rHIS ENGINEER S,4TS Don't Wrlte Off the Centrlfusal CorTTpress*tr Ey \ff. F. *unptny In ali i-,ranches oi engineering, ;ls ir: urost fields of endeavor. there are alternative. everi conilicting, schools of opinion u'hich verv in poi)ularitv trr the' u'hinrs oi' the time. Aeronautical engirteering provides no e rception. F or vears tire adlo- cates oi the rn onoplane fc,ught 3 ir-rs- ing fight agai nst the pop ularit,v of the iriplanc-.. until the positiorl \lras ret'erseci lr--v the derland for highe:: perforrlran- ces in general ancl the introcluction of the, ihick cantilever u'irtg il particuiar. ir \\'ilsi the salne u'ith engines. In a I)eace lrivirig u,r;rid, r.r'here \r'ar seetleri to ire an alrarrrJoncd pastinre :rncl econonrv csl r,rperalioll-(otlttrlercial op- eration. \f ils rrf i-rrilnc irrtportllllce. the air coc;icrl cnginc \\rAS sul)rente. T'hen conditions altercd anci otirer standards lussertecl tircnrselves to govern tire t'tlttc r",i tirc clrginc. \\''ar, rt'ith its cotr irlu irrjccl disrcgard ior cc()nor];\rr clcnranclcC tire supcrirrr ;rcrforrnence o{ thc I4crlins:trtd tireir inritutions atirJ lcit bcl:incJ e rel)c\t'cd rtlachrtrcnt ior thc liq uirl coolccl cl)- ginc. 'l"iutt iight, tlutt c.r,nf'lict <.,i opili- ir;n., is rl()!{, ()\,(r. {trr airt'rlft;tistr"rr: rngitrcs oi' ritlrrr t \'])(' ir:n'c rc:rcltt,rl lll the zenith oi their tleveioptlrent antl are rapidiv lieing re piace ci lr)' gas tlrr- bine s),ste llls rhat req r-rire no spe ciltic cooling cievices otht'r tl-ratt the col)- versicltt c;it hc:rt ir-rto rrseirrl rt"orli. Nevertheless thcrc is Il0 Iack oi opinionatile conflict. (ias turlrittes havc aireaclv deleiopecl intc, drstinctive tvpes. cach u,ith its o\\'It pe cuiiarities thar provicle focd tor argutxent as to their advantages and cJisadvanta[es. N:rtur- alir' \\,e f,nd adr'ocate s of e;rch t)'pe ; reardr, to support the ir cri;inions r'r'ith sound arglilnents i',ut u.ith conlellietlt clisregard for sottttr of the cr',n sjdc;:a- tions that couicl deirreciate their tite,- r.,ries. Clossifying ComPonent A.s far as aircraft are concertrctl. the gas'turbinc svstell-i is usecJ as a turlrri- ie't, either u'ith or r'l'ithout lt prc;1.lellcr attat.iuncrtt. itncl, at the prese llt t inle. tlrc lr)ost ilistinctivcll' classiitf ing c()lll- p()llcnt is the r.()tl)llrclssor. This alsr, is thc (:()tIl1;t,rtrcnt ttrlrt clluses ti-re tnr.rst arguttretlt-: thc ;rtlr'tIl)tllgt=s lrrttl ,lis- atlr rtllt:tge s oi tlrc lrxi:tl tr'pcs lls lrgltitrst tlrr,sc ol tlrc (('ntriiugal 11''1lcs. .I"iit icrttrt'r is ilr fln't,t':tt tirc lll()ltlcttt. l'he conreilsirs c:i rilrrilir',ii see ms tr, bt' tiiat the: ariul corlr prcssor u'il1 sooll ottst aitogethcr its rival r.rrrrl. certuinir " ciesign tclrrle r-rcie s poini tou'ur tis suiii a happ,cninl. Ilaling seeu a lot oi slracic: n'r,rk clonc l:or therrr" Lirc nraiur- j.tt' o1t clesigne rs llo\\. eiitering tite-: turbr,- j"r ricitJ:rre concentratinE on the arial tvpe oi urnit l',ccuuse. uncler r:erlain cc.,nclirion.s. u,i'ric'h arc encoLlrrrerecl in high-specd flighr. it is the ri'lorc eiTici- c:rt r-niicirine. ltlou.ever. an;iai collrpres- s()r ran ()i)e rate u'itir greater elTicierrc\r than its rir al can, hut r,r,hat is ire - qucntlv anc] convenieni].,, overioc,ker] is the l":ict that it rlr;e s so onll :rt or Ilcar pc:ik opcrating cc,nclitions. The st'r'cral stages of a n axial cronrpressor (ilr) eesilv Llc rr-ratcl-recl to give elTicient o1)craLion 1:rrlvidccl on]r, one "set rif op- crutittg r:r,n<-litiorrs is invr;lved. Ii the trnit is rc(luircd to ol)crarc under r.r,id- cli, r';rrr,ilrg corlclitions rllany extra ci;f- {"icult ics rr rc crlcoLl ttteretl and r:-r uch cxl)crirrrt,rrtal u'ork ),ct retnltins [reJclrc Pencentoge Efficiency , r00 Centrifugol copcrcify Incre,ase - ?