man­u­fac­tur­ing. Among the po­ten­tial can­di­dates are a hous­ing with in­te­grat­ed cool­ing, light­weight en­gine blades or a re­designed vari­able guide vane ac­tu­a­tor—a mech­a­nism cur­rent­ly made up of many small parts that have to be as­sem­bled man­u­al­ly.

“Ad­di­tive man­u­fac­tur­ing can al­so help achieve the tar­gets for re­duc­ing fu­el con­sump­tion and emis­sions in avi­a­tion,” Welling says. “Fol­low­ing na­ture’s ex­am­ple, we can make air­craft en­gines lighter, qui­eter and more ef­fi­cient.”