The Air Trans­port Ac­tion Group re­port in­di­cates how fuel ef­fi­ciency co-re­lates with the dis­tance an air­craft can fly, the pay­load it can carry and, more im­por­tantly, of­fers bet­ter en­vi­ron­men­tal per­for­mance

SP's Airbuz - - Front Page - BY R. CHAN­DRAKANTH

IT IS ES­TI­MATED THAT there are nearly 24,000 air­craft in com­mer­cial ser­vice in the world and that num­ber is go­ing to in­crease rapidly con­sid­er­ing how air travel has be­come a con­ve­nient mode of trans­port for do­mes­tic and in­ter­na­tional travel. Planes fly faster, are qui­eter, larger and so com­fort­able that trav­el­ling has taken on a new ex­pe­ri­ence. There have been con­tin­u­ous in­no­va­tions and im­prove­ments that are trans­form­ing the avi­a­tion in­dus­try driven by en­vi­ron­men­tal and op­er­a­tional man­dates.

There have been sig­nif­i­cant tech­no­log­i­cal ad­vances in en­gines, which have led to lower fuel burn. The en­gine man­u­fac­tur­ers con- tinue to pur­sue re­search to fur­ther im­prove fuel ef­fi­ciency and also ex­plore al­ter­na­tive fu­els to re­duce car­bon foot­print.

CFM In­ter­na­tional has shown the way in in­no­va­tion, bring­ing about 15 per cent fuel im­prove­ment on its LEAP en­gine, com­pared to its best CFM56 en­gines. The en­gines also have high level of dis­patch re­li­a­bil­ity and good life-cy­cle main­te­nance costs. The LEAP en­gine is built for 99.98 per cent dis­patch re­li­a­bil­ity which means more time in the air and less main­te­nance time. The LEAP en­gine’s fan blades are man­u­fac­tured from 3D wo­ven resin trans­fer mold­ing car­bon fiber com­pos­ite, an in­dus­try first for CFM. This tech­nol­ogy re­sults in fan blades that are not only lightweight but also durable

that each In­di­vid­ual blade is strong enough to sup­port the weight of a wide-body air­plane like the Air­bus A350 or Boe­ing 787.

The Air Trans­port Ac­tion Group (ATAG) in its re­port has put out how fuel ef­fi­ciency co-re­lates di­rectly with the dis­tance an air­craft can fly, the pay­load it can carry and, more im­por­tantly, of­fer en­vi­ron­men­tal per­for­mance. For most of the twen­ti­eth cen­tury, avi­a­tion pi­o­neers were ob­sessed with speed, first break­ing the sound bar­rier and then push­ing air­craft speeds higher and higher. It was the key to win­ning the air war and the key to ex­plor­ing space. In the civil mar­ket, faster air­craft could fly higher above the worst of the weather and con­nect the world’s con­ti­nents in ever de­creas­ing times. 3D PRINTED, LIGHTER AND STRONGER. The LEAP en­gine is the first en­gine to use ad­di­tive man­u­fac­tur­ing to ‘ grow’ com­plex, fully dense yet lighter en­gines. Its fuel noz­zles are 25 per cent lighter than pre­vi­ous mod­els and five times more durable than parts man­u­fac­tured con­ven­tion­ally. SPEED IS NOT EV­ERY­THING. It was only in the 1960s that it be­came clear that the cost of speed had to be mea­sured in more than just dol­lars. Fast jets may have made in­ter­con­ti­nen­tal travel pos­si­ble for a new gen­er­a­tion of pas­sen­gers, but they were also ex­tremely noisy, es­pe­cially for those com­mu­ni­ties liv­ing in the vicin­ity of air­ports. The avi­a­tion in­dus­try had to re-con­nect with the so­ci­ety it served and re-think its pri­or­i­ties.