*t;g-n l"-tnl * Curves showing the efficie,nces of typico{ compressorlr .,1 l{iCR.'{ I;7' tn}{l , t iRl){ } Il7' I F i t.f $-rr thc maiority of thcse cltl lre t.,r'crcornc. Whcn thc conditir.rns changc lrr,nr those uuder '"vhich an :txiltl cotnl,ressor ol)er.rtes with greatcst cfiicie ncv. knorvn es the design point' the incir.lcrrce on sorne or all oi the bladcs changcs and crruses e retluction in ovcr-all cificiencv. li the change continucs, either bv alter- ing the rnass 1.lorv :1t constent rotational speed or vice versrt, the incidence on sc,me of the biades will ever.rtually relch stelling r,alue and an undesir- eble condition known as surging rvill resuit. Compleie Breokdown This is follorveC. unless the unit is rcturneti to rnore sr-ritabIe operating conditions. bv conrplete breakdorvn of tlre airilon, an,-1 failure oi' the engine to operate. There is onl-r, one rota- tional speed end onlv one mass air- iiorv :rt thet speed when all stages of lrn axial compressor are matchecl and oprbie oi opereting rvith a high de- gree r>l etTicienct'. On the other hand, rvhile it aiso operatcs ,'vith greetest efficicncy r-rnde r certain deiineci con- tlitions. the centrifugai type of cotn- pressor is tiorv so drasticalh, affected lrv rrrv chrnge in those coniitions. The re is no danger of stalling the lrilrtlrs lt lou' spcc,is lrt.l eor.tscqttentlv less rr<,luble in mainlainin-q ihe nir- i:lolr, or in starting the operlting cvcle. The .rxiai Ltotrpressor is. in itact, ver,v iempernruent,rl rnd [uss1, lbout its wtrking con.litiorls. .\t the design point it can. ii :r'ell ,lesigned and main- tlinerl iu gco.l ,nech,ltrical conclition. operate rvith ,ur ove r-alI efiiciencv of rbout 3i 1 . as rgainst somcw'hiit less tlran 30'',- in the ctse of r comparable rrentriiugxl ti'pe. :\ I'erv clcsir:rble :rtl- \-llntilge oi cor.rrse, but. es urentioned lretore. anv dilersion iroLn the ,.lesign point lvili crLrse I gre0ter reclr-rcrion in overall elTicie ncv oi ttre former tvpe than it i,vill in the case of the latter. Tvpicel et{icierrcl curves are shos-n in the accorl-rp;roving greph fronr w.hich it ivi11 be i,ien thrlt the exial unit rlain- trins its arltlntttges in efficiencv onlv in the vicinitr.ol thc design point. Under other corr.litiorrs ti-re centriiugul tvpe oi unir is the nrore efTicieur. This lbilitv ro r.r'rrrinrein r high (le- -lr('c ()l t{licicrrcr' ,r,r,'1..r r',rrr i,rg ,.,,,' rlitions, rvhich rr'e crn eell t'lcribiiit,,,, is an asset oI de betable vaiue r.vhen lpplied to aircrrft engines. but space .4ugust, 1949 THE AEROCAR One 0f the most e lusive 0b- jectives oi aviation has alrvavs be e n the roadable airPlitne. Above and belorv are - Photo- graphs 0f a model 0E a rnachine rvhich constitutes the -latest Llt- ternpt to malie it comllination auto-airpiene. Knox'n AS thc,\erocar and rrade br, -'\erocer [nc.. oi Long- \:iet\:: W;rsiringtrin, this project has lctua]1'"' acl:,,gnce d far bevond the rntitle i st.lge . .