Confining his subject matter strictly to a discussion of the Wright Whirlwind engine and its bearing on the present status of the air-cooled aircraft-engine, the author says that the type of engine specified embodies in its development two distinct forms of cylinder construction, the first having been developed by Charles L. Lawrance and the second by S. D. Heron. The application of these cylinders to the engine under discussion is outlined and the subsequent development is traced.
The development of the J-5 type of engine was undertaken in an effort to place the air-cooled engine fully on a par with the water-cooled type as regards fuel consumption. The cylinder is characterized by a hemispherical combustion-chamber employing two valves with axes inclined at 70 deg. The valve-seats are of aluminum-bronze shrunk into the cast-aluminum head. The cylinder-barrel with integral cooling-fins and hold-down flange is screwed and shrunk into the aluminum-head casting. Among the advantages claimed for this cylinder over the Lawrance type of cylinder are superior head-cooling due to the larger fin-area provided by the hemispherical combustion-chamber and the relatively large space between the valve-ports; the superior barrel-cooling due to the integral steel-fins, which avoids the necessity of conducting the heat across a thermal gap between the aluminum barrel and the steel liner; the high fuel-economy presumably due to the excellent combustion-chamber shape and to the efficiency of the valve cooling; greater strength and ability to withstand abuse due to the hemispherical shape of the combustion-chamber and the superior cooling; and remarkable freedom from detonation presumably due to the combustion-chamber shape, valve cooling and spark-plug position. The shape of the combustion-chamber is also said to offer the further advantage that relatively large valves can be employed without unduly crowding the valve-seats together at the center of the head.
Cooling efficiency and fuel consumption are considered and the results of endurance tests of the J-5 engine are stated. Briefly, the engine was subjected to a 50-hr. test under full throttle at 2000 r.p.m. and showed a fuel consumption of 0.508 lb. per hp-hr.; to a 50-hr. test under full throttle at 1800 r.p.m., in which the fuel consumption was 0.458 lb. per hp-hr.; and to a 50-hr. test while supercharged, developing 295 hp. at 2150 r.p.m. and showing a fuel consumption of 0.510 lb. per hp-hr. Domestic aviation-gasoline was used in the foregoing tests. The author believes that the results of these endurance tests place the air-cooled engine definitely on an equal footing with the best water-cooled engines and that the air-cooled engine will become the standard of comparison. His final conclusion is that the development of the air-cooled engine will advance with the utmost rapidity during the next 3 years, since there is still room for great improvement in all respects including specific weight, power output per cubic inch, cooling capacity, durability, and facility of production.


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