The re­port states that in the 1980s and 1990s, avi­a­tion ex­perts pushed the en­ve­lope of ef­fi­cient aero­nau­ti­cal de­sign to its limit. Faced with the chal­lenge of de­liv­er­ing more power at lower noise lev­els, en­gine de­sign­ers de­vel­oped the ex­tra­or­di­nary ‘ high-by­pass ra­tio’ en­gine which, since the 1970s, has de­liv­ered a quan­tum in­crease in power and a dra­matic drop in noise lev­els. Thanks to the con­tin­ued evo­lu­tion of the high-by­pass tur­bo­fan, air­craft are now 50 per cent qui­eter on an av­er­age to­day than they were ten years ago.

Aerospace en­gi­neers are con­stantly work­ing on how to make planes more ef­fi­cient. The re­port men­tions how un­like ground ve­hi­cles, which don’t need to be op­ti­mised for ef­fi­ciency to the same ex­tent as air­craft be­cause they can re­fuel of­ten, long-dis­tance air­craft must carry all their fuel with them. Fuel is ex­pen­sive, heavy and takes up a great deal of stor­age space. Its weight can limit the range of an air­craft and it needs to be stored in tanks which af­fect the wing size and the pay­load. LOWER CO2 EMIS­SIONS. The avi­a­tion in­dus­try has come to mea­sure its tech­ni­cal progress in the in­creas­ing ef­fi­ciency of its air­craft and en­gines. Fuel is one of the high­est cost items of an air­line op­er­a­tion and oil prices are volatile. There­fore, when an air­line de­cides to buy new air­craftt, fuel con­sump­tion is a pri­mary con­sid­er­a­tion. There is also a di­rect link be­tween re­duced fuel use and en­vi­ron­men­tal per­for­mance.Each tonne of fuel saved means ap­prox­i­mately 3.15 tonnes fewer CO emis­sions, states the

re­port. The most di­rect way for an air­line to im­prove its fuel ef­fi­ciency is to mod­ernise its fleet with new air­craft in­cor­po­rat­ing the lat­est tech­nol­ogy.

His­toric trends in im­prov­ing ef­fi­ciency show that mod­ern air­lin­ers are around 80 per cent more fuel ef­fi­cient than those in the 1960s, ATAG states. These ef­fi­ciency lev­els have been achieved with step changes in de­sign such as the in­tro­duc­tion of tur­bo­fan en­gines with in­creas­ingly high by­pass ra­tios — cou­pled with year-on-year ‘in­cre­men­tal’ im­prove­ments to en­gine de­sign and op­er­a­tion. TURBOPROPS, A STEPCHANGE IN POWER. Air­craft en­gines play the most im­por­tant role in de­ter­min­ing fuel ef­fi­ciency. The ar­rival of the tur­bo­prop en­gine in the early 1940s was a step-change in power, re­li­a­bil­ity and ef­fi­ciency over the pis­ton en­gines then be­ing used on re­gional air­craft. A tur­bo­prop en­gine is a gas tur­bine which pow­ers a pro­pel­ler. Pure tur­bo­jets en­able air­craft to fly faster; but also use more fuel than a tur­bo­prop, mak­ing the tur­bo­prop a per­fect en­gine for air­craft cruis­ing be­tween 480 and 650 kmph. A tur­bo­fan­pow­ered jet air­craft flies at around 800 kmph.

In re­cent years there has been a resur­gence of in­ter­est in the tur­bo­prop tech­nol­ogy given their po­ten­tial eco­nomic and en­vi­ron­men­tal per­for­mance ben­e­fits, es­pe­cially among re­gional air­craft de­vel­op­ers. A mod­ern tur­bo­prop can con­sume 25 to 40 per cent less fuel than an equiv­a­lent tur­bo­fan en­gine on short-haul routes. HIGH BY­PASS RA­TIO TUR­BO­FAN EN­GINES. ATAG states that the ap­pear­ance of the high by­pass ra­tio tur­bo­fan en­gine in the late 1960s, changed the civil avi­a­tion in­dus­try al­most overnight. This new en­gine de­sign was more than twice as pow­er­ful, but much qui­eter and cheaper to op­er­ate than the tur­bo­jets it re­placed. It opened the door to a new gen­er­a­tion of wide-body air­craft and a step change in en­gine ef­fi­ciency which would see a grad­ual di­min­ish­ing of air­craft noise foot­print over the next 40 years.