\ s hort time .rgo },lor-rlton Pr. Trt,lor. ntanager of -'\crocar. toln.J ^.t i;'c;',,tlt ilftd . I irport . "\\,:orris L'rllnot con'','ev the ile- reii rii sllcli r c.levetropmenl . \,\,'e har-e spent iour ve.irs doint it. The fiight corllponent is nolv Llnder construction (shouitj now be com ple teci ) end rve antici- pate ftight lests in the sLlm n-Ie r. 0r-rr operarion of thc car Io i.late inclicates setisfrrctorll :1tlto anplicatioit of the eir-cooied air- crair engine. This is the Intlsi rlifficuir blrt leesr speciacriiar part el.rhc proicct. Ttre .irive linc is ciirect from;r Crosslev i.rLrtonrobilc. bttr tr-trne (l aroLlnt'l to r)lake rire r'itir i1 irorlt ri:trcei ilrive . . ." 'Ihe iiimcnsions of the Aero- car:ls;.1n eirl;ilne .lre eirpro.Yi- llrlrtelv thrt of the a\-erilge stnrlii lighrpirure. Prin'cr is l"rv ri Frrnk' iin ::; u-iLh ;l i)lirrirnrtrtr outptlt tlr I l; hp. The cnrising spee d iurs beerr e stimltteci rlt t)\"e r i 00 m pil. ('ili tlrc eir ) : tics ignc..i rox(i sl)eee(1 is i;0 rrph. rr-lrtrirnum. Cl-rengeoler- tirne ir,rtl rtirplrtir': to :lLltolnobilc is ]r-rsr t)ttc lttlrlLlte . Carr\:inq r\\'o l)ilsscltgers. the rrircrrlL't irls rr ih,ing rttlgc t'lt tubustion spece and trtr- bine diar.neter u"ill be tire. controlling factors. The adlantage ttined fronr small cornpressor tliamcter r.vill Lre nullified bv lirtue of the fact that it rl'ill be absorbecl in thc olerall dian.reter of the engine. And hon' rnuclr ldvantige is a feu' inches reduction ia engine overall dia- rneter an1's'a\-i 'lllo the designer stili laboring under the Christnras tree cornplex it is likeil to rrean quite a lot. An1' saling in frontal area, no matter hcu' slight. can be considererl a saving Srrcc so )orrg as engirrcs are allou,ed to hang on the outside of the airframe like en afterrhought and cancel out a goodlv portion of their propulsile efl'ort l,r' drrrgging on the airstrear.n. An Enlighiened Age But ra'hat u'as good enough for the piston engine era is not necessarily good enough in a rnore crnlightened age and therc are indications that greeter efforts are alreeclr being made to place the engirres insidr the airfran.re u-hcre thev can do their u,ork u'ithout. at thc samc tinre inrpcding tl'rc progrcss ;ilri ctrgitre u'ill evtlr sLlrprss its rir'.il in this rcsirtct. Tc bcgin rvith. tlte ltlatles ol atI eriti t olr pre ssoi- lll ilsr lle lll;-r tlu l:acture ri lrntl instullcrl u'ith e xll'clt-le ecL:Ltrec\I. rnintrtc errors itt ltlacie llrofile or settillg cllusc'\'crv troticettllle iosses irl cflici- c:nc\'. f'hcrei'orc. the ltt:.lttttiacturing costs lrrer l,igh rrrtd thc te ntptetion to rctluce' tl)t'sc. irr silite oi tlre c.onseqLlelit recluctiot-r in the qtraiitv oi the finish- c'rl 1-rrr,tlrtct is evcr ltresent. A Prime Exomple This ixilrpcncrl in tire case r:f the Gerr-nan I-leinkel-I-lirth OII turbo-ier: u'hic,h \\'as l-rcing tooled up for illass prc,duction torvarcl tire etrcl of lhe \\'er. 'l-his enrinc itrcorltoraie'ci lr rirree-stafc asiel cr)nlpiessor u,r:lking iir series ll'ith r{ diagonei stagr ancl it \1'AS cill.ilneei thrt tlre arrenge tnr:ttt iurci det'cio1",r'ct ri n-rnxin'rr.lr'lr c,r'crall atiiai"retic elTicienct' ol over 8ti'.. Thcr: chatiges ir-r cl.:ar"- Arlces [o sllou' easier rnanufactltrt ltr

Don't write off the Centrifugal Compressor

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