History of aicraft piston engines

Cylinder barrels w ere uniformly of steel design

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Unformatted text preview: engines, all descendants of the H ispano-Suiza a nd Curtiss. I n all these engines t he valves w ere seated in inserts embedded in the a luminum head, a nd t hus h ad b etter valve cooling than t he o riginal Hispano-Suiza design. I n every case t he basic structure consisted of cast aluminum crankcase with e n bloc w ater jackets a nd c ylinder heads, also of cast aluminum. Cylinder barrels w ere uniformly of steel. Design details varied, especially in the m ethod of t aking t he c ylinder-head-to-crankcase l oad. This was successfully done as follows (fig. 34 i llustrates t he evolution of liquid-cooled cylinder construction) : 37 T hrough the cylinder b arrels—Liberty (fig. 3 4b), H ispano-Suiza (fig. 3 4c), P ackard (fig. 34e), and Daimler-Benz (fig. 34h) T hrough the aluminum water-jacket s tructure—Curtiss (fig. 34d and f) a nd Junkers V-12 gasoline engine By long bolts from cylinder heads to c rankcase—Curtis OX-5 (fig. 34a), R olls-Royce (fig. 34g) and Allison T h e i m p r o v e m e n t in performance of liquid-cooled engines since 1 918 h as been astonishing. T h e following figures for two engines of nearly the s ame piston displacement a n d representing design ideas 30 years a p a r t illustrate this d e v e l o p m e n t : 1918 Liberty E ngine 12 5x7 420 1,700 118 1, 985 1. 78 2 .04 N umber of cylinders Bore and stroke, in M aximum hp R pm B rake mean effective pressure, psi . . . . . . M ean piston speed, ft-min H p per sq in. piston area W eight, lb, per hp, dry (without water, oil, r adiators) 1948 Packard M erlin 12 5. 4x6 2, 250 3 ,000 360 3, 000 8.2 0. 78 Figure 34.—Liquid-cooled cylinder development: a b c d e f 9 h Year 1 914 1 917 1 915 1921 1 922 1 923 1 934 1 935 Name C urtiss O X-5 L iberty H ispano-Suiza C urtiss K -12 ' P ackard V - 1 2 -' C urtiss C -12 3 R olls-Royce Merlin D aimler-Benz 4 Barrel C ast iron S teel Jacket M onel s heet S teel, w elded C ast a l u m i n u m // it S teel, w elded C ast a l u m i n u m // // 1 // ;/ Load by S tuds B arrel // J acket B arrel J acket S tuds B arrel Water jacket is cast integral with crankcase. A luminum casting containing valve ports and camshaft was continuous over 6 separate steel c ylinders. 3 Improvement on K-12 by bolting separate water-jacket casting to crankcase for easier assembly and disassembly. 4 Unique fastening of cylinder barrels to crankcase by means of a ring nut. 2 39 T hese improvements are attributable not only to i mproved detail design, b ut also to important developments in fuel, supercharging, and cooling fluid, which will be discussed later. s gs» F igure 3 5.—British a ir-cooled cylinder d e v e l o p m e n t : Left, A BC steel cylinder with f i n n e d a l u m i n u m cap, 1 9 1 7 ; this cylinder had poor head and valve cooling ( f r o m Journal of the American Society of Naval Engineers, v ol. 3 8, n o. 4, p. 8 7 2 , 1 926). Right, C ylinder developed by Dr. A. H . G ibson at Royal Aircraft Establishment, 1918, anticipated the essential features of m o d e r n aircooled aircraft-engine c ylinders—that i...
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