The ATAG re­port ex­plains that the tur­bo­fan in­cor­po­rates two changes in jet de­sign. It adds a sec­ond low-pres­sure tur­bine and a large fan mounted in front of the com­pres­sor. The fan pulls in large amounts of air into the en­gine in­take, some of which is di­rected into the hot core of the en­gine where it is com­pressed and then ig­nited; but most of which by­passes the core where it cre­ates most of the en­gine’s thrust. If there is twice as much cold air by­pass­ing the core as the hot air go­ing through it, the by­pass ra­tio is 2:1. The higher the by­pass ra­tio, the bet­ter the fuel con­sump­tion as more thrust is be­ing gen­er­ated with­out burn­ing more fuel. High by­pass ra­tio tur­bo­fans are also much qui­eter than tur­bo­jets, in part be­cause the flow of cold air sur­round­ing the ex­haust from the en­gine core re­duces the noise pro­duced by the ex­haust gases.

The first com­mer­cial high by­pass ra­tio tur­bo­fan en­gines had around a 5:1 by­pass ra­tio. The lat­est mod­els are around 11:1. It is also im­pres­sive that the lat­est model of en­gines for wide­body air­craft gen­er­ate over 1,15,000 pounds of thrust each — more than the thrust of four en­gines in the late 1960s, all while us­ing less fuel, pro­duc­ing lower emis­sions and with a noise foot­print just a frac­tion of that of the first jet air­craft, the re­port men­tions. MORE EF­FI­CIENT EN­GINES BY 2020. The ATAG re­port fore­casts that a steady in­vest­ment in ad­vanced tech­nol­ogy has en­abled jet en­gine ef­fi­ciency to im­prove at an av­er­age of one per cent a year. This means that en­gines avail­able in 2020, are likely to be at least ten per cent more ef­fi­cient than en­gines de­signed to­day. En­gine man­u­fac­tur­ers and gov­ern­ment re­searchers are work­ing so that this trend can con­tinue over the next few decades.

The re­port states that re­cent tech­nol­ogy ad­vances have opened the door for the fur­ther de­vel­op­ment of tech­nol­ogy that has been used in smaller air­craft en­gines for some time — the geared tur­bo­fan. A gear sys­tem (much like in a car) al­lows the fan sec­tion of a geared tur­bo­fan en­gine to op­er­ate at a lower speed and the low-pres­sure com­pres­sor and tur­bine to op­er­ate at much higher speeds thus in­creas­ing en­gine ef­fi­ciency and low­er­ing fuel con­sump­tion, gaseous emis­sions and noise lev­els. This new type of en­gine for nar­row-body com­mer­cial air­craft, that en­tered ser­vice in 2013, pro­vided 15 to 20 per cent im­prove­ment in ef­fi­ciency over the en­gines they re­placed. These en­gines have re­duced noise foot­prints. New mod­els of the geared tur­bo­fan should con­tinue the his­tor­i­cal ef­fi­ciency im­prove­ment of one per cent per year or more.

So also, open-ro­tor en­gines which are gas tur­bines driv­ing two high speed pro­pel­lers mov­ing in op­po­site di­rec­tions are trend­ing. The ap­pli­ca­tion of new aero­dy­namic and ma­te­rial tech­nolo­gies could see the re­turn of the pro­pel­ler-driven en­gine on larger air­craft, but with higher flight speeds and lower noise lev­els. This con­cept was first de­vel­oped in the early 1980s, but was not pur­sued due to the rel­a­tively low fuel cost then Now with the in­tense in­ter­est in fuel econ­omy and more ad­vanced de­sign tech­niques, the open-ro­tor de­sign may have a re­nais­sance. The re­port fore­casts that by 2020, they could be ready for in-ser­vice use on some air­craft.


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