7/29/2019 1937 - 0855

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A P R I L I , 1937- FLIGHT. a

An ADVANCEDIncreased Power andStructural Revision ofthe Cirrus Major 150E ARLY birds in the privateflying movement may recallthat the Cirrus I (circa1925) gave a maximumof 60 h.p. and that without valvegear enclosure, side coolingchute, cylinder baffles, flametrap,exhaust stubs or spinner, but including dual ignition, it turned thescales at 2881b. The latest Cirrus

offering (which should attract notonly the private owner who wantsa completely modern power plantgiving those welcome ' ' few morehorses," but also the operator oflight commercial machines) produces 150 h.p. for near enoughthe same weight; and whereasthe Cirrus I consumed 5.6 gallons ofpetrol an hour at ' ' full bore' ' theMajor 150, as the new engine isknown, requires only 6J gallons perhour in obtaining 138 h.p.

The Major 150 (which has been com pleted since i ts manufacturers became the Cirrus Engine Section of BlackburnAircraft, Ltd., of Br o u g h , E. Yorks) exhibits a n u mb e r offeatures, external and internal, which differ from those ofthe Mark I Major . It will quickly be discovered on inspect ion tha t the re are no long cylinder holding-down bolts andt h a t the heads are similar to those on the Cirrus Minor,which are " Y " alloy castings spigoted and secured to thebarre ls by twe lve s tuds , a laminated copper washer assuring gas- t ightness. The top half of the valve gear casingis cast integrally with the heads . The wholly machinedbarre ls are re ta ined by four shor t s tuds on the c rankcase .Fully f loating gudg eon pins carry the " Y " alloy pistons.

\ FOUR-IN-LINEModern

p RefinementsI* J Throughoutwhich have two compression and twoscraper r ings apiece , and plain white-metal bear ings are used at both endsof the Hiduminium connec t ing rods .The c ranksha f t has f ive pla in bear ing sand a f ron t ba l l th rus t bea r ing ; theauxil iary dr ives are taken from agear at the rear end.T h e K.E. 965 va lves are opera tedfrom a five-bearing camshaft bydouble-ball-ended push-rods and one-piece rockers. The tul ip inle t valvesare larger than the mu s h r o o m exh a u s t s . All va lve gea r is to ta l ly enclosed, but the rocker boxes arereadily removed by unsc rewing aknur led knob , and clearances are t h e neasily checked and adjus ted at eachball cup on the rocke r s . The ball itselfh as a flat which bears on the v a lv estem and, being free to t u r n in the cup, it ret a ins its f la t contact , thus helping to r educestem and guide wear . The push- rod cove rtubes are spr ing- loaded and h a v e an oil- t ightseal on Dermat ine r ings .

The Claude l -Hobson downdraught ca rbure tter feeds through a cast Alpax a lloy manifold and has an independent a l t i tude cont ro l . The fittingof a flame-trap allows a warm air intake inside the cowl ings o t h a t an air- induction scoop need not be fitted.Specia l a t tention has been paid to accessibil i ty and nea t ness of ins ta l la t ion , and, in this connection, noticeable andcommendable is the absence of external oil-pipes, thesebeing shrunk into the alloy crankcase casting and the l eadsto the bear ing webs dr i l led through from the outs ide andplugged. A single main oil-pipe feeds the t r iple oscil la t ingpis ton- type pump, which has the a d v a n t a g e , it is cla imed,of operating with greater l if t than the gea r type for low-placed oil t a n k s . The oil-pump gear , which can be seen

H 222mm-

Installation diagrams of the Cirrus Major 150, giving main dimensions in millimetres.