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Aviation History
1936
1936 - 1095.PDF
454 FLIGHT. APRIL 30, 1936. COWLING and COOLING Part II. "Baffling" Problems Solved: The Advent of Controlled Cooling ONE of the most acceptable contributions made to international aviation by the American National Advisory Committee for Aero nautics is the N.A.C.A. cowling for radial engines. This cowling has come into prominence dur ing the past three or four years, and in one form or another • features on a very large pro portion of modern radial- engined military and commer cial aeroplanes. There are a number of current variations, but in no guise should the N.A.C.A. cowling be confused with the deep-chord Townend ring which, from some points of view, may appear similar. In its original form the cowling, mounted on an Ameri can single-seater fighter, gave encouraging results, and in its essentials resembled the latest and most highly developed types now in use. Basically it was a long-chord ring with a nose-piece which curved over in the form of a lip, leav ing a circular opening of comparatively small diameter for the admission of the cooling air which flowed past the cylinders and out of an annular slot at the rear. The ex terior, of course, was designed to offer as little resistance as possible to the flow of air over the fuselage. Although on the face of it this seems an amazingly simple arrangement, the whole cowling had to be designed with extreme caution in relation to a fuselage or nacelle behind it. The size and location of the annular opening for the return of the cooling air to the main stream also occasioned close study. To this day there is a certain amount of scepticism among British constructors regarding the N.A.C.A. cowling. When first tried over here it was, in fact, by no means How "H "-type Engines are Cowled and Cooled (Continued from " Flight' April 16, 1936.) of an unqualified success, mainlv because of cooling troubles. The explanation of this lies in the comparatively steep climb of British machines made at a low forward speed and to the higher cylinder temperatures permitted in the U.S.A. Geared engines—particularly if supercharged, into the bargain —were the worst offenders, for there was comparatively little slipstream cooling from their big, slow-running airscrews. But things are different to day. It is due to the specially studied and baffled N.A.C.A. cowlings that the geared and supercharged engines on such successful machines as the Douglas, Boeing, Vultee and Northrop can operate within permissible temperature limits. One recalls a particularly good illustration of this point. Just before the England-Australia race there were com ments on the dangerously tight-fitting cowlings on some of the American entries. Colonel Fitzmaurice was forced to fly his Bellanca Irish Swoop to Mildenhall with no cowling over its fourteen-cylinder geared and supercharged Twin Wasp Junior engine. He announced, to the mystification of certain of the parochial-minded spectators, that he had been afraid that, without its cowling, his engine would overheat! They stood aghast. That story raises another point. A great deal of trouble has been experienced with'N.A.C.A. cowlings threatening to -come adrift in the air due to the forward force they exert. While travelling at something like 300 m.p.h. an American racing pilot discovered that his cowling was slowly creeping forward into the airscrew! He managed to put his machine down before that pushful component The first two show the ,sPe^'£he~ third In these three views the main features of a modern baffled installation are readily seen. '' shoulder '' which conducts the cooling air out of the '' gills " ; in the second the inter-cylinder baffles are visible, shows the complete installation. The nose portion forms the exhaust ring. Actually this installation is of one Bristol Pegasus Ill's in a Douglas D.C.2.
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