AIRCRAFT PROPULSION — TAYLOR 267 



design. In every case the basic structure consisted of cast aluminum 

 crankcase with en-bloc water jackets and cylinder heads, also of cast 

 aluminum. Cylinder barrels were uniformly of steel. Design details 

 varied, especially in the method of taking the cylinder-head-to-crank- 

 case load. This was successfully done as follows : 



1. Through the cylinder barrels, Hispano-Suiza, Daimler-Benz, fig. 10, 3, 6. 



2. Through the aluminum water-jacket structure, Curtiss and Junkers, fig. 



10, 4- 



3. By long bolts from cylinder heads to crankcase, Rolls-Royce and Allison, 

 fig. 10, 5. 



Figure 10 illustrates the evolution of liquid-cooled cylinder 

 construction. 



The improvement in performance of liquid-cooled engines since 

 1918 has been astonishing. The following figures illustrate this 

 development : 



1918 1948 



Engine Liberty Packard 



"Merlin" 



Maximum hp 420 2,250 



R.p.m 1,700 3,000 



Brake mean effective pressure, psi 118 360 



Mean piston speed, ft./min 1, 985 3, 000 



Hp. per square inch piston area 1.78 8.2 



Weight per hp., "dry" pounds 2.04 0.78 



("Dry" weight is for complete engine without water, oil, or radiators.) 

 These improvements are attributable not only to improved detail 

 design, but also to important developments in fuel, supercharging, 

 and cooling fluid, which will be discussed in a later section of this 

 lecture. 



AIR-COOLED ENGINES, 1918-40 



The "Gnome" and its rotary descendants (LeRhone, Clerget, B.R., 

 Oberiirsel, etc.) were obsolescent by 1918. Also obsolescent were air- 

 cooled engines using cast-iron cylinders with integral heads and fins. 

 These included the radial "Anzani," and the "Renault" Vee type with 

 its descendants, the R.A.F. and F.I.A.T. 



During the first World War it had become evident that the simple 

 cast-iron cylinder" had reached its limit, and the Royal Aircraft 

 Factory of Great Britain had employed Prof. A. H. Gibson, assisted 

 by S. D. Heron, to develop more effective air-cooled cylinders. By 

 1918 they had constructed and tested steel cylinders with cast-alumi- 

 num heads, capable of higher specific outputs than any cast-iron 

 cylinder (fig. 11). However, the practical use of the aluminum-head 

 cylinder in England was seriously delayed by a parallel development 

 starting in 1917 of air-cooled radials with steel, flat-head cylinders, 

 capped by a bolted-on valve-port assembly of cast-iron or cast almni- 



" The chief limitations on the cast-iron cylinder are poor heat conductivity as compared 

 with aluminum, and low strength as compared with steel. 

 672-174—63 19